Valérie Maraval
email: valerie.maraval@lcc-toulouse.fr

Dr Chongwei Zhu

Dr Emmanuel Gras
email: emmanuel.gras@lcc-toulouse.frchauvin@lcc-toulouse.fr

Carine Duhayon

Prof Francis R Lacassin

Xiuling Cui

Remi Chauvin
email: chauvin@lcc-toulouse.fr.

Professor Marian Mikolajczyk

Prof R Chauvin
email: chauvin@lcc-toulouse.fr

Prof X Cui

Daniel Romero-Borja

Jose ´-Luis Maldonado

Gabriel Ramos-Ortı

Alix Saquet

Valerie Maraval
email: valerie.maraval@lcc-toulouse.fr.

V Maraval

Valérie Maraval

Dr Nathalie Saffon-Merceron

Rhodium Carbonyl Complexes The Forgotten Nitroaromatic Phosphines as Weakly Donating P-ligands: An N-Aryl-benzimidazolyl Series in RhCl(CO) Complexes

Keywords: coordination bond, nitroaromatic chemistry, nitroarylphosphines, P ligands, phosphines, rhodium carbonyl complexes

Time flies so quickly, after an intensive period of thirty-nine months, my PhD career has quietly come to an end. Over the past three years, I gained tremendous acknowledge in chemistry, my experimental skill and research ability were also significantly improved. Undoubtedly, it would not be possible to conduct my research and complete my dissertation without these people

Acknowledgment

chemistry, enthusiasm for people, immense knowledge and meticulous working attitude have had a profound impact on me. I have learnt so much from and because of you, you always can enlighten me when I encountered difficulties. I sincerely thank you for your guidance and helping me grow as a research chemist. It has been my honor to be your PhD student. CARVALHO, thanks for your help, man.

My appreciation also goes to our collaborators: Dr. E. GRAS, who works at LCC in Toulouse, supervised me as a co-supervisor in my first year and gave me a great support, I whole-heartedly appreciate you. Also, I want to thank Prof. H. F. HSU for the measurements of DSC, POM and PXRD experiments in Taiwan, Prof. Chun-hsien Chen for conducting STM measurement in Taiwan in carbo-mesogen project, Dr. A. POATER for performing the calculation for carbo-OPEs in Spain, Prof. J. L. MALDONADO for exploring of OPV application in Mexico.

I am also indebted to the following crystallographers: Dr. C. DUHAYON, it is so nice of you, you got involved in all the measurements and analyses of single crystals in my PhD career, I very much appreciate you. Dr. B. KAUFFMANN, who is from Bordeaux, my paper would not have been possible to be published without the high-quality data of single crystals. My appreciation also goes to Dr. N. SAFFON for attempts at picking single crystals. Last but not the least, I would like to thank my family for their unconditional support and encouragement in these years, I haven't been able to find more time to accompany you, in particular for my grandfather, I couldn't go back to see you last time until you left us forever. But I want to say I really love all of you, thank you.

• • • • • • 2a: R 1 = H 2b: R 1 = t Bu R 1 R 1 R 1 R 1 • • • • • • • • • • • • n Oct

5I 5J = 3D

Introduction

In the continuing debate on the fundamental nature of the coordination bond, [1] the ligands of some reference Lewis acids (LAs) are commonly classified between the electron-rich and electron-poor categories: for transition metal LAs, this prebonding characteristic makes it possible to predict strong or weak ligand-to-metal charge transfer. Beside the long studied class of electron-rich ligands, ranging from alkylphosphines to diaminocarbenes and onium ylides, [2] the class of electron-poor phosphane counterparts has attracted less systematic attention but remains challenging for appraising coordination limits while decreasing the strength of s-donation. [3] The need for electron-poor ligands is, however, more practically motivated by catalysis issues for rate-determining steps requiring a relatively low electron density at a metal center balanced by sufficient stability of the complex. Even weak s-donation can indeed be compensated by strong p-back bonding, as it happens with phosphites identified as ligands of choice for catalytic transformations such as hydroformylation. [4] As esters of phosphorous acid, phosphites are however sensitive to PÀO bond protolysis, and two main kinds of more robust electrondeficient triarylphosphine ligands can be distinguished: the electron-poor neutral phosphines, mainly represented by fluoroarylphosphine, [5] N-heteroarylphosphines (e.g., imidazolophosphines), [6] and the highly electron-poor a-cationic phosphines, such as imidazolio-, diaminocyclopropenio-, or pyridinio-phosphines. [6a, 7, 8] These carbenio-phosphines, optimally described as carbene-phosphenium adducts, [9] have been shown to exhibit P-donating ability in ternary C!P!LA coordination motifs, [7a] even in the case of the extremely electron-poor a-diationic dicyclopropeniophosphines. [10] While cyclopropeniophosphines give particularly stable Pd complexes acting as efficient catalysts (e.g., for cycloisomerization of enynes), [7d, 11] imidazolio-phosphines and their complexes are more reactive, un-dergoing PÀC bond cleavage in the presence of weak nucleophiles (such as Cl À ), thus restricting the scope of possible applications. [9,12] With the view to enhancing the electron-deficiency of the parent imidazolophosphines without the detrimental effect of the a-positive charge, N-methylation of the former (CH 3

+ N-coordination) could be replaced by CH-substitution with neutral electron-withdrawing groups (Figure 1). Examination of this issue drew the author's attention to the fact that an a priori simple way to make a triarylphosphine ligand more electrondeficient while remaining neutral seems to have been forgotten: alternative to fluorination, nitration should indeed be particularly efficient. Indeed, considering Hammett constants s p and s m as crude means of comparison of the electron-withdrawing effect of a substituent through an aromatic system, [13] one of the largest values is attained for NO 2 (s m = 0.71, s p = 0.78), standing close to that of the cationic substituent + NMe 3 (s m = 0.88, s p = 0.82), and much higher than those of other neutral substituents such as F (s m = 0.34, s p = 0.06), CF 3 (s m = 0.43, s p = 0.54) or CN (s m = 0.56, s p = 0.66). [14] Prior to any coordination chemistry considerations, the oxymoronic redox nature of nitro-substituted arylphosphines can be considered as a basic challenge, [15] at least from the thermodynamic standpoint (the nitro-nitroso isomerization 4-NO 2 -C 6 H 4 -PPh 2 !4-NO-C 6 H 4 -P(O)Ph 2 is calculated to be exothermic by DZPE = À23.2 kcal mol À1 ; see the Supporting Information). [16] Direct nitration of aryl-phosphines are prevented by the P-oxidizing potency of the nitronium ion, [17] and most of related synthetic efforts have focused on oxidized P = O or P= S precursors. [18] Coordination complexes of nitroarylphosphines are actually limited to the formal cases of such P!O or P!S de-rivatives: to the best of the our knowledge, indeed, no experimental example of corresponding P!metal complexes has ever been reported, [19] thus unveiling a quite general challenge. While the basic triphenylphosphine series will deserve a natural attention, in particular for the reference (4-nitrophenyl)diphenylphosphine (see Conclusion), [15b, 20] the forgotten nitration strategy for lowering further the electron deficiency of aromatic phosphine ligands is hereafter addressed within the above-summarized concern in the benzimidazolyl phosphine series (Figure 1 a).

While modern routes to arylphosphines consist in Cu-, Ni-or Pd-catalyzed Ar-P coupling reactions from Ar-X + E-PPh 2 (X = I, Br, OTf; E = H, Ph, SnBu 3 , Cl), nitro-ArX substrates are rarely exemplified, [21] and have even been claimed to be incompatible with generally efficient conditions. [START_REF] Bramborg | For di-n-octyl-benzene[END_REF] Yet, the most employed approach to tertiary phosphines remains based on nucleophilic substitution processes at P centers with lithium or Grignard reactants, as also illustrated in the arene/heteroarene series, [23] in particular for imidazole and benzimidazole representatives. [6e, 12b] For the present objective, (N-aryl-1H-benzoimidazol-2yl)diphenylphosphines have thus been targeted from the more or less nitrated NH,N 2 CH benzimidazole precursors 1 a-d by substitution of ClPPh 2 with lithium salts of N-aryl-N 2 CH derivatives 2 a-h (Figure 1 b). The propensity of nitro-arene/heteroarene substrates to undergo addition or redox processes in the presence of lithium reagents has indeed been reported for alkyl lithiums only. [START_REF] Balci | ], as it contributes only a little to the total shielding (2 ppm), which is generally hidden by other larger[END_REF] Moreoever, since N-methyl-5-nitro-1Hbenzoimidazol-2-yl lithium has been shown to undergo selective electrophilic chlorination with NCS, [25] reaction of the 1Nphenyl congener 2 b with the analogous Ph 2 P-Cl electrophile appears as a natural possibility to prepare the set of eight more or less nitrated N-aryl-1H-benzoimidazolophosphines 3 ah (Figure 1). Their coordinating properties were then envisaged to be compared by the n CO stretching frequencies of carbonyl complexes thereof (LA = Ni(CO) 3 in Figure 1 a). [26] Instead of Ni(CO) 3 serving to define the Tolman's electronic parameters, LA = RhCl(CO) is here preferred for the sake of comparison with former results on related complexes of chelating bisimidazolophosphines, [START_REF] Gouterman | [END_REF] and more generally because of the added value of the complementary 103 Rh NMR probe for rhodiumphosphine complexes. [28]

Results and Discussion

Synthesis of nitro-benzimidazolophosphines

The four NH,N 2 CH benzimidazole precursors 1 a-d were provided either as commercially available for 1 a, or prepared following known procedures; the nitro derivative 1 b or 1 c (in tautomeric equilibrium) was thus elaborated from 4-nitro-1,2-benzenediamine by condensation of triethylorthoester in the presence of a catalytic amount of TiCl 4 and the dinitro derivative 1 d was obtained by nitration of 1 b,c with fuming HNO 3 in concentrated H 2 SO 4 (see the Experimental Section and cited references).

N-Phenylation of 1 a and 1 b,c was implemented by coppercatalyzed C-N coupling from iodobenzene under conditions reported by Buchwald et al., [29] yielding 2 a in 90 % yield, [30] and the isomers 2 b and 2 c in 64 % and 23 % yield, respectively, after separation by column chromatography. [31] The method however failed to produce 2 d from 1 d, in correlation with the very low N-nucleophilicity of 1 d resulting from the cooperative effect of the two nitro groups.

N-p-Nitrophenylation of 1 a-c was carried out by S N Ar of 4fluoro-nitrobenzene, affording the known nitro derivative 2 e in 95 % yield, [30] and the isomers 2 f and 2 g in 53 % and 34 % yield, respectively. [32] Using the same procedure from 1 d, the trinitro derivative 2 h was isolated in 86 % yield (Scheme 1).

Phosphinylation of the lithium salts of 2 a-c-2 e-h by nucleophilic substitution of ClPPh 2 required optimization of the initial deprotonation step. Inspired by the above-mentioned report on the selective deprotonation and reactivity of the N-methyl congener of 2 b, [25] the use of lithium diisopropylamide (LDA) as a base in THF was envisaged, with a strict control of the temperature at À78 8C. [START_REF]At a higher temperature of À40 8C, LDA was indeed[END_REF] Applied to 2 b, these conditions indeed allowed isolation of 3 b in 83 % yield, in the absence of any oxyazobenzene side-product (Scheme 2). [START_REF]At a higher temperature of À40 8C, LDA was indeed[END_REF] The same procedure gave access in 56 % yield to the reference non-nitrated benzimidazolophosphine 3 a, previously reported to be available in 20 % yield only under metal-free conditions (in the presence of NEt 3 as a base). [START_REF] Zou | [END_REF] In summary, application of the LDA procedure to 2 a-c-2 e-g afforded 3 a-c-3 e-g in 45-83 % yield, while only trace amounts of 3 h were obtained from the trinitro substrate 2 h. The phosphinylation selectivity was first evidenced by NMR spectroscopy by the disappearance of the amidine C 1 H singlet signal at 8.10-8.90 ppm and the appearance of a 31 P{ 1 H} singlet signal in the range À21.3/À24.5 ppm.

Single crystals of 3 b, 3 c, 3 e and 3 f deposited from solvent mixtures of pentane and dichloromethane (DCM) were found suitable for X-ray diffraction (XRD) analysis (see the Supporting Information). [35] Notably, the structure of the 5-nitrobenzimidazolophosphine 3 b was resolved in the uncommon P6 1 space group of the hexagonal system. In all the structures, the C-P distances are virtually identical (1.83 AE 0.01 ) . In each case, another phosphine-rhodium complex numbered as 6 b, 6 e or 6 f was concomitantly formed as an initially non-identified side-product, the structural assignment of which could be achieved by crystallographic analysis only (see below, Figure 3).

A one-pot procedure was also attempted, providing the target complexes with slightly higher overall yields, as illustrated from 3 a, 3 c and 3 g (Scheme 3). Two equivalents of 3 c were thus treated with half an equivalent of [Rh(COD)Cl] 2 in DCM for 2 h at r.t., and subsequently with bubbling carbon monoxide for 15 min., affording 5 c in 81 % yield. The same treatment from 3 a and 3 g provided directly 5 a and 5 g in 79 % and 73 % yield, respectively. In all cases involving a nitro ligand (not in the case of 5 a), the side-product of initially unknown structure 6 x (x = b,c, e-g) was also observed (see below).

For the sake of reference to the original concern, the RhCl(CO) complex 5 a' of the cationic benzimidazoliophosphine 3 a' was also targeted. Treatment of 3 a with one equivalent of methyl triflate (MeOTf) in DCM at À78 8C actually led to the N-methylated target product 3 a' in mixture with the P-methylated isomer 3 a'' in a 5:1 ratio, as evidenced by the disappearance of the 31 P NMR signal of 3 a (À24.49 ppm) and appearance of two signals at À15.48 and + 14.36 ppm consistent Scheme 2. Selective C-phosphinylation of nitro-functionalized benzimidazoles. Scheme 3. Sequential and one-pot, two-step syntheses of RhCl(CO) complexes of nitro-substituted benzimidazolophosphines. From 6 x, initially non-identified side-products denoted as 6 x (x = b,c e-g) were also obtained (see Figure 3).

with the structures of 3 a' and 3 a'', respectively. This lack of N/P selectivity in the reaction of the hard methylating agent MeOTf with imidazolophosphine is unprecedented, but correlated with the absence of a second P center in the monophosphine 3 a as compared to the cases of the N-aryl benzimidazolo-and imidazolo-diphosphines BIMINAP ( 2 , 12b, 36] Under the same conditions, treatment of the 5-nitrobenzimidazolophosphine 3 b with MeOTf gave a mixture of the N-and P-methylated isomers 3 b' and 3 b'' in a 3:2 ratio according to NMR analysis (see the Supporting Information): this further lowering of N/P selectivity can be interpreted by the electron-withdrawing effect of the nitro group decreasing the electron density of the N atom more than that of the more remote P atom.

- (diphenylphosphanyl)-1-[2-(diphenyl- phosphanyl)naphthalen-1-yl]-1H-1,3- benzodiazole) and BIPHIMIP (2-(di- phenylphosphanyl)-1-[2-(diphenyl- phosphanyl)phenyl-1H-imidazo- le). [6e
As the two cations 3 a' and 3 a'' could not be efficiently separated, the 5:1 mixture was used in coordination experiments. Treatment of this mixture with 0.25 mol. equivalent of [Rh(COD)Cl] 2 with respect to 3 a', before bubbling carbon monoxide for 15 min allowed the complex 5 a' to be isolated in a high 85 % yield after removal of 3 a'' by washing the DCM-containing residue with cold pentane (Scheme 4).

The P 2 RhCl(CO) complexes of type 5 have been characterized by 1 H, 13 C, 31 P and 103 Rh NMR and IR spectroscopies (see below). Remarkably, no MS method, among ESI, APCI and MALDI, was found suitable to produce molecular peaks of the complexes, preventing structural confirmation by HRMS: the lability of primary cationic species generated in the MS chamber is actually correlated with the weak donating ability of the monodentate ligands. The structures of 5 a-c, 5 f-g and 5 a' were more precisely determined by XRD analysis of single crystals grown slowly from DCM solutions (Table 1, Figure 2). Nota-bly, the structure of the dinitro ligand complex 5 f was resolved with the chiral space group P2 1 2 1 2 1 . In the crystal state, all the complexes were found to exhibit a square planar-like geometry, with a trans arrangement of the two phosphine ligands, and an occupation disorder of the facing Cl and CO ligands, except for 5 f and 5 a'. While the Rh-Cl and Rh-C distances vary in the ranges 2.38 AE 0.03 and 1.81 AE 0.02 , respectively, the C-P distances remain close to 2.31 AE 0.01 . The C-O distance, varying in the range 1.14 AE 0.03 (Table 1), appears not to be a significant indicator of the global electron-donating ability of the phosphine ligand. [37a] This can be ascribed to the cis-orientation of the P-Rh-CO bonds, and to the long recognized considerably weaker geometrical cis-influence of a P ligand on the lengthening of a geminal Rh-L bond (with an Scheme 4. N-vs. P-methylation of the benzimidazolophosphine 3 a, and P-coordination of the benzimidazoliophosphine product 3 a' at a RhCl(CO) center. even weaker correlated influence on the C=O bond length for L = CO) as compared to the corresponding trans-influences. [37b] For the a priori least donating dicationic ligand 3 a', the intermediate C-O distance value of 1.14 is, however, also correlated with the unique conformational features of the complex 5 a'. In the neutral complexes 5 a-c, 5 f-g, indeed, the

Tentative analysis of coordination properties of nitro-benzimidazolophosphines

Disregarding the classical broadness of the 32-51), ruling out any slow equilibrium between a main trans form (found in the crystal state) and significant proportion of the putative cis isomer. The latter is indeed expected to be thermodynamically highly disfavored by the bulkiness of the P environment. Notably, the 31 P coordination shift Dd31 P (x) = d31 P (5 x)Àd31 P (3 x) (x = a-g, a') is found larger for the cationic ligand (Dd31 P (a') = 53.6 ppm) than for the neutral ligands, for which Dd31 P is found to depend on the presence of NO 2 groups on the benzimidazole core only (Table 2): Dd31 P % 45.5 AE 0.1 ppm for a non-nitrated benzimidazole core (x = a, e), Dd31 P % 46.6 AE 0.3 ppm otherwise (x = b, c, f, g). At last, the 1 J RhP coupling constant does not vary significantly remaining in the range 129.6 AE 1.5 Hz for all the neutral complexes, and just reaching 132.8 Hz for the dicationic complex 5 a'.

In a more classical approach, the IR stretching frequency of the CO co-ligand (n CO ) and 103 Rh, 31 P NMR chemical shifts (d103 Rh , d31 P (5 x)) of the (3 x) 2 RhCl(CO) complexes 5 x in CD 2 Cl 2 solutions were selected for appraising the coordinating properties of 3 x, x = a-g, a' (Table 2). The "pre-coordinating" properties of the latter was also tentatively envisaged to be revealed by its 31 P NMR chemical shift in the free state, d31 P (3 x).

As previously observed in related RhX(COD)(phosphine) complexes, [28] no correlation is observed between d103 Rh (5 x) and either d31 P (5 x) or d31 P (3 x). P-Coordination to non-metal hard Lewis acids such an oxygen atom is the singlet spin state (promoted oxygen, O*) was also envisaged in the corresponding phosphine oxides 3 xO, x = a-g, generated by treatment of 3 x with H 2 O 2 (3 aO and 3 bO were also isolated and character- The n CO and d103 Rh parameters thus appear to play complementary roles for appraising the effects of nitro substituents on either the benzimidazole core or pending N-phenyl group, respectively.

Whatever the nitro-decoration of the benzimidazole core, indeed, an N-phenylated ligand gives n CO = 1968 AE 1 cm À1 (5 ac) and an N-p-nitrophenylated ligand gives n CO = 1979 AE 1 cm À1 (5 e-g). Using the 103 Rh NMR probe (see the Experimental Section), whatever the N-aryl substituent, the presence of a nitro substituent on the benzimidazole core (at either position 5 or 6) gives d103 Rh = À315 ppm, vs. d103 Rh = À288 ppm for the nonnitrated reference 5 a (the value for 5 e could, however, not be determined due to solubility issues). The n CO and d103 Rh values for the dicationic complex 5 a' are out of range, but relatively consistent with the expected effects of "electronegative" substituents on the global donating character of the P atom towards the RhCl(CO) center.

The sensitivity of the n CO value to p-nitro-substitution at the N-phenyl group is remarkable (+ 10 cm À1 for a remote NO 2 group, nine-bond away from the CO ligands), in particular with regard to the vanishing effect of nitro substitution at the benzimidazole core in spite of p-conjugation with the coordinating P center. Whatever the electronic process at stake (partial p-conjugation and/or sinductive attraction through the N-Ar bond), the observation is in line with former observations of a marked effect of N-nitroaryl and N-fluoroaryl substitution on intrinsic p-accepting ability or catalytic properties of imidazol-2-ylidene ligands. [38] Dinuclear nitro-benzimidazolophosphine side products: CH 2 Cl 2 -clathrate complexes Each of the nitro-containing complexes 5 b,c, 5 e-.g (Scheme 3) was actually obtained in mixture with a side-product containing a Rh-P bond, as evidenced by 31 P NMR spectroscopy of the crude material, and denoted as 6 b,c, 6 e-g (see the Experimental Section). The exact structure of these complexes could, however, not be assessed by spectroscopic methods. In the case of the dinitro ligand 3 f, however, crystals of 6 f deposited from a DCM solution of the residue obtained from the supernatant of crystals of 5 f after reaction of 3 f with 4 f (Scheme 3). X-ray diffraction analysis showed a dinuclear structure, where the two Rh centers are in distorted bipyramidal environments, coordinated by a m-CO and two P,N-bridging ligands 3 f (Figure 3). The corresponding structures are assigned Table 2. Selected IR, NMR spectroscopic or crystallographic data for the ligands 3 a-c, 3 f,g, 3 a' or complexes thereof. [a,b] charge Z

x [a] n CO (5 x) [c] [cm À1 ] d103 Rh (5 x) [f,d] [ppm] [e] d31 P (5 x)

[ppm]

Dd31 P (x) [g] [ppm] [a] Substitution pattern (x = a-g, a') of N-phenyl-benzimidazole core as defined in Figure 1 (X, Y, Z = H, NO 2 ) and Scheme 4 (for a'). [b] NMR spectra of solutions in CD 2 Cl 2 ;

[c] from IR spectra in the solid state recorded by the ATR (attenuated total reflection) technique; [d] chemical shift with respect Rh(acac) 3 with the frequency ratio X' = 3.186447 %; [e] chemical shift for the formal frequency ratio X = 3.160000 %; [f] the 1 J Rh-P coupling constants remain similar, varying from 128.3 Hz for 5 e to 132.8 Hz for 5 a';

[g] coordination shift: Dd31 P (x) = d31 P (5 x)Àd31 P (3 x); [h] from X-ray diffraction data (see Table 2 and the Supporting Information). A search in the CCDC database for similar complexes featuring such a [Rh 2 (m-CO)Cl 2 ] core gave 18 related examples, five of them featuring P,N coordination to the Rh centers, with Rh-Rh bonding distances ranging from 2.57 to 3.01 . [39] The Rh-Rh distance of 2.63 measured in 6 f is thus quite short, smaller than the average value of 2.68 over the series. The RhÀCl bonds of 6 f (bent from the Rh-Rh axis by ca. 1638) are significantly shorter than all the corresponding bonds within the CCDC sampling (2.36 vs. 2.42 to 2.45 ). The C-O distance of 1.17 measured in 6 f is identical to the average value over the CCDC series. The Rh-P bonds of 6 f are found to be quite short (2.21-2.22 ), and much shorter than in the parent complex 5 f (2.31 ). The RhÀN bonds are, however, found to be consistently shorter (2.08-2.10 ).

