Fethi Elaieb

David Sémeril

Dominique Matt

Michel Pfeffer

Pierre-Antoine Bouit

Muriel Hissler

Christophe Gourlaouen

Jack Harrowfield

arene-fused phospholes A calix[4]arene-based biarylphosphine has been synthesised and catalytically converted into two diastereomeric, calixarene-fused phospholes. Calix[4]arene-fused

Keywords:

An upper rim, o-(diphenylphosphinyl)phenyl-substituted calix[4]arene has been prepared and its coordinative properties investigated. When heated in the presence of palladium, the new biarylphosphine undergoes conversion into two diasteromeric, calixarene-fused phospholes. In both, the P lone pair adopts a fixed orientation with respect to the calixarene core. The more hindered phosphole (8), i.e. the one with the endo-oriented lone pair (cone angle 150°-175°), forms complexes having their metal centre positioned very near the calixarene unit but outside the cavity, this inducing an unusual chemical shift of one of the methylenic ArCH 2 Ar protons owing to interactions with the metal centre. As expected for dibenzophospholes, the complex [Rh(acac)(CO)•8], when combined with one equivalent of free 8, efficiently catalyses the hydroformylation of styrene, the catalytic system displaying high regioselectivity in favour of the branched aldehyde (b/l ratio up to 30). The optical and redox properties of the derivatives have also been investigated.

Introduction

Cavity-shaped molecules equipped with P(III) donor atoms have attracted increasing interest in the last two decades due to successful applications in transition metal catalysis. [START_REF]CDCl 3 , 500 MHz):  = 7.89 (d, 1H, arom. CH, C 6 H 4 , 3 J = 6.0 Hz), 7.76 (d, 1H, arom. CH, calixarene[END_REF] Notably, a number of publications have shown how the presence of a conical cavity fixed near a catalytic centre may drastically influence the outcome of carbon-carbon bond forming reactions both in terms of activity and selectivity. [2] A current challenge in this chemistry concerns the synthesis of calix [4]arenes in the so-called cone conformation substituted by a P(III) atom having its lone pair permanently located on the endo-face of the cavity. Conical molecules with this feature are expected to result in complexes with a highly crowded metal environment, if not with a metal centre embedded in the cavity. [2i, 2j, 3] A number of conecalix [4]arenes bearing a PR 2 group as upper rim substituent have already been reported, but in none of them does the P doublet adopt a fixed endo-orientation, this being due to the rotational freedom of the PR 2 moiety about the corresponding P-C calix bond. [4] Blocking the mobility of endo-P-conformers would certainly increase the time-averaged bulkiness of the corresponding ligand.

Here, we describe the synthesis of a calix [4]arene-based biarylphosphine and its catalytic conversion into two calix [4]arene-fused phospholes, one of them having its P __________ a Laboratoire de Chimie Inorganique Moléculaire et Catalyse, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 1 rue Blaise Pascal, F-67008 Strasbourg Cedex, France. E-mail: dmatt@unistra.fr, eric.brenner@unistra lone pair rigidly positioned on the concave side of the cavity. The coordinative properties of the latter were investigated towards Pd(II), Au(I) and Rh(I). Both ligands constitute the first examples of unsymmetrical dibenzophospholes sharing one of their benzo rings with that of a calix[4]arene receptor. [5] Two other calixarenes linked to a phosphole unit have been reported to date but in these the phosphole unit is remote from the cavity. [6]

Results and discussion

Synthesis and coordinative properties of a phosphole precursor.

Our strategy for preparing a calix [4]arene merged with a phosphole ring was based on a recent paper by Chatani et al. where it was shown that biarylphosphines of the general formula Ph 2 P(o-Ar-C 6 H 4 ) may, in the presence of [Pd(OAc) 2 ], undergo catalytic conversion into a dibenzophosphole (Scheme 1). [7] We anticipated that applying this methodology to the (unreported) biaryl-phosphine 3 (Scheme 2), in which the P-remote arene ring is part of a conical calix [4]arene skeleton, would result in a calixarene-fused phosphole. Scheme 1. Chatani's method for the catalytic synthesis of a phenyl-phosphole The synthesis of precursor 3 was performed in two steps, as in Scheme 2. Thus, reaction of the bromoaryl-substituted calixarene 1 [8] with n-BuLi, followed by addition of PPh 2 Cl to the resulting mixture and subsequent treatment with BH 3 •THF gave the phosphine borane adduct 2 in 75% yield. Deprotection with MeOH/toluene gave 3 quantitatively. The 31 P NMR spectrum of 3 shows a single resonance at -12.4 ppm (cf.  P (PPh 3 ) = -4 ppm ;  P [Ph 2 P(o-Ph-C 6 H 4 )] = -11.9 ppm ). The corresponding 1 H NMR spectrum, which exhibits two distinct AB patterns for the bridging ArCH 2 Ar groups (both with AB separations of ca. 1.3 ppm), is fully consistent with a calix [4]arene in the cone conformation. [START_REF] Gutsche | Calixarenes, Monographs in Supramolecular Chemistry[END_REF] The coordinative properties of 3 towards Au(I) and Pd(II) were investigated. Thus, reaction of 3 with [AuCl(THT)] gave 4 quantitively (Scheme 3). Complex 4 was characterised by 1 H-, 13 C-, and 31 P-NMR spectroscopy (see experimental section) as well as by a single crystal X-ray diffraction study (Fig. 1), which revealed a typical "pinched cone" structure of the calixarene core in the solid state. The P-Au-Cl rod is located outside the calixarene cavity with the gold atom lying above one of the C-C bonds of the phosphinated phenol ring. The values of the shortest Au•••C calix separations, 3.278 Å and 3.373 Å, are indicative of weak η 2 -Au•arene interactions, similar to those recently proposed by Echavarren et al. for the biarylphosphine complex [AuCl(Cy 2 P{o-Ph-C 6 H 4 })]. [START_REF] He E O-Me | [END_REF] Scheme 2. Synthesis of phosphine 3 Scheme 3. Complexes obtained from phosphine 3 5). Spectroscopic data is fully consistent with the presumed structure of this complex (see experimental part). In particular, assignment of the trans stereochemistry was made by comparing the chemical shift of the P atom ( P = 22.3 ppm) with that measured for a related complex, trans-[PdCl 2 {Ph 2 P(o-Ph-C 6 H 4 )} 2 ] ( P = 22.3 ppm). [11] A preliminary X-ray study confirmed this assignment.

Catalytic conversion of phosphine 3 to the calix-fused phosphole 8

Thermal treatment of a solution of 3 in toluene for 24 h in the presence of [Pd(OAc) 2 ] (5 mol %), and subsequent reaction with BH 3 .THF afforded the two isomeric phospholeborane adducts 6 (20 %) and 7 (60 %), which were separated by column chromatography (Scheme 4). Both compounds possess a stereogenic phosphorus atom, one bearing an exo-, the other an endo-oriented BH 3 moiety (here the terms exo and endo stand respectively for a BH 3 moiety directed towards the convex or concave part of the cavity). Owing to the C 1 molecular symmetry, the bridging methylene groups of each calixarene appear as four distinct AB patterns in the corresponding 1 H NMR spectra. Scheme 4. Synthesis of calix-phosphole 8 and derivatives 9, 10 and 11.

As generally observed for P(III)-borane adducts, the 31 P NMR spectra of 6 and 7 display each a rather broad signal due to 31 P-11 B coupling. Remarkably, while all aromatic protons of 7 are to be found in the range 7.92-6.04 ppm, the 1 H NMR spectrum of the exo-adduct 6 displays signals at higher field for three aromatic protons (5.87 (d), 5.65 (t) and 4.71 (d)), probably owing to a ring current effect exerted by the endo-oriented PPh ring on the three H atoms of the phenoxy ring closest to the phosphorus atom. Note that both calixarenes are inherently chiral, and therefore must each form as a racemic mixture. It is also important that, as shown previously, [12] when the above reaction was performed with analogues of 3 bearing either a PCy 2 or a P i Pr 2 substituent (instead of PPh 2 ), no phosphole formation occurred.

Phosphole-borane deprotection was achieved only for endo adduct 7. A very efficient deprotection method consisted of reacting a toluene solution of 7 with MeOH at 40 °C for 5 h (Scheme 4). After heating, the solution was evaporated to dryness, affording pure 8 quantitatively. The phosphorus atom of 8 gives a peak at -11.5 ppm in the 31 P NMR spectrum. Prolonged heating of a CDCl 3 solution of 8 at temperatures above 45 °C induced the very slow formation of the isomer resulting from pyramidal inversion at phosphorus (appearance of a signal at -13.9 ppm). The ultimate proof for the endo stereochemistry of 7 came from an X-ray diffraction study (Fig. 2) performed on the corresponding oxide 9, which can be obtained by reacting 8 with H 2 O 2 (Scheme 4). A determination of the Tolman cone angle of the phosphole-P based on the solid state data of 9 led to a value of ca. 150°. As shown in Fig. 2, in the solid, the calixarene core of 9 adopts a typical "flattened cone" conformation in which two facing phenoxy rings are roughly parallel while the other two make an angle of ca. 75°. In fact, in solution the time-averaged cone angle of 8 is likely to be significantly higher than 150°, as conical calixarenes are known to undergo a "breathing motion" in which the facing phenoxy rings alternately come close together then move away from each other (giving rise to the so-called flattened cone / flattened cone equilibrium [1a] ). Thus, a simulation with Spartan [13] showed that the highest possible cone angle of 8 is 175°. For comparison, both 1,3,5-triphenylphosphole and PPh 3 have a cone angle of 145°. [5c, 14] Determination of the percent buried volume of 8 using the SambVca tool [15] led to a value of 35.0 (vs. 31.7 for PPh 3 ). The corresponding steric map (Fig. 3) clearly established the proximity of the calixarenyl-P lone pair and the calixarene unit.

Figure 2. Solid state structure of 9. The two conformers seen in the solid form a kryptoracemate. [16] The dihedral angles between the facing phenoxy rings are 14.3° and 79.1°, respectively, in conformer A, and 5.9° and 74.6°, respectively, in conformer B. To obtain insight into its coordinative behaviour, phosphole 8 was reacted with the cyclopalladated complex [PdCl(8-mq)] 2 (8-mqH = 8-methylquinoline). This reaction afforded complex 10 in 73% isolated yield. In the 31 P NMR spectrum, the phosphorus atom is observed at 25.7 ppm, a normal value for [PdCl(8-mq)(phosphine)] complexes. [17] In accord with the C 1 molecular symmetry, the Pd-bound CH 2 group of 10 appears as an ABX spectrum in the 1 H NMR spectrum, with  A = 3.12 ppm and  B = 2.42 ppm (J(BA) = 14.5 Hz; 3 J(PA) = 0 Hz and 3 J(PB) = 7.5 Hz). The PdCH B signal at 2.41 ppm is shifted somewhat upfield when compared with those of other [PdCl(8-mq)(phosphine)] complexes found in the literature (typical  around 3.2 ppm). [17] The observed shielding is likely to reflect the magnetic anisotropy created by the flat dibenzophospholyl unit located beneath one of the PdCH 2 atoms. This interpretation is consistent with the data inferred from the solid state structure of 10 (vide infra). An unusual feature which reflects the metal/cavity contiguity concerns the AB pattern of one of the four bridging ArCH 2 Ar groups, the B signal of which has undergone a strong downfield shift upon complexation ( B = 4.52 ppm, instead of an expected value around 3.0 ppm), this leading to an AB separation of only 0.17 ppm. The other three ArCH 2 Ar signals show the normal pattern with AB separations of about 1.3 ppm, in accord with those usually observed for conical calix[4]arenes. In fact, owing to the fixed orientation of the P lone pair in 8, complexation of the "PdCl(8-mq)" moiety positions the Pd-Cl bond close to one of the ArCH 2 groups, thereby allowing: a) the metal-bound Cl atom to weakly interact with the equatorial CH atom; b) the metal atom to create an anagostic CH...Pd bond, and c) the phosphorus atom to give rise to a van der Waals interaction with the equatorial ArCH atom. All three interactions are compatible with the observed downfield shift. Note that anagostic bonds, which are electrostatic interactions in nature, are well documented in palladium chemistry. [18] The structure of complex 10 was established by a single-crystal X-ray diffraction study (Fig. 4). The study confirmed that the P-Pd vector lies on the concave side of the calixarene and revealed that the metallacyclic unit lies out of the pinched cavity. In the crystal, two molecules (A and B) are present, which display notable differences. In molecule A the quinolylinyl group lies as expected in the metal plane, while in B it is bent by ca. 36° towards the A molecule so as to enable  - stacking interactions with the neighbouring quinolinyl plane (shortest intermolecular C...C distances: 3.24 Å, 3.25 Å). The study further confirmed the close proximity of both the Pd and Cl atoms to an equatorial ArCH 2 Ar atom of the calixarene core. The corresponding Pd...H eq (3.05 Å in A and 3.01 Å in B) and Cl...H eq (3.0 Å in A and 3.45 Å in B) separations are compatible with the above postulated weak interactions, although at the upper limit for such interactions. However, due to the flexibility of the calixarene core, the time-averaged separations may be shorter in solution than those seen in the solid. DFT optimisation starting from the X-ray structure led to a H eq ...Cl separation of 2.63 Å, a value which is fully consistent with an hydrogen bond (electrostatic interaction). The same calculation further established an electrostatic Pd...H eq interaction (2.76 Å; see SI), as well a P... H eq dispersion interaction (2.88 Å).