The crystals of 6 f are actually clathrates, with 6.7 DCM molecules per molecule of 6 f. The high solvent content was first suspected after observing disintegration of isolated crystals in polyisobutene blend oils used as cryo-protectants for XRD analysis (PARATONE or PARABAR 10312; the use of a perfluoropolyether oil, PFO-XR 75, was finally required). The solvate molecules are spread over 12 positions, eight of them being partially occupied and forming a chain with short distances between positions strongly occupied by Cl atoms (Cl•••Cl % 3.5 ), thus suggesting that the chain cohesion is due to halogen bonding, [40a] today widely invoked in crystal engineering. [40b,c] Chains of DCM molecules were also proposed to occur in a related dirhodium complex, [39i] but the extended van der Waals gallery within the crystal network of 6 f (Figure 3) meets more general challenges in the search for metal-organic inclusion compounds of the clathrate type or porous coordination polymers, [41a] in particular for DCM guest molecules which are more currently found hosted by organic lattices. [41b-e] Within the family of the Werner clathrates, based on a discrete packing of MX 2 L 4 complexes (M = divalent transition metal ion, X = small anionic ligand, L = pyridine ligand), [41f] and related Hoffmann clathrates based on a grid of CN-bridged coordination polymer (initiated by the cadmium(II)-CCl 4 clathrate), [41g,h]

Conclusion

The disclosed strategy, upstream based on the use of LDA as the optimal base for the deprotonation of more or less nitrated N-aryl benzimidazole precursors dedicated to react with ClPPh 2 , allowed a pioneering exploration of the coordination chemistry of nitroaromatic phosphines as neutral electron-poor ligands with decreased s-donating ability. The approach and results open natural prospects in organometallic chemistry such as the synthesis of tri-or tetra-nitro counterparts of the ligands 3, the design of chelating diphosphine congeners, and the comparison with possible analogous complexes of nitrated triphenylphosphines such as (4-NO 2 -C 6 H 4 ) 3 P standing as a paradigm. As a preliminary analysis, reduction of the P atom of known p-nitrophenylphosphine oxides with the classical HSiCl 3 reagent is, however, expected to be tricky: in spite of an early report, [15e] recent results indeed indicate that competing reduction of the nitro group by HSiCl 3 could occur, even under milder conditions. [42] In an alternative strategy, (4-nitrophenyl)diphenylphosphine, partly described 40 years ago, [15b, 20] was targeted from 4-nitro-iodobenzene and ClPPh 2 but could not be isolated, and further efforts in this direction are naturally envisaged. Nevertheless, targeting the particular category of the benzimidazolyllphosphine complexes 4 and 5 gave the opportunity of evidencing unique features such as: (i) empirical binary "orthogonal spectroscopic indicators" of the presence or not of nitro groups on distinct parts of the ligand (the benzimidazole core and the N-aryl substituent), based on an observed contrast between two ranges of values separated by ca. 5 times the spectroscopic resolutions: 10 cm À1 and 30 ppm, respectively, for the n CO and d Rh probes at the RhCl(CO) center; (ii) in the dicationic complex 5 a', an electrostatic sandwiching of a chloro ligand by two imidazolium rings resulting from a packing effect, and possibly balanced by enhanced polarization of the Rh-Cl bond; (iii) serendipitous finding of an organic-organometallic clathrate of high solvent content (the DCM solvate complex 6 f). A more general occurrence of such features could be sought for in other systems involving other transition metals (Ni, Pd, Pt) and ligands or co-ligands thereof. Finally, beyond coordination chemistry, the results are naturally aimed at exploring the use such complexes in homogeneous catalysis.

Experimental Section

General remarks THF and diethyl ether were dried and distilled over sodium-benzophenone. Pentane and dichloromethane (DCM) were dried with a PureSolv-MD-5 Innovative Technology system for the purification of solvents. [Rh(COD)Cl] 2 and other reagents were employed as received from commercial sources, in particular, solutions of nBuLi were 2.5 M in hexane. All reactions were carried out under an argon atmosphere by using Schlenk and vacuum line techniques. Column chromatography was carried out on silica gel (60 , C.C 70-200 mm). Previously reported procedures were used for the preparation of the phosphines and their precursors, in particular for the previously described compounds 1 b and 1 c, [43] 1 d and 1 e, [44] 2 a, [45] and 3 a. [6e,29b] Procedures for the preparation of new compounds For the characterization of the reported compounds by 1 H, 31 P, 13 C NMR and IR spectroscopies, by mass spectrometry, and by melting point, see the Supporting Information. Preparation of 2 b and 2 c. [44] A mixture of 1 b (2.69 g, 16.5 mmol), Cu I (0.263 g, 1.38 mmol), 1,10-phenanthroline (0.48 g, 2.76 mmol), Cs 2 CO 3 (9.42 g, 28.9 mmol) was evacuated twice and back-filled with argon in a dried Schlenk tube, then iodobenzene (1.52 mL, 13.8 mmol) and DMF (20 mL) was added with a syringe. The reaction mixture was stirred at 100 8C for 48 h. After the mixture was cooled down to ambient temperature, the solution was filtered on silica gel, extracted with EtOAc, dried over MgSO 4 and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel eluted with a 3/2 EtOAc/pentane mixture to deliver 2 b (2.108 g, 8.8 mmol, 64 %) and 2 c (0.75 g, 3.1 mmol, 23 %) as yellow solids.

Preparation of 2 f and 2 g. [46] A mixture of 1 b (1. 63 g, 10 mmol) and NaOH (0.40 g, 10 mmol) in 20 mL DMF was treated with 4-nitrofluorobenzene (2.12 mL, 20 mmol) at room temperature under argon. The mixture was stirred at 70 8C for 5 h before addition of water. The resulting suspension was extracted with EtOAc (3 40 mL), and the organic layers were combined, dried over MgSO 4 and concentrated to dryness under reduced pressure. Column chromatography of the residue on silica gel eluted with a 3/2 EtOAc/pentane mixture afforded the corresponding products 2 f (1. 51 g, 5.3 mmol, 53 %) and 2 g (0.97 g, 3.4 mmol, 34 %) as yellow solids. The same procedure from 1 e afforded 2 e as a yellow solid in 95 % yield. Starting from 1 h, and changing the chromatographic eluting system to a 1/1 EtOAc/pentane mixture, 2 h was obtained as a yellow solid in 86 % yield.

General procedure for preparation of the nitroaromatic phosphines 3 b,c, 3 e-h

A solution of 2 a-c, 2 e-h (1 equiv) in THF was treated with a solution of freshly prepared LDA (1.2 equiv) at À78 8C. The mixture was slowly warmed up to À40 8C, then stirred for 1 h at this temperature. After cooling back to À78 8C, chlorodiphenylphosphine was added dropwise and the solution was slowly warmed up, then stirred at r.t. for 4 h. After addition of a saturated aqueous NH 4 Cl solution and dilution with DCM, the aqueous layer was separated and the organic layer was dried over MgSO 4 and concentrated to dryness under reduced pressure. The residue was purified by column chromatography on silica gel eluted with a 3/1 DCM/pentane mixture to give the corresponding products as yellow solids (for more details, see the Supporting Information): 3 a (78 %), 3 b (83 %), 3 c (70 %), 3 e (62 %), 3 f (77 %), 3 g (45 %), 3 h (< 5 %).

General procedure for generation of the phosphine oxides 3 xO (x = a-c, e-g)

The phosphine oxides were generated according to a previously reported procedure, [47] by treatment of a solution 3 x in THF with H 2 O 2 (3 equiv) at room temperature under TLC monitoring. After addition of NaHCO 3 and Na 2 S 2 O 3 solutions, the reaction mixture was separated, and the aqueous layer was extracted with DCM. The combined organic layer was dried over Na 2 SO 4 and concentrated under reduced pressure affording the corresponding phosphine oxide in quantitative 31 P NMR spectroscopic yield without further purification. The products were analyzed by 31 P NMR spectroscopy only (see Table 2), except for 3 aO and 3 bO which were more completely characterized (see the Supporting Information).

General procedures for the preparation of rhodium complexes

Method A. A solution of 3 x (x = b, f, e) and [Rh(cod)Cl] 2 (0.5 equiv) in DCM was stirred at r. t. for 4 h. After concentration under reduced pressure, the residue was washed with pentane and dried to afford the corresponding rhodium complex as brown solids: 4 b (95 %), 4 e (93 %), 4 f (94 %). A solution of 4 x and the corresponding phosphine 3 x (1 equiv) in DCM was treated with bubbling carbon monoxide for 15 min. After concentration under reduced pressure, the residue was washed with diethyl ether (or a DCM/pentane mixture) to give the corresponding rhodium complex 5 b (60 %), 5 e (74 %), 5 f (76 %). Minor amounts of the dimeric rhodium complex 6 b (18 %), 6 e (14 %) or 6 f (15 %) were also detected by 31 P NMR spectroscopy of the crude material (approximate spectroscopic yields given). Crystals of 6 f deposited from a DCM solution could be characterized by XRD analysis (see below and the Supporting Information). Method B. A solution of 3 x (x = a, c, g) and[Rh(cod)Cl] 2 (0 .25 equiv) in DCM was stirred at r. t. for 4 h. Carbon monoxide was then bubbled through the solution for 15 min. After evaporation of the solvent under reduced pressure, the crude mixture was washed with diethyl ether (or a DCM/pentane mixture) to give the corresponding rhodium complex 5 a (79 %),5 c (81 %) or 5 g (73 %) as a yellow solid. Minor amounts of the dimeric rhodium complex 6 c (4 %) or 6 g (13 %) were also detected by 31 P NMR spectroscopy of the crude material (approximate spectroscopic yields given).

Rhodium complex 5 a'. To a solution of 3 a (152 mg, 0.4 mmol) in DCM (4 mL) at À90 8C was added methyl trifluoromethanesulfonate (45 mL, 0.4 mmol). The mixture was slowly warmed up to À40 8C and stirred for 2 h. After evaporation of the solvent under reduced pressure, the residue was washed with cold pentane, dried under reduced pressure and then analyzed as a 5:1 N + Me:P + Me mixture of the methylation products of 3 a, which could not be separated. To a solution of this mixture in DCM (10 mL) was added [Rh(cod)Cl] 2 (41 mg, 0.083 mmol), and stirring was pursued at r. t. for 4 h. Carbon monoxide was then bubbled through the solution for 15 min. The solvent was evaporated under reduced pressure, and the residue was washed with diethyl ether to afford 5 a' (130 mg, 68 %) as a yellow solid.

103 Rh NMR spectroscopy 103 Rh/ 31 P{ 1 H} HMQC spectra were recorded on a Bruker AV400 spectrometer, equipped with a three-canal probe H{P}{X}-TBI 5 mm using saturated solutions of 5 x in CD 2 Cl 2 (in the cases of 5 e and 5 f, saturated concentration did not allow achieving sufficient acquisition in available time). A preliminary search for the 103 Rh resonances was performed through 31 P{ 1 H} experiments with 103 Rh inversion using a sequence adapted from the literature giving a narrow range for 103 Rh chemical shifts. [48] In this range, precise chemical shifts of 103 Rh were measured via an inverse correlation HMQC using both 103 Rh-31 P coupling constants. The exact spectrometer 1 H frequency of n 0 = 400.1318 MHz corresponds to the resonance of tetramethylsilane. The 103 Rh frequency ratio X can be assigned to either the formal value X = 3.16 % (for which rhodium metal is just an approximate reference giving d103 Rh % 0 ppm), [49] or to the observable value X' = 3.186447 % defined from the real reference Rh(acac) 3 (for which d103 Rh = 0 ppm if saturated in CDCl 3 solution). [50] Each frequency ratio defines its own chemical shift scale in ppm: d = (nÀXn 0 )/(Xn 0 ) 10 6 and d' = (nÀX' n 0 )/(X' n 0 ) 10 6 , where n is the physical resonance frequency observed for the nominal field of the spectrometer. By elimination of n, the scales are related by the equation: 10 6 , where x = X'/X = 1.008369 (giving d(Rh(acac) 3 ) = 8369 % 8358 ppm for d'(Rh(acac) 3 ) = 0). [49a] The d103 Rh values in Table 2 are given in both scales.

d = d'x + (xÀ1)

Crystallographic studies

Intensity X-ray diffraction data from single crystals were collected at low temperature on an Apex2 Bruker diffractometer equipped with a 30 W air-cooled microfocus source (l = 0.71073 ) or on an Oxford-Diffraction Gemini (l = 0.71073 or 1.54180 ). The structures were solved using direct methods or SUPERFLIP, and refined by means of least-squares procedures on F using the programs of the PC version of CRYSTALS. Atomic scattering factors were taken from the International Tables for X-Ray Crystallography. [51] All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined using a riding model. Absorption corrections were introduced using the program MULTISCAN. For the free phosphines 3 b and 3 f, it was not possible to resolve diffuse electron-density residuals (enclosed solvent molecules). Treatment with the SQUEEZE facility from PLATON resulted in a smooth refinement. [52]

Supporting Information

It includes yields, spectroscopic and other characterizations of all new compounds. 1 H, 31 P, 13 C, 103 Rh-31 P{ 1 H} HMQC NMR spectra and crystallographic data are also provided. 2)

The forgotten nitro-aromatic phosphines as weakly donating Pligands: a N-aryl-benzimidazolyl series in RhCl(CO) complexes

SnCl 2 HCl 3) NaOH Ph R Ph Ph Ph R TMS f, R = , X = Li, 10% g, R = p-NH 2 -C 6 H 4 , X = MgBr, 26% h, R = p-NMe 2 -C 6 H 4 , X = MgBr, 6% i, R = p-indolyl-C 6 H 4 , X = MgBr, 71% j, R = p-carbazolyl-C 6 H 4 , X = Li, 69% k, R = p-anisyl-C 6 H 4 , X = MgBr, 8% N Ph Et n n C 6 H 13 C 6 H 13 l, n = 0, X = Li, 3% m, n =1, X = Li, 0% n, n = 0, X = Li, 59% o, n = 1, X = MgBr, 51% C 8 C 10 Ph Ph Ph Ph OMe OMe OMe OMe O O H H MnO 2 d e f-o 1

Introduction

By January 1995, the title term ''carbo-benzene'' was proposed for 1, as a putative example of Hu ¨ckel-aromatic carbo-mer, 1 namely a structure devised by D 6h symmetry-preserving C 2 -expansion of the benzene molecule (Fig. 1). 2 In spite of an attempt of synthesis via the hexaoxy- [6]pericyclynediol 2 (itself targeted via a [9+9] macrocyclization route from the triynal 3), 3 the ''bare'' carbo-benzene 1 could not be obtained and remains hitherto experimentally unknown. 4 Exactly at the same time, Ueda et al. communicated the synthesis of 3,6,9,12,15,18-hexaphenyldodecadehydro[18]annulene 4 and a few congeners, 5 standing as the first examples of carbo-benzene derivatives, in tri-or hexa-substituted versions (Scheme 1). The highly chromophoric compound 4 and its [6]pericyclynetriol precursor 5 were described in more details by the same authors in 1998. 6 The employed route was based on a [11+7] macro-cyclization step, where the bis-terminal tetrayne 6 reacts as a dinucleophile with the skipped bis-ynal 7 as a dielectrophile. The original synthetic route thus consisted of 15 steps, with 1% overall yield, and 59% yield for the 5 -4 reductive aromatization step. 5,6 In 2007, the same hexaphenylcarbo-benzene 4 was reported to be also accessible by reductive aromatization of the [6]pericyclynediol 8 or [6]pericyclynetetraol 9, in 12 or 22% yield, respectively. 7 The precursors 8 and 9 were themselves obtained through [14+4] macro-cyclization processes, in nine steps with 11% overall yield, and eight steps with 12% overall yield, respectively. 8 A much shorter alternative route would be based on a [8+10] macro-cyclization process and a key [6]pericyclynedione 10, 9 which more recently proved to be efficient for the synthesis of centro-symmetric tetraphenyl-carbo-benzene targets. 10 Application of this method to the preparation of the carbo-benzene paradigm 4 is hereafter described, along with the synthesis of the a priori more lipophilic p-bis-(di-3,5-tert-butylphenyl) derivative 11. In the 1998 pioneer report, 6 X-ray diffraction (XRD) analysis of a single crystal of 4 allowed confirmation of the quasi-D 6h symmetric structure and provided information on bond distances and bond angles. Nevertheless, the quality of the crystallographic structure was likely not sufficient for deposition of a coordinate listing at the CCDC, where no corresponding cif file is currently available. The challenge of gaining accurate crystallographic data to make a cif file of 4 available at the CCDC is particularly addressed below.

Results and discussion

The carbo-benzene targets 4 and 11 were thus envisaged by reductive aromatization of the [6]pericyclynediols 12 and 13. The latter were targeted from the known [6]pericyclynedione 10, respectively, obtainable by oxidation of the corresponding secondary [6]pericyclynediol 14 (Scheme 2). 9 An optimal procedure for the synthesis of 14 is based on a [8+10] macro-cyclization step involving the C 8 triyne 15 and C 10 dialdehyde 16. As compared to the previously used [11+7] and [14+4] strategies (see the Introduction), the advantage of the [8+10] strategy is its late divergence character: the sensitive dialdehyde 16 is indeed readily obtained from the triyne 15 just before the macro-cyclization step, providing the [6]pericyclynediol 14 in ca. 40% yield (see the ESI † for a detailed comparison of the original and improved synthesis strategies). 9 The key [6]pericyclynedione 10 is then obtained by oxidation of 14 with MnO 2 . From 10, the targets 4 and 11 were prepared in two steps following a procedure previously experienced for the synthesis of other carbo-benzenes. 10 The addition of two equivalents of either PhLi or PhMgBr to diketone 10 was thus attempted. Treatment of 10 with PhLi was found to induce opening of the C 18 ring, allowing access to the diadduct 12 in a trace amount only. In contrast, the use of PhMgBr allowed isolation of 12 with a remarkably high 82% yield (Scheme 2). The Grignard reagent was thus also used for anchoring two 3,5-ditert-butylphenyl groups to 10, providing the [6]pericyclynediol 13 with 64% yield.

Using a classical procedure, 10 reductive aromatization of 12 and 13 in dichloromethane (DCM) solution with 10 equivalents of SnCl 2 and 20 equivalents of HClÁEt 2 O, followed by neutralization with 1 M aqueous NaOH, gave the targets 4 and 11 with the same 65% yield. This procedure differs from the original one by the nature of the solvent and the hydrolysis conditions. 6 The results confirm recent observations that the use of DCM as a solvent instead of diethyl ether, along with milder hydrolytic conditions (1 M instead of 10 M NaOH), provides higher yields in carbo-benzenes, essentially by enhancement of the solubility of both reagents and products. 10 In comparison with the original method, 5,6 not only the yield in 4 of the last reductive elimination step has been improved from 59 to 65%, but also the total number of steps has been reduced from 15 to 12, while the global yield has been increased from about 1% to 8% (see the ESI † for comparative synthesis schemes).

The hexa-aryl-carbo-benzenes 4 and 11 have been isolated as poorly soluble dark red solids. The introduction of two tertbutyl groups on two phenyl substituents of 4 thus appears to have a limited effect on the solubility of such rigid carbon-rich compounds. Indeed, the solubility of 11 was determined to be ca. 0.46 AE 0.03 mg mL À1 , namely less than twice the solubility of 4 of ca. 0.29 AE 0.03 mg mL À1 , in spite of the presence of four tert-butyl groups on two of the aromatic substituents of 11. For comparison, direct anchoring of aliphatic chains at two vertices the C 18 macrocycle was recently reported to be much more efficient with the view of increasing the solubility of carbo-benzenes. 13 In spite of this, accurate spectroscopic data could be obtained for both 4 and 11 ( 1 H NMR, 13 C NMR, UV-vis), thus confirming the data ranges of Ueda et al. for 4. 5,6 In particular, 1 H NMR spectra of 4 and 11 reveal the characteristic deshielding of the ortho-1 H nuclei of the aryl substituents resulting from the magnetic anisotropy induced by the strong diatropic C 18 ring current (Fig. 1). 1,[5][6][7]10 The UV-vis absorption spectrum of 4 in chloroform solution confirms the l max value of 472 nm previously reported (Fig. 2). 6 Carbo-benzene 11 exhibits an identical spectral profile with the same l max value. The molar extinction coefficient of 4 was however measured to be lower than the value initially reported (234 000 vs. 363 000 L mol À1 cm À1 ). 6 The absorption spectra of 4 and 11 are classical for carbo-benzenes, and their common maximum absorption wavelength l max = 472 nm is a median value of all the reported values, varying from 424 nm for the octupolar triphenyl-carbo-benzene, 5,6 to 521 nm for the quadrupolar para-N,N-dimethylanilinyl-tetraphenyl-carbo-benzene. 10b

The structures of 4 and 11 were confirmed by XRD analysis of single crystals deposited from chloroform solutions (Fig. 3 and Table 1). 14 Contrary to the pioneer crystallographic data, 6 the quality of the present crystals of 4 proved to be sufficient for refined resolution, having allowed a new deposition at the CCDC. 14 The same solvate allotropic variety, involving one CHCl 3 molecule per molecule of 4, was obtained. Noteworthily, the highly planar centro-symmetric molecule 4 thus crystallizes in the Sohncke chiral space group P2 1 2 1 2 1 . Crystallization of a highly symmetrical achiral molecule such as 4 in a chiral space group is not common, but examples have been previously reported for other rigid compounds. 15 Geometrical features of the macrocycle of 4 are typical of generic carbo-benzenes, with average sp 2 C-spC and spC-spC bond lengths of 1.39 and 1.22 Å, respectively. The average angle at the sp 2 vertices of the macrocycle is 118.91. The C 18 ring is slightly distorted: the maximum deviation from planarity is 0.11 Å, while the globally hexagonal shape is not regular, the diameters (between facing sp 2 vertices) varying from 7.79 Å to 8.17 Å. Torsion angles between the phenyl mean planes and the macrocycle mean plane vary from 2.91 to 29.81. In the crystal of 11, the molecules pack in a parallel fashion, the distance between the mean planes of two successive carbo-benzene macrocycles being 3.62 Å, i.e. much larger than in the recently reported first examples of p-stacked carbo-benzenes. 13a No p-stacking is indeed observed here between two C18 rings, or between a C18 ring and any C6 ring of the aryl substituents. Instead of a chlorine atom of the chloroform molecule co-crystallized with 4 (see above), one of the methyl groups of a tert-butyl substituent of 11 pointing towards the center of the C 18 ring of the nearest neighbouring molecule: the closest H atom of this methyl group resides 1.43 Å away from the centroid and 1.38 Å from the mean plane of the neighboring C 18 ring (Fig. 4).

The electrochemical behavior of 4 and 11 has also been studied (Table 2). Cyclic (CV) and square-wave (SWV) voltammograms were recorded for 4 and 11 in chloroform solutions (see the ESI †). More conventional DCM solutions could indeed not be used because of an extremely low solubility in this solvent. For a reference dibutyl-carbo-benzene exhibiting sufficient solubility While the first reduction process was found to occur reversibly at similar potentials (À0.72 V for 4, À0.74 V for 11), the second reduction was found to be irreversible for both compounds (Table 2). These values are consistent with previous values reported for other para-diaryl-tetraphenyl-carbo-benzenes, the first reduction occurring between À0.75 and À0.85 V depending on the nature of the aryl groups. 10a,b This process is however made easier upon substitution of the C 18 ring by acetylenic substituents: the lowest reduction potential (in absolute value) of À0.60 V observed to date for any carbo-benzene was indeed measured for a para-bis-fluorenylethynyl-substituted representative. 10f In the oxidation regime, the first peak potentials of the two carbo-benzenes have comparable values (1.14 V for 4 and 1.19 V for 11), but the process was found reversible for 11 only: the oxidation product of 4 indeed undergoes polymerization, leading to a deposit on the electrode. A second non-reversible oxidation process was also observed for 11. Carbo-benzenes generally undergo irreversible oxidation, most of them leading to a polymeric film on the electrode after the first oxidation process, the latter occurring at potentials between +0.51 and +0.90 V for donor-substituted hexaaryl-carbo-benzenes, 10a,b and reaching +1.17 V for a fluorenylethynyl-substituted derivative exhibiting a more extended p-conjugation. 10f The low first reduction potential value of 4 and 11 (ca. À0.73 V) suggests their possible use as electron acceptors, thus as possible alternatives to C 60 (and PCBM) for photovoltaics (the first reduction potential of C 60 is À0.55 V in chloroform). 16 The accessible and possibly reversible character of the first oxidation of 11 (at 1.19 V) might also be compatible with its use as an organic electron donor. However, the very low solubility of these hexaaryl-carbo-benzenes, even that of the slightly more soluble derivative 11, did not allow preparation of highly regular thin solid films using the ''wet method'', thus preventing measurement of their efficiency for charge transport. 17 Indeed, while microscopic optical images clearly show the non-uniformity of the films, AFM measurements showed a film roughness of ca. 355 nm (Fig. 5). This entails a poor optical quality of the films, as evidenced by

Conclusions

Hexaphenyl-carbo-benzene 4 is a fully symmetrical paradigm and model of the carbo-benzene family: 20 years after its first description, its synthetic accessibility has been significantly improved through the implementation of a [8+10] macro-cyclization strategy, and its characterization has been completed by accurate crystallographic and electrochemical data. The expected enhancement of solubility upon substitution of 4 by four tert-butyl groups was found to be limited, preventing the use of thin films of 11 for charge transport in organic photovoltaics. Nevertheless, the much higher solubility of recently described p-dialkyltetraphenyl-carbo-benzenes 13 allows consideration of their possible use for such applications. The results of the envisaged studies will be communicated in due course. 2,3,7,8,9,13,14,15-nonaen-5,11,17-triyne (4). A solution of [6]pericyclynediol 12 (77 mg, 0.087 mmol) in DCM (50 mL) was treated with SnCl 2 (165 mg, 0.87 mmol) and HCl (0.87 ml, 1.74 mmol, 2 M in Et 2 O) at À78 1C. The mixture was stirred at À78 1C for 10 min, then at room temperature for 25 min. After the addition of aqueous 1 M NaOH (1.74 mL) and filtration through celite s , the organic layer was washed with brine three times, dried over MgSO 4 , and concentrated under reduced pressure. The residue was purified by washings with Et 2 O (3 Â 5 mL) and pentane (3 Â 5 mL) to obtain 4 as a dark violet solid with 65% yield (38 mg, 0.057 mmol). Na: 701.2245, found: 701.2225. UV-vis (CHCl 3 ): l max = 472 nm (e = 234 000 L mol À1 cm À1 ). Melting-decomposition temperature: 221 1C.

4.2.2 1,10-Bis (3,5-di-tert-butylphenyl)-4,7,13,16-tetraphenylcyclooctadeca-1,2,3,7,8,9,13,14,15-nonaen-5,11,17-triyne (11). A solution of [6]pericyclynediol 13 (130 mg, 0.123 mmol) in DCM (100 mL) was treated with SnCl 2 (233 mg, 1.23 mmol) and HCl (1.3 mL, 2.453 mmol, 2 M in Et 2 O) at À78 1C. The mixture was stirred at À78 1C for 20 min, then at room temperature for 15 min. After the addition of 1 M aqueous NaOH (2.6 mL) and filtration through celite s , the organic layer was washed with brine three times, dried over MgSO 4 and concentrated under reduced pressure. The residue was purified by washings with Et 2 O (3 Â 5 mL) and pentane (3 Â 5 mL) to obtain 11 as a dark red solid with 65% yield (47 mg, 0.052 mmol). 1 4.2. 3 4,7,13,16-Tetramethoxy-1,4,7,10,13,16-hexaphenylcyclooctadeca-2,5,8,11,14,17-hexayne-1,10-diol (12). A solution of [6]pericyclynedione 10 (86 mg, 0.126 mmol) in THF (20 mL) was treated with PhMgBr (0.1 mL, 0.291 mmol) at 0 1C. The reaction mixture was stirred for 1 h at this temperature and 0.5 h at room temperature. After the addition of a saturated aqueous solution of NH 4 Cl, the aqueous layer was separated and extracted with Et 2 O. The combined organic layers were dried over MgSO 4 and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (pentane : ethyl acetate 4 : 1) to obtain 12 as a yellow oil with 82% yield (87 mg, 0.104 mmol). 4,7,13,16-tetraphenylcyclooctadeca-2,5,8,11,14,17-hexayne-1,10diol (13). A solution of [6]

Crystal structure determination

Intensity data were collected at low temperature on an Apex2 Bruker diffractometer equipped with a 30 W air-cooled microfocus source or on an Oxford-Diffraction Gemini (l Mo = 0.71073 Å). The structures were solved using SUPERFLIP, and refined by means of least-squares procedures on F using the programs of the PC version of CRYSTALS. 11 Atomic scattering factors were taken from the International Tables for X-ray Crystallography. 12 For 4, the asymmetric unit consists in a whole carbo-benzene molecule. For 11, it contains half a molecule. Both asymmetric units contain a disordered CHCl 3 solvent molecule. All nonhydrogen atoms were refined anisotropically. Hydrogen atoms were refined using a riding model. Absorption corrections were introduced using the program MULTISCAN.

Voltammetric measurements

Voltammetric measurements were carried out using a potentiostat Autolab PGSTAT100 controlled by GPES 4.09 software.

Experiments were performed at room temperature in a homemade airtight three-electrode cell connected to a vacuum/argon line. The reference electrode consisted of a saturated calomel electrode (SCE) separated from the solution by a bridge compartment. The counter electrode was a platinum wire of ca. 1 cm 2 apparent surface. The working electrode was a Pt microdisk (0.5 mm diameter). The supporting electrolyte [n-Bu 4 N][PF 6 ] was used as received (Fluka, 99% electrochemical grade) and simply degassed under argon. The chloroform solutions used in the electrochemical study was 10 À3 M in carbo-benzene and 0.1 M in the supporting electrolyte. Before each measurement, the solutions are degassed by bubbling argon, and the working electrode was polished using a polishing machine (Presi P230). Typical instrumental parameters for recording square-wave voltammograms were: SW frequency f = 20 Hz, SW amplitude E sw = 20 mV, and scan increment DE = 5 mV.

Solid film fabrication and AFM measurements

Glass substrates were cleaned with ethanol in an ultrasonic bath and were rubbed with alcohol-wetted cotton. Substrates were then dried with clean and dry air and kept at 85 1C over 15 min. Before deposition of the compound layers by spin-casting (blend of 11:PCBM) from a chlorobenzene solution (at 30 mg mL À1 ), substrates were treated with UV oxygen plasma for 5 min. The solution was stirred for 4 h and deposited by spin-coating at 1500 rpm for 30 s in a N 2 glovebox. Morphology, roughness and thickness were analyzed by means of atomic force microscopy (AFM) using a microscope easyscan2 from Nanosurf, with a maximum square scanning area of 110 mm, operating in contact mode under ambient conditions (see the ESI †). (n = 2, 8, 14, 20) are thus presented and compared to the monoalkyl series produced concomitantly. In both series, a dramatic enhancement of solubility in organic solvents (CH 2 Cl 2 , CHCl 3 ) is observed for n ≥ 8, and in the dialkyl series, the meltingdecomposition temperature of the solid products is shown to decrease linearly from 208 °C for n = 2 to 149 °C for n = 20. Fluoroalkyl analogues with R = n-C 8 H 4 F 13 are also described. The products display classical UV-vis electronic spectra of carbo-benzenes in solution (λ max = 445.5 ± 1 nm, ε ≈ 200 000 L•mol -1 •cm -1 ). They are also characterized by UV-vis absorption in the solid state, which is found to be correlated with the color and crystal packing. The methylene groups of R provide an experimental probe of the magnetic anisotropy and aromaticity of the C 18 ring through the progressive NMR shielding of the 1 H nuclei from ca. 4.70 to 1.25 ppm going away from the border of the ring (as far as 8 Å away). All alkyl-carbobenzenes were also found to be highly crystalline. Seven of them have been characterized by X-ray diffraction analysis and the C 18 columnar packing compared in a systematic manner. Crystals of the diethyl and bistetradecyl derivatives, containing no solvent molecule, provided the first examples of direct π-stacking of carbo-benzene rings, with inter-ring distances very close to calculated interlayer distances in AB and ABC α-graphityne (3.255 and 3.206 Å vs 3.266 and 3.201 Å, respectively).

INTRODUCTION

Within the continually growing family of π-conjugated carbon allotropes, two main types can be distinguished: the graphenic type based on sp 2 -C atoms only, exemplified by fullerenes, carbon nanotubes (CNTs) and graphene, and the graphynic type based on mixed sp 2 -and sp-C atoms, 1 exemplified by graphdiyne 2 and the yet unknown α-, β-, γ-, or 6,6,12graphynes.

Molecular fragments of either known or unknown, 2D or 3D carbon allotropes, including graphene or α-graphyne, graphite, or α-graphityne, 3 are targeted for property promises inherited from the parent pure-carbon material with the view to designing devices made of diverse components (photovoltaic cells, organic light-emitting diodes, field-effect transistors...). In contrast to the nonselective methods employed for the preparation of mixtures of graphenic nanocarbons (arc discharge, laser ablation, chemical vapor deposition), 4 the bottom-up organic synthesis approach allows access to atomically defined molecular fragments containing oligocyclic carbon cores formally extruded from either CNTs and graphene, 5 γ-graphyne, 6 γ-graphdiyne, 7 or α-graphyne. 8 The decrease of solubility vs the size of the all-carbon core is however a recurring issue requiring recourse to solubilizing substituents of sp 2 vertices at the core periphery. As no substituent can be attached to sp-C atoms, the case of graphynic cores is thus particularly challenging. In the case of αgraphyne, the primary carbon core is the carbo-mer of the C 6 ring of graphene, 9 i.e. a ca. three-times larger C 18 ring with a circumscribed nuclear diameter of ca. 8 Å and a van der Waals hole diameter of ca. 5 Å. The corresponding molecular fragments are carbo-benzene derivatives 1 (Figure 1), generally poorly soluble in organic solvents, except in chloroform (albeit to a limited extent). 9b,10 This lack of solubility has prevented systematic studies of chemical properties of carbo-benzenes. For synthesis and yield issues, indeed, most of the carbo-benzenes reported to date are of the type 1a, bearing at least four phenyl substituents, the remaining two vertices being either unsubstituted (CH) or substituted by other aryl or alkynyl groups. More or less soluble related carbo-meric structures have also been investigated. 10c Partial saturation of the carbo-benzenic C 18 ring to carbo-cyclohexadiene rings or release of its macrocyclic stiffness in carbo-butadienes 3 was thus shown to induce a higher solubility (Figure 1). 10c,d Although 2 and 3 are easier to handle and characterize, the macro/carbo-aromatic character of carbo-benzenes 1a, extensively investigated at the theoretical level, 9b,10c is crucial to provide them with various properties such as unprecedented single-molecule conductance (106 nS with Ar = 4-NH 2 -C 6 H 4 , n = 0; vs 2.7 nS for the acyclic analogue 3), 11 high two-photon absorption cross-section (656 GM at 800 nm with Ar = 9,9-dihexyl-9H-fluoren-2-yl, n = 1), 12 or chemical reversibility of the reduction to pro-aromatic carboquinoids such as 4 (Ar = 9-hydroxy-2,7-diheptyl-9H-fluoren-9yl, n = 0; Ar is here aromatic but not aryl). 13 In the two latter cases and in the case of the carbo-naphthalene 5, 8 attachment of alkyl chains on the fluorenyl(idene) or phenyl substituents was required to secure some solubility. Replacement of bare phenyl substituents by alkyl-phenyl groups (alkyl = n C 5 H 11 , t Bu) was however observed to have a minor solubilizing effect. 8,10a,b,14 Direct attachment of alkyl chains on the C 18 core while removing two aryl substituents should be a priori a more efficient method with the view to enhancing the solubility of carbo-benzene derivatives. Only two alkyl-substituted carbobenzenes have been described to date: an octupolar tri(tertbutyl) derivative 1b 10b and very recently a quadrupolar di(isopropyl) derivative 1c: 15 with branched short (C 2 ) alkyl chains, however, none of them is lipidic in nature, and the gain in solubility remains weak. Lipidic carbo-benzenes were therefore envisaged in the quadrupolar series with two n-alkyl chains at the para positions (substitution pattern of 1a and 1c). Their synthesis and physicochemical properties (solubility, magnetic aromaticity, light absorption, crystal packing) are hereafter described and discussed.

RESULTS AND DISCUSSION

2.1. Synthesis of Mono-and Dialkyl-carbo-benzenes. The target p-di-n-alkyl-carbo-benzenes were envisaged by reductive aromatization of the corresponding [6]periyclynediols 6a-e (Scheme 1), themselves envisaged from the [6]pericyclynedione 7, 16 that proved to be a relevant last-butone pivotal precursor of most quadrupolar carbo-benzenes known to date (but not 1c). 9b,10c Following an optimized procedure, the diketone 7 is obtained as a statistical mixture of five diastereoisomers in 10 steps and ca. 10% global yield from benzoyl chloride and bis-trimethylsilylacetylene, the C 18 ring being formed in a [8 + 10] cyclization step from a C 8 diterminal triyne and the corresponding C 10 triyndial. 16a The alkyl groups were then introduced by double-nucleophilic attack of 7 with two equivalents of the corresponding alkyl Grignard reagents (in the presence of an optimized excess of three equivalents): The Journal of Organic Chemistry Article aryl Grignard congeners indeed proved to be optimal nucleophiles for 7, giving higher yields than the lithium counterparts. 10c Four alkyl chains R = n-C n H 2n+1 differing by a minimal C 6 increment were selected: n = 2, 8, 14, 20. The C 8 chain was also considered in the partially fluorinated version R = n-C 8 H 4 F 13 . While ethyl and tetradecyl magnesium bromides were used from commercially available solutions, the other Grignard reactants were prepared from the corresponding bromoalkanes. In all cases, the Grignard reaction with 7 led to two main products, always obtained in comparable ratios as mixtures of isomers (Scheme 1). The major product is the diadduct 6a-e (isolated in 30-45% yield), while the minor one is the monoadduct 8a-e resulting from the reduction of one of the keto groups of 7 to a carbinol vertex (and isolated in 20-28% yield). Smaller quantities of the known double-reduction product 9 were also obtained in 6-20% yield. 16a The reducing ability of alkyl Grignard reagents, in particular toward hindered ketones, is due to the presence of a H atom in the β-position, allowing β-elimination leading to the corresponding terminal olefin and "HBr + Mg 0 " as a formal reducing agent. The exact mechanism of the reduction has been largely studied, 17 and several procedures were proposed to enhance the selectivity in addition vs reduction. 18 The recommended use of apolar solvents such as toluene, or additives such as CeCl 3 have been attempted but proved to be inefficient on dialkynylketone substrates such as 7. Nevertheless, taking advantage of this, isolation of an extended library of both monoalkyl- [6]pericyclynediols 8a-e and dialkyl- [6]pericyclynediols 6a-e offered the opportunity to target both the dissymmetrical monoalkyl-carbo-benzenes 10a-e and the symmetrical dialkylcarbo-benzenes 11a-e.

Using a classical treatment with anhydrous SnCl 2 and etheral HCl, the [6]pericyclynediols 6a-e and 8a,b,d,e were converted to the corresponding carbo-benzenes 11a-e and 10a,b,d,e, isolated in 13-71% yield and 12-40% yield, respectively (Scheme 1). 9b,10a-c By comparison, the aromatization of 9 was previously reported to give the unsubstituted tetraphenyl-carbobenzene 12, along with an HCl adduct thereof. 19 The present products were obtained as dark blue-violet solids, giving orange solutions in chloroform. The solubility of the mono-and diethyl representatives 11a and 10a in any organic solvent happens to be very low, preventing full characterization of 11a in solution. As anticipated in the hydrocarbon series, the solubility was found to increase with the chain length from C 2 to C 14 and then to decrease back for C 20 . In contrast, no significant effect on the solubility was observed upon fluorination of the C 8 chain of 11b into 11e. The corresponding magnetic anisotropy has long been established by calculation of nucleus-independent chemical shifts NICS(x), 20 x Å above the centroid of the C 18 ring on the normal to the ring mean plane passing through this center (NICS(0) = -17.9 ppm for unsubstituted carbo-benzene vs -8.0 ppm for benzene). 21 According to the Biot-Savart law, the magnetic deshielding should decrease versus the distance from the ring border, and the aliphatic chains of 11a-e directly anchored to this border provide a unique experimental probe to appraise the distance effect through the variation of the 1 H chemical shifts of the CH 2 groups along the chains. In 11b-d, containing at least six CH 2 groups in almost identical local environments, the progressive shielding of the C 1 H 2 signals away from the C 18 macrocycle is the same for the three compounds and highly regular (Figure 2). The first methylene group (directly connected to the carbo-benzene ring and numbered as k = 1) thus resonates at very low field, at ca. 4.7 ppm in 11a-d (4.72 ppm in 11a; 4.68 ppm in 11b vs 2.58 ppm in the parent 1,4-dioctylbenzene), [START_REF] Bramborg | For di-n-octyl-benzene[END_REF] while the chemical shift of the next groups (numbered as k = 2, 3,...) undergoes an exponential decay down to ca. 1.25 ppm. 23 With six or seven methylene groups having significantly different 1 H chemical shifts, the dioctyl derivative 11b bears the shortest aliphatic chain serving as an experimental probe of the magnetic anisotropy of the aromatic carbo-benzene macrocycle away from the C 18 ring border (as far as 7.7 Å for k = 6, 8.9 Å for k = 7: see Figure 2 and X-ray crystal structure of 11b, section 4 and SI).

In 11e, the two first methylene protons are further deshielded by the neighboring fluorine atoms. The amplitude of the main curve (11a-d) shows that the alkyl protons are highly sensitive to the aromatic (diatropic) ring current. No such deshielding effect is observed on the 13 C and 19 F nuclei of the CH 2 and CF 2 groups along the alkyl substituents in 11a-d or 11e, the corresponding chemical shifts remaining almost unchanged upon aromatization of the [6]pericyclynediol precursors 6a-e. This is in accordance with earlier recognition of the lower sensitivity of 19 F and 13 C nuclei to ring current effects, as compared to 1 H nuclei. [START_REF] Balci | ], as it contributes only a little to the total shielding (2 ppm), which is generally hidden by other larger[END_REF] Although ring current effects in 13 C NMR have been evidenced in particular cases, 25 the 19 F NMR chemical shifts have been more generally considered to be more sensitive to steric than to electronic effects. 26 In the dissymmetrical monoalkyl series 10a,b,d,e, 1 H and 13 C NMR chemical shifts of the CH 2 groups are identical to those observed for the dialkyl counterparts. The 1 H nucleus directly connected to the C 18 macrocycle resonates at 9.81 ± 0.03 ppm, which is comparable to the chemical shift of 9.87 ppm for the corresponding nuclei in the unsubstituted tetraphenyl-carbobenzene 12. imposable and exhibit the classical pattern of carbo-benzenes (Figure 3): 9b,10c,12,19 a main band at λ max = 446.5 ± 0.5 nm in the dialkyl series 11a-e, 444.5 ± 0.5 nm in the monoalkyl series 10a,b,d,e, accompanied by three smaller bands at 502.0 ± 0.5, 519.0 ± 0.5 (sh), and 551.5 ± 0.5 nm. The presence of one or two alkyl substituents on the C 18 macrocycle has thus a negligible effect on the absorption properties in solution, but the dialkyl-carbo-benzenes have different colors in the solid state. For comparison, the UV-vis spectrum of the unsubstituted tetraphenyl-carbo-benzene 12 is virtually identical (with λ max = 444 nm). 19 As previously demonstrated, 12 the main one-photon absorption band of carbo-benzenes, whatever their substitution pattern, corresponds to two transitions centered on the C 18 rings, analyzable by the Gouterman fourorbital model devised for porphyrins. [START_REF] Gouterman | [END_REF] The dialkyl-carbo-benzenes displaying different colors in the solid state (11a and 11c are dark blue, 11b is dark violet, and 11d and 11e are dark red), the solid UV-vis absorption spectra of the solids were also recorded and found consistent with the observed colors despite the broadness of the bands, with one or two maxima in the range 450-650 nm (analogous spectral shapes are observed for the solid monoalkyl congeners 10a,b,d,e: see SI). In spite of the structural similarity of the molecules, different intermolecular interactions in the solid state should thus be invoked to explain the color variation: related crystallochromy, i.e., correlation of the solid state color with the crystal packing as a function of the length of alkyl substituents, was recently reported for a series of tetraalkyltetracenes. 28 A correlation between the crystal packing of 11a-e and their color in the solid state is tentatively sought for hereafter.