Finally, in accord with the observation of an upfield-shifted Pd-CH signal, in both molecules a CH atom sits in the shielding zone of the flat phospholyl unit (distance to the plane: 2.78 Å in A; 2.45 Å in B).

To determine whether replacement of the "PdCl(8-mq)" moiety in 10 by a smaller metal fragment would modify the NMR signature of the ArCH 2 group closest to the metal, we prepared complex 11 (Scheme 4, Fig. 6), which was obtained quantitatively by reacting 8 with [AuCl(THT)] (THT = tetrahydrothiophene). Its solid state structure was established by an X-ray diffraction study (Fig. 5). As for 10, the 1 H NMR spectrum of 11 shows 4 different AB Dibenzo [b,d]phosphole 8 can be regarded as a triarylphosphine, and as such justifies its use in catalytic reactions. [19] In order to assess 8 as a ligand for styrene hydroformylation, we prepared the mono-phosphole complex [Rh(acac)(CO)( 10)] ( 12), which was obtained by reacting [Rh(acac)(CO) 2 ] with 1 equiv. of 8 (Scheme 5). Spectroscopic data are fully consistent with the proposed structure. Thus, for example, the IR spectrum of 12 shows a strong absorption band at 1975 cm -1 for the CO ligand and the 31 P NMR spectrum shows a doublet at 56.0 ppm (J(PRh) = 172 Hz) for the phosphorus atom. As for 10, the 1 H NMR spectrum of 12 features four AB patterns for the methylene ArCH 2 groups, three with a  AB value of ca. 1.3 ppm, the fourth with an AB separation of only 0.22 ppm. The existence of a tight AB pattern may here be attributed to a strong CH...O acac interaction, as inferred from a DFT calculation. The latter calculation rules out an anagostic CH...Rh bond (although CH anagostic interactions with Rh have been reported [20] ).

Scheme 5. Synthesis of rhodium complex 12

Catalytic runs with 12 were carried out in toluene at 60 °C under a H 2 /CO (1:1) pressure of 30 bar and with a Rh/styrene ratio of 1000 (Table 1). Using 12 alone as catalyst resulted in a 69.0 % styrene conversion after 7 h (Table 1, entry 1). As usual for Rh/phosphine hydroformylation catalysts, adding one equivalent of free ligand to the complex induced a significant activity increase, the styrene conversion reaching then 81.7 % after 7 h (Table 1, entry 2). The TOF determined after 1 h was 160 mol(styrene) mol(Rh) -1 h -1 , vs. 75 mol(styrene) mol(Rh) -1 h -1 when using PPh 3 under the same conditions. We noted that addition of a second equivalent of phosphole induced a slight decrease in activity with respect to the runs carried out with one equivalent of 8 (Table 1, entry 3). High regioselectivity in favour of the branched aldehyde (superior to those reported for other unsymmetrical benzophospholes [19] ) was observed for each run, the branched/linear ratio amounting to 96.8 : 3.2 in the best case (Table 1, entry 3). In comparison, PPh 3 resulted in a b/l ratio of 93.5 : 6.5. Similar good performances were observed with the substrates 4-fluoro-styrene and 4-t Bustyrene (Table 1, entries 5 and6). No hydrogenation products (ethylbenzene, 2phenylpropanol) were detected in these experiments.

Table 1. Rhodium-catalysed hydroformylation of vinyl arenes [a] Entry extra 8 (equiv./Rh) Time (h) Conversion (%) [b] Aldehydes distribution [b] l (%) [a] Conditions: complex 12 (2 mol), 8, vinyl arene (2 mmol), toluene/n-decane (20 mL/0.25 mL), P(CO/H 2 ) = 30 bar (CO/H 2 1:1 v/v), 60°C; [b] determined by GC using decane as internal standard.

Photophysical and electrochemical properties of phosphole oxide 9 and gold complex 11

The following studies were undertaken to quantify the influence of the calixarene moiety on the electronic properties of the phosphole ring. The optical properties of the calixphosphole derivatives 9 and 11 were investigated by means of electronic absorption and fluorescence spectroscopy in dichloromethane. Their absorption spectra exhibit both a broad -* transition with a moderate extinction coefficient at 345 and 349 nm, respectively (Fig. 4 and Table 2). The observed bands are characteristic of P-bridged biphenyl derivatives, [21] and, as expected, an analogous band could not be detected for the phosphine complex 4 (Fig. S3). We further noted that the absorption bands are red-shifted compared to that of 5-phenyldibenzophosphole oxide (DBPO) (Fig. 7) taken as reference (9,  = 13 nm; 11,  = 17 nm), thus revealing that the presence of the calixarene core induces a lowering of the HOMO-LUMO gap.

Figure 7: Structure of DBPO Phosphole oxide 9 and gold complex 11 display similar fluorescence spectra (Fig. 8) with emission maxima centered at 412 and 415 nm, respectively. In both cases, the excitation spectra are similar to the absorption spectra (Fig. S1 andS2) and the Stokes shifts are moderate (9, ῡ = 4557 cm -1 ; 11, ῡ = 4714 cm -1 ), suggesting some rearrangement of these molecules upon photoexcitation. As for the absorption properties, fluorescence arises from the dibenzophosphole core (note that the phosphine complex 4 shows no luminescence) and the emission maxima are red-shifted compared to those of the DBPO (9,  em = 46 nm; 11,  em = 49 nm). The fluorescence quantum yield measured for complex 11 is lower ( = 0.01) than that measured for phosphole oxide 9, which turned out to be an efficient fluorophore ( = 0.33). Compound 9 also emits as a thin film and the solid-state photoluminescence is almost superimposable on that of the solution (Figure S1). This latter observation is consistent with the absence of fluorophore stacking interactions in the solid state (see experimental part). 2). Both compounds display an irreversible oxidation wave, at +1.03 V and +1.17 V, respectively. A quasi-reversible reduction can be seen at -2.67 V for 9, while the reduction of compound 11 (-2.67 V) is irreversible. Note that no reduction was observed for the phosphine complex 4. These data, when compared to those of DBPO and DBPAuCl (Table 2) indicate that and 11 are easier to oxidise and more difficult to reduce than the two reference compounds, this reflecting the electron-donating behaviour of the calixarene core towards the dibenzophosphole unit. [21] 332 2900 366 0.042 ---2.35 c

DBPAuCl [21] 333

Conclusions

Thermal treatment of the new calixarene-based biarylphosphine 3 in the presence of catalytic amounts of palladium results in two separable, calixarene-fused phospholes with directionally rigid P lone pairs. With the sterically encumbered endo-P-calixarene 8, metal complexes are formed in which the metal centre sits very close to the calixarenyl substituent, thereby creating binding interactions with but one methylene ArCH atom of the calixarene core. The dibenzophosphole complex [Rh(acac)(CO) (8)] efficiently catalyses the hydroformylation of styrene with production of high proportions of branched aldehyde, reflecting the steric effect of the adjacent cavity which may pass through various weak interactions. Ligand 8 constitutes the first example of a calix[4]arene integrating a phosphole functionality in the cavity wall.

As revealed by photophysical and electrochemical studies, the calixarene moiety behaves as an electron donating group with respect to the phosphole unit, endowing it with unique properties compared to known systems. In particular, 9 turned out to be an efficient fluorophore both in solution and in the solid state. Future work will aim at exploiting such molecules as sensors.

Experimental Section

General Methods: All manipulations were performed in Schlenk-type flasks under dry argon. Solvents were dried by conventional methods and distilled immediately prior to use. CDCl 3 was passed down a 5 cm thick alumina column and stored under nitrogen over molecular sieves (4 Å). Routine 1 H, 13 C{ 1 H} and 31 P{ 1 H} NMR spectra were recorded with Bruker FT spectrometers (AVANCE 400 and 500). 25,26,27,28-tetrapropyloxycalix[4]arene (1), [8] [AuCl(THT)], [22] [PdCl 2 (PhCN) 2 ] [START_REF] Hartley | The Chemistry of Platinum and Palladium[END_REF] and [PdCl(8-mq)] 2 [START_REF] Cope | [END_REF] (8-mqH = 8-methylquinoline) were prepared according to literature procedures. General procedure for the hydroformylation experiments. The hydroformylation experiments were carried out in a glass-lined, 100 mL stainless steel autoclave containing a magnetic stirring bar. In a typical run, the autoclave was charged with 12 (2 mol) and extra 8, then closed and flushed twice with vacuum/N 2 . Toluene (20 mL), the vinyl arene (2 mmol) and decane (0.25 mL) were added under N 2 . The autoclave was then pressurised (30 bar, CO/H 2 1:1 v/v) and heated at 60°C. At the end of each run, the autoclave was cooled to room temperature before being depressurised slowly. A sample was taken and analysed by GC using a WCOT fused silica column (25 m x 0.25 mm).

Optical and electrochemical properties. UV-Visible spectra were recorded at room temperature on a specord 205 spectrophotometer. The emission and excitation spectra measurements were recorded on a FL 920 Edimburgh Instrument and corrected for the response of the photomultiplier. Quantum yields were calculated relative to quinine sulfate ( = 0.55 in H 2 SO 4 0.1M). The electrochemical studies were carried out under argon using an Eco Chemie Autolab PGSTAT 30 potentiostat for cyclic voltammetry with the three-electrode configuration: the working electrode was a platinum disk, the reference electrode was a saturated calomel electrode and the counter-electrode a platinum wire. All potential were internally referenced to the ferrocene/ ferrocenium couple. For the measurements, concentrations of 10

5-(2-Diphenylphosphanyl-phenyl)-25,26,27,28-tetrapropyloxycalix[4]arene (3):