2.4. Crystal Properties of Lipidic Carbo-benzenes. Beyond their lipidic nature, both mono-and dialkyl-carbobenzenes proved to be highly crystalline. Seven representatives, 10b,d and 11a-e, could thus be characterized by X-ray diffraction (XRD) analysis of single crystals deposited from DCM or CHCl 3 solutions (Table 1, Figure 4; for 10b and 10d, see Figure S1 in the SI). 29 The weak diffracting power of crystals of the fluorinated dioctyl-carbo-benzene 11e limited the acquisition of data but allowed qualitative confirmation of the structure (see SI, Figure S2).

In the dialkyl series 11a-d, the C 18 ring exhibits a classical quasi-planar quasi-hexagonal conformation (with a maximal deviation of 0.058(2) Å for 11a) and classical bond lengths (spC ... spC ≈ 1.22-1.23 Å, sp 2 C ... spC ≈ 1.37-1.39 Å). 9b,10c The alkyl carbon chains, stretched in a planar zigzag arrangement, a Chemical vertical overlap of successive C 18 rings (see Figure 5).

The Journal of Organic Chemistry

Article can be coplanar with the C 18 macrocycle (dihedral angles of 6.6(1)°for 11b, 3.3(1)°for 11d) or not (dihedral angle of 40.2(2)°for 11a, 22.0(1)°for 11c). With two fully stretched eicosyl chains, the carbo-benzene 11d is the largest carbobenzenic structure ever described, with a distance of 57.435(11) Å between the two carbon atoms of the CH 3 ends (Table 1).

In the crystal state, the macrocycles of 11a-d form slanting columnar arrangements, where the distance between the C 18 mean planes of two successive carbo-benzene molecules varies from 3.206 to 3.398 Å. The deviation from "columnar verticality" (Θ = tilting angle between the column axis and the normal to the mean planes) varies from 55.0°for 11c to 71.5°for 11d. The first examples of π-stacking between carbobenzene rings are observed in the crystal structures of 11a and 11c (Figure 5), where the small Θ values allow partial vertical overlap of successive C 18 macrocycles separated by distances very close to those calculated for ABC or AB α-graphityne (2.201-3.266 Å). 3 The maximal extent of vertical overlap is thus attained in crystals of 11c (top Figure 5), where the distance between the C 18 mean planes (3.206 Å) corresponds to the shortest internuclear distances of ca. 3.36 and 3.41 Å occurring between pairs sp-C and sp 2 -C(Ph) vertices of successive C 18 rings, respectively. π-Stacking between phenyl substituents, even at low overlap extent, can also significantly contribute to the stabilization of the tilted columnar arrange-ment. 30 Nevertheless, the molecular packing indicates significant dispersive intermolecular interactions between tetradecyl chains arranged in a parallel manner: six alternating methylene groups of one chain interact with their closest congeners in the neighboring molecule through C•••C distances in the range 4.50-4.58 Å, revealing an intermolecular van der Waals contact between ideally located H atoms (internuclear H•••H distances of ca. 2.8 Å). The π-stacking between carbo-benzene rings is however not merely driven by the London forces between the C 14 alkyl chains of 11c: the same configuration is also observed for the much shorter (not interacting) C 2 alkyl chains of 11a, with a slightly larger deviation from columnar verticality (Θ = 57.7°) and shortest internuclear distances of ca. On the basis of these analyses, a tentative correlation between the intermolecular interactions and the colors of the dialkyl-carbo-benzenes 11a-d in the solid state can be proposed. The common blue color of solid 11a and 11c can be correlated with the comparable extent of π-stacking interactions between the C 18 macrocycles (Θ ≈ 55°). Furthermore, the C 2 and C 14 alkyl chains of these two carbobenzenes stretch out of the C 18 ring mean planes, while the carbon chains and the macrocycle are coplanar in all other cases. Also noteworthy, crystals of 11d and 11b, red and violet, with and without π-stacking between phenyl substituents, respectively, exhibit the same space group (P-1). The decrease of π-stacking efficiency from 11a and 11c to 11d and 11b is also correlated with their different colors and UV-vis absorption spectra, the wavelength of the right edge of the broad band decreasing in the same order of magnitude: from ca. 700 nm for 11a and 11c to ca. 675 and 660 nm for 11d and 11b, respectively (see SI).

As a macroscopic crystal property, the variation of the melting point of the dialkyl-carbo-benzenes 11a-e has been investigated. Although the dark color of the crystals prevented visual monitoring of the melting process, melting-decomposition temperature values could be determined (Table 1). While detectable melting-decomposition points of most nonlipidic carbo-benzenes are in the range 200-250 °C, 10c a regular decrease of this temperature with the chain length n is observed: from 208 °C for n = 2 to 149 °C for n = 20 (Figure 6). Noteworthy, the melting-decomposition temperature of the fluorooctyl derivative 11e is just slightly higher (196 °C) than that of the octyl analogue 11b (188 °C). In the hydrocarbon series, extrapolation of the linear fit to very long chains (n > 20) suggests possible thermotropic behavior at temperatures compatible with molecular stability.

CONCLUSION

The disclosed series of carbo-benzenes combining oxymoronic features of lipidic and aromatic/chromophoric hydrocarbons opens new prospects in the context of carbo-benzene and futurist α-graphyne chemistry.

The dioctyl derivative 11b bearing the shortest alkyl chain serves as an experimental 1 H NMR probe of the magnetic aromaticity of the carbo-benzene macrocycle, as far as ca. 8 Å away from the C 18 ring border. The octyl chains of 11b also provide sufficient solubility to allow future studies of the chemical reactivity of the carbo-benzene ring, in particular toward metallic ions or small π-electron-rich organic guests to form π-inclusion complexes of various types. 32 The analogue 11e is the first example of a fluorinated carbo-benzene derivative.

The diethyl and bistetradecyl derivatives 11a and 11c afford first examples of π-stacking of carbo-benzene rings, thus providing experimental evidence of the possible cohesion of α-graphyne layers in α-graphityne. The maximum overlap extent is attained in crystals of 11c, where the distance of 3.206 between stacked C 18 ring planes fits with the calculated interlayer distances of 3.266 and 3.201 Å in AB and ABC αgraphitynes, respectively. 3 The biseicosyl derivative 11d exhibits the lowest meltingdecomposition temperature ever reported for a carbo-benzene derivative (149 °C). At lower temperature and possibly greater chain lengths (n > 20), reversible thermotropic behavior might be envisaged. The columnar packing of dialkyl-carbo-benzenes in the crystalline state suggests that liquid crystal properties of putative carbo-benzenic mesogens might involve discotic assemblies.

EXPERIMENTAL SECTION

4.1. General Remarks. THF, diethyl ether (Et 2 O), pentane, and dichloromethane (DCM) were dried by filtration under dry argon over two alumina-containing columns. All other reagents were used as commercially available. In particular, commercial solutions of n-BuLi were 2.5 M in hexane, solutions of ethylmagnesium bromide were 3 M in THF, and solutions of HCl were 2 M in Et 2 O. [6]Pericyclynedione 7 was prepared according to previously published procedures. 16a All reactions were carried out under an argon atmosphere using Schlenk tubes and vacuum line techniques. Column chromatography was carried out on silica gel (60 Å, CC 70-200 μm). Silica gel thin layer chromatography plates (60F254, 0.25 mm) were revealed by treatment with an ethanolic solution of phosphomolybdic acid (20%). NMR chemical shifts are given in ppm with positive values to high frequency relative to the tetramethylsilane reference. Coupling constants J are given in Hertz; wavelengths λ in nanometers, and UVvis extinction molar coefficients ε in L•mol -1 •cm -1 .

4.2. Experimental Procedures. 4.2.1. General Procedure for the Preparation of Grignard Reagents RMgBr, R = n-C n H 2n+1 (n = 2, 8, 14, 20), n-C 8 H 4 F 13 . To a solution of magnesium metal (0.441 mmol, 1 equiv) in THF (0.5 mL) a solution of alkyl bromide (0.530 mmol, 1.2 equiv) was added dropwise at room temperature. The mixture was stirred for 2 h at 50 °C and then cooled to room temperature. The resulting solution of alkylbromomagnesium bromides RMgBr was used directly without any further purification.

4.2.2. General Procedure for the Preparation of Lipidic [6]-Pericyclynediols 6a-e and 8a-e. A solution of [6] pericyclynedione 7 (100 mg, 0.147 mmol) in THF (30 mL) at -10 °C was treated with a freshly prepared solution of RMgBr (0.441 mmol in 0.5 mL of THF). The mixture was stirred at -10 °C for 4 h. After treatment with saturated aqueous solution of NH 4 Cl, the aqueous layer was separated and extracted by diethyl ether, the organic layers were combined, then dried over MgSO 4 , and concentrated to dryness under reduced pressure. The residue was purified by chromatography on silica gel to afford the diadduct 6, the monoadduct 8, and the double-reduction product 9 as yellow oils.

4.2.3. General Procedure for Preparation of Lipidic Carbobenzenes 10a,b,d,e and 11a-e. A solution of [6]pericyclynediol 6 or 8 in DCM was treated with anhydrous SnCl 2 (10 equiv) and HCl (20 equiv; 2 M in Et 2 O) at -78 °C. The mixture was stirred at -78 °C for 10 min and then at room temperature for 20 min. After treatment with 1 M aqueous NaOH (20 equiv) and filtration through Celite, the organic layer was separated, washed with brine (3×), dried over MgSO 4 , and concentrated to dryness under reduced pressure. The residue was purified by chromatography on silica gel to give the carbobenzene 11 or 10 as a strongly colored solid.

4.3. Analytical Characterization. 4.3.1. Details for the Pericyclynediols 6a, 8a, and 9. [6]Pericyclynedione 7 (0.147 mmol, 100 mg) was reacted with commercial C 2 H 5 MgBr (0.441 mmol, 3 M in THF) in THF (30 mL). Chromatography on silica gel eluted with pentane:EtOAc = 4:1 and then 3:1 gave 6a (0.067 mmol, 50 mg, 45%) and 8a (0.042 mmol, 30 mg, 28%) as yellow oils, along with the known bis-secondary [6]pericyclynediol 9 (0.028 mmol, 19 mg, 20%). 16a 1 ,10-Diethyl-4,7,13,16-tetramethoxy-4,7,13,16-tetraphenylcyclooctadeca-2,5,8,11,14,17-hexayne-1,10-diol (6a). 1 H NMR (300 MHz, CDCl 3 ) δ 7.89-7.57 (m, 8H), 7.51-7.28 (m, 12H), 3.69-3.20 (m, 12H), 3.07-2.38 (m, 2H), 2.15-1.85 (m, 4H), 1.27-1.08 (m, 6H). 13 C{ 1 H} NMR (101 MHz, CDCl 3 ) δ 139. 3, 129.1, 129.0, 128.5-128.4, 126.5-126.4, 87.0-86.8, 84.5-84.4, 81.1-81.0, 71.9-71.8, 64.4, 64.3, 53.3-53.2, 36.6-36.4, 9.1-8.9.

HRMS (MALDI-TOF/DCTB): m/z [M] +• calcd for C 50 H 44 O 6 740.3132, found 740.3099.

1 -Ethyl-4,7,13,16-tetramethoxy-4,7,13,16-tetraphenylcyclooctadeca-2,5,8,11,14,17-hexayne-1,10-diol (8a). 1 H NMR (400 MHz, CDCl 3 ) δ 7. 76-7.67 (m, 8H), 7.40-7.32 (m, 12H), 5.44-5.22 (m, 1H), 3.65-3.31 (m, 12H), 3.03-2.23 (m, 2H), 2.11-1.93 (m, 2H), 1.20-1.06 (m, 3H).

13 C{ 1 H} NMR (101 MHz, CDCl 3 ) δ 139. 6-139.2, 129.1-129.0, 128.5-128.4, 126.5-126.4, 87.2-86.9, 84.70-83.5, 82.2-81.9, 81.2-81.1, 71.8-71.7, 64.4-64.3, 53.4-53.3, 52.4-52.3, 36.7-36.5, 9.1-8.8 4,7,13,16-Tetramethoxy-4,7,13,16-tetraphenylcyclooctadeca-2,5,8,11,14,17-hexayne-1,10-diol (9). 16a Yellow oil. Spectral characteristics identical to those of an authentic sample. 1 1 H NMR (400 MHz, CDCl 3 ) δ 7.81-7.62 (m, 8H), 7.44-7.28 (m, 12H), 5.31 (m, 2H), 3.66-3.32 (m, 12H), 3.05-2.62 (m, 2H).

4.3.2. Details for the Pericyclynediols 6b and 8b.

[6]-Pericyclynedione 7 (0.147 mmol, 100 mg) was reacted with n-

Introduction

Among -conjugated carbon allotropes and beyond the foremost graphene type, graphynic materials, composed of both sp 2 -C and sp-C atoms, have been considered at the theoretical level 1 but have been more sparingly studied at the experimental level. Nevertheless, several molecular fragments of ␥-graphyne, 2 ␥-graphdiyne, 3 and even ␣-graphyne 4 have been described. A key issue in the synthesis and study of such carbon-rich compounds is their limiting solubility, approaching that of graphite upon increase of the size of the carbon core within a C-H bond periphery. As a solution, peripheral decoration by lipophilic groups is currently envisaged. This can be illustrated by the recent report of a ring carbo-mer of naphthalene, 5 with eight p-pentylphenyl substituents of the C 32 core having allowed full characterization of this first example of fused polycyclic ␣-graphyne fragment, in or from solutions in CHCl 3 . 4 However, the solubilizing effect of the p-pentylphenyl groups appeared limited, even on the smaller carbo-benzene congener C 18 (4-n-C 5 H 11 -C 6 H 4 ) 6 . The carbo-benzene C 18 ring is actually the smallest cyclic primitive motif of ␣-graphyne, and most of the derivatives reported hitherto bear only H, aryl, or alkynyl substituents. 6 Very recently, direct anchoring of alkyl chains at the sp 2 vertices of the C 18 ring was envisaged in a series of p-dialkyltetraphenyl-carbo-benzenes 1a-1e, which could be obtained in two steps, namely by addition of alkylmagnesium bromides to the [6]pericyclynedione 2 followed by reductive aromatization of the [6]pericyclynediol products 3a-3e (Scheme 1). 7 However, the Grignard approach was not found to be selective, and beside the diadducts 3a-3e, the single and double reductions products 4a-4e (resulting from the monoadduct) and 5 are also formed. The reducing power of alkyl Grignard reagents is actually known to be due to the presence of a H atom in ␤ position of the Mg atom, 8 but several recommended methods to overcome this effect, e.g., through the change of solvent, failed to improve the reaction outcome. The use of alternative or additive metals should thus be envisaged.

In general nucleophilic addition of Nu-MX n to carbonyl groups, beyond lithium (M = Li, n = 0) and magnesium (M = Mg, n = 1, X = Br, Cl, I) cations, cerium cations (M = Ce, n = 2, X = Cl) have also been reported to provide higher selectivity under smooth conditions. 9 In the present context, targeting the [6]pericyclynediols 6a-6b from the bis-terminal tetrayne 7a-7b and dialdehyde 8, while reactions of the MgBr + salts alone appeared almost unproductive (0%-6%), 6a,6b,6h addition of CeCl 3 was shown to improve the yield to 12%-14%, likely via the corresponding CeCl 2 + salts (Scheme 2).

As part of ongoing efforts to improve access efficiency to carbobenzene molecules, the study of the metal effect on the double nucleophilic addition to the diketone 2 has been undertaken for Nu = n-Bu, a model nucleophile of intermediate length, with the view to obtaining the hitherto unknown representative p-di-n-butyltetraphenyl-carbo-benzene 1f. This target, bearing both aliphatic and aromatic substituents, is also devised to serve as a standard for electrochemical studies in the carbo-benzene series.

Experimental

General

THF was dried with a PureSolv MD5 Innovative Technology system for the purification of solvents. All other reagents were used as commercially available. In particular, commercial solutions of n-BuLi were 2.5 mol/L in hexane, and solutions of HCl were 2 mol/L in diethyl ether. All reactions were carried out under argon atmosphere using Schlenk tube and vacuum line techniques. Column chromatography was carried out on silica gel (60 Å, 70-200 m). Silica gel thin layer chromatography plates (60F254, 0.25 mm) were revealed under UV light and (or) by treatment with an ethanolic solution of phosphomolybdic acid (20%). The following analytical instruments were used: 1 H and 13 C NMR spectroscopy: Avance 300, Avance 400, and Avance 400 HD; mass spectrometry: Quadrupolar Nermag R10-10H; UV-vis absorption: Perkin-Elmer UV-vis Win-Lab Lambda 950; X-ray diffraction: Apex2 Bruker, micro-focus X-ray source (Mo K␣ radiation). NMR chemical shifts are given in ppm with positive values to high frequency relative to the tetramethylsilane reference. Coupling constants (J) are given in Hertz. UV-vis absorption wavelengths () are given in nanometers, and the corresponding maximum extinction molar coefficient () is given in L mol -1 cm -1 .

Crystal structure determination

Intensity diffraction data for 1f were collected at 100 K. The structure was solved by direct methods using SIR92 and refined by full-matrix least-square procedures on F using the programs of the PC version of CRYSTALS. 10 Atomic scattering factors were taken from the International Tables for X-ray Crystallography. 11 All nonhydrogen atoms were refined anisotropically. Hydrogen atoms were refined using a riding model. Absorption corrections were introduced using the program MULTISCAN.

Voltammetric measurements

Voltammetric measurements were carried out with a potentiostat Autolab PGSTAT100 controlled by GPES 4.09 software. Experiments were performed at room temperature in a homemade, airtight, three-electrode cell connected to a vacuum/argon line. The reference electrode consisted of a saturated calomel electrode (SCE) separated from the solution by a bridge compartment. The counter electrode was a platinum wire of approximately 1 cm 2 Scheme 1. Last two steps of previous syntheses of p-dialkyl-carbo-benzenes. The intermediates 2-5 were used as mixtures of stereoisomers. Scheme 2. Improvement of a [11+7] macrocyclization from a C11 tetrayne and a C7 dialdehyde through the use of a cerium(III) reagent. apparent surface. The working electrode was a Pt microdisk (diameter, 0.5 mm). The supporting electrolyte [n-Bu 4 N][PF 6 ] was used as received (Fluka, 99% electrochemical grade) and simply degassed under argon. The solutions used in the electrochemical study were 10 -3 mol/L in carbo-benzene and 0.1 mol/L in supporting electrolyte. Before each measurement, the solutions were degassed by bubbling argon, and the working electrode was polished with a polishing machine (Presi P230). Typical instrumental parameters for recording square-wave voltammograms were as follows: SW frequency (f) = 20 Hz, SW amplitude (E sw ) = 20 mV, and scan increment (dE) = 5 mV.

Experimental characterizations and procedures of new products

Characterization of 1,10-dibutyl-4,7,13,16-tetraphenylcyclooctadeca-1,2,3,7,8,9,13,14,15-nonaen-5,11,17-

triyne (1f)

A solution of [6]pericyclynediol 3f (50 mg, 0.063 mmol) in dichloromethane (DCM, 30 mL) was treated with SnCl 2 (120 mg, 0.63 mmol) and HCl (1.26 mmol, 2 mol/L in Et 2 O) at -78 °C. The mixture was stirred at -78 °C for 10 min and then at room temperature for 20 min. After treatment with 1 mol/L aqueous NaOH (1.26 mL) and filtration through Celite ® , the organic layer was washed with brine (three times), dried over MgSO 4 , and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (pentane:DCM, 4:1) to give 1f as a dark red solid (25 mg, 0.04 mmol, 63% yield). 1 Na, 763.3036; found, 763.3085. -4,7,13,16-tetramethoxy-4,7,13,16tetraphenylcyclooctadeca-2,5,8,11,14,17-hexayne-1,10-diol (3f) Procedure for the preparation of 3f with n-BuMgBr To a suspension of magnesium turnings (3.2 mg, 0.13 mmol) in THF (0.5 mL) at room temperature was added dropwise n-BuBr (0.06 mL, 0.53 mmol). The mixture was stirred for 2 h at room temperature. A solution of [6]pericyclynedione 2 (30 mg, 0.04 mmol) in THF (5 mL) at 0 °C was treated with the freshly prepared solution of n-BuMgBr. The mixture was stirred at 0 °C for 3 h before treatment with a saturated aqueous solution of NH 4 Cl. The aqueous layer was extracted with diethyl ether, and the combined organic layers were dried over MgSO 4 and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (pentane:EtOAc, 5:1, then 3:1) to give the diadduct 3f (18 mg, 0.0226 mmol, 51% yield), the monoadduct 4f (9 mg, 0.012 mmol, 28% yield), and the known di-reduction diol product 5 (5 mg, 0.007 mmol, 16% yield), 6h,11 as yellow oils.

Characterization of 1,10-dibutyl

Procedure for the preparation of 3f with n-BuMgCl

A solution of [6]pericyclynedione 2 (40 mg, 0.06 mmol) in THF (6 mL) at 0 °C was treated with commercial n-BuMgCl (0.18 mmol, 2 mol/L in diethyl ether). The mixture was stirred at 0 °C for 1 h and then at room temperature for 3 h before treatment with a saturated aqueous solution of NH 4 Cl. The aqueous layer was extracted with diethyl ether, and the combined organic layers were dried over MgSO 4 and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (pentane:EtOAc, 5:1, then 3:1) to give the diadduct 3f as a yellow oil (25 mg, 53% yield).

Procedure for the preparation of 3f with n-BuLi

A solution of [6]pericyclynedione 2 (40 mg, 0.06 mmol) in THF (6 mL) at -78 °C was treated with n-BuLi (0.12 mmol, 2.5 mol/L in hexane). The mixture was stirred while slowly warming up to -30 °C over 1.5 h before addition of an aqueous solution of NH 4 Cl. The aqueous layer was extracted with diethyl ether, and the combined organic layers were dried over MgSO 4 and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (pentane:EtOAc, 5:1) to give 3f as a yellow oil (33 mg, 0.04 mmol, 70% yield).

Procedure for the preparation of 3f with n-BuLi and CeCl 3

To a suspension of CeCl 3 (37 mg, 0.15 mmol) in THF (10 mL) at -78 °C was added n-BuLi (0.15 mmol, 2.5 mol/L in hexane), and the resulting mixture was stirred for 0.5 h at this temperature. After treatment with a solution of [6]pericyclynedione 2 (50 mg, 0.0735 mmol) in THF (8 mL) at -78 °C, the mixture was slowly warmed up to -20 °C during 2 h before addition of an aqueous solution of NH 4 Cl. The aqueous layer was extracted with diethyl ether, and the combined organic layers were dried over MgSO 4 and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (pentane:EtOAc, 5:1) to give 3f as a yellow oil (53 mg, 0.07 mmol, 90% yield). 1 4-87.0, 84.5-84.3, 81.2-80.1 (CϵC), 71.9-71.8

Results and discussion

p-Di-n-butyl-tetraphenyl-carbo-benzene 1f was targeted through the "classical" route, i.e., by reductive aromatization of the corresponding [6]pericyclynediol 3f, itself envisaged from the [6]pericyclynedione 2 and various n-Bu-MX n reagents, MX n = MgBr, MgCl, Li, CeCl 2 (Scheme 3). 12 Following previous experiences (Scheme 1), addition of two equivalents of n-butylmagnesium bromide to 2 gave 3f in 51% yield, along with the reduced monoadduct 4f and the known bis-secondary [6]pericyclynediol 5, 6h,13 isolated in yields of 28% and 16%, respectively.

Replacing n-BuMgBr by n-BuMgCl led to the diadduct 3f with a similar 53% yield but without reduction side product, as indicated by the absence of any CHOH 1 H NMR signal in the range of 5-6 ppm. This change in nucleophilic vs redox selectivity can be attributed to the electronegativity-driven higher nucleophilic reactivity of the chlorinated magnesium salt compared with the brominated congener. Traces of the non-reduced mono-ketone monoadduct were detected by 1 H NMR spectroscopy but could not be separated from other unidentified products, which were likely polymeric in nature.

Addition of two equivalents of n-butyllithium to 2 followed by aqueous quenching at -30 °C was found to proceed selectively, allowing the diadduct 3f to be isolated in 70% yield. This result contrasts with the poor efficiency of the addition of aryllithium reagents to the same diketone 2, the intermediate lithium alkoxide evolving by retro-additive opening of the macrocycle towards stabilized arylketones such as 9 (Scheme 3). 14 Such a ring opening was not observed with n-BuLi, provided that the reaction mixture was quenched at -30 °C.

Finally, the addition of two equivalents of n-butylcerium dichloride, assumed to be formed in situ from n-BuLi and dry CeCl 3 , to 2 was found to proceed very selectively, affording the [6]pericyclynediol 3f with a 90% isolated yield. This result is in line with the results disclosed above (M = Li > Mg, X = Cl > Br) and with previous reports on the general use of cerium reagents. 6a,6b,9 The target 1f was finally obtained by classical reductive treatment of the [6]pericyclynediol 3f with SnCl 2 and HCl in DCM. 6 It was isolated with 63% yield as a stable, dark red solid, soluble in chlorinated organic solvents (chloroform and DCM).

Single crystals of 1f deposited from a DCM solution were analyzed by X-ray diffraction, confirming the anticipated structure (Fig. 1). The C 18 macrocycle of 1f is quasi-planar with a quasiregular hexagonal shape, with the maximal deviation from planarity being 0.028 Å. The measured bond lengths in the C 18 ring are classical for a carbo-benzene (spC-spC ≈ 1.22-1.23 Å, sp 2 C-spC ≈ 1.37-1.38 Å). The n-butyl chains exhibit a zigzag arrangement almost perfectly coplanar with the C 18 ring, as previously observed for a few other dialkyl-carbo-benzenes. 7a Two of the phenyl substituents are also quasi-coplanar with the C 18 ring, whereas the two other substituents adopt a torsion angle of approximately 25°. The distance between two successive C 18 mean planes is 3.45 Å, which is longer than the shortest corresponding distance of 3.21 Å measured for the bis-tetradecyl-carbo-benzene: no directstacking between C 18 rings of 1f is observed in the crystal, where cocrystallized DCM molecules prevent van der Waals contact between nearest macrocycles. 7a The dibutyl-carbo-benzene 1f was also characterized by 1 H and 13 C NMR in CDCl 3 solution. The 1 H NMR spectral profile is similar to those reported for other dialkyl-carbo-benzenes, with a strong deshielding at 9.51 ppm of the o-CH nuclei of the four equivalent phenyl substituents. 7a This effect reveals the strength of the diatropic C 18 ring current, which also progressively affects the 1 H signals of the n-butyl chain versus the distance of the CH 2 groups to the C 18 ring border, as previously analyzed for other n-alkylcarbo-benzenes (Supplementary Fig. S1). 7a The UV-vis absorption pattern of 1f in chloroform solution is typical for dialkyl-tetraphenyl-carbo-benzenes ( max = 446 ± 0.5 nm), with one main band at 446 nm, accompanied by three smaller bands at higher wavelengths (Supplementary Fig. S2). 7a The chro-Scheme 3. En route and access to p-di-n-butyl-tetraphenyl-carbo-benzene. mophoric intensity of 1f is also classical in this series, with a maximum extinction coefficient of 208 000 L mol -1 cm -1 .

The title target 1f has been selected as a model for an analysis of the solvent effect on the electrochemical behavior of carbo-benzene derivatives, which might be not soluble enough in DCM to allow the study of redox properties in this solvent, requiring the use of chloroform instead. 15 For the sake of comparison, solutions of 1f in both chloroform and DCM were thus investigated by square wave (SW) and cyclic (CV) voltammetry (Table 1).

In the reference DCM solvent, 1f lends itself to three successive reduction processes, two of them being reversible at E 1/2 red = -0.82 V and -1.26 V, these values being comparable with the values previously reported for other carbo-benzene derivatives. 6f,6i,15 The aromaticity of the C 18 ring indeed attenuates its sensitivity to substituents. 6f In chloroform, the two first reductions occur at similar potentials (albeit turning less reversible at -0.82 V and -1.32 V), whereas the third reduction peak occurring at E P red = -1.98 V in DCM cannot be detected because of the narrower electrochemical observation window of CHCl 3 , which is reduced at this potential. These results also show that replacement of two aryl substituents by alkyl counterparts has a weak but electronically consistent effect on the reduction potential values (-0.72 V and -1.15 V for hexaphenyl-carbo-benzene). 15 In both solvents, three oxidation processes are also observed at comparable potentials, with a loss of reversibility of the second wave observed in DCM (E 1/2 ox2 = +1.63 V) by passing to chloroform (E P ox2 = +1.69 V).

The influence of the solvent on the redox potentials is thus limited, but affects the reversibility of the processes, possibly because of the higher viscosity and lower dielectric constant of chloroform ((CHCl 3 ) = 0.537 mPa•s > (DCM) = 0.413 mPa•s, (CHCl 3 ) = 4.81 < (DCM) = 8.93). A high dielectric constant indeed favors charge dissociation thus enhancing the conductivity of the electrolytic solution.

Conclusion

The metal switch study of the reaction of a model alkyl nucleophile with the [6]pericyclynedione 2 brings out the dichlorocerium(III) reagent as the most selective for the production of 3f. The improvement is particularly eloquent by comparison with the bromomagnesium reagent affording also the double reduction product 5 and the single addition-reduction product 4f (that could, however, be profitably used for a carbo-benzene library purpose). 7a The synthesis results provide a global increase of the yield of prepara-tion of p-di-n-butyl-tetraphenyl-carbo-benzene 1f from 32% to 57% over the two last steps. The cerium method can thus henceforth be envisaged for the synthesis of other alkyl-carbo-benzenes.

The disclosed voltammetry results, the first ones in the alkylcarbo-benzene series, indicate that the electrochemical behavior of carbo-benzenes is little sensitive to solvent (DCM vs chloroform) and substituent (alkyl vs aryl) effects. More generally, the "hybrid" member of the carbo-benzene family 1f, with two alkyl chain and four phenyl ring substituents, could now serve as a soluble standard for other comparative studies. Since the early report by S. Chandrasekhar et al. describing mesomorphic properties of a hexasubstituted benzene derivative, 1 a large variety of disc-like p-conjugated rigid cores have been envisaged for the design of discotic-type liquid crystal (LC) mesogens. Such cores have been diversely substituted by two, three, four, six or more dispersion groups, conferring them the selfassembling properties governing the mesophase formation. In the case of extended cores such as discoid polycyclic aromatic hydrocarbons (PAHs), or heterocyclic counterparts, nanosegregation between the aromatic cores and outer aliphatic chains has been shown to act as a driving force for the formation of columnar mesophases. 2 The discoid symmetry order (so) of these cores varies from so = 3 for triangular triphenylene 3 and its expanded hexadehydrobenzo [12]annulene (DBA) counterparts, 4 to so = 4 for tetragonal porphin, 5 and up to so = 6 for hexagonal hexabenzocoronene (HBC). 6 Most of the latter are thus condensed polycycles, where the peripheral macrocycle encompasses smaller rings filling the discoid interior (e.g. 5 and 13 primitive rings in porphin and HBC, respectively). In contrast, due to the decrease of aromaticity vs. ring size, the mesogenic properties of macro-monocycles have been sparsely investigated beyond the case of DBA, 4 where rigidity is restored by both double insaturations and benzannelation, albeit for moderate size (C 12 ring) and discoid character (so = 3). This challenge actually meets former designs of discotic LCs based on larger shape-persistent primitive macrocyclic cores of the oligo-phenylacetylene type. 7 A ''tubular'' discotic LC devised from a hollow phenylacetylene macrocycle (PAM C 30 ring) decorated with six dispersion groups providing the mesogen with a regular hexagonal discoid character (so = 6) has thus been evidenced in the range of 144-110 1C. 7a A larger mesogenic core (C 58 ring) filled with intra-annular polar groups was shown to give stable columnar mesophases which were fully characterized at 120 1C or 110 1C. 7b With the view of gaining insight into the mesogenic properties of truly monocyclic (non-benzannelated) macro-aromatics, the carbo-benzene ring of 1 appears to be a relevant candidate (Scheme 1), both in terms of size (C 18 , diameter E 0.8 nm) and discoid character (so = 6). As a three-fold expanded carbo-meric version of benzene, 8 the 18-p-electron carbo-benzene ring is aromatic just as the 6-p-electron parent is. 9 This C 18 core also possesses other remarkable features, such as an all-carbon composition, an extended flexible flatness, a strong magnetic anisotropy, and a structural/ chromophoric analogy with the C 16 N 2 porphyrin core, thus providing carbo-benzene derivatives with unique properties. 10 The same features make the same C 18 core also attractive for LC design upon anchoring of selected dispersion groups. Lipidic carbo-benzenes p-(C n H 2n+1 ) 2 C 18 Ph 4 bearing two n-alkyl chains of various lengths (n = 2, 8, 14, and 20) at the para-positions were recently described, 11 but none of them was found to display any LC behaviour. An increase of the number of dispersion groups is thus here envisaged by anchoring two pyrogallol ether groups at the same para positions, and more precisely two long-chain trialkoxyphenylethynyl groups.

The synthesis of the targets 1a and 1b was intended from the [6]pericyclynedione 2, 12 following a method widely used for the preparation of other para-disubstituted tetraphenyl-carbobenzenes. 8b,c,11 The precursors of the selected dispersion groups classically used in LC design, the ethynylpyrogallol ethers 3a and 3b with alkyl chain lengths of n = 12 and 18, respectively, were prepared from commercially available 5-bromo-1,2,3-trimethoxybenzene. 13 The addition of two equivalents of the bromomagnesium salt of 3a or 3b to the diketone 2 afforded the expected [6]pericyclynediols 4a and 4b as mixtures of diastereoisomers in 64 and 25% yields, respectively. The low isolated yield of 4b was due to the tricky procedure required for the purification of such a highly paraffinic molecule. The reaction of 2 with the lithium salt of 3a (generated with n-BuLi) was also attempted, allowing the diadduct 4a to be obtained in up to 75% yield (Scheme 1). After the treatment of 4a and 4b with SnCl 2 and HCl, the carbo-benzenes 1a and 1b were finally obtained in 58% and 18% yields, respectively (Scheme 1). The two products were isolated as dark blue-violet solids, giving red-violet dichloromethane (DCM) or chloroform solutions. The dodecyl derivative 1a was however found to be much more soluble than the octadecyl homologue 1b, the latter dissolving in chloroform only and at a very low concentration. Both 1 H and 13 C NMR spectra of 1b could however be recorded in CDCl 3 solution at 320 K. A signature of the presence of the aromatic C 18 macrocycle of 1a and 1b is the diatropic ring current-induced deshielding of the ortho-1 H nuclei of the phenyl substituents at ca. 9.5 ppm, as observed for all aryl-substituted carbo-benzenes. Both 1a and 1b also exhibit similar UV-vis absorption spectra in chloroform solution, with the same maximum absorption wavelength at 490 nm. In most cases, whatever the solvents and conditions employed, 1a and 1b were found to give thin hair-like crystals, or incidentally bipyramidal crystals (see photographs in the ESI †), of extremely low diffracting power. Nevertheless, after many attempts, single crystals suitable for XRD analysis were obtained from a chloroform solution of 1a, thus allowing confirmation of the structure (Fig. 1). 14 Due to weak diffraction intensities and low resolution, non-hydrogen atoms could only be refined with isotropic displacement parameters, but in the absence of any solvate molecule, no disorder is found in the structure, in particular in the dodecyl chains aligned in a parallel manner in parallel triads (approximately along the a axis and the ab plane).

Mesophases of 1a, more soluble and available in a larger amount than 1b, could also be analysed in detail. As a literature reference, the oligophenyleneethynylene (OPE) derivative 5a, carbo-meric parent of 1a (Scheme 1), was recently reported for its self-assembling properties in solution, but the possible thermotropic LC behaviour of the pure substance was not mentioned. 15 Porphyrinic analogues of type 6 with two or four trialkoxyaryl dispersion groups (Scheme 1) were also reported to exhibit LC behaviour at low temperature. 16 The phase behaviour of 1a was investigated by the combination of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD). Under POM, a viscous birefringent liquid was observed upon heating between 100 and 130 1C (Fig. 2). Further heating was found to give a dark image, indicating either decomposition of 1a or formation of its isotropic phase, which remained the same upon cooling even to room temperature. The birefringent texture of the viscous liquid upon heating (usually not as indicative as natural textures obtained by cooling a perfect liquid phase, since solid state attributes can remain and interfere) does not show characteristic features for an explicit identification of phases. In the DSC thermogram between 0 and 120 1C, signals can be detected upon Scheme 1 Synthesis of the hexaalkyloxy-di(ethynylphenyl)-tetraphenylcarbo-benzenes 1a and 1b, and previously reported reference congeners 5a and 6. heating only, and a phase transition at 109 1C is in accordance with POM observations. Further heating leads to an exothermic signal starting at ca. 130 1C, interpretable as the signature of either a recrystallization or a decomposition process. As no signal is observed in the second or third heating/cooling runs, the initial exothermic signal at 136 1C is ascribed to thermal decomposition. The lowest reported melting-decomposition temperature for a tetraaryl-carbo-benzene is just 12 1C higher (148 1C for p-dieicosyl-tetraphenyl-carbo-benzene), 11 and although most hexaaryland dialkynyltetraaryl-carbo-benzenes reported to date have been shown to melt or decompose above 200 1C, the ''p-frustration'' brought by the trialkoxyphenylethynyl groups onto the p-electronrich C 18 core of 1a can account for a specific thermal instability. 17 When the DSC thermogram of 1a is recorded between 0 and 115 1C to avoid thermal decomposition, the non-reproducibility of the signal at 109 1C is ascribed to the thermal history of the virgin crystals (powders). However, after one night annealing at room temperature, a new signal at 55.1 1C appears on heating and a signal at 27.8 1C can be observed on cooling. These DSC data for two cycles between 0 and 115 1C are consistent with POM observations (see the ESI †).

The LC behaviour of 1a was confirmed by PXRD, allowing investigation of molecular packing patterns in different states. Upon heating the crystalline phase at temperatures above 109 1C and below 130 1C, a wide angle broad halo at 4.7 Å of molten chains evolved, indicating the fluid phase formation. 18 In the small angle regime, signals are simplified by comparison to the complicated patterns of the crystalline phase. The PXRD pattern at 115 1C (Fig. 3) can be indexed to a columnar rectangular (Col rec ) phase. Detailed analysis of the PXRD data allowed the determination of the two-dimensional lattice constants of the Col rec phase at 115 1C (Table 1) The 2D lattice constants of the LC phase are consistent with a specific domain in STM images of 1a, which is primarily revealed as a macrocycle decorated by six phenyl-like groups (Fig. 4). Although the 2D packing is not perfectly regular and compact, it clearly shows a 48 Â 43 Å rectangular pattern analogous to the one determined by PXRD analysis. The distances between neighbouring molecules of 1a are found to be ca. 16, 21, 24, and 25 Å. As observed in the single crystal along the a axis, 18 the alkyl chains are aligned in a parallel manner with the [0110] direction of the underlying graphite substrate, and are interdigitated between neighbouring molecules, thus locking rotation of the mesogen about the column axes.

A schematic molecular packing deduced from PXRD and STM investigations is shown in Fig. 5. For the 2D lattice, STM resolves 3 chains per molecule of 1a while the other chains are presumably fluxional in the solution. This is a common packing pattern for alkane-decorated aromatics because of the limited space and insufficient attractions from the substrate. 19 For the 3D columnar phase, the fluxional chains inferred from STM images are likely coplanar with the molecular plane due to van der Waals interactions between alkyl chains of the nearest upper and lower layers (vide infra, Fig. 5c). 18 The macrocyclic cores thus stack face-to-face into columns by p-p interactions, assisted by nanosegregation of domains of interdigitated molten side-chains and p-p interaction of the peripheral phenyl/phenylethynyl groups. The alkyl chains are arranged in a trans manner with respect to the para-dialkynyl axis, thus driving an anisotropic in-plane packing by chain interdigitation.

The extended aromatic core of the carbo-benzene 1a (58 sp 2 -or sp-C atoms) is embedded in a 34% more extended oxyparaffinic surrounding (78 sp 3 des oléfines ou l'hydroformylation, a pourtant longtemps attiré l'attention des chimistes. 6 Les P-ligands pauvres en électrons sont généralement conçus suivant différentes approches :

• • • • • R • • • • • • R n R C 2 R R 0 4 R i 4 R 2 -OPPn R R n R 2 -OPEn
-substitution du squelette des triarylphosphines par des groupements accepteurs tels que CF 3 ou CN, 7 -introduction de liaisons P-O exerçant un effet électro-accepteur sur l'atome de phosphore libre ou complexé par effet inductif (-I), 8 -introduction d'une charge positive au voisinage de l'atome de phosphore, rendant ainsi sa paire libre moins disponible, 9 -remplacement des substituants aryle des phosphines neutres par des groupes hétéroaryle pouvant exercer un effet électro-attracteur (-M) sur l'atome de phosphore par π-donation de la paire libre du P dans l'orbitale antiliante π* de l'hétérocycle. 10 Dans l'objectif d'augmenter encore le caractère pauvre en électrons d'hétéroarylphosphines tout en conservant leur caractère neutre, l'utilisation de substituants accepteurs a été considérée à travers l'étude du cas du groupement nitro. Une série de (Nphényl-benzimidazol-1-yl)diphénylphosphines portant un nombre variable de groupes NO 2 sur les cycles phényle ou benzimidazolyle a donc été préparée en présence de LDA comme base optimale, et les complexes trans-L 2 Rh I Cl(CO) correspondants ont été obtenus suivant deux stratégies (Schéma 1). Les premières études sur les matériaux carbonés ont principalement porté sur deux allotropes du carbone : le graphite et le diamant, correspondant à des réseaux d'atomes de carbone hybridés sp 2 et sp 3 respectivement. La structure tridimensionnelle en couches du graphite lui confère des applications comme lubrifiant solide et comme additif pour renforcer les fibres de carbone. 12 Le diamant, avec sa dureté et son indice de réfraction élevé, est quant à lui principalement utilisé en joaillerie et dans les têtes de forage pour l'exploration géologique. 13 Ces différentes applications, basées sur les propriétés chimiques et physiques distinctes de ces deux allotropes du carbone, ont attiré l'attention de la communauté scientifique vers le développement de nouveaux matériaux carbonés.