A solution of [5-(2-phosphanyl-phenyl)-25,26,27,28-tetrapropyloxycalix[4]arene] borane (0.520 g, 0.60 mmol) in MeOH/toluene (1:4 mixture, 15 mL) was refluxed for 5 h. After cooling to room temperature, the solution was evaporated to dryness and the residue dried overnight under vacuum at 40°C to afford quantitatively phosphine 3 (0.511 g, yield 100 %). [START_REF]CDCl 3 , 500 MHz):  = 7.89 (d, 1H, arom. CH, C 6 H 4 , 3 J = 6.0 Hz), 7.76 (d, 1H, arom. CH, calixarene[END_REF] H NMR (CDCl 3 , 400 MHz):  = 7.34-7.28 (m, 7H, arom. CH, PPh 2 and C 6 H 4 ), 7.24-7.13 (m, 5H, arom. CH, PPh 2 and C 6 H 4 ), 7.00-6.96 (m, 1H, arom. CH, C 6 H 4 ), 6.94-6.90 (m, 1H, arom. CH, C 6 H 4 ), 6.67 (d, 2H, arom. CH, calixarene, 3 J = 6.9 Hz), 6.62-6.57 (m, 1H, arom. CH, calixarene), 6.56 (s, 2H, arom. CH, calixarene), 6.51 (d, 2H, arom. CH, calixarene, 3 J = 6.6 Hz), 6.42 (t, 2H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.24 (d, 2H, arom. CH, calixarene, 3 J = 7.2 Hz), 4.45 and 3.14 (AB spin system, 4H, ArCH 2 Ar, 2 J = 13.2 Hz), 4.38 and 3.01 (AB spin system, 4H, ArCH 2 Ar, 2 J = 13.2 Hz), 3.88 (t, 2H, OCH 2 , 3 J = 7.8 Hz), 3.82 (t, 6H, OCH 2 , 3 J = 7.8 Hz), 1.99-1.86 (m, 8H, CH 2 CH 3 ), 1.03 (t, 9H, CH 2 CH 3 , 3 J = 7.5 Hz), 0.96 (t, 3H, CH 2 CH 3 , 3 J = 7.2 Hz); (25 mL) was added to a stirred solution of 3 (0.100 g, 0.17 mmol) in CH 2 Cl 2 (25 mL). After stirring for 0.5 h, the solution was concentrated to ca. 2 mL and n-hexane (20 mL) was added. A white precipitate formed, which was separated by filtration and dried under vacuum (0.122 g, yield 96 %). [START_REF]CDCl 3 , 500 MHz):  = 7.89 (d, 1H, arom. CH, C 6 H 4 , 3 J = 6.0 Hz), 7.76 (d, 1H, arom. CH, calixarene[END_REF] H NMR (CDCl 3 , 500 MHz):  = 7.58-7.56 (m, 2H, arom. CH, PPh 2 ), 7.49-7.44 (m, 8H, arom. CH, PPh 2 ), 7.37 (t, 1H, arom. CH, C 6 H 4 , 3 J = 7.2 Hz), 7.19 (t, 1H, arom. CH, C 6 H 4 , 3 J = 7.5 Hz), 6.97 (d, 2H, arom. CH, calixarene, 3 J = 7.0 Hz), 6.86-6.82 (m, 1H, arom. CH, C 6 H 4 ), 6.74-6.70 (m, 1H, arom. CH, C 6 H 4 ), 6.71 (t, 2H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.62 (d, 2H, arom. CH, calixarene, 3 J = 7.0 Hz), 6.31 (t, 1H, arom. CH, calixarene, 3 J = 7.2 Hz), 6.26 (d, 2H, arom. CH, calixarene, 3 J = 7.2 Hz), 5.84 (s, 2H, arom. CH, calixarene), 4.46 and 3.14 (AB spin system, 4H, ArCH 2 Ar, 2 J = 13.0 Hz), 4.39 and 2.97 (AB spin system, 4H, ArCH 2 Ar, 2 J = 13.5 Hz), 4.05-3.96 (m, 4H, OCH 2 ), 3.90 (t, 2H, OCH 2 , 3 J = 6.5 Hz), 3.69 (t, 2H, OCH 2 , 3 J = 7.0 Hz), 2.02-1.95 (m, 4H, CH 2 CH 3 ), 1.95-1.86 (m, 4H, CH 2 CH 3 ), 1.15 (t, 3H, CH 2 CH 3 , 3 J = 7.2 Hz), 1.08 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz), 0.91 (t, 6H, CH 2 CH 3 , 3 J = 7.2 Hz); 13

trans-P,P-Dichlorido-bis[5-(2-diphenylphosphanyl-phenyl)-25,26,27,28-tetrapropyloxycalix[4]arene] palladium (II) (5):

A solution of [PdCl 2 (PhCN) 2 ] (0.020 g, 0.052 mmol) in CH 2 Cl 2 (10 mL) was added to a stirred solution of 3 (0.088 g, 0.103 mmol) in CH 2 Cl 2 (10 mL). After stirring for 0.5 h, the solution was concentrated to ca. 2 mL and n-hexane (20 mL) was added. The resulting yellow precipitate was separated by filtration and dried under vacuum (0.072 g, yield 95 %). [START_REF]CDCl 3 , 500 MHz):  = 7.89 (d, 1H, arom. CH, C 6 H 4 , 3 J = 6.0 Hz), 7.76 (d, 1H, arom. CH, calixarene[END_REF] H NMR (C 6 D 6 , 400 MHz):  = 8.08 (q, 2H, arom. CH, C 6 H 4 , 3 J = 6.8 Hz), 8.00-7.96 (m, 6H, arom. CH, PPh 2 ), 7. 14-7.10 (m, 6H, arom. CH, calixarene), 7.08-7.704 (m, 6H, arom. CH, C 6 H 4 ), 7.04-7.00 (m, 14H, arom. CH, PPh 2 ), 6.79 (s, 6H, arom. CH, calixarene), 6.71-6.69 (m, 4H, arom. CH, calixarene), 6.63-6.62 (m, 6H, arom. CH, calixarene), 4.56 and 3.17 (AB spin system, 8H, ArCH 2 Ar, 2 J = 13.5 Hz), 4.43 and 3.14 (AB spin system, 8H, ArCH 2 Ar, 2 J = 13.5 Hz), 3.88-3.84 (m, 8H, OCH 2 ), 3.83-3.78 (m, 8H, OCH 2 ), 1.99-1.88 (m, 16H, CH 2 CH 3 ), 1.03 (t, 6H, CH 2 CH 3 , 3 J = 7.5 Hz), 0.94 (t, 12H, CH 2 CH 3 , 3 J = 7.5 Hz), 0.93 (t, 6H, CH 2 CH 3 , 3 J = 7.5 Hz); 13 C{ 1 H} NMR (C 6 D 6 ,125 MHz)

Synthesis of [5-(P-phenyl-5H-benzo[b]phosphindolyl)-25,26,27,28-tetrapropyloxycalix[4]arene] boranes exo-6 and endo-7:

A solution of phosphine 3 (4.000 g, 4.69 mmol) and [Pd(OAc) 2 ] (0.105 g, 0.47 mmol) in toluene (50 mL) was heated at 110°C for 24h. After cooling the solution to room temperature, the solvent was removed in vacuum. The crude product was then dissolved in THF. The solution was cooled to 0°C before addition of BH 3 .THF (1M in THF, 18.8 mL, 18.76 mmol). After stirring for 2 h, the solution was evaporated to dryness. The residue was purified by column chromatography (CH 2 Cl 2 /petroleum ether, 5:95 v/v) to afford benzophosphole boranes 6 and 7 as white solids. Phosphole borane 6: (0.740 g, yield 20 %; R f = 0.28, CH 2 Cl 2 /petroleum ether, 5:95 v/v); 1 H NMR (CD 2 Cl 2 , 400 MHz):  = 7.96 (d, 1H, arom. CH, C 6 H 4 , 3 J = 7.6 Hz), 7.78 (d, 1H, arom. CH, calixarene, 4 J(PH) = 2.4 Hz), 7.70-7.60 (m, 4H, arom. CH, P(BH 3 )Ph and C 6 H 4 ), 7.43-7.37 (m, 2H, arom. CH, P(BH 3 )Ph), 7.34 (dt, 2H, arom. CH, P(BH 3 )Ph, 3 J = 7.6 Hz), 4 J(PH) = 1.6 Hz), 7.12-7.08 40 (m, 2H, arom. CH, calixarene), 6.90 (t, 1H, arom. CH, calixarene, 3 J = 7.4 Hz), 6.18-6.1 (m, 2H, arom. CH, calixarene), 6.06 (d, 1H, arom. CH, calixarene, 3 J = 7.2 Hz), 5.87 (d, 1H, arom. CH, calixarene, 3 J = 7.6 Hz), 5.65 (t, 1H, arom. CH, calixarene, 3 J = 7.6 Hz), 4.71 (d, 1H, arom. CH, calixarene, 3 J = 7.6 Hz), 4.55 and 3.33 (AB spin system, 2H, ArCH 2 Ar, 2 J = 14.0 Hz), 4.45 and 3.58 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.6 Hz), 4.45 and 3.15 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.6 Hz), 4.39 and 3.07 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.4 Hz), 4.14-4.09 (m, 2H, OCH 2 ), 4.01 (t, 2H, OCH 2 , 3 J = 8.2 Hz), 3.68 (t, 2H, OCH 2 , 3 J = 7.0 Hz), 3.66-3.56 (m, 2H, OCH 2 ), 2.01-1.84 (m, 8H, CH 2 CH 3 ), 1.12 (t, 3H, CH 2 CH 3 , 3 J = 7.4 Hz), 1.05 (t, 3H, CH 2 CH 3 , 3 J = 7.4 Hz), 0.88 (t, 6H, CH 2 CH 3 , 3 J = 7.4 Hz), 0.90-0.77 (m, 3H, P(BH 3 )); 13 C{ 1 H} NMR (CD 2 Cl 2 , 125 MHz):  = 159.87 (d, arom

Phosphole borane 7:

(2.219 g, yield 60 %; R f = 0.26, CH 2 Cl 2 /petroleum ether, 5:95 v/v); 1 H NMR (CD 2 Cl 2 , 500 MHz):  = 7.91 (d, 1H, arom. CH, C 6 H 4 ,3 J = 8.0 Hz), 7.80 (d, 1H, arom. CH, calixarene, 4 J(PH) = 2.0 Hz), 7.67-7.59 (m, 4H, arom. CH, P(BH 3 )Ph and C 6 H 4 ), 7.49 (dt, 12H, arom. CH, C 6 H 4 , 3 J = 7.5 Hz, 4 J(PH) = 1.0 Hz), 7.40 (dt, 2H, arom. CH, P(BH 3 )Ph, 3 J = 7.7 Hz, 4 J(PH) = 2.0 Hz), 7.36 (dt, 1H, arom. CH, P(BH 3 )Ph, 3 J = 7.7 Hz, 5 J(PH) = 4.0 Hz), 7.15 (d, 2H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.94 (t, 1H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.37 (d, 1H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.24-6.15 (m, 3H, arom. CH, calixarene), 6.11 (d, 1H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.05 (d, 1H, arom. CH, calixarene, 3 J = 7.5 Hz), 4.57 and 3.35 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.5 Hz), 4.45 and 3.17 (AB spin system, 2H, ArCH 2 Ar, 2 J = 14.0 Hz), 4.42 and 3.15 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.5 Hz), 4.23 and 3.51 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.5 Hz), 4.14-4.05 (m, 2H, OCH 2 ), 4.02 (t, 2H, OCH 2 , 3 J = 8.2 Hz), 3.71-3.66 (m, 2H, OCH 2 ), 3.58 (t, 2H, OCH 2 , 3 J = 7.0 Hz), 2.87-1.98 (m, 3H, P(BH 3 )), 1.98-1.88 (m, 6H, CH 2 CH 3 ), 1.84-1.76 (m, 6H, CH 2 CH 3 ), 1.13 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz), 1.02 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz), 0.87 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz), 0.85 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz); 13 Phosphole 8: A solution of phosphole borane 7 (2.000 g, 2.53 mmol) in MeOH/toluene (1:4 mixture, 15 mL) was heated at 40°C for 5 h. After cooling to room temperature, the solution was evaporated to dryness and the residue dried overnight under vacuum to afford quantitatively benzophosphole 8 (1.964 g, yield 100 %). [START_REF]CDCl 3 , 500 MHz):  = 7.89 (d, 1H, arom. CH, C 6 H 4 , 3 J = 6.0 Hz), 7.76 (d, 1H, arom. CH, calixarene[END_REF] H NMR (CDCl 3 , 400 MHz):  = 7.86 (d, 1H, arom. CH, C 6 H 4 , 3 J = 7.6 Hz), 7.69 (s, 1H, arom. CH, calixarene), 7.66-7.63 (m, 1H, arom. CH, C 6 H 4 ), 7.41 (t, 1H, arom. CH, C 6 H 4 , 3 J = 7.6 Hz), 7.42 (t, 2H, arom. CH, PPh, 3 J = 7.6 Hz), 7.33-7.28 (m, 3H, arom. CH, PPh), 7.22-7.18 (m, 1H, arom. CH, C 6 H 4 ), 7.04 (d, 2H, arom. CH, calixarene, 3 J = 7.6 Hz), 6.79 (t, 1H, arom. CH, calixarene, 3 J = 7.2 Hz), 6.51 (d, 1H, arom. CH, calixarene, 3 J = 7.2 Hz), 6.31-6.26 (m, 3H, arom. CH, calixarene), 6.23-6.20 (m, 2H, arom. CH, calixarene), 4.60 and 3.34 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.2 Hz), 4.49 and 3.19 (AB spin system, 2H, ArCH 2 Ar, 2 J = 12.8 Hz), 4.46 and 3.17 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.2 Hz), 4.35 and 3.52 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.6 Hz), 4.05 (t, 2H, OCH 2 , 3 J = 8.4 Hz), 4.02 (t, 2H, OCH 2 , 3 J = 8.8 Hz), 3.76 (t, 2H, OCH 2 , 3 J = 6.6 Hz), 3.71-3.61 (m, 2H, OCH 2 ), 2.02-1.81 (m, 8H, CH 2 CH 3 ), 1.20-0.77 (m, 3H, P(BH 3 )), 1.13 (t, 3H, CH 2 CH 3 , 3 J = 7.6 Hz), 1.05 (t, 3H, CH 2 CH 3 , 3 J = 7.6 Hz), 0.92 (t, 6H, CH 2 CH 3 , Cq-O, 3 J(CP) = 5.9 Hz), 155.53 (s, arom Cq-O), 155.21 (s, arom Cq-O), 144.08-120.88 (arom. C's) (30 % in water, 2.00 ml, 2.50 mmol). The solution was stirred at room temperature for 1 h, then treated with a mixture of CH 2 Cl 2 (10 mL) and water (20 mL). The aqueous layer was separated and washed with CH 2 Cl 2 (2 x 10 mL). The organic phases were combined and washed with water (2 x 10 mL). After drying over Na 2 SO 4 , the solution was filtered through a glass frit before being evaporated to dryness to afford phosphole oxide 9 as a white solid (0.050 g, yield 98 %). [START_REF]CDCl 3 , 500 MHz):  = 7.89 (d, 1H, arom. CH, C 6 H 4 , 3 J = 6.0 Hz), 7.76 (d, 1H, arom. CH, calixarene[END_REF] 7.44 (dt, 2H, arom. CH, P(O)Ph, 3 J = 7.5 Hz, 4 J(PH) = 3.0 Hz), 7.30 (dt, 1H, arom. CH, C 6 H 4 , 3 J = 7.5 Hz, 4 J(PH) = 3.5 Hz), 7.14 (d, 2H, arom. CH, calixarene, 3 J = 7.0 Hz), 6.94 (t, 1H, arom. CH, calixarene, 3 J = 7.2 Hz), 6.71 (d, 1H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.27 (t, 1H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.22 (t, 1H, arom. CH, calixarene, 3 J = 7.5 Hz), 6.14-6.07 (m, 3H, arom. CH, calixarene), 4.55 and 3.29 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.0 Hz), 4.44 and 3.16 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.0 Hz), 4.41 and 3.14 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.5 Hz), 4.16 and 3.60 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.0 Hz), 4.11-4.05 (m, 1H, OCH 2 ), 4.04-3.98 (m, 3H, OCH 2 ), 3.71-3.66 (m, 2H, OCH 2 ), 3.58-3.53 (m, 2H, OCH 2 ), 2.00-1.87 (m, 6H, CH 2 CH 3 ), 1.82-1.75 (m, 2H, CH 2 CH 3 ), 1.12 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz), 1.01 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz), 0.88 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz), 0.86 (t, 3H, CH 2 CH 3 , 3 J = 7.5 Hz); 13 C{ 1 H} NMR (CDCl 3 , 101 MHz):  = 160.10 (d, arom Cq-O, 3 J(CP) = 10.4 Hz), 158.11(s, arom Cq-O), 155.11 (s, arom Cq-O), 15507 (s, arom Cq-O), 142.98-120.58 (arom. C's) (10 mL) was added to a stirred solution of 8 (0.049 g, 0.06 mmol) in CH 2 Cl 2 (10 mL). After stirring at room temperature for 0.5 h, the reaction mixture was concentrated to about 2 mL and n-hexane (20 mL) was added. The yellow precipitate formed was separated by filtration and dried under vacuum (0.050 g, yield 73 %). [START_REF]CDCl 3 , 500 MHz):  = 7.89 (d, 1H, arom. CH, C 6 H 4 , 3 J = 6.0 Hz), 7.76 (d, 1H, arom. CH, calixarene[END_REF] H NMR (CDCl 3 , 500 MHz):  = 9.53 (tt,1H, arom. CH of 8-mq, 3 J = 3.5 Hz, 5 J = 1.0 Hz), 8.14 (dd, 1H, arom. CH of 8-mq, 3 J = 8.5 Hz, 4 J = 1.0 Hz), 7.90 (t, 1H, arom (15 mL). After stirring at room temperature for 0.5 h, the solution was concentrated to about 2 mL and MeOH (5 mL) was added. A yellow precipitate formed, which was separated by filtration then dried under vacuum (0.081 g, yield 52 %). 1 H NMR (C 6 D 6 , 500 MHz):  = 8.00-7.95 (m, 2H, arom. CH, PPh), 7.81 (t, 1H, arom. CH, C 6 H 4 , 3 J = 8.0 Hz), 7.71 (d, 1H, arom. CH, calixarene, 3 J = 7.5 Hz), 7.68 (d,1H,arom. CH,calixarene,4 J(PH) = 1.5 Hz), 7.62 (d,1H,arom. CH,calixarene,3 J = 7.5 Hz),1H,arom. CH,calixarene),1H,arom. CH, C 6 H 4 ), 7.07 (dd, 1H, arom. CH, C 6 H 4 , 3 J = 7.5 Hz, 4 J(PH) = 1.5 Hz), 7.01-6.96 (m, 4H, arom. CH of PPh, calixarene and C 6 H 4 ), 6.92 (td, 1H, arom. CH, PPh, 3 J = 7.0 Hz, 5 J(PH) = 1.0 Hz), 6.47 (t, 1H, arom. CH, calixarene, 3 J = 7.7 Hz), 6.35-6.30 (m, 2H, arom. CH, calixarene), 6.26 (d, 2H, arom. CH, calixarene, 3 J = 7.5 Hz), 5.17 (s, CH, acac), 4.77 and 4.55 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.5 Hz), 4.67 and 3.31 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.7 Hz), 4.55 and 3.17 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.5 Hz), 4.52 and 3.12 (AB spin system, 2H, ArCH 2 Ar, 2 J = 13.5 Hz), 4. 34-4.24 (m, 2H, OCH (CH 2 CH 3 ), 10.12 (CH 2 CH 3 ); 31 P{ 1 H} NMR (C 6 D 6 , 121 MHz):  = 56.0 (d, PPh, 1 J(PRh) = 172 Hz) ppm; IR:  = 1975 (strong, CO), 1579 (medium s, acac), 1516 (ms, acac) cm -1 ; elemental analysis calcd (%) for C 58 H 62 O 7 PRh (Mr = 1004.99): C 69.32, H 6.22; found (%): C 68.36, H 6.02. Despite repeated elemental analyses, the values obtained for the C analysis were not satisfactory. 16) Å 3 , Z = 2, D = 1.453 g cm -3 , μ = 3.097 mm -1 , F(000) = 1104.0, T = 173(2) K. The sample was studied on a Kappa APEX II diffractometer (graphite monochromated Mo-K α radiation, λ = 0.71073 Å). The data collection (2θ max = 59.8°, omega scan frames by using 0.7° omega rotation and 30 s per frame, range hkl : h -15,15 k -16,16 l -29,29) gave 53983 reflections. The structure was solved with SIR-97, [25] which revealed the non-hydrogen atoms of the molecule. After anisotropic refinement, all of the hydrogen atoms were found with a Fourier difference map. The structure was refined with SHELXL97 [26] The sample was studied on a Kappa APEX II diffractometer (graphite monochromated Mo-K α radiation, λ = 0.71073 Å). The data collection (2θ max = 133.4°, omega scan frames by using 0.7° omega rotation and 30 s per frame, range hkl: h -43,28 k -44,45 l -45,42) gave 161417 reflections. The structure was solved with SIR-97, [25] which revealed the non-hydrogen atoms of the molecule. After anisotropic refinement, all of the hydrogen atoms were found with a Fourier difference map. The structure was refined with SHELXL97 [26] 13,13 k -25,25 l -36,36) gave 22333 reflections. The structure was solved with SIR-97, [25] which revealed the non-hydrogen atoms of the molecule. After anisotropic refinement, all of the hydrogen atoms were found with a Fourier difference map. The structure was refined with SHELXL97 [26] by the full-matrix least-square techniques (use of F square magnitude; x, y, z,

X-ray

Figure 1 .

 1 Figure 1. Molecular structure of 4.

Figure 3 .

 3 Figure 3. Steric map of 8 (determined from the X-ray structure of 11). View along the P-lone pair, taken as z axis (located in the middle of the Figure). The red-orange domain corresponds to the calixarene moiety. The coloured scale indicates the height on the z axis.

Figure 4 .

 4 Figure 4. Solid state structure of the phosphole palladium complex 10 showing the two inequivalent molecules present in the unit cell.

Figure 5 .

 5 Figure 5. Molecular structure of the gold phosphole complex 11.

Figure 6 .

 6 Figure 6. Possible interactions (dashed lines) involving an equatorial ArCH atom in 10 and the formula of 11

Figure 8 :

 8 Figure 8: Electronic absorption (blue and green) and emission (violet and red) spectra of compounds 9 and 11 in dilute CH 2 Cl 2 solutions

  C{ 1 H} NMR (CD 2 Cl 2 , 125 MHz):  = 159.91 (d, arom Cq-O, 3 J(CP) = 10.8 Hz), 158.53 (s, arom Cq-O), 155.60 (s, arom Cq-O), 155.48 (s, arom Cq-O), 143.98-121.48 (arom. C's), 77.46 (s, OCH 2 ), 77.32 (s, OCH 2 ), 77.12 (s, OCH 2 ), 77.05 (s, OCH 2 ), 31.87 (s, ArCH 2 Ar), 31.30 (s, ArCH 2 Ar), 31.18 (s, ArCH 2 Ar), 29.73 (d, ArCH 2 Ar, 3 J(CP) = 4.9 Hz), 23.96 (CH 2 CH 3 ), 23.86 (CH 2 CH 3 ), 23.43 (CH 2 CH 3 ), 23.35 (CH 2 CH 3 ), 11.11 (CH 2 CH 3 ), 10.92 (CH 2 CH 3 ), 9.98 (CH 2 CH 3 ), 9.95 (CH 2 CH 3 ); 31 P{ 1 H} NMR (CD 2 Cl 2 , 162 MHz):  = 23.3 (br. s, P.BH 3 ) ppm; MS (ESI): m/z = 827.39 [M + K] + expected isotopic profile; elemental analysis calcd (%) for C 52 H 58 O 4 PB (Mr = 788.80): C 79.18, H 7.41; found (%): C 79.27, H 7.58.

  Crystal Structure Determination for Gold Complex 4: Single crystals of 4 suitable for X-ray analysis were obtained by slow diffusion of methanol into a chloroform solution of the complex. Crystal data: C 58 H 61 AuClO 4 P, Mr = 1085.46 g mol -1 , triclinic, space group P -1, a = 11.288(5) Å, b = 11.576(5) Å, c = 20.999(5) Å,  = 87.574(5)°,  = 86.443(5)°,  = 64.980(5)°, V = 2481.3(

  by the full-matrix least-square techniques (use of F square magnitude; x, y, z, ij for C, O and P atoms; x, y, z in riding mode for H atoms); 590 variables and 14382 observations with I > 2.0 σ(I); calcd. w = 1/[σ 2 (F o 2 ) + (0.0224P) 2 + 1.5095P] where P = (F o 2 + 2F c 2 )/3, with the resulting R = 0.0299, R W = 0.0589 and S W = 1.048, Δρ < 1.810 e Å -3 . CCDC 1455340. X-ray Crystal Structure Determination for Phosphole Oxide 9: Single crystals of 9 suitable for X-ray analysis were obtained by slow diffusion of methanol into a chloroform solution of the complex. Crystal data: C 52 H 55 ClO 5 P, Mr = 790.93 g mol -1 , cubic, space group I 2 1 3, a = 38.0572(4) Å, b = 38.0572(4) Å, c = 38.0572(4) Å,  = 90,  = 90°,  = 90, V = 55120.2(17) Å 3 , Z = 48, D = 1.144 g cm -3 , μ = 0.880 mm -1 , F(000) = 20256, T = 173(2) K.

  by the full-matrix least-square techniques (use of F square magnitude; x, y, z, ij for C, O and P atoms; x, y, z in riding mode for H atoms); 1074 variables and 16277 observations with I > 2.0 σ(I); calcd. w = 1/[σ 2 (F o 2 ) + (0.0760P) 2 + 11.7206P] where P = (F o 2 + 2F c 2 )/3, with the resulting R = 0.0482, R W = 0.1279 and S W = 1.054, Δρ < 0.403 e Å -3 . CCDC 1455997. X-ray Crystal Structure Determination for Palladium Complex 11: Single crystals of 11 suitable for X-ray analysis were obtained by slow diffusion of methanol into a chloroform solution of the complex. Crystal data: C 62 H 63 ClNO 4 PPd, Mr = 1058.96 g mol -1 , triclinic, space group P-1, a = 9.8908(7) Å, b = 19.6964(14) Å, c = 27.456(2) Å,  = 94.474(2),  = 90.746(2)°,  = 91.791(2), V = 5329.2(7) Å 3 , Z = 4, D = 1.320 g cm -3 , μ = 0.477 mm -1 , F(000) = 2208, T = 173(2) K. The sample was studied on a Kappa APEX II diffractometer (graphite monochromated Mo-K α radiation, λ = 0.71073 Å). The data collection (2θ max = 56.1°, omega scan frames by using 0.7° omega rotation and 30 s per frame, range hkl: h -