Après la première synthèse en 1985 du Buckminster fullerene, 14 formé de 60 atomes de carbone équivalents hybridés sp 2 , les nanotubes de carbone, composés d'atomes de carbone de même hybridation, ont commencé à être étudiés en 1991. 15 Plus récemment, le « parent » de ces deux allotropes du carbone, un feuillet de graphène, a été synthétisé pour la première fois par Geim et al. 16 Ce réseau bidimensionnel d'atomes de carbone arrangés en nid d'abeilles a été étudié notamment pour ses propriétés électroniques, mais il présente également des propriétés mécaniques et thermiques exceptionnelles. 17 19 L'α-graphyne peut donc être considéré comme le carbo-mère du graphène, ou carbo-graphène, dont les motifs constitutifs de base sont des cycles carbo-benzènes, largement étudiés dans l'équipe depuis 20 ans. La symétrie D 6h , le caractère discotique creux, l'aromaticité magnétique et le système conjugué riche en électrons π du cycle carbo-benzène le rend attractif pour de possibles applications dans de nombreux domaines tels que l'optique non linéaire 20 ou la conductivité électrique. 21 Bien que le représentant non substitué C 18 H 6 soir encore inconnu, plus de 30 carbo-benzènes diversement substitués ont été décrits. 1 Tous les carbo-benzènes sont préparés à partir de précurseurs hexaoxy [6]péricyclynes, [START_REF] Bramborg | For di-n-octyl-benzene[END_REF] dont les six substituants hydroxyle ou alkoxyle sont éliminés dans des conditions acides et réductrices dans une dernière étape conduisant à la formation du macrocycle aromatique en C 18 . 1 Différentes voies de synthèse, toutes basées sur une étape clé de macrocyclisation notée

[X+Y] entre un dinucléophile X et un diélectrophile Y, ont été envisagées pour préparer ces hexaoxy [6]péricyclynes (Schéma 2). 23 Schéma 2. Différentes stratégies de macrocyclisation développées pour la synthèse des précurseurs hexaoxy [6]péricyclynes de carbo-benzènes. pentylphényle, 27 mais l'effet de ces derniers sur la solubilité est apparu limité, tout comme celui des groupements 3,5-di-tert-butylphényle. 26 L'introduction de chaînes alkyles sur les substituants phényle des carbo-benzènes ayant peu d'influence sur leur solubilité, l'insertion directe de chaînes aliphatiques sur le cycle en C 18 a alors été envisagée. Alors que les substituants iso-propyl n'améliorent pas la solubilité, 28 les groupements tert-butyl directement insérés sur le macrocycle ont récemment été montrés augmenter de façon significative la solubilité des carbo-benzènes dans les solvants organiques. 29 Sur la base de ces résultats préliminaires, l'insertion directe de chaînes alkyles linéaires de longueurs variables sur les positions para des carbo-benzènes a été envisagée comme nouvelle approche visant à améliorer la solubilité de ces molécules. Une série de longueurs de chaînes (n = 2, 4, 8, 14, 20) a été proposée, et les carbo-benzènes correspondants ont été préparés suivant la méthode classique en deux étapes à partir de la [6]péricyclynedione. L'utilisation de réactifs bromures d'alkyl magnésium a conduit à la formation de mélanges des diadduits ciblés et des mono-adduits réduits, permettant ainsi la préparation parallèle de séries de dialkyl-et de monoalkyl-carbo-benzènes (Schéma 4). Le résultat de la réaction en fonction de la nature du nucléophile utilisé a également été exploré afin de déterminer quel réactif conduit à la plus grande sélectivité en diadduit. Trois types de nucléophiles ont été envisagés : alkyl lithien (C - Li + ), alkyl halomagnésien (C -MgX + , X = Cl, Br), et alkyl cérien (C -CeCl 2 + ), ce dernier donnant le diadduit avec un rendement élevé, sans formation observée de produit de réduction. 30 Les propriétés physico-chimiques, telles que la solubilité, la température de fusion-décomposition, les propriétés d'absorption, le comportement électrochimique et l'empilement cristallin des dialkyl-carbo-benzènes obtenus ont été étudiées et discutées en fonction de la longueur de chaîne. 31

Schéma 4. Synthèse des dialkyl-et monoalkyl-carbo-benzènes à partir de la [6]péricyclynedione en utilisant RMgBr comme base.

Assemblages supramoléculaires 3D et 2D et comportement thermotropique d'un mésogène de type carbo-benzène

Les cristaux liquides sont présents dans de nombreux dispositifs électroniques faisant partie intégrante de notre vie quotidienne, comme les smartphones, les ordinateurs portables et les écrans de télévision. La phase cristal liquide, qui est un état intermédiaire entre l'état cristallin et l'état amorphe, est formée par l'auto-organisation spontanée de molécules mésogènes. Suivant la forme de ces molécules mésogènes, les cristaux liquides sont communément classés en deux catégories : calamitiques (mésogènes en forme de bâtonnets) 32 et discotiques (mésogènes en forme de disque). [START_REF]At a higher temperature of À40 8C, LDA was indeed[END_REF] Les premières mésophases calamitiques ont été décrites par Reinitzer au début du 20 ème siècle, [START_REF] Zou | [END_REF] et depuis, le comportement cristal liquide de mésogènes linéaires en forme de bâtonnet a été largement étudié et a conduit à des applications concrètes, notamment dans les affichages à cristaux liquides (LCD). 35 Les cristaux liquides discotiques sont connus depuis que Chandrasekhar a décrit la formation de mésophases de ce type par des mésogènes de type benzène hexasubstitué il y a une quarantaine d'années. [START_REF]N-alkyl congeners of N-phenyl imidazolo-monophosphines (non-benzannelated analogues of 3 a) were reported to undergo selective Nmethylation with Me 2 SO 4 or[END_REF] Récemment, les cristaux liquides discotiques ont fait l'objet d'intenses recherches pour leurs applications potentielles dans les transistors organiques à effet de champ, dans les diodes électroluminescentes organiques et dans les dispositifs photovoltaïques organiques. [START_REF]At a higher temperature of À40 8C, LDA was indeed[END_REF][START_REF]Even in the neutral ligand sub-series, the C -O distance takes the smallest value of 1.11 in 5 a for the a priori most electron-donating representative 3 a and[END_REF] Les mésogènes discotiques présentent typiquement un coeur rigide et plat aromatique décoré par plusieurs chaînes aliphatiques flexibles, et ils conduisent à la formation de deux principaux types de mésophases : nématiques et colonnaires. [START_REF]At a higher temperature of À40 8C, LDA was indeed[END_REF]35 Des mésophases lamellaires, dont la structure reste ambigüe encore aujourd'hui, peuvent aussi être formées par des mésogènes discotiques. 38 Dans les mésophases colonnaires, les mésogènes s'organisent en colonnes parallèles, dont la formation est induite par des interactions coopératives à la fois des coeurs aromatiques centraux et des chaînes latérales qui les entourent.

Dans ces mésophases, les distances coeur-coeur intra-colonnaires sont généralement courtes (environ 3,5 Å), permettant un recouvrement des orbitales π de deux mésogènes adjacents, alors que les distances inter-colonnaires sont généralement plus grandes (de l'ordre de 20 à 40 Å) et dépendent de la longueur des chaînes flexibles. Les coeurs aromatiques les plus communément utilisés pour l'élaboration de cristaux liquides à mésophases colonnaires sont des dérivés macro-polycycliques pouvant contenir des hétéro-atomes (N, O, S) tels que les porphyrines, les phtalocyanines, les hexaazatriphénylènes (HAT), 39 les triphénylènes ou les hexa-périhexabenzocoronènes (HBC). 40 Les constantes mesurées pour le réseau 3D ont été trouvées être en accord avec les images STM du réseau 2D obtenu en déposant une solution de carbo-mésogène sur une surface de HOPG (Figure 1). 41

Carbo-bi-and -ter-phényles : carbo-mères de cycle de [n]OPE

Suite au rapport initial par Ratner en 1974, 42 l'électronique moléculaire est devenu un sujet de recherche incontournable qui a considérablement attiré l'intérêt de la communauté scientifique. 43 Il est aujourd'hui reconnu que les molécules organiques π-conjuguées ayant un petit gap HOMO-LUMO peuvent potentiellement trouver des applications dans des dispositifs électroniques moléculaires. 44 Durant les dernières décennies, de nombreux efforts ont porté sur le développement de nouvelles molécules organiques pouvant être utilisées dans des dispositifs électroniques en remplacement des circuits à base de silicium dans le but de miniaturiser les circuits intégrés. 45 Les molécules organiques π-conjuguées parmi lesquels les oligomères et les polymères ont de nombreux avantages tels que de faibles coûts de production, une mise en oeuvre simple, et surtout la possibilité de modifier leur structure moléculaire afin de moduler les propriétés optiques et électroniques. 46 Les fils moléculaires oligo(phénylène-éthynylène)s (OPE) ont été considérés comme modèles pour l'étude des propriétés structurales et électroniques des polymères poly(phénylène-éthynylène) correspondants. 47 Les remarquables propriétés optiques et électroniques des OPE ont conduit à des applications dans de nombreux domaines tels que dans les diodes organiques électroluminescentes, 48 les chimiosenseurs, 49 les interrupteurs moléculaires 50 ou les matériaux pour l'optique non-linéaire. 51 Malgré les nombreux travaux visant à synthétiser des OPE pour l'étude de leurs propriétés de transport de charge, fabriquer un circuit intégré moléculaire applicable dans des dispositifs reste aujourd'hui un défi. 50,52 Les propriétés de transport de charge de fils moléculaires ne dépendent pas seulement de facteurs physiques tels que la température ou de l'interface molécule-électrode, mais aussi de la nature chimique de la molécule et en particulier de sa conjugaison, de ses caractéristiques redox, de sa longueur et de ses substituants. 53 En règle générale, le transport de charge est amélioré dans les molécules rigides, présentant un système π-conjugué étendu et un potentiel redox faible. 46,54 Le cycle carbo-benzène à 18 électrons π délocalisés, trois fois plus grand mais trois fois moins aromatique au niveau énergétique que son parent benzène à 6 électrons π, 55 a récemment été montré, à travers l'étude du p-dianilinyl-carbo-benzène, présenter une conductance moléculaire sans précédent de 106 nS, soit dix fois plus grande que celle de molécules comparables de mêmes dimensions. 56 Cette conductance élevée, associée à la rigidité, la Des voies de synthèse basées sur des procédés de mono-addition nucléophile sur la [6]péricyclynedione ont été utilisées pour préparer ces carbo-OPE (Schéma 4). Le carbo-OPE 2 a été synthétisé avec un rendement de 7 % à partir de la [6]péricyclynedione. Les deux carbo- Enfin, ces résultats ouvrent des perspectives d'applications dans différents domaines tels que la catalyse, la chimie hôte-invité des clathrates, le photovoltaïque organique, l'élaboration de cristaux liquides, l'électronique moléculaire et la photochimie.

  Additionally, I would like to acknowledge my thesis committee members: Prof. Mogens Brøndsted NIELSEN (University of Copenhagen, Denmark), Dr. Irena STARA (Institute of Organic Chemistry and Biochemistry, Czech Republic), Dr. Philippe BLANCHARD (Universite d'Angers, France), Dr. Suzanne FERY-FORGUES (Université Paul Sabatier, France), Prof. Xiuling CUI (invited people, Huaqiao University and Zhengzhou University, China), and Dr. Emmanuel GRAS (invited people, LCC-CNRS, France) for their time, their encouragement, and insightful comments, which broaden my horizons in the future research. I would like to thank the other past and present group members: Dr. Y. CANAC, many thanks to you for your help in my first year; Dr. C. LEPETIT, thank you for your concern in my first year; Prof. V. BERNARDES-GENISSON, you are a very kind lady, I always feel warm when seeing you; C. BARTHES, you always answered very patiently my questions whatever any question I asked, thank you so much for what you have done for me; K. COCQ, you are the King in carbomer chemistry, at least in my opinion. Thank you very much for sharing your experience with me and your pertinent suggestion for me; C. POIDEVIN, thank you for taking me to visit city center of Toulouse when I arrived here, and your French lesson to me despite some bad words sometimes; D. LISTUNOV, although you look serious sometimes, you are a good chemistry and warm-hearted Acknowledgment person, many thanks to you for discussion with me; C. D. MBOYI and A. MANKOU, You are really nice people, and helped me a lot in my first year, many thanks to both of you; M. CHAMMAM, thank you for what you have done for me, especially in my defense recently; E. M.

I

  am hugely appreciative to Dr. A. SAQUET for electrochemical measurements of all the molecules in carbo-mer research. I would like to thank Dr. Y. COPPEL for launching solid NMR experiment and helping resolve NMR spectra, and Dr. C. BIJANI for NMR measurements by using 500 MHz and 600 Acknowledgment MHz spectrometer, and F. LACASSIN for carrying out 103 Rh NMR experiments for the Rh I complexes in the first chapter of this manuscript. Special mention goes to my M.sc supervisor Prof. X. L. CUI for coming to my defense from the distant China. I am grateful for conversations with the following people: O. SADEK, S. AYALA-MARISCAL, A. POCINHO, W. KHODJA, A. FERNANDEZ-ALVAREZ, C. ZHANG, X. D. LIN, L. CHEN, J. R. QIU, Y. P. WANG, who all work at LCC. Many thanks also go to my friends in Toulouse: L. Q. LANG, Q. LIAO, J. H. WANG, Z. H. ZHAO, you made my free time enjoyable by playing cards and eating together at weekends. I also want to thank LCC (CNRS) for providing a safe and comfortable workplace, and UPS for offering us various interesting and useful courses and training. My sincere thanks go to CSC (China Scholarship Council) for my PhD scholarship. The IDEX emergence program 2014 of Toulouse is acknowledged for financial support (carbo-device project).

Figure 1 .

 1 Figure 1. a) top: alternative manners to tune the P-s-donating ability of benzimidazolophosphines towards a Lewis acid (LA): C-nitration vs. N-alkylation (expected order of inductive effects: I 0 < I NO2 < I + ); b) bottom: selected targets and synthetic approach.

  and the torsion angles between the N-Ar and benzimidazole mean planes have a median value of 68.5 AE 1.38. The amidine sp 2 -C1 atom is found slightly pyramidalized, with a tilting angle of the C-P bond axis versus the imidazole ring mean plane of ca. 4.7 AE 0.38 for 3 c and 3 e-f, but reaching 11.38 for 3 b. Coordination complexes of nitro-benzimidazolophosphines With the view to comparing the coordinating properties of the benzimidazolophosphines through IR n CO values of RhCl(CO), complexes of type 4 (Scheme 3), 3 a-c and 3 e-h were first sequentially reacted with [Rh(COD)Cl] 2 (for cleavage of the m-Cl bridges; COD = 1,5-cyclooctadiene) before displacement of the COD ligand by a second equivalent of the phosphine and a carbonyl ligand. Reaction of 3 b with half an equivalent of [Rh(COD)Cl] 2 in DCM for 2 h at room temperature led to the COD complex 4 b in 95 % yield. P-Rh coordination was established by the change of the 31 P{ 1 H} NMR signal, shifting from À22.88 to + 19.00 ppm, and splitting from a singlet to a doublet with a coupling constant of 150.7 Hz characteristic of a 1 J PRh coupling. Moving the nitro group from the benzimidazole core in 3 b to the Ar N-substituent in 3 e did not alter the reactivity with the Rh I dimer, giving 4 e in 93 % yield. Likewise, reaction of the dinitro benzimidazolophosphine 3 f with [Rh(COD)Cl] 2 gave 4 f in a similar 94 % yield. Further displacement of the COD ligand of 4 b, 4 e and 4 f was achieved by adding one additional equivalent of the respective phosphines 3 b, 3 e and 3 f, followed by CO bubbling for 15 min, thus affording the diphosphine RhCl(CO) complexes 5 b, 5 e and 5 f in 74 AE 2 % yield (Scheme 3

  ImPh 2 P-(Rh)-PPh 2 Im unit adopts a staggered conformation, with perfectly anti-periplanar imidazolyl groups in 5 a-c and 5 g (Im-P-P-Im dihedral angles = 1808), and synclinal-gauche imidazolyl groups wrapping the RhÀCl bond in 5 f (Im-P•••P-Im dihedral angle = 458, N 2 C•••Cl % 3.28 ). In contrast, the dicationic complex 5 a' exhibits a perfectly eclipsed conformation of the Rh-Cl bond with both the syn-periplanar imidazolyl groups (Im-P•••P-Im dihedral angle = 2.88); the shortness of the N 2 C + •••Cl dÀ distances (3.01 AE 0.01 ) is attributed to the electrostatic effect.

Figure 2 .

 2 Figure 2. XRD molecular views of 5 a-c, 5 f-g and 5 a'. Thermal ellipsoids at the 50 % probability level. For clarity, hydrogen atoms are omitted. The ellipsoid diagrams of the triflate anions of 5 a" are also omitted. The N-Ph and P-Ph ipso atoms reveal a p-stacking interaction: C8-C14 % 3.26 (5 a), 3.20 (5 b, 5 c), 3.18 (5 f), 3.14 (5 a'); C8-C20 % 2.24 (5 g); C34-C40 % 3.14 (5 a'). In the dication 5 a', the sandwiching of the Cl atom by the benzimidazolium moieties is indicated by the short distances: Cl1-C1 % Cl1-C27 = 3.01 AE 0.01 , Cl1-N1 % Cl1-N3 = 3.20 , Cl1-N2 % Cl1-N4 = 3.41 AE 0.00 Cl1-C26 % Cl1-C52 = 3.55 AE 0.05 .

Figure 3 .

 3 Figure 3. Lewis structure of the dinuclear side-products formed along with the target complexes 5 b,c, 5 e-g (Scheme 3; top), crystallographic molecular view of 6 f with thermal ellipsoids at the 50 % probability level (bottom left), and free van der Waals gallery available for hosting DCM solvent molecules within the network of molecules of 6 f (bottom right).

  one may cite the Werner DCM-clathrate [Ni(NCS) 2 (3-cyanopyridine) 4 ]• 2 CH 2 Cl 2 . [41i] More particular examples are the recently described dinuclear clathrates [Cd 2 I 2 (m-L) 2 ]•CH 2 Cl 2 (L = 4,4'-bis(2methylimidazol-1-ylmethyl)biphenyl),[41j] and [Ag(NO 3 ) 2 Pt(m-benzothiadiazol-4-ylethynyl)(4-diphenylaminopyridine)]•CH 2 Cl 2 .[41k]

Fig. 1

 1 Fig. 1 Aromatic region of the 1 H NMR spectra of 4 and 11 in highly diluted CDCl 3 solutions (400 MHz, 12 h acquisition time).

Fig. 2

 2 Fig. 2 Normalized absorption spectra of 4 and 11 in chloroform solution.

Fig. 3

 3 Fig. 3 Molecular views of the X-ray crystal structures of carbo-benzenes 4 (top) and 11 (bottom). Numbering of non-equivalent C atoms is indicative of the crystal symmetry. For clarity, hydrogen atoms and solvent molecules are omitted.

Fig. 4

 4 Fig. 4 Views of the crystalline molecular packing of 4 (top) and 11 (bottom) evidencing both the absence of p-stacking between the C 18 rings, and interactions with solvent molecules (for 4) and between two carbo-benzene molecules (for 11).

Table 2 a

 2 CV and SWV data for the carbo-benzenes 4 and 11 in chloroform solutions Half-wave potential E 1/2 = (E red P + E ox P )/2, in V/SCE. b Separation between the two peak potentials: DE P = |E red P À E ox P |, in V. c Peak current ratio RI P = |I ox P /I red P |. d E P values measured from CV in V/SCE. e Reversibility observed at a high scan rate only. f The compound underwent polymerization and deposited on the electrode.

Fig. 5

 5 Fig. 5 Morphology of spin-casted films of 11 (blended with PC 71 BM: 1 : 1, w/w ratio) on a glass substrate: microscopic optical image taken using a digital camera installed on the AFM instrument used (top), and the AFM image showing the film roughness (rms) B355 nm (bottom). An additional AFM image is available in the ESI. †

  (QCQCQ, -CC-), 105.63 (QCPh-), 35.55 (-C(CH 3 ) 3 ), 31.88 (-C(CH 3 ) 3 ). HRMS (MALDI-TOF/DCTB): m/z: [M] + calculated for C 70 H 62 902.4852, found: 902.4787. UV-vis (CHCl 3 ): l max = 472 nm (e = 248 000 L mol À1 cm À1 ). Melting-decomposition temperature: 230 1C.

1 H

 1 NMR (400 MHz, CDCl 3 ) d 7.89-7.62 (m, 12H, o-C 6 H 5 ), 7.49-7.27 (m, 18H, m-, p-C 6 H 5 ), 3.71-3.35 (m, 12H, -OCH 3 ), 3.35-3.05 (m, 2H, -OH).

  Lipidic Carbo-benzenes: Molecular Probes of Magnetic Anisotropy and Stacking Properties of α-Graphyne Chongwei Zhu, †, ‡ Arnaud Rives, †, ‡ Carine Duhayon, †, ‡ Valeŕie Maraval,* , †, ‡ and Remi Chauvin* , †, ‡ † CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, 31077 Toulouse Cedex 4, France ‡ Universitéde Toulouse, UPS, ICT-FR 2599, 118 route de Narbonne, 31062 Toulouse Cedex 9, France * S Supporting Information ABSTRACT: Solubilization of the C 18 fundamental circuit of αgraphyne has been envisaged by decoration with aliphatic chains R = n-C n H 2n+1 . The synthesis and characterization of p-dialkyl-tetraphenylcarbo-benzenes

Figure 1 .

 1 Figure 1. Examples of π-conjugated carbo-meric molecules of variable solubility.

2 . 2 . 2 aa 1 H

 2221 Scheme 1. Synthesis of Mono-and Dialkyl-carbo-benzenes by Addition of Alkyl or Fluoroalkyl Grignard Reactants to the [6]Pericyclynedione 7, Followed by Reductive Aromatization of the [6]Pericyclynediol Products 6 and 8 Using Anhydrous SnCl 2 a

19

 19

2 . 3 .

 23 Absorption Spectroscopy of Mono-and Dialkylcarbo-benzenes. The mono-and dialkyl-carbo-benzenes 10a,b,d,e and 11a-e are highly chromophoric, with molar extinction coefficients in chloroform solution always around 200 000 L•mol -1 •cm -1 , all the measured values being in the range 185 000 < ε < 219 000 L•mol -1 •cm -1 . Their UV-vis absorption spectra in CHCl 3 are almost perfectly super-

Figure 2 .

 2 Figure 2. Variation of the 1 H NMR chemical shifts of the CH 2 groups of the alkyl chains of 11b-e vs the CH 2 rank (top left), variation of the 1 H NMR chemical shifts of the CH 2 groups of the alky chains of 11b and parent 1,4-dioctylbenzene 22a vs the CH 2 rank (top right), 23 and full 1 H NMR spectrum of the dioctyl-carbo-benzene 11b in CDCl 3 (bottom); (*) acetone; (**) CH 2 Cl 2 .

Figure 3 .

 3 Figure 3. Normalized UV-vis absorption spectra of the monoalkyl-carbo-benzenes 10a,b,d,e (left) and dialkyl-carbo-benzenes 11a,b,d,e (right) in chloroform solution.