  .fr b Laboratoire de Chimie et Systémique Organométallique, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 1 rue Blaise Pascal, F-67008 Strasbourg Cedex, France.Institut des Sciences Chimiques de Rennes (UMR 6226 CNRS), Université deRennes 1, Groupe "Phosphore et Matériaux Moléculaires", Campus de Beaulieu, 263, avenue du Général Leclerc, F-35042 Rennes Cedex, France

c d Laboratoire de Chimie Quantique, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 1 rue Blaise Pascal, F-67008 Strasbourg, France e Institut de Science et Ingénierie Supramoléculaire (ISIS), UMR 7606 CNRS, Université de Strasbourg, 8 rue Gaspard Monge, 67083 Strasbourg cedex, France †CCDC 1455997; 1545340-1545342. For crystallographic data in CIF or other electronic format see DOI:

Table 2 :

 2 Optical and electrochemical data for 9 and 11

		 (nm) a abs	 (L.mol -1 .cm -1 ) a	 (nm) a em	 a,b	 (nm) film	ox E [V vs Fe] c	red E [V vs Fe] d
	9	349	2500	415	0.33	405	+1,03	-2,67 e
	11	345	2150	412	0.01	-	+1,17	-2,64
	DBPO

  Measured in dichloromethane b) Measured relative to quinine sulfate (H 2 SO 4 , 0.1 M),  = 0.55. c) All potentials were obtained during cyclic voltammetric investigations in 0.2 M Bu 4 NPF 6 in CH 2 Cl 2 . Platinum electrode diameter 1 mm, sweep rate: 200 mV s -1 . All potentials are referenced to the reversible formal potential of ferrocene/ferrocenium d) All potentials were obtained during cyclic voltammetric investigations in 0.1 M Bu 4 NPF 6 in THF. Platinum electrode diameter 1 mm, sweep rate: 200 mV s -1 . All potentials are referenced to the reversible formal potential of ferrocene/ferrocenium. e) quasi reversible. f) Ep c

	366	0.134	-	-	-2.26 f,c
	a)

  [START_REF]CDCl 3 , 500 MHz):  = 7.89 (d, 1H, arom. CH, C 6 H 4 , 3 J = 6.0 Hz), 7.76 (d, 1H, arom. CH, calixarene[END_REF] H chemical shifts are referenced to residual protiated solvent signals (δ = 7.26 ppm for CDCl 3 and 7.11 ppm for C 6 D 6 ),13 C chemical shifts are reported relative to deuteriated solvent signals (δ = 77.16 ppm for CDCl 3 and 128.06 for C 6 D 6 ) and the 31 P NMR spectroscopic data are given relative to external H 3 PO 4 . Chemical shifts and coupling constants are reported in ppm and Hz, respectively. Elemental analyses were performed by the Service de Microanalyse, Institut de Chimie, Université de Strasbourg. 5-(2-bromophenyl)-

diphenylphosphanyl-phenyl)-25,26,27,28-tetrapropyloxycalix[4]arene] gold (I) (4): A

  13 C{ 1 H} NMR (CDCl 3 , 125 MHz):  = 156.89 (s, arom Cq-O), 156.39 (s, arom Cq-O), 156.15 (s, arom Cq-O), 148.79-121.94 (arom. C's), 77.11 (s, OCH 2 ), 77.05 (s, OCH 2 ), 31.09 (s, ArCH 2 Ar), 31.05 (s, ArCH 2 Ar), 23.40 (CH 2 CH 3 ), 10.52 (CH 2 CH 3 ), 10.45 (CH 2 CH 3 ); 31 P{ 1 H} NMR (CDCl 3 , 162 MHz):  = -12.4 (s, PPh 2 ) ppm; MS (ESI): m/z = 891.41 [M + K] + expected isotopic profiles; elemental analysis calcd (%) for C 58 H 61 O 4 P (Mr = 853.08): C 81.66, H 7.21; found (%): C 81.48, H 7.08. solution of [AuCl(THT)] (0.037 g, 0.17 mmol) in CH 2 Cl 2

	Chlorido	[5-(2-

  C{ 1 H} NMR (CDCl 3 , 125 MHz):  = 157.66 (s, arom Cq-O), 156.08 (s, arom Cq-O), 155.63 (s, arom Cq-O), 149.00-121.80 (arom. C's), 77.76 (s, OCH 2 ), 77.15 (s, OCH 2 ), 76.61 (s, OCH 2 ), 31.05 (s, ArCH 2 Ar), 30.94 (s, ArCH 2 Ar), 23.75 (CH 2 CH 3 ), 23.58 (CH 2 CH 3 ), 23.08 (CH 2 CH 3 ), 11.04 (CH 2 CH 3 ), 10.86 (CH 2 CH 3 ), 10.01 (CH 2 CH 3 ); 31 P{ 1 H} NMR (CDCl 3 , 162 MHz):  =

	26.9 (s, PPh 2 ) ppm; elemental analysis calcd (%) for C 58 H 61 O 4 PAuCl (Mr = 1085.50): C
	64.17, H 5.66; found (%): C 64.08, H 5.54.

  :  = 157.17 (s, arom Cq-O), 156.70 (s, arom Cq-O), 156.29 (s, arom Cq-O), 147.25-122.57 (arom. C's), 76.95 (s, OCH 2 ), 76.86 (s, OCH 2 ), 31.60 (s, ArCH 2 Ar), 31.36 (s, ArCH 2 Ar), 23.79 (CH 2 CH 3 ), 23.67 (CH 2 CH 3 ), 23.64 (CH 2 CH 3 ), 10.68 (CH 2 CH 3 ), 10.59 (CH 2 CH 3 ), 10.54 (CH 2 CH 3 ); 31 P{ 1 H} NMR (C 6 D 6 , 162 MHz):  = 22.3 (s, PPh 2 ) ppm; MS (ESI): m/z = 1903.73 [M + Na] + expected isotopic profiles; elemental analysis calcd (%) for C 116 H 122 O 8 P 2 PdCl 2 (Mr = 1883.48): C 73.97, H 6.53; found (%): C 74.05, H 6.68.

  ArCH 2 Ar), 31.34 (s, ArCH 2 Ar), 31.22 (s, ArCH 2 Ar), 29.66 (d, ArCH 2 Ar, 3 J(CP) = 4.1 Hz), 23.97 (CH 2 CH 3 ), 23.48 (CH 2 CH 3 ), 23.31 (CH 2 CH 3 ), 11.12 (CH 2 CH 3 ), 11.05 (CH 2 CH 3 ), 10.04 (CH 2 CH 3 ), 9.86 (CH 2 CH 3 ); 31 P{ 1 H} NMR (CD 2 Cl 2 , 162 MHz):  = 23.0 (br. s, P.BH 3 ) ppm; elemental analysis calcd (%) for C 52 H 58 O 4 PB (Mr = 788.80): C 79.18, H 7.41; found (%): C 79.23, H 7.55.

	Cq-O,
	3 J(CP) = 11.4 Hz), 158.59 (s, arom Cq-O), 155.78 (s, arom Cq-O), 155.68 (s, arom Cq-O),
	145.08-121.42 (arom. C's), 77.47 (s, OCH 2 ), 77.39 (s, OCH 2 ), 77.14 (s, OCH 2 ), 77.12 (s,
	OCH 2 ), 32.07 (s,

  , 77.09 (s, OCH 2 ), 76.97 (s, OCH 2 ), 76.91 (s, OCH 2 ), 76.61 (s, OCH 2 ), 31.58 (s, ArCH 2 Ar), 31.19 (s, ArCH 2 Ar), 30.30 (d, ArCH 2 Ar, 3 J(CP) = 8.1 Hz), 23.68 (CH 2 CH 3 ), 23.53 (CH 2 CH 3 ), 23.24 (CH 2 CH 3 ), 23.17 (CH 2 CH 3 ), 10.95 (CH 2 CH 3 ), 10.78 (CH 2 CH 3 ), 10.14 (CH 2 CH 3 ), 10.06 (CH 2 CH 3 ); 31 P{ 1 H} NMR (CDCl 3 , 162 MHz):  = -11.5 (s, PPh)

	ppm; MS (ESI): m/z = 797.37 [M + Na] + expected isotopic profiles; elemental analysis calcd
	(%) for C 52 H 55 O 4 P (Mr = 774.97): C 80.59, H 7.15; found (%): C 80.72, H 7.32.
	Phosphole oxide 9: To a solution of phosphole 8 (0.050 g, 0.06 mmol) in CH 2 Cl 2 (10 mL)
	was added dropwise H 2 O 2

  H NMR (CDCl 3 , 500 MHz):  = 7.81-7.73 (m, 3H, arom. CH, C 6 H 4 and P(O)Ph), 7.66 (t, 1H, arom. CH, C 6 H 4 , 3 J = 8.5 Hz), 7.62 (d, 1H, arom. CH, calixarene, 4 J(PH) = 4.0 Hz), 7.55 (t, 1H, arom. CH, C 6 H 4 , 3 J = 8.0 Hz), 7.53 (t, 1H, arom. CH, P(O)Ph, 3 J = 8.0 Hz),

  , 77.13 (s, OCH 2 ), 76.92 (s, OCH 2 ), 76.88 (s, OCH 2 ), 76.62 (s, OCH 2 ), 31.61 (s, ArCH 2 Ar), 31.16 (s, ArCH 2 Ar), 30.98 (s, ArCH 2 Ar), 28.55 (d, ArCH 2 Ar, 3 J(CP) = 3.1 Hz), 23.68 (CH 2 CH 3 ), 23.58 (CH 2 CH 3 ), 23.18 (CH 2 CH 3 ), 23.09 (CH 2 CH 3 ), 11.01 (CH 2 CH 3 ), 10.86 (CH 2 CH 3 ), 9.93 (CH 2 CH 3 );

	31 P{ 1 H} NMR (CDCl 3 , 162 MHz):  = 33.4 (s, P(O)Ph) ppm; elemental analysis calcd (%) for
	C 52 H 55 O 5 P (Mr = 790.97): C 78.96, H 7.01; found (%): C 79.04, H 7.11.
	Palladium complex 10: A solution of [Pd(8-mq)Cl] 2 (0.018 g, 0.03 mmol) in CH 2 Cl 2

  . CH, C 6 H 4 , 3 J = 8.2 Hz),7.86-7.80 (m, 3H, arom. CH, PPh and MHz):  = 157.95(d, 3 J(CP) = 11.7 Hz), 157.15 (s, arom Cq-O), 154.21 (s, arom Cq-O), 153.73 (s, arom Cq-O), 142.41-120.37 (arom. C's), 76.09 (s, OCH 2 ), 75.92 (s, OCH 2 ), 75.89 (s, OCH 2 ), 75.71 (s, OCH 2 ), 30.75 (s, ArCH 2 Ar), 30.12 (s, ArCH 2 Ar), 30.05 (s, ArCH 2 Ar), 28.71 (d, ArCH 2 Ar, 3 J(CP) = 7.1 Hz), 22.66 (CH 2 CH 3 ), 22.56 (CH 2 CH 3 ), 22.12 (CH 2 CH 3 ), 22.07 (CH 2 CH 3 ), 10.00 (CH 2 CH 3 ), 9.84 (CH 2 CH 3 ), 8.95 (CH 2 CH 3 ), 8.92 Rhodium complex 12: A solution of [Rh(acac)(CO) 2 ] (0.040 g, 0.15 mmol) in CH 2 Cl 2 (15 mL) was added to a stirred solution of benzophosphole 8 (0.120 g, 0.15 mmol) in CH 2 Cl 2

	(CH 2 CH 3 ); 31 P{ 1 H} NMR (CDCl 3 , 162 MHz):  = -22.8 (s, PPh) ppm; MS (ESI): m/z =
	1029.31 [M + Na] + expected isotopic profile; elemental analysis calcd (%) for
	C 52 H 55 AuClO 4 P (Mr = 1007.39): C 62.00, H 5.50; found (%): C 62.05, H 5.53.

  CH 2 CH 3 , 3 J = 7.5 Hz), 0.84 (t, 3H, CH 2 CH 3 , 3 J = 7.2 Hz), 0.83 (t, 3H, CH 2 CH 3 , 3 J = 7.2 Hz); 13 C{ 1 H} NMR (C 6 D 6 , 125 MHz):  = 190.32 (dd, 1 J ( CRh) = 75.2 Hz, 2 J(CP) = 24.9 Hz, CO), 187.88 (s, CO, acac), 184.33 (s, CO, acac), 159.94(d, arom Cq-O, 3 J(CP) = 10.7 Hz), 158.69 (s, arom Cq-O), 155.50 (s, arom Cq-O), 155.34 (s, arom Cq-O), 142.47-120.82 (arom. C's), 100.59 (s, CH, acac), 77.13 (s, OCH 2 ), 76.97 (s, OCH 2 ), 76.94 (s, OCH 2 ), 32.13 (s, ArCH 2 Ar), 31.59 (s, ArCH 2 Ar), 31.54 (s, ArCH 2 Ar), 29.74 (d, ArCH 2 Ar, 3 J(CP) = 5.3 Hz), 27.40 (d, 3 J(CRh) = 5.4 Hz, CH 3 , acac), 27.03 (s, CH 3 , acac), 23.93 (CH 2 CH 3 ), 23.73 (CH 2 CH 3 ), 23.49 (CH 2 CH 3 ), 22.07 (CH 2 CH 3 ), 11.07 (CH 2 CH 3 ), 10.83 (CH 2 CH 3 ), 10.22

	2 ), 4.15-4.05
	(m, 2H, OCH 2 ), 3.64-3.57 (m, 2H, OCH 2 ), 3.52-3.44 (m, 2H, OCH 2 ), 2.19-2.10 (m, 2H,
	CH 2 CH 3 ), 2.05-1.97 (m, 2H, CH 2 CH 3 ), 1.81-1.72 (m, 2H, CH 2 CH 3 ), 1.76 (s, 3H, CH 3 , acac),
	1.54-1.56 (m, 2H, CH 2 CH 3 ), 1.51 (s, 3H, CH 3 , acac), 1.02 (t, 3H, CH 2 CH 3 , 3 J = 7.2 Hz), 0.93
	(t, 3H,

J = 7.5 Hz); 13 C{ 1 H} NMR (CDCl 3 , 101 MHz):  = 157.98 (s, arom Cq-O), 157.80(d, arom

The structure was solved with SIR-97, [25] which revealed the non-hydrogen atoms of the molecule. After anisotropic refinement, all of the hydrogen atoms were found with a Fourier difference map. The structure was refined with SHELXL97 [26] by the full-matrix least-square techniques (use of F square magnitude; x, y, z, ij for Au; C, Cl, O and P atoms; x, y, z in riding mode for H atoms); 531 variables and 10857 observations with I > 2.0 σ(I); calcd. w = 1/[σ 2 (F o 2 ), with the resulting R = 0.0497, R W = 0.0825 and S W = 1.023, Δρ < 2.370 e Å -3 . CCDC 1545342.

Computational details

Calculations were performed using the ADF 2013 package. [START_REF] Adf | [END_REF] Slater type orbitals were used with all-electron double-ζ quality basis sets at DFT level with B3LYP functional. [START_REF] Stephens | [END_REF] Dispersive interactions were taken into account through the recent Grimme corrections with damping function. [29] Scalar relativistic effects were included through ZORA Hamiltonian. [30] Full geometry optimization was performed on each structures. The NMR shielding of the protons of the methylene groups was computed using ADF NMR modules. Single points with Gaussian 09 package [31] were done at DFT level with B3LYP functional on ADF optimized structure in order to compute wavefunctions suitable for topological analyses. The atoms were described by the def2-SV basis sets on all atoms [32] and associated pseudopotentials for Rh, Pd and Au cations. [33] The weak interactions were studied through the NCI analysis of the Gaussian wavefunction. [34]


Natarajan Millusamy

Eric Brenner

David Sémeril
email: dsemeril@unistra.fr

Dominique Matt
email: dmatt@unistra.fr

Jack Harrowfield

The use of resorcinarene-cavitands in metal-based catalysis

Introduction. Synthesis and properties of generic resorcinarenes and resorcinarene-cavitands

Resorcinarenes are a class of macrocycles first correctly identified in 1940, [1] although their chemistry can be traced back to work of Baeyer in the nineteenth century. [2] Typically, these compounds can be obtained in high yields by condensation of resorcinol or its derivatives and an aldehyde in EtOH/H 2 O under acidic conditions, the thermodynamically strongly favoured end product from an initially complex mixture of linear species being the macrocycle resulting from condensation of four units each of resorcinol and aldehyde (Scheme 1), [3] although under certain conditions a less stable macrocycle incoprporating six units can be isolated. [4] In fact, the use of a solvent for their preparation is not mandatory, [5] although solvent-free synthesis may result in inseparable mixtures of isomers. [6] Methods for their functionalisation have been widely explored so that numerous very sophisticated derivatives have become accessible. [7] The first crystallographic characterisation of a resorcinarene was reported in 1968 (Fig. 1). [8] OH The stereochemistry of the resorcinarenes is complicated both by the facts that the substituents on the bridging units may adopt different relative orientations (usually defined with respect to the mean plane of the macrocycle) and that facile rotation about the C-C bonds linking the aromatic rings to the bridging atoms leads to several conformational minima. Hydrogen bonding is also an important stereochemical influence in parent resorcinarenes where hydroxyl groups are retained. The rapid equilibration between different isomers in acidic media coupled to differences in solubility can, however, mean that a single species can be crystallised in good yield from a given reaction mixture. [3,9] Importantly, this is usually the cis,cis,cis isomer, the formal precursor to all bowl-shaped cavitands. The conformational flexibility of generic resorcinarenes is revealed in numerous solid state structure determinations (321 currently in the CSD, plus several thousand for derivatives) by X-ray diffraction where the conformation varies considerably depending on associated molecules present in the lattice as well as the nature of the bridge substituent. Thus, for example, for the simplest resorcinarene, generated from acetaldehyde and resorcinol, as the cis,cis,cis isomer, it has been found in several instances [10] to adopt a crown or cone conformation close to C 4v symmetry, in others [11] C 2v -symmetric conformations varying between a "flattened" cone (when the distortion is slight) and a boat or saddle forms (as seen also in Figure 1) where greater distortion occurs, as well as to adopt a chair form of at most C s symmetry. [12] With bridge substituents other than methyl, as well as for isomers other than the cis,cis,cis, a similar range of conformations is known [13] the chair form of the cis,trans,cis isomer with 4hydroxyphenyl substituents, for example, being established in early work. [14] Some examples of conformations established by X-ray crystallography for the cis,cis,cis isomer of the tetramethyl resorcinarene are given in Figure 2. [11b, 11c] (d) a chairlike conformer of C s symmetry. [12] Modification of the cis,cis,cis resorcinarene core was first achieved by introduction of methylene bridges between oxygen atoms of adjacent resorcinolic rings. [9a] The term "cavitand" was coined to describe these materials which, locked into a symmetrical cone conformation, were considered to define a rigid molecular cavity. [15] Heteroatoms, [9a, 15a, 15b, 16] hydrocarbon chains, [17] phenylene [18] or quinoxaline-diyl [19] units can also be used for linking the resorcinol rings and thus create a cavitand (Fig. 3). While inhibiting conformational changes of the resorcinarene core, these links can be associated with their own conformational equilibria giving rise to control of the cavitand's behaviour as a receptor, as seen with the "vase" and "kite" forms of the quinoxaline-bridged species. [START_REF] Cram | Container Molecules and their Guests[END_REF] Combined with the rigidity of cavitands, the many possible variations in the bridging groups has been the basis of the continual development of cavitand chemistry over the past 4 decades. Major advances have concerned : a) the ability of many resorcinarene-cavitands to function as receptors towards small molecules and ions; [21] b) the ease of extension of the core for the construction of larger container molecules for the encapsulation of neutral and ionic compounds, [22] including metal complexes; [23] c) the ease with which they can be selectively functionalised at inequivalent sites, facilitating the synthesis of sophisticated multitopic ligands. [7,24] The ease of linking resorcinarene units one to another has of course been the basis of the development of the major field of carcerand chemistry. [22a, 22d, 25]

O O O O O O O O R R R R O O O O O O O O R R R R PPh PPh PhP PhP O O O O O O O O R R R R SiR 2 SiR 2 R 2 Si R 2 Si O O O O O O O O R R R R O O O O O O O O R R R R N N N N N N N N Figure 3. (Upper)
Examples of resorcinarene-based cavitands; (Lower) Orthogonal views of the molecular species with the lattice of a vase-form pyrazine-bridged cavitand, [START_REF] Roncucci | [END_REF] showing the well-formed, symmetrical cavity.

The following pages provide a survey on the catalytic applications of ligands based on the resorcinarene cavitand platform. While extensive studies have been made of equilibrium binding, catalysis based on metal ion complexes of cavitands has, in contrast to the situation for ligands based on the similar calix [4]arene core, [17] been given quite limited attention. [7,27] Catalysis employing non-rigidified resorcinarenes has been reported but examples are few. [28]

Catalytic chemistry with cavitands substituted with P donors

The first use in transition metal catalysis of a ligand built upon a resorcinarene-cavitand was reported in 2002 by Gibson and Rebek. [29] The authors used the phosphite-oxazoline chelator 1 (Fig. 4) to perform allylic alkylations. Here, the ligand core was an expanded cavitand unit known to bind size-and shape-complementary molecules such as adamantanes. In the presence of palladium(II) and allyl acetate, the ligand produced an allyl palladium η 3complex, in which the allyl fragment appeared to be oriented towards the cavity axis and within the cavity (Scheme 2). Two ways of coordinating the allylic fragment (H 2 C 1 -C 2 H=C 3 HR ' ) -are possible, depending on whether the carbon trans to phosphorus is the terminal carbon atom C 1 or carbon atom C 3 of the allyl ligand. The left pathway in Scheme 2 was expected to dominate as this minimises steric repulsions. Nucleophilic attack by, for example, malonate, was found to occur selectively on carbon C(1), consistent with the supposed steric effect and electronic factors. The electronic factor influencing the selectivity was considered to be that the C atom trans to the P atom, which has a stronger trans influence than N, is more electrophilic. Note that the reference ligand 2 [29] displayed the same selectivity for a linear product.

The reaction rate was found to depend on the substrate (substrates tested: S a -S e , Table 1). For example, the conversion of substrates S b and S c was complete after 2 days, while that of the bulkier substrates S d and S e was approximately four times lower (Table 1). Remarkably, the smallest substrate S a exhibited the lowest reaction rate. Careful examination of competitive experiments (conducted by mixing pairs of substrates) relying on MS analyses revealed that the allylic complexes formed by oxidative addition were more rapidly formed with substrate S a (bearing a secondary homoallylic C atom) than with S b (tertiary homoallylic atom), the latter more rapidly than S c (quaternary homoallylic atom). The rate of the oxidative addition (i.e. formation of the allyl-Pd complex) varied in the order R' = t Bu > i Pr >> i Bu. However, as mentioned before, the reactivity of the complexes in the presence of malonate followed a different order. Once the S a -complex formed, for example, the reaction was inhibited. [b] 74 2 h 78

OAc S e 6 d [b] 60 2 h 82 [a] [Pd(C 3 H 5 )Cl] 2 (1.4 mol %), L (3.2 mol %), CH 2 (CO 2 Me) 2 (3 equiv) and N,Obis(trimethylsilyl)acetamide (BSA). [b] Substrate was not completely converted.

For the substrates S b , S d , and S e , all of which have a tertiary carbon atom in the homoallylic position, pairwise comparison of these substrates using Pd(II) and reference ligand 2 showed no significant difference in reaction rates for either the oxidative addition or the overall reaction. The ability of the palladium catalyst formed with 1 to stabilise the transition state of the oxidative addition decreased in the order cyclohexyl > iso-propyl > 1ethylpentyl. This substrate specificity strongly correlated with the selectivity in product formation (P b , P d , P e ). Thus, the observed selectivities appear to be a direct consequence of the molecular recognition properties of the cavity and underscore the potential of cavitandcontaining catalysts in organic synthesis.