  3.29 and 3.55 Å between pairs of sp-C and sp 2 -C(Ph) vertices in successive C 18 rings, respectively. The π-stacking of C 18 rings in crystals of 11a and 11c is actually correlated with the absence of cocrystallized solvent molecule. No such stacking is observed in crystals of 11b (Θ = 65.9°) and 11d (Θ = 71.5°) containing CHCl 3 and DCM molecules, respectively. In crystals of the dioctyl-carbo-benzene 11b, an interaction between each C 18 ring and one CHCl 3 molecule is revealed by a short spC 2 •••ClC contact (ca. 3.41 Å), with a spC 2 •••Cl-C angle of ca. 150.8°: this arrangement is indicative of a σ-hole-directed C-Cl•••π halogen bond, previously evidenced and analyzed in the carbo-mer series. 10c,31As observed earlier for o-tetraphenyl-carbo-benzenes,19 the Cl

Figure 4 .

 4 Figure 4. Molecular views of the X-ray crystal structures of the dialkyl-carbo-benzenes 11a-d. Numbering of nonequivalent C atoms indicative of the crystal symmetry. Thermal ellipsoids at the 50% probability level. For clarity, hydrogen atoms and solvent molecules (for 11b and 11d) are omitted (for more details, see SI).

Figure 5 .

 5 Figure 5. Views perpendicular to the C 18 mean planes of 11a and 11c in the crystal (top), and perspective view of the 55°-tilted columnar packing of 11c (bottom), showing the "vertical" overlap of successive C 18 rings illustrative of the one calculated in AB or ABC α-graphityne.3

Figure 6 .

 6 Figure 6. Variation of detectable melting-decomposition temperatures of dialkyl-carbo-benzenes vs the chain length n.

  H NMR (300 MHz, CDCl 3 ) ␦ 7.81-7.64 (m, 8H, o-C 6 H 5 ), 7.45-7.30 (m, 12H, m-, p-C 6 H 5 ), 3.73-3.21 (m, 12H, OCH 3 ), 3.04-2.51 (m, 2H, OH), 2.10-1.89 (m, 4H, CH 2 Pr), 1.78-1.51 (m, 4H, CH 2 Et), 1.39-1.23 (m, 4H, CH 2 Me), 1.00-0.81 (m, 6H, CH 2 CH 3 ). 13 C{ 1 H} NMR (75 MHz, CDCl 3 ) ␦ 139.6-139.3 (i-C 6 H 5 ), 129.1-129.0 (p-C 6 H 5 ), 128.5-128.4 (m-C 6 H 5 ), 126.5-126.4 (o-C 6 H 5 ), 87.

Fig. 1 .

 1 Fig. 1. Molecular view of the X-ray crystal structure of 1f. Thermal ellipsoids at the 50% probability level. For clarity, hydrogen atoms are omitted.

  Chem. Commun., 2017, 53, 5902--5905 This journal is © The Royal Society of Chemistry 2017 Cite this: Chem. Commun., 2017, 53, 5902 3D and 2D supramolecular assemblies and thermotropic behaviour of a carbo-benzenic mesogen † Chongwei Zhu, ab Tsai-Hui Wang, c Chien-Jhang Su, c Shern-Long Lee, d Arnaud Rives, ab Carine Duhayon, ab Brice Kauffmann, e Vale ´rie Maraval,* ab Chun-hsien Chen, * d Hsiu-Fu Hsu* c and Remi Chauvin * ab Hexaalkoxy-di(phenylethynyl)-tetraphenyl-carbo-benzenes bearing six C n H 2n+1 aliphatic chains (n = 12, 18) have been synthesized and characterized, including by single crystal XRD analysis. For n = 12, a liquid crystal behaviour was observed in the range of 109-130 8C. DSC, POM and PXRD analyses evidenced a rectangular columnar mesophase at 115 8C. The determined 3D lattice constants are consistent with 2D STM images of the so-called ''carbo-mesogen'' deposited on an HOPG surface.

Fig. 1

 1 Fig. 1 Molecular view of the X-ray crystal structure of 1a, with thermal ellipsoids drawn at the 30% probability level. For clarity, hydrogen atoms are omitted.

Fig. 2

 2 Fig. 2 Polarizing micrograph of 1a at 109 1C on heating as a viscous liquid showing birefringent textures indicating the phase to be liquid crystalline (the identity of the LC phase cannot be determined from the POM texture only). Scale: white box length = 50 mm.

  : a = 48.5 Å, b = 45.0 Å, and Z = 3 (Z: number of molecules in a unit cell). No signal could be attributed to the intracolumnar correlation along the c axis.

  -CH 2 or O centers). This balance allows a LC behaviour of the pure substance in a rectangular columnar mesophase resulting from unprecedented differential supramolecular associations around C 18 macro-monocycles. These results open natural prospects for a new generation of functional tubular discotic LCs based on such a type of rigid cores. C. Z. thanks the China Scholarship Council for his PhD scholarship. The ANR program (ANR-11-BS07-016-01) is acknowledged for the postdoctoral fellowship of A. R. and for funding of working facilities. R. C. thanks the Centre National de la Recherche

Fig. 3

 3 Fig. 3 Powder X-ray diffractogram of 1a at 115 1C in the LC phase range indicating a columnar rectangular geometry. Left: 2D-XRD; right: 1D-XRD.

Fig. 4

 4 Fig. 4 STM images of 1a. (a) STM image showing the in-plane molecular packing into ordered arrays; (b) high resolution STM image exhibiting the macrocycle organization by intermolecular chain interdigitation framing a rectangular pattern of 48 Â 43 Å 2 tiles (see TOC scheme or Fig. 5c); (c) proposed packing for panel b. Conditions: substrate, HOPG (highly oriented pyrolytic graphite); solvent, 1,2,4-trichlorobenzene; concentration, ca. 0.1 mM; E bias , À800 mV; i tunneling , 0.18 nA; room temperature.

  carbo-benzene. 1: R = n Oct, R 0 = Ph n = 1: carbo-biphenyl. 2: R = n Oct, R 0 = R 1 = Ph n = 2: carbo-terphenyl. 3: R = n Oct, R 0 = R 2 = Ph ; 3a: R 1 = Ph; 3b: R 1 = 4-n Pent-C 6 H 4 n = 3: carbo-quaterphenyl. 14: R = n Oct, R 0 = R 1 = R 2 Ar = Ph, 20 % from 4 3b, Ar = 4-n Pent-C 6 H 4 , 9 % from 11

Schéma 1 . 11 2.

 111 Méthode générale de préparation des ligands (N-phényl-benzimidazol-1-yl)diphénylphosphine à substituants nitro et des complexes de Rh(I) correspondants. La fréquence d'élongation de la bande C=O en spectroscopie infra-rouge et le déplacement chimique en RMN du 103 Rh ont été utilisés comme sondes pour mesurer le caractère électrodonneur des ligands phosphorés synthétisés, qui se sont avérés être très faiblement σ-donneurs en comparaison des ligands non-nitrés correspondants et des dérivés cationiques N-méthylbenzimidazolium. Les hexaaryl-carbo-benzènes revisités : nouvelle voie de synthèse, donnés cristallographiques et comportement électrochimique L'élément carbone est d'une importance primordiale dans la construction chimique de la vie sur Terre et il est également à la base de la chimie organique. Environ 10 7 molécules organiques et polymères ont été synthétisés par les chimistes, leur diversité structurale étant basée sur des liaisons C-C et C-X stables, et accompagnée par de nombreuses propriétés chimiques et physiques. Leurs applications sont très variées, allant des médicaments aux matériaux.

  Les structures des graphynes, composés d'atomes de carbone hybridés sp et sp 2 , proposées par Baughman en 1987, 18 ont été largement étudiés au niveau théorique. Ces graphènes expansés sont formellement obtenus par insertion d'unités C 2 dans toutes les liaisons covalentes du graphène (α-graphyne) ou dans une partie d'entre elles (γ-graphyne), et peuvent donc être formellement obtenus par le processus de carbo-mérisation, défini en 1995, et consistant en l'insertion d'unités C 2 dans toutes les liaisons covalentes, ou dans une partie topologiquement définie des liaisons d'une structure de Lewis parente.

  De façon générale, les coeurs aromatiques étendus plans permettant un bon recouvrement des orbitales π sont susceptibles de renforcer la stabilité de l'arrangement colonnaire et l'ordre supramoléculaire. Les chaînes dispersives attachées au coeur central jouent aussi un rôle important dans la formation des mésophases colonnaires. La nature, le nombre et la position de ces chaînes sur le coeur mésogène peuvent fortement modifier les températures de transition de phase, la solubilité des molécules mésogènes, les distances intercolonnaires et l'ordre intra-colonnaire des mésophases. Les chaînes flexibles les plus utilisées sont des chaînes alkyles linéaires ou branchées, des groupes alkylphényle ou alkoxyphényle. Alors que les macro-poly-hétérocycles aromatiques tels que les porphyrines ont été largement considérés comme coeur mésogène, aucune attention n'a été portée aux macro-monocycles aromatiques. En particulier, le cycle carbo-benzène en C 18 , dont le caractère macroaomatique est souvent comparé aux circuits en C 16 N 2 à 18 électrons π des porphyrines, n'avait jamais été envisagé comme coeur mésogène avant ce travail. Pourtant, le cycle carbo-benzène à 18 électrons π délocalisés, analogue trois fois expansé du benzène, représente un nouveau type de coeur attractif pour l'élaboration de cristaux liquides discotiques. De plus, la forme hexagonale des carbo-benzènes en font une plateforme idéale sur laquelle il est possible d'insérer des chaînes alkyles sur différentes positions. Les para-dialkyl-carbo-benzènes lipidiques portant deux chaînes alkyle linéaires récemment décrits ne présentent pas de comportement cristal liquide, suggérant que la présence de deux chaînes sur le coeur mésogène n'est pas suffisante pour induire la formation de mésophases. 31 Deux paratrialkoxyphényléthynyl-carbo-benzènes ayant différentes longueurs de chaînes ont donc été préparés (n-C 12 H 25 et n-C 18 H 37 ), et le comportement mésogène de l'un d'entre eux a été étudié. La formation d'une mésophase colonnaire rectangulaire à 115 °C a été mise en évidence par microscopie optique à lumière polarisée (POM), par calorimétrie différentielle à balayage (DSC), par diffraction des rayons X sur poudre (PXRD) et par microscopie à effet tunnel (STM).

Figure 1 .

 1 Figure 1. Molécules carbo-mésogènes portant des chaînes alkyle de longueurs différentes.

  planéité et la richesse en électrons π des carbo-benzènes, a encouragé l'élaboration d'une série de carbo-mères de cycle d'OPE (carbo-OPE). La préparation d'un carbo-OPE 2 (carbo-mère de squelette du biphényle) et de deux carbo-OPE 3 (carbo-mères de squelette du terphényle) a alors été envisagée. Afin de les rendre solubles, ces trois cibles ont été conçues avec des chaînes n-octyle solubilisantes aux deux extrémités de leur squelette π-conjugué. De même, l'un des carbo-terphényle a été ciblé avec des chaînes pentyle sur les quatre substituants phényle du macrocycle central.

OPE 3 ,

 3 premiers exemples de molécules composées de trois cycles carbo-benzènes, ont été préparés suivant deux stratégies différentes. Ces trois carbo-OPE ont été entièrement caractérisés par RMN1 H et 13 C, par spectroscopie UV-visible, par spectrométrie de masse et par électrochimie. Deux d'entre eux ont également été caractérisés par diffraction des rayons-X sur des monocristaux obtenus à partir de solutions dans le chloroforme. Les carbo-OPE 3 présentent un très faible potentiel de première réduction (0,42 ± 0.03 V/SCE), sans précédent en série carbo-mère. Des études théoriques ont également été réalisées afin d'évaluer l'aromaticité des cycles carbo-benzènes de cette série de carbo-OPEn (n = 1 -4) à travers la détermination des valeurs de NICS au centre de chaque macrocycle (calculs DFT).57

Schéma 4 . 6 .Schéma 5 .

 465 Stratégies de synthèse des carbo-OPE. Des hémi-butatriènes endo-aromatiques aux unités[3]cumulènes pontants : carbo-barrélènes et carbo-stilbènesAu cours des dernières décennies, les chromophores macrocycliques polyacétyléniques π-conjugués ont attiré l'attention des chimistes pour leurs propriétés structurales, électroniques et optiques remarquables.[START_REF] Ramsaywack | Pour des exemples récents[END_REF] En chimie des carbo-mères, au-delà des carbo-benzènes qui sont les plus étudiés, l'élaboration et la synthèse de nouveaux types de molécules expansées de cette famille est encore aujourd'hui un sujet de recherche active dans l'équipe. Par exemple, la synthèse multi-étapes d'un carbo-naphtalène, plus petit fragment polycyclique fusionné d'αgraphyne (ou carbo-graphène), a été récemment décrite.[START_REF] Gouterman | [END_REF] Dans ce contexte, la synthèse de carbo-mères tricyclique du barrélène tendu (bicyclo[2.2.2]-2,5,7-octatriène) a été envisagée, le barrélène parent étant lui-même attractif, non seulement pour sa structure particulière, mais aussi pour ses possibles applications dans divers domaines. Depuis le premier rapport sur le barrélène par Zimmerman en 1960,59 de nombreux dérivés du barrélène ont été décrit et étudiés pour leurs propriétés électroniques,60 pour leurs applications en catalyse 61 et pour leur capacité à subir des réarrangement photo-induits.62 Le carbo-barrélène, avec son triple système π-conjugué riche en électrons, est attractif non seulement pour ses possibles propriétés optiques et électroniques, mais aussi parce que sa structure tridimensionnelle creuse peut être considérée comme une cage organique rigide pouvant éventuellement encapsuler de petites molécules ou ions. Ces dernières années, l'utilisation de molécules comme conteneurs hôtes capables d'encapsuler de petits invités a fait l'objet d'intenses recherches,63 en particulier pour les nombreuses applications qui découlent de cette propriété telles que la stabilisation d'espèces instables,64 la reconnaissance moléculaire,65 la discrimination de molécules chirales, 66 la croissance de cristaux67 ou la catalyse68 par exemple. Les composés cages sont en général classés en deux catégories : les cages supramoléculaires formées par auto-organisation de petites molécules69 et les cages covalentes obtenues par synthèse organique.70 Les cages covalentes, dont la construction requiert des synthèses multi-étapes aux rendements parfois faibles, sont donc plus rares que leurs homologues supramoléculaires. Malgré ce désavantage, les structures creuses rigides covalentes restent attractives pour leur plus grande stabilité ouvrant des possibilités d'applications comme hôte chiral,71 comme récepteur ou comme capteur.72 Le fullerène C 60 et ses dérivés ont été par exemple largement étudiés en tant que cages covalentes pouvant encapsuler le dihydrogène.73 Ici, la synthèse de carbo-barrélènes, possibles cages covalentes composées de trois unités dialcynylbutatriènes connectées entre elles par deux sommets hybridés sp 3 , a été envisagée par double addition nucléophile cyclisante d'un équivalent de triyne sur la[6]péricyclynedione en présence de LiHMDS comme base, suivie d'une étape d'élimination réductrice. Deux carbobarrélènes et un dérivé partiellement réduit bis-butatriénique ont été isolés sous forme de solides brun-jaunes très solubles et suffisamment stables pour pouvoir être caractérisés par RMN, spectroscopie UV-visible, spectrométrie de masse et électrochimie (Schéma 5). Ils ont également été caractérisés par analyse par diffraction des rayons-X sur des monocristaux obtenus à basse température.74 Le cation NH 4 + a été envisagé comme invité pour ce nouveau type de cage covalente dans des travaux préliminaires. A ce jour, aucune preuve expérimentale claire d'encapsulation de NH 4 + dans le carbo-barrélène n'a pu être mise en évidence, mais des calculs théoriques suggèrent qu'une interaction stabilisante devrait se produire entre ces deux molécules (ΔE tot = -44.4 kcal/mol). Stratégies de synthèse des carbo-barrélènes et des carbo-stilbènes.Inspirée par la formation d'un produit secondaire lors de la synthèse des carbo-barrélènes, la préparation de carbo-stilbènes a été envisagée (Schéma 5). La propriété de photoisomérisation des dérivés du stilbène parent (1,1-diphényléthène), conduisant à de nombreuses applications comme colorant, dans des dispositifs optiques[START_REF]Likhtenshtein in Stilbenes: Applications in Chemistry[END_REF] et même en biomédecine, 76 a en effet motivé la synthèse et l'étude de carbo-stilbènes, qui pourraient aussi s'avérer présenter des propriétés optiques et électroniques intéressantes. Deux carbo-stilbènes ont été préparés suivant une stratégie de synthèse optimisée, mais leur très faible solubilité n'a pas permis leur entière caractérisation. Ils ont cependant pu être caractérisés par RMN 1 H, spectroscopie UVvisible, spectrométrie de masse et électrochimie. Les spectres RMN 1 H ont montré la formation d'un mélange des deux isomères cis-et trans-des carbo-stilbènes, mais aucune évidence d'interconversion cis-trans, souvent observée pour les dialcynylbutatriènes, 77 n'a pu être détectée par RMN à température variable entre 25 et 55 °C. 74 Ce travail de thèse couvre deux thèmes de recherche distincts : la chimie organométallique de coordination, et la chimie organique de synthèse. Une quarantaine de produits finaux, dont 33 composés organiques et sept complexes de Rh I ont été obtenus, isolés et caractérisés. La structure de 27 d'entre eux a pu être confirmée par analyse par diffraction des rayons X. On peut remarquer un point commun formel entre ces deux thématiques de recherche, qui est le rôle clé des bases encombrées LDA et LiHMDS dans la préparation des phosphines nitro-aromatiques d'une part, et des carbo-benzènes, carbo-OPEs, carbo-barrélènes et carbostilbènes d'autre part. En termes de versatilité de synthèse, 24 carbo-benzènes ont été préparés à partir du précurseur [6]péricyclynedione clé. L'augmentation de la solubilité observée par substitution directe du macrocycle par des chaînes alkyles devrait permettre de manipuler plus facilement des molécules carbo-mères plus étendues, comme de longs films moléculaires carbo-OPE.

Table 1 .

 1 Crystallographic data for the complexes 5 a-c, 5 f,g and 5 a'. Rh C 55 H 44 Cl 9 N 6 O 5 P 2 Rh C 51 H 36 Cl N 6 O 5 P 2 Rh C 53 H 38 Cl 5 N 8 O 9 P 2 Rh C 53 H 38 Cl 5 N 8 O 9 P 2 Rh C 58.5 H 51 Cl 8 F 6 N 4 O 7 P 2 RhS 2 C 57.7 H 47.4 Cl 15.4 N 8 O 9 P 2 Rh 2

		5 a	5 b	5 c	5 f	5 g	5 a'	6 f
	CCDC no	1496162	1496160	1496161 1496163	1496164	1496165	1496166
	Empirical	C 51 H 38 Cl
	formula N 4 OP 2 M r 923.19	1352.92	1013.19	1273.05	1273.05	1548.67	1810.59
	Cryst.	monoclinic triclinic	triclinic	orthorhombic orthorhombic triclinic	triclinic
	system
	Space	P2 1 /n	P 1	P 1	P2 1 2 1 2 1	Pbca	P 1	P 1
	group
	T [K]	100	100	100	100	120	100	100
	a []	10.704(3) 9.5819(3)	8.8037(4) 14.0668(9)	15.9457(5)	14.7172(11) 10.5619(3)
	b []	11.496(4) 10.7141(4)	10.9560(6) 16.7870(13)	11.2917(3)	15.0289(11) 17.8643(6)
	c []	17.080(4) 14.7256(6)	12.0990(6) 22.524(2)	29.2082(11)	18.4532(14) 19.6796(7)
	a [8]	90	98.0370(16) 87.651(2) 90	90	91.977(3)	97.7610(16)
	b [8]	99.466(9) 102.8561(16) 79.310(2) 90	90	109.881(2) 90.9492(15)
	g [8]	90	102.9773(16) 69.853(2) 90	90	117.436(2) 104.4739(14)
	V [ 3 ]	2073.1(5) 1407.26(6)	1076.24(9) 5318.8(5)	5259.08(19)	3316.0(4)	3557.48(13)
	D c	1.479	1.596	1.563	1.590	1.608	1.551	1.690
	Z	2	1	1	4	4	2	2
	m(Mo Ka )	0.599	0.842	0.593	0.698	0.706	0.761	1.146
	[mm À1 ]
	Refl. mea-	31 654	86 814	52 472	79 662	76 783	10 6296	18 0292
	sured
	Refl.	4800/	12 318/0.026 4759/	13 763/0.058 7694/0.098	21 412/	24 511/0.035
	unique/R int	0.143		0.038			0.030
	Refl.	2792	10 661	4427	11 405	4876	16 438	18 966
	[I > 3s(I)]
	Nb param-	274	403	313	704	352	811	928
	eters
	R	0.0560	0.0389	0.0266	0.0309	0.0621	0.0560	0.0348
	R w	0.0609	0.0348	0.0233	0.0312	0.0751	0.0540	0.0366
	S = GooF	1.121	1.049	1.073	1.093	0.999	1.030	1.077
	D1 max /	1.20/À1.99 0.98/À0.67 0.41/	0.57/À0.41	0.95/À1.03	2.40/À0.96 2.10/À1.27
	D1 min			À0.72
	[e À3 ]

  1

Table 1

 1 Selected crystallographic data for 4 and 1114

		4	1 1
	Empirical formula	C 54 H 30 , CHCl 3	C 70 H 62 , 2(CHCl 3 )
	Formula mass	798.21	1142.02
	Crystal system	Orthorhombic	Triclinic
	Space group	P2 1 2 1 2 1 (CCDC 1231497)	P% 1
	T [K]	100	120
	a [Å]	12.4948(5)	10.1720(5)
	b [Å]	16.0972(6)	11.8006(8)
	c [Å]	20.2765(9)	12.8576(7)
	a [1]	90	90.105(5)
	b [1]	90	101.559(5)
	g [1]	90	94.484(5)
	V [Å 3 ]	4078.24(18)	1507.20(8)
	D c	1.300	1.258
	Z m [mm À1 ]	4 0.263	1 0.327
	Refl. Measured	97 066	23 700
	Refl. unique/R int	9935/0.048	6699/0.045
	Refl. with I 4 3s(I)	7863	4214
	Nb parameters	560	379
	R	0.0351	0.045
	R w	0.0369	0.0516
	Flack parameter	0.05(5)	-
	Nb Friedel-pairs	4448	-
	Dr

max /Dr min [e Å À3 ] 0.66/À0.58 0.50/À0.33 in either solvents, such a solvent change was recently shown to make redox processes less reversible, but keep the redox potential values almost unchanged, thus allowing a comparison between data obtained from either DCM or chloroform solutions. 13b

  H NMR (400 MHz, CDCl 3 ) d 9.48 (d, J = 7.3 Hz, 12H, o-C 6 H 5 ), 8.01 (t, J = 7.7 Hz, 12H, m-C 6 H 5 ), 7.74 (t, J = 7.4 Hz, 6H, p-C 6 H 5 ). 13 C{ 1 H} NMR (101 MHz, CDCl 3 ) d 140.25 (i-C 6 H 5 ), 130.56 (o-C 6 H 5 ), 129.92 (m-C 6 H 5 ), 129.44 (p-C 6 H 5 ), 118.46 (QCQCQ, -CRC-), 104.53 (QCPh-). HRMS (MALDI-TOF/DCTB): m/z: [M + Na] + calculated for C 54 H 30

1

  H NMR (400 MHz, CDCl 3 ) d 9.59À9.55 (m, 8H, o-C 6 H 5 ), 9.45 (d, J = 1.7 Hz, 4H, o-C 6 H 3 ), 7.96 (dd, J = 8.1, 7.2 Hz, 8H, m-C 6 H 5 ), 7.83 (t, J = 1.7 Hz, 2H, p-C 6 H 3 ), 7.72 (t, J = 7.3 Hz, 4H, p-C 6 H 5 ), 1.78 (s, 36H, -C(CH 3 ) 3 ). 13 C{ 1 H} NMR (101 MHz, CDCl 3 ) d 152.55 (m-C 6 H 3 ), 140.39 (i-C 6 H 5 ), 130.50 (o-C 6 H 5 ), 129.85 (m-C 6 H 5 ), 129.34 (p-C 6 H 5 ), 127.05 (i-C 6 H 3 ), 125.02 (o-C 6 H 3 ), 124.22 (p-C 6 H 3 ), 118.17

  13 C{ 1 H} NMR (101 MHz, CDCl 3 ) d 140.90-140.69 (i-C 6 H 5 -C(OH)o), 139.49-139.24 (i-C 6 H 5 -C(OCH 3 )o), 129.

	13-
	128.92 (p-C 6 H 5 ), 128.73-128.49 (m-C 6 H 5 ), 126.56-126.40 (o-C 6 H 5 -
	C(OCH 3 )o), 125.78-125.74 (o-C 6 H 5 -C(OH)o), 87.22-86.63,
	84.65-84.37, 82.96-82.57 (-CRC-), 72.02-71.91 (4C(OH)Ph),
	65.10, 65.07 (4C(OCH 3 )Ph), 53.48, 53.45 (-OCH 3 ). HRMS (MALDI-
	TOF/DCTB): m/z: [M] + calculated for C 58 H 44 O 6 836.3138, found:
	836.3015.