The catalytic efficiency of cavitand-based phosphines is not necessarily related to the receptor or confining properties of the cavity. Thus, it was found that cavitand phosphine 3 having its P atom separated from the cavity by a methylene group resulted, in the presence of Pd(II), in a fast Suzuki-Miyaura (SM) cross-coupling catalyst. [30] The reaction rates were found to be 5-7 times faster than that those observed with PPh 3 . A possible explanation is that during the catalytic process intermediates are formed in which one of the O atoms close to the P forms with this atom a chelate ring. This could stabilise monophosphine complexes in the same manner as do Buchwald phosphines, and incidently favour the oxidative addition step. An argument for this interpretation, which thus would exclude a supramolecular effect, is that the cavity-free anisole phosphine 4 showed activities comparable to those of the cavitand phosphine. When repeating the experiments with benzyldiphenylphosphine, the activity dropped by ca. 50%. Scheme 3. Suzuki-Miyaura cross-coupling catalysis by cavitand-phosphine 3 and three cavity-free phosphines Diphosphines 5 and 6 (Fig. 5) were tested in the coupling of 4-bromotoluene with PhB(OH) 2 and were shown to be more effective than monophosphine 3. Their higher performance was attributed to the formation of complexes with PMP angles larger than 90°, these resulting either from steric repulsions occuring in cyclic oligomeric intermediates (which may form with ligand 5) or arising from the formation of strained chelate complexes (which may form with ligand 6). Larger PMP angles are known to favour the final reductive elimination step of the catalytic process. [30] O The first tetraphosphine built upon a cavitand (7) was reported in 2009 (Scheme 4). [31] Complexation studies coupled with MS measurements revealed that each pair of adjacent phosphine arms of this ligand may function as a chelating unit. The authors showed that in the presence of [Pd(OAc) 2 ] and a base, ligand 7 is active in Heck coupling reactions (Scheme 4). The catalytic results indicated that the rate of the reaction had a maximal value when only one equivalent of cavitand was added to the palladium, any excess of 7 drastically decreasing the yield. This finding together with 31 P NMR investigations indicated that the presence of free phosphane units is required for stabilisation and/or generation of the catalytically active species. The activities themselves were not unusual when compared with that of PPh 3 . Disappointingly, the presence, after complexation, of four phosphine ligands near the metal centre did not markedly accelerate the reaction, unlike the observations made by Santelli for similar reactions with another tetraphosphine, cis,cis,cis-1,2,3,4-tetrakis(diphenylphos phinomethyl)cyctopentane (TEDICYP), in which motions of the P atoms are more restricted. [32] O A structural study combined with molecular modelling revealed that monophosphine 8 (Fig. 6), a cavitand with a P atom directly attached to the upper rim of the bowl, behaves as a ligand with variable bulk, its encumbrance depending on the orientation of the P lone pair. [33] Thus, when the P atom points towards the cavitand axis, its cone angle is by ca. 45° greater than if it points towards the exterior of the cavity. Consistent with its strong crowding, ligand 8, when combined with [Pd(OAc) 2 ], provided an efficient catalyst for the coupling of a variety of aryl boronic acids with aryl chlorides. Depending on the substrates used, the catalytic system was found to be 3-7 times more active than PPh 3 (study carried out with aryl bromides, see Table 2). Comparison with bulkier triarylphosphines as well as phosphines 9 and 10, bearing respectively one and two o-MeO groups on one of their aryl substituents -all leading to higher activities -, suggested that the high catalytic activity of 8 [a] [Pd(OAc) 2 ] (5 x 10 -7 mmol, 1 x 10 -4 mol %), phosphine (1 x 10 -6 mmol, 2 x 10 -4 mol %), ArBr (0.5 mmol), PhB(OH) 2 (1 mmol), NaH (60 % dispersion in mineral oil; 1 mmol), 1,4dioxane (1.5 mL), decane (0.050 mL), 100°C, 1 h. The conversions were determined by GC, the calibrations being based on decane.

electron-rich, and (ii) its increased bulkiness when the P lone pair points towards the cavitand axis, this favouring the formation of monoligated intermediates. However, care must be taken with the interpretation that P,O chelation increases the activity, as it was recently found that when the metal centre bears a positive charge (which is not the case here), P,O chelation may result in cavitand cleavage with formation of a phosphino-enolato metal complex, [34] this being inactive in cross coupling. Note that nickel complexes of this type were found active in ethylene oligomerisation.

The design of coordination complexes (excluding complexes resulting from a reversible, supramolecular self-assembly process) that allow metal-catalysed reactions to take place inside a restricted space (bowl, clip, capsule) with the aim of controlling activity and selectivity are currently attracting the attention of several research groups. [29,35] In the particular field of resorcinarene chemistry, Iwasawa et al. have used the digold complexes 11 and 12 (Figure 7), both based on a cavity flanked by aromatic rings, in the catalytic crossdimerisation of terminal alkynes. [19] For example, the reaction of ethynylbenzene with 1octyne in the presence of a mixture of 11 (1 mol %) and 2 equiv. of AgOTf gave after 20 h (rt) cross adduct 14 (58 %) and homoadduct 15 with a 14/15 ratio of 3.0:1 (Scheme 5, top). With the less expanded cavity 12 the yield of 14 dropped to 6% with a 14/15 ratio of 4.3:1, while model compound 13 did not catalyse the reaction at all. The authors also investigated the homodimerisation of 1-octyne, leading to 16 and its isomer iso-16 (Scheme 5, bottom) The bis-quinoxaline-bridged complex 11 gave 16 selectively in 63 % yield. In contrast, with bis-pyrazine 12, the yield of 16 droped to 18 %, and the formation of small amounts of iso-16 was observed (16:iso-16 = 97:3). With the non-walled cavitand 13, only trace amounts of coupling adducts were observed. Overall, these studies illustrate the superiority of quinoxaline-expanded cavitand 11 over that of 12 and 13 in the catalytic dimerisation of terminal alkynes. The authors proposed that the catalysis with 11 occurred in a supramolecular manner, the quinoxaline parts providing a stronger π-cloud than that found in the interior of 11 and 12, thereby strongly enhancing the interaction of the two alkyne partners. The confinement created by 11 further limits the number of transition-state geometries, this possibly being at the origin of the slightly higher selectivity found with 11 vs. 12. The authors also showed that the presence of two introverted Au atoms is quintessential for catalysis. [36] Similar results were obtained with analogues of 11 having NMe 2 instead of OMe substituents on phosphorus. [37] 2 The same research team also synthesised cavitands 17-19, all equipped with three quinoxaline walls and bearing a single, inwardly directed P-Au unit (Scheme 6). [38] Complex 17 turned out to be efficient in the catalytic hydration of 9-ethynylanthracene (Scheme 6). All three complexes also catalysed a Conia-ene reaction of the β-keto ester alkyne 20 (Scheme 6). The main conclusion of these investigations was that the top of the catalytic site of these complexes remains open so that guests can sample the space, enter and leave, and thus these complexes may efficiently operate as catalysts. The first Buchwald-type biarylphosphine based on a cavitand, 21, was reported by Elaieb et al. (Fig. 8). This ligand displayed activities in SM coupling of bulky aryl chlorides with sterically hindered arylboronic acids that were ca. 40 % higher than those of the Buchwald analogue S-Phos ( 22), which is devoid of a cavity. Its better performance has been attributed to the permanent exo-positioning of the metal during catalysis, which enables steric interactions of two pentyl substituents with the second coordination sphere of the metal, this influencing the reductive elimination step (a similar effect was invoked with catalysts derived from 34-36, vide infra). Several recent publications have illustrated the manner in which cavitands can be used for the generation of molecular capsules. [39] Capsule synthesis may be realised by covalent construction, [22d] a procedure extensively developed as the basis of carcerand chemistry but, more conveniently, such molecules can also be generated by self-assembly processes, these involving either metal complexation, [22c, 40] hydrogen bonding [41] or van der Waals interactions. [42] Many of the reported cages have been shown suitable for hosting large guests. An example of capsule formation through metal chelation and which does not involve a selfassembly process, is provided in the use of a diphosphine built on a backbone consisting of two covalently linked cavitands (23). [43] Reaction of 23 with [PtCl 2 (PhCN) 2 ] under high dilution afforded the metallo-capsules cis-24 and trans-24 (Scheme 7). The former was used succesfully in combination with SnCl 2 for the hydroformylation of styrene. The activity and selectivity (Table 3 towards the branched aldehyde were both significantly superior to those observed for the reference complex trans-PtCl 2 L 2 , in which L is the monophosphane-monocavitand 8, as well as PPh 3 . The increased activity of the capsular complex may reflect the initial formation of a hydrido intermediate with a somewhat distorted trigonal-bipyramidal structure that facilitates the intracapsular olefin/PtH insertion step. The observed aldehyde selectivity can be understood as a consequence of the shape of the capsule, which is sterically better suited for hosting a branched Pt-alkyl unit than a linear one (Scheme 8). The catalytic outcome with trans-24 was similar obtained with trans-[PtCl(SnCl 3 )( 23)] (run performed without additional SnCl 2 ).

1

Catalytic chemistry with cavitands bearing N-heterocyclic carbene (NHC) units

El Moll et al. have described the synthesis of the imidazolium salts 23-33 (Fig. 9). [44] These are procarbenes which were assessed in Suzuki-Miyaura cross-coupling between phenyl boronic acid and several aryl bromides. Note that before this study imidazolium salts built on a resorcinarene skeleton had already been reported, but their use was restricted to molecular recognition studies. [45] In combination with [Pd(OAc) 2 ] and a base, 23-33 provided efficient Suzuki-Miyaura catalysts for the cross-coupling of aryl bromides with phenylboronic acid. The highest activity (TOF = 41,600 mol(ArBr) mol(Pd) -1 h -1 ) was observed in the arylation of 1-bromonaphthalene in the presence of the proximallydisubstituted cavitand 28. In fact, only relatively small differences in activity were observed within the three series of imidazolium salts, indicating that they all behave as single-site NHC sources.

R = Ph

24 R = Mes 25 R = i Pr 2 C 6 H 3 O O O C 5 H 11 O H 11 C 5 H 11 C 5 C 5 H 11 O O O O N N R + Br - 26 R = n Bu 27 R = Ph 28 R = Mes 29 R = i Pr 2 C 6 H 3 O O O C 5 H 11 O H 11 C 5 H 11 C 5 C 5 H 11 O O O O N N R + 2 Br - N N R + 30 R = n Bu 31 R = Ph 32 R = Mes 33 R = i Pr 2 C 6 H 3 O O O C 5 H 11 O H 11 C 5 H 11 C 5 C 5 H 11 O O O O N N R + 4 Br - N N R N N R + N N R + + Figure 9. Procarbenes 23-33
Cavitands having an imidazolium ring directly attached through an N atom to the upper rim of a cavitand (Fig. 10) have also been assessed in coupling reactions. For example, the three imidazolium salts 34-36 were used as catalyst precursors in Suzuki-Miyaura (SM) cross-coupling. [46] In these pro-carbenes, the second N atom was substituted by an alkyl group (R = n-propyl, iso-propyl, benzyl), and the bridging atoms of the resorcinarene unit had pentyl substituents. Optimal catalytic performances were obtained by using an imidazolium/Pd ratio of 1:1. The catalytic systems displayed high activities, which increased in the order R = npropyl (34) < i-propyl (35) < benzyl (36). With 36, activities up to 30,100 mol(converted ArX) mol(Pd) -1 h -1 were reached in the arylation of bromotoluene at 100°C in dioxane. Comparative studies showed that the performance of 36 was up to 10 times superior to that of related salts devoid of a cavity-shaped unit (37-39). These experiments illustrate the active role of the cavity core of the ex-36 carbene ligand, the steric encumbrance of which facilitates the reductive elimination step (Figure 11, left part). Modification of the cavitand structure by replacement of the pentyl substituents of 36 with phenyl groups (leading to 40) resulted in considerably lower activities, this being consistent with steric interactions between the metal centre and two pentyl groups of the ex-36 carbene during catalysis (Figure 11, right part). The fact that the catalytic outcome may be influenced by the nature of the bridge substituents is further evidence that the Pd catalysts obtained from 34-36 have their metal centre preferentially located outside the cavity.