4.2.4 1,10-Bis(3,5-di-tert-butylphenyl)-4,7,13,16-tetramethoxy-

  pericyclynedione 10 (165 mg, 0.243 mmol) in THF(20 mL) was treated with 3,5-di-tertbutyl-C 6 H 3 MgBr NJC Paper (0.625 mmol in 1 mL THF) at 0 1C. The reaction mixture was stirred for 1.5 h at this temperature and 0.5 h at room temperature. After the addition of a saturated aqueous solution of NH 4 Cl, the aqueous layer was separated and extracted with Et 2 O. The organic layers were combined, dried over MgSO 4 and concentrated under reduced pressure. CH 3 ) 3 ), 31.20-31.10 (-C(CH 3 ) 3 ). HRMS (MALDI-TOF/DCTB): m/z: [M + Na] + calculated for C 74 H 76 O 6 Na: 1083.5540, found: 1083.5476.

	The residue was purified
	by chromatography on silica gel (pentane : ethyl acetate 4 : 1) to
	obtain 13 as a yellow oil with 64% yield (165 mg, 0.156 mmol).
	1 H NMR (400 MHz, CD 2 Cl 2 ) d 7.93-7.54 (m, 12H, o-C 6 H 5 ), 7.54-
	7.24 (m, 14H, m, p-C 6 H 5 , p-C 6 H 3 ), 3.70-3.40 (m, 12H, -OCH 3 ),
	3.36-3.17 (m, 2H, -OH), 1.41-1.22 (m, 36H, -C(CH 3 ) 3 ).
	13 C{ 1 H} NMR (101 MHz, CD 2 Cl 2 ) d 151.41-151.34 (m-C 6 H 3 ),
	139.88-139.68 (i-C 6 H 5 ), 139.62-139.52 (i-C 6 H 3 ) 129.08-128.94
	(p-C 6 H 5 ), 128.56-128.46 (m-C 6 H 5 ), 126.45-126.26 (o-C 6 H 5 ),
	123.34, 123.25 (p-C 6 H 3 ), 120.24-120.10 (o-C 6 H 3 ), 87.24-86.94,
	84.63-84.37, 82.65-82.54 (-CRC-), 72.02-71.81 (4C(OH)Ph),
	65.77-65.70 (4C(OCH 3 )Ph), 53.37-53.19 (-OCH 3 ), 34.96, 34.93
	(-C(

Table 1 .

 1 Selected Crystallographic Data for 11a-d

	molecule	11a	11b	11c a	11d	11d b	12 b,c
	R	C 2 H 5	C 8 H 17	C 14 H 29	C 20 H 41	C 20 H 41	H
	crystallization solvent	CHCl 3	CHCl 3	CHCl 3	DCM	CHCl 3	DCM
	cocrystallized solvent	no	yes	no	yes	yes	no
	melting-decomposition point (°C)	208	188	170	149
	deviation from C 18 ring planarity (Å)	0.058(2)	0.045(1)	0.036(3)	0.035(5)	0.049	0.032
	angle between C 18 and alkyl planes (deg)	40.2(2)	6.6(1)	22.0(1)	3.3(1)	7.8
	angle between the C 18 and Ph planes (deg)	10.99(4)	1.63(2)	8.31(7)	7.50(11)	5.4	10.8
		8.18 (4)	3.27(2)	7.07(7)	3.54(13)	1.9	18.5
		11.03(4)	5.88(3)		4.54(10)
		8.33(4)	8.46(2)		1.53(11)
	distance between closest C 18 planes (Å)	3.255	3.215	3.206 a	3.398	3.277	2.984
	Θ (deg)	57.7	65.9	55.0 a	71.5	74.4	71.6
	space group	P2 1 /c	P -1	P2 1 /n	P -1	P-1	P2 1 /c
	no. of axes, angle between them (deg)	2, 64.5(1)	1	2, 70.07(2)	1
	diameter (maximum C•••C distance, Å)	12.269(4)	27.711(2)	39.930(7)	57.435(11)	57.367	16.7

Characterization of 1-butyl-4,7,13,16-tetramethoxy-4,7,13,16- tetraphenylcyclooctadeca-2,5,8,11,14, 17-hexayne-1,10-diol (4f), a side product obtained during the preparation of 3f 1

  H NMR (400 MHz, CDCl 3 ) ␦ 9.51 (dd,3 J HH = 8.0, 4 J HH = 1.2 Hz, 8H, o-C 6 H 5 ), 7.97 (dd,3 J HH = 8.2, 7.2 Hz, 8H, m-C 6 H 5 ), 7.73-7.66 (m, 4H, p-C 6 H 5 ), 4.69 (t, 3 J HH = 7.5 Hz, 4H, CH 2 Pr), 3.04-2.92 (m, 4H, CH 2 CH 2 Me), 2.02-1.91 (m, 4H, CH 2 Me), 0.91-0.82 (m, 6H, CH 3 ). 13 C{ 1 H} NMR (101 MHz, CDCl 3 ) ␦ 139.9 (i-C 6 H 5 ), 129.8 (o-C 6 H 5 ), 129.8 (m-C 6 H 5 ), 129.3 (p-C 6 H 5 ), 122.1, 119.4, 116.0 (=C=C=, CϵC), 106.5 (C-Bu), 103.0 (C-Ph), 40.4 (CH 2 Pr), 34.0 (CH 2 Et), 22.8 (CH 2 Me), 14.3 (CH 3 ). H NMR (400 MHz, CDCl 3 ) ␦ 7.81-7.64 (m, 8H, o-C 6 H 5 ), 7.45-7.31 (m, 12H, m-, p-C 6 H 5 ), 5.43-5.24 (m, 1H, CHOH), 3.64-3.33 (m, 12H, OCH 3 ), 2.91-2.31 (m, 2H, OH), 2.07-1.95 (m, 2H, CH 2 Pr), 1.76-1.60 (m, 2H, CH 2 Et), 1.41-1.30 (m, 2H, CH 2 Me), 0.93-0.82 (m, 3H, CH 3 ). 13 C{ 1 H} NMR (101 MHz, CDCl 3 ) ␦ 139.48 (i-C 6 H 5 ), 129.10 (p-C 6 H 5 ), 128.53 (m-C 6 H 5 ), 126.46 (o-C 6 H 5 ), 87.10, 84.67, 82.91 (CϵC), 75.96, 72.98 (C(OMe)Ph), 63.71 (C(OH)Bu), 53.36-53.31 (OCH 3 ), 53.26 (CHOH), 42.82 (CH 2 Pr), 26.66 (CH 2 Et), 22.35 (CH 2 Me), 11.41 (CH 2 CH 3 ). HRMS (MALDI-TOF/DCTB) (m/z): [M+Na] + calcd for C 50 H 44 O 6

	HRMS (MALDI-TOF/DCTB) (m/z): [M] + calcd for C 50 H 38 , 638.2974;
	found, 638.3000; [M+Na] + calcd for C 50 H 38 Na, 661.2871; found,
	661.2931.
	UV-vis (CHCl 3 ): max = 446.45 nm ( = 208 000 L mol -1 cm -1 ).
	Melting-decomposition temperature: 188 °C.

  (C(OMe)Ph), 63.7 (C(OH)Bu),53.4-53.3 (OCH 3 ), 43.0-42.8 (CH 2 Pr), 26.8-26.5 (CH 2 Et), 22.4-22.3 (CH 2 Me), 14.2-13.9 (CH 2 CH 3 ). HRMS (MALDI-TOF/DCTB) (m/z): [M+H] + calcd for C 54 H 53 O 6 , 797.3842; found, 797.3771.

Table 1 .

 1 Voltammetric data for 1f in DCM and chloroform solutions. P values are measured from CV, in V/SCE. a Reversibility is observed at high scan rates only.b The third reduction cannot be observed in CHCl 3 because the solvent is reduced at this potential.

		Reductions				Oxidations
	Redox
	event no.	E 1/2 (⌬E P )	R I P	E P	red	E 1/2 (⌬E P )	RI P	E P	ox
	DCM
	First	-0.82 (68)	0.97			1.15 (78)	1.04
	Second	-1.26 (63)	0.97			1.63 (107)	1.15
	Third			-1.98			2.06
	CHCl 3
	First	-0.82 a (59)	1.01			1.18 a (53)	0.68
	Second			-1.32 b			1.69
	Third							2.05
	Note: Supporting electrolyte: solvent + 0.1 mol/L [TBA][PF 6 ]; scan rate: 0.2 V/s. The half-wave potential (E 1/2 ) = (E P ox )/2, in V/SCE. The separation between red + E P the two peak potentials was calculated as follows: ⌬E P = |E P ox |, in V. The red -E P peak current ratio (RI P ) = |I P ox /I P red |. E

Table 1

 1 PXRD data of 1a at 115 1C (seeFig. 3)

		d-Spacing (Å)
	Phase	Obsd	Calcd	Miller indices	Lattice constants (Å)
	Col rec	33.01	33.01	11	a = 48.52
		24.26	24.26	20	b = 45.04
		16.53	16.51	22	Z = 3
		15.19	15.22	31
		12.10	12.13	40
		11.37	11.71	41
		4.68		(Alkyl)

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2846 Full Paper

Scheme 1. Syntheses of nitro-functionalized benzimidazoles (for the 4,5-X 2 isomer of 1 d, 1 d', see the Supporting Information).Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2847 Full Paper

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2849 Full Paper

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2850 Full Paper

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2851 Full Paper

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2852 Full Paper

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2853 Full Paper

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2854 Full Paper

Chem. Asian J. 2017, 12, 2845 -2856 www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2855 Full Paper

www.chemasianj.org 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2856 Full Paper

Scheme 1 Strategies envisaged for the preparation of the unsubstituted carbo-benzene 1 (top); known syntheses of hexaphenyl-carbo-benzene 4 (bottom). Scheme 2 Synthesis of carbo-benzene targets via a [8+10] macrocyclization route. Paper NJC Published on 30 March 2017. Downloaded by Universite Paul Sabatier on 09/11/2017 16:34:04.View Article Online

(a) R.Chauvin, Tetrahedron Lett., 1995, 36, 397-400; (b) V.Maraval and R. Chauvin, Chem. Rev.,

2006, 106, 5317-5343; (c) K. Cocq, C. Lepetit, V.Maraval and R. Chauvin, Chem. Soc. Rev., 2015, 44, 6535-6559. 2 In simple words, a carbo-mer is a molecular structure derived from a parent Lewis covalent structure by systematic insertion of one dicarbon unit in each original covalent bond (single, double, triple) of given type (e.g. any bond, or C-C bond only). 3 The [9+9] macrocyclization under basic conditions was not attempted because of the instability of the triynal precursor 3, which prevented its isolation. For more details, see: R.Chauvin, Tetrahedron Lett., 1995, 36, 401-404. 4 The structure of 1 has however been extensively studied at the theoretical level, in both the ground state and excited states by DFT and TDDFT calculations, respectively.

carbo

J. Org. Chem. 2017, 82, 925-935

J. Org. Chem. 2017, 82, 925-935 927

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Can. J. Chem. Vol. 95, 2017 Published by NRC Research Press Can. J. Chem. Downloaded from www.nrcresearchpress.com by University of British Columbia on 10/31/17For personal use only.

Résumé en français

Acknowledgements C.Z. thanks the China Scholarship Council for financial support. R.C. thanks the CNRS for half a teaching sabbatical in 2014-2015 and 2015-2016. A determining support was also indirectly provided by the ANR program (ANR-11-BS07-016-01). The authors are also indebted to Dr. ValØrie Maraval for efficient logistic management. Acknowledgements C. Z. thanks the China Scholarship Council for his PhD scholarship. The Toulouse IDEX Emergence program 2014 is acknowledged for funding (Carbo-device project). R. C. Thanks the Centre National de la Recherche Scientifique (CNRS) for half a teaching sabbatical in 2015-2016. The authors thank the French-Mexican International Associated Laboratory (LIA) ''Molecular Chemistry with Applications in Materials and Catalysis'' funded by the CNRS and the CONACyT.

Notes and references

Acknowledgements C.Z. thanks the China Scholarship Council for his Ph.D. scholarship. The ANR program (ANR-11-BS07-016-01) is acknowledged for funding. R.C. thanks the Centre National de la Recherche Scientifique (CNRS) for half a teaching sabbatical in 2015-2016.

C.Z. thanks the China Scholarship Council for his Ph.D. scholarship. The ANR program (ANR-11-BS07-016-01) is acknowledged for the postdoctoral fellowship of A.R. and for funding. R.C. thanks the Centre National de la Recherche Scientifique (CNRS) for half a teaching sabbatical in 2015-2016. The authors also thank Dr. Yannick Coppel for the CP-MAS NMR analysis of 11a and Dr. Nathalie Saffon-Merceron for the X-ray diffraction analysis of 11c.

Conflict of interest

The authors declare no conflict of interest.

ARTICLE

Selective access to p-dialkyl-carbo-benzenes from a [6]pericyclynedione: the n-butyl nucleophile model for a metal switch study Chongwei Zhu, Carine Duhayon, Alix Saquet, Valérie Maraval, and Remi Chauvin Abstract: The synthesis, spectroscopic properties, comparative electrochemical behavior in CHCl 3 vs CH 2 Cl 2 , and X-ray crystal structure of p-di-n-butyl-tetraphenyl-carbo-benzene are described. The selectivity of preparation of the ultimate [6]pericyclynediol precursor has been examined by comparing the reactivity of the [6]pericyclynedione substrate with four n-Bu-MX n nucleophiles involving more or less halogenated metal centers MX n (0 ≤ n ≤ 2): Li, MgBr, MgCl, CeCl 2 /LiCl. The cerium reagent is found to be the most efficient, giving approximately twice the yield given by Grignard reagents in the target diadduct (90% vs 51%-53%). The dibutyl-carbo-benzene product happens to be soluble in both CHCl 3 and CH 2 Cl 2 : cyclic voltammograms of either solution exhibit almost identical peak potentials with reduced reversibility of the redox processes in CHCl 3 .

Key words: alkylcerium, alkyne, aromatics, carbo-benzene, carbo-mer.

Résumé : Nous décrivons la synthèse du p-di-n-butyl-tétraphényl-carbo-benzène, ainsi que ses propriétés spectroscopiques, son comportement électrochimique comparatif dans le CHCl 3 p/r au CH 2 Cl 2 et sa structure cristalline, déterminée par radiocristallographie. Nous avons examiné la sélectivité de la synthèse du dernier précurseur, le [6]péricyclynediol, en comparant les réactivités d'un substrat précurseur, une [6]péricyclynedione, avec quatre nucléophiles de formule n-Bu-MX n dont les centres métalliques M sont plus ou moins halogénés, où MX n (0 ≤ n ≤ 2) = Li, MgBr, MgCl, CeCl 2 /LiCl. Le réactif a `base de cérium s'est révélé le plus efficace, le rendement en diadduit cible étant d'environ le double des rendements obtenus avec les réactifs de Grignard (90 % p/r a `51-53 %). Il se trouve que le dibutyl-carbo-benzène généré est soluble tant dans le CHCl 3 que dans le CH 2 Cl 2 : les diagrammes de voltampérométrie cyclique des deux solutions présentent des potentiels de crête presque identiques, la réversibilité des processus rédox étant toutefois réduite dans le cas du CHCl 3 . [Traduit par la Rédaction] Mots-clés : alkylcérium, alcyne, aromatiques, carbo-benzène, carbo-mère. [6]pericyclynedione 4 (most stable stereoisomer)

Supplementary data

SUPPORTING INFORMATION η η

SUPPORTING INFORMATION

Chapter 5

SUPPORTING INFORMATION

Abstract

The manuscript is divided into six chapters and two independent parts, the first part being dedicated to the investigation of the effect of nitro substituents on aromatic phosphine ligands (L). A series of (N-phenyl-benzimidazol-1-yl)diphenylphosphines substituted with 1 to 3 nitro groups at different positions of the N-phenyl and benzimidazolyl cores, were synthesized, and compared with the non-nitrated parent and cationic N-methyl-benzimidazolium counterpart. In the corresponding trans-L 2 Rh I Cl(CO) complexes, prepared in two steps and fully characterized, moderate but systematic variations of the C=O IR stretching frequency and 103 Rh NMR chemical shift provide an empirical quantification of regio-specific effects of the nitro-substituents on the global donating character of the P-ligand. Dinuclear (μ-CO)(LRhCl) 2 side-products were shown to give unique clathrate crystals with a high content (6.7:1) of dichloromethane solvate.

The second part, gathering five chapters, concerns the study of new types of highly πconjugated carbo-mers, primarily devised to palliate the limiting poor solubility of the aromatic C 18 carbo-benzene core. The synthesis and characterization of reference hexaaryl-carbo-benzenes are revisited. An improved 12-step synthetic route to the long known hexaphenyl derivative and p-bis-3,5-di-tert-butylphenyl homologue is described. Both carbo-benzenes were fully characterized, in particular by X-ray diffraction analysis and electrochemistry. Their use in organic photovoltaic solar-cells was found to be hampered by their very low solubility preventing the formation of high quality thin films.

The third chapter focusses on a series of p-dialkyl-tetraphenyl-carbo-benzenes with two aliphatic chains R = C n H 2n+1 , n = 2, 4, 8, 14, 20. The synthetic route based on nucleophilic addition of RMgBr to a key [6]pericyclynedione ultimately led to both the dialkyl-and reduced monoalkyl-carbo-benzenes, the reduction process being found suppressed by using a RLi/CeCl 3 reactant. A dramatic enhancement of solubility in chlorinated solvents was observed for n ≥ 8. A direct π-π stacking of C 18 rings, driven by aliphatic dispersions forces, could be evidenced for the first time in the X-ray crystal structure of the bis-tetradecyl derivative, giving experimental support to the existence of the α-graphityne 3D carbon allotrope (putative carbo-mer of graphite).

The fourth chapter describes two trialkoxyarylethynyl-tetraphenyl-carbo-benzenes and the study of the mesogen properties of one of them. A columnar rectangular mesophase, evidenced at 115 o C by DSC, POM and PXRD analyses, opens prospects for a systematic study of related liquid crystals. The 3D lattice constants are consistent with 2D STM images of the carbo-mesogen deposited on HOPG.

The fifth chapter reports on three skeletal carbo-mers of bis-and ter-phenyls, devised for their acquaintance with OPP or OPE molecular wires. A carbo-terphenyl was found to exhibit a very low first reduction potential (-0.39 V/SCE), unprecedented in the carbo-mer series.

In the last chapter, new types of carbo-mers are exemplified: carbo-barrelenes and carbostilbenes. Their preparation relies on the addition of triyne dinucleophiles to either one or two equivalents of a [6]pericyclyne(di)one precursor. In the tricyclic series, two non-macroaromatic carbo-barrelenes and one partially reduced bis-butatrienic derivative, both containing two sp 3 -C bridgeheads, were found to be sufficiently stable to allow full characterization, including by crystallography. The cage-ability of a carbo-barrelene toward small molecules such as NH 4 + , albeit not clearly proven yet, was investigated both theoretically and experimentally. The carbo-stilbene product was evidenced as an unseparated mixture of two isomers. In the absence of crystal of suitable quality for crystallography, they were assigned to the cis and trans diastereoisomers on the basis of 1 H NMR spectroscopy and DFT calculations.

Key words: nitroaromatic phosphine ligands, [6]pericyclynes, aliphatic carbo-benzenes, liquid crystals, carbo-barrelene, carbo-stilbene, carbo-oligo-phenylene(ethynylenes)