It is worth mentioning here that SM tests were also performed starting from the isolated PEPPSI-Pd complex 41 [47] (Fig. 12) (PEPPSI [48] = pyridine-enhanced precatalyst preparation stabilization and initiation) as well as related bulky ones, [49] which led to similar conclusions regarding the role played by the flexible pentyl groups at the lower rim. The investigations carried out with 41 further revealed that this catalyst is very effective in the coupling of aryl chlorides with sterically hindered boronic acids. However, there was no clear indication that the cavity subunit operated as a receptor. Imidazolium salts 34-36 have been further assessed in Ni-catalysed Kumada-Tamao-Corriu cross-coupling of aryl halides with arylmagnesium halides (Scheme 9). [50] Such reactions are generally performed with palladium, but it is highly desirable to conduct these reactions with more cost-efficient catalysts, notably those based on nickel. Actually, the 1:1 combination of 34-36 with [Ni(cod) 2 ] (cod = 1,5-cyclooctadiene) resulted in very efficient systems, the activities of which varied in the same order as above for the SM coupling reactions: R = n-propyl (34) isopropyl (35) ≈ benzyl (36). A remarkable turnover frequency of 60,400 mol(ArX) mol(Ni) -1 h -1 was obtained in the coupling of 2-bromo-6methoxynaphthalene with PhMgBr (100 °C in dioxane, with precursor 36) (Scheme 10). The high activities of these cavitands were attributed to steric effects that facilitated the reductiveelimination/product decoordination step. Comparative experiments carried out with the benzyl-bridged resorcinarene 40, as well as cavity-free imidazolium salts bearing 2methoxyaryl substituents, indicated that the efficiency of the above catalytic systems again was mainly due to steric interactions between the metal and the flexible pentyl substituents attached to the two methine carbon atoms closest to the heterocycle. As usual with nickel, homocoupling products were observed in the above runs, although their proportion did not exceed 13%. Allylic substitution with organo-copper compounds has recently emerged as a method which usefully complements the palladium-catalysed version of this reaction. The main advantage of copper over palladium, besides its lower price, is that it generally allows the reaction to occur with S N 2' selectivity, i.e. to favour the γ-product over the α one (Scheme 11). This in turn is relevant to the synthesis of chiral compounds. The procarbene salts 36 and 42-46, all having one of their nitrogen atoms substituted by a 2,8,14,20tetrapentylresorcinarenyl (TPR) group, were tested in situ in the copper-catalysed arylation of cinnamyl bromide with arylmagnesium halides. [51] The catalytic systems produced mixtures of linear (l) and branched (b) arylation compounds in variable proportions, the highest b/l ratio (78:22) being observed LG = leaving group Scheme 11. Allylic substitution for the crowded imidazolium salt 44 (in which the second nitrogen atom bears a bulky mesityl group). Although bulky substituents are expected to favour the reductive elimination step leading to the γ-product, [51] the bulky TPR group had only a small influence on the selectivity (Figure 13). The authors proposed that it would make sense to modify the catalyst structure so as to force the metal centre to remain located permanently above the cavitand entrance (rather than being pushed towards its exterior), markedly augmenting the ligand bulk. Finally, it should be mentioned that starting from an isolated [CuBr(NHC)] complex instead of using an imidazolium/Cu(OTf) 2 mixture for the catalytic runs did not significantly modify the catalytic outcome. [51]

Catalysis using cavitands substituted with nitrogen donors

Cavitands substituted with groups that contain a nitrogen donor atom have been little used in catalysis. Chavagnan et al. have prepared the bis-iminophosphorane 47. [52] Molecular modeling revealed that because of the large N...N separation, 47 cannot act as a chelating ligand. A 1:1 mixture of 47 and [Rh(COD) 2 ]BF 4 was used as a catalytic system for the competitive hydrogenation of 1:1 mixtures of terminal olefins (Table 4). A remarkable substrate-selectivity factor of 39.2 in favour of the linear olefin was observed after 1 h in the reduction of a hex-1-ene / 3-ethyl-pent-1-ene mixture. After 8 h, the selectivity was still as high as 4.1. Carrying out the test with hex-1-ene and dec-1-ene gave selectivity factors of 5.4 and 1.6 respectively after 1 h and 8 h. The substrate selectivity was considerably lower with a mixture of olefins of similar size, such as styrene and 3-ethyl-pent-1-ene (Table 4). By carrying out comparative studies with the iminophosphoranes 49, 50-52 (Table 5) the authors came to the conclusion that substrate discrimination is only observed if: a) two iminophosphorane units are available per Rh centre; b) the nitrogen atoms are substituted with an aryl ring that bears a methoxy group; and c) the two iminophosphorane units are tethered to the same resorcinarene platform. Consistent with these observations, they concluded that both iminophosphorane moieties of 47 are involved in the catalytic process. Owing to the large N•••N separation, this cannot occur via catalytic intermediates containing an N,Nchelated rhodium centre. Instead, one of the two nitrogen atoms and a methoxy group of the other anisyl-iminophosphorane moiety must form a chelating N,O unit that spans the wider face of the cavitand. This would locate the rhodium centre above the main entry to the cavity and orientate two free coordination sites towards the cavity interior (Figure 14). The observed substrate selectivity can then be seen as due to a shape selective process controlled by the cavity size. Conditions: [a] [Rh(cod) 2 ]BF 4 (1 mol %), ligand, olefins (1.0 mmol of each), P(H 2 ) = 5 bar, THF (5 mL), r.t., 1 h. The conversions were determined by GC; [b] [Rh(cod) 2 ]BF 4 (0.1 mol %), 50 (0.2 mol %), olefins (each 10.0 mmol), 0.1 h; [c] [Rh(cod) 2 ]BF 4 (0.1 mol %), 51 (0.1 mol %), olefins (each 10.0 mmol), 0.25 h.

Conclusions

As shown in the present review, the potential of resorcinarene-derived cavitands in catalysis arises mainly from two features: i) their ability to function as ligands suitable for metal confinement and thus for making catalytic reactions either substrate selective or by increasing efficiently reaction rates through supramolecular assistance by the cavity walls; ii) their ability to create controlled steric interactions with a coordinated metal centre and/or its first coordination sphere, thereby increasing the efficiency of carbon-carbon bond forming reactions. Interestingly, their use as platforms for the attachment of different ligating sites for the generation of multifunctional ligands that may give rise to anchimeric assistance has as yet been little exploited. As generic cavitands can be easily expanded so as to provide large, bowl-shaped structures as well as capsular containers, it may be anticipated that future research in this field will focus on sophisticated microreactors (including water-soluble versions) that will enable highly selective transformations. Such chemistry has been explored with carcerand systems but the novel aspects of what is presently proposed are the ready accessibility of the cavities and the fact that the appended species are sites of catalytic activity.

Figure 1 .

 1 Scheme 1. Synthesis of resorcinarenes

Figure 2 .

 2 Figure 2. Orthogonal views of the conformations of the cis,cis,cis isomer of tetramethylresorcinarene found in different solid state adducts. For clarity, H-atoms are omitted. (a) A conformer of near C 4v symmetry; [10a] (b), (c) increasingly distorted conformers of near C 2v symmetry;[11b, 11c] (d) a chairlike conformer of C s symmetry.[12]

Figure 4 .

 4 Figure 4. Cavitand phosphite 1 and reference ligand 2

  Scheme 2. Nucleophilic attack on the two possible η 3 -allyl complexes [Pd(RC 3 H 4 )•1]. The steric hindrance created by the geminal phenyl groups of the oxazoline moiety favors the left pathway, which results in the linear alkylation product.

Figure 8 .

 8 Figure 8. Biarylphosphines 21 and 22

Figure 11 .Figure 12 .

 1112 Figure 10. Procarbenes 34-40

36 Ph

 36 Scheme 9. Kumada-Tamao-Corriu cross-coupling with nickel

Figure 13 .

 13 Figure 13. Branched/linear aldehyde ratios obtained in the copper-catalysed allylic alkylation of cinnamyl bromide and phenyl magnesium bromide with salts 36 and 42-46 (Reaction conditions: [Cu(OTf) 2 ] (1 mol-%), imidazolium salt (1 mol-%), PhCH=CHCH 2 Br (0.32 mmol), PhMgX (0.39 mmol), Et 2 O (3 mL), -78 °C, 1 h)

Figure 14 .

 14 Figure 14. Proposed catalytic intermediate formed with 47

Table 1 .

 1 Allylic alkylation of substrates S a-e using ligands 1 and 2.[a]

		OAc	H 2 C(CO 2 Me) 2
		R	Pd / L BSA, KOAc	R	CO 2 Me
			CH 2 Cl 2, 20°C		CO 2 Me
		S a-e			P a-e
			Ligand 1			Ligand 2
	Substrate
		Reaction time	Yield (%) Reaction time Yield (%)
	OAc	S a	6 d [b]	38		2 h	85
	OAc
		S b	2 d	76		2 h	91
	OAc
		S c	2 d	96		2 h	81
	OAc
		S d	6 d

Table 2 .

 2 Suzuki-Miyaura cross-coupling of aryl bromides catalyzed by [Pd(OAc) 2 ]/triarylphosphines.[a]

							PPh 2
	O	O	O	O	O	O	O O	PPh 2	OMe	MeO	PPh 2	OMe
	H 11 C 5	H 11 C 5	C 5 H 11	C 5 H 11
				8			9			10
	Figure 6. Cavitand-phosphine 8 and cavity-devoid ligands 9 and 10
	arose from a combination of two features, namely (i) its ability to form P,O chelate
	complexes, this making the metal environment sterically more crowded and the metal more

  ) of the system

			H 11 C 5				O				Ph 2 P	O	O
	H 11 C 5 H 11 C 5 H 11 C 5	O	O	O	O	O	O		O O O	O	O	O	O	C 5 H 11 C 5 H 11	C 5 H 11
		O	O	PPh 2						23		C 5 H 11
									[PtCl 2 (PhCN) 2 ]	THF (high dilution)
	H 11 C 5	H 11 C 5	C 5 H 11	C 5 H 11	H 11 C 5	H 11 C 5	C 5 H 11	C 5 H 11
	O														O O
	O Ph 2 P	O	O		O	O	O		O	O	O O	O	O	O	O	O
														Ph 2 P	Cl
	Cl	Pt	Cl											+	Pt
	O Ph 2 P O		O	O		O	O		O O	O O Ph 2 P	O Cl	O	O	O	O	O	O
													O
		H 11 C 5		H 11 C 5	C 5 H 11		C 5 H 11		H 11 C 5	H 11 C 5	C 5 H 11	C 5 H 11
						trans-24 (39 %)		cis-24 (3 %)

Scheme 7. Formation of metallocapsules from diphosphine 23

Table 3 .

 3 Hydroformylation of styrene with cis-24/SnCl 2

	Entry	Platinum complex	Time (h)	Conversion (%)	Aldehydes distribution Linear (%) Branched (%)
	1	trans-24	24	55	36	64
	2	trans-[PtCl 2 (8) 2 ]	24	15	46	54
	3	trans-[PtCl 2 (PPh 3 ) 2 ]	24	40	53	47
	4	trans-[PtCl(SnCl 3 )(23)]	16	60	38	62

General conditions:

[Pt]

(1 mol %), SnCl 2 (2 mol %; except for entry 4: 0%), styrene (1 mmol), P(CO/H 2 ) = 45 bar, T = 100°C, toluene (5 mL). The conversions were determined by 1 H NMR spectroscopy.

Table 4 .

 4 Competitive hydrogenation of α-olefins catalysed by the [Rh(cod) 2 ]BF 4 /47 system.Olefin discrimination also occurred with the glucosidic substrate 48 (Scheme 12) which contains two C=C double bonds in different steric environments. When the reaction with 48 was conducted with a H 2 pressure of 5 bar and with 2 mol-% of the catalyst, product 49, in which only the allylic double bond had been hydrogenated, was formed exclusively in 84 % yield after 14 h.

	Entry	R 1 CH=CH 2	R 2 CH=CH 2	Time (h)	Hydrogenated products (%) R 1 CH 2 CH 3 /R 2 CH 2 CH 3
	1				1	19.6 / 0.5 = 39.2
	2				5	62.6 / 8.4 = 7.4
	3				8	84.6 / 20.4 = 4.1
	4				1	13.5 / 2.5 = 5.4
	5				5	48.1 / 10.2 = 4.7
	6				8	77.4 / 47.8 = 1.6
	7				5	36.2 / 15.0 = 2.4
	8				8	58.2 / 29.0 = 2.0
	Conditions: [Rh(cod) 2 ]BF 4 (1 mol %), 47 (1 mol %), olefins (1.0 mmol of each), P(H 2 ) = 5
	bar, THF (5 mL), r.t. The conversions were determined by GC.
				[Rh(cod) 2 ]BF 4 / 47 (each 2 mol %)
		BnO O	O	H 2 (5 bar)		BnO O	O
		TsO	OMe	THF, 14 h (84 %)		TsO	OMe
		48				49
	Scheme 12. Diolefin hydrogenation leading to 49

Table 5 .

 5 Competitive hydrogenation of α-olefins, influence of the ligand.[a]

	MeO						OMe								OMe	n Bu							n Bu
	O O Ph 2 P	N	O	O	O	O N	O PPh 2	O	O O	O	O	O	O	O PPh 2 N	O	OMe	O O Ph 2 P N	O	O	O	O	O PPh 2 N	O
																Ph 3 P N
	H 11 C 5		H 11 C 5	C 5 H 11	C 5 H 11	H 11 C 5	H 11 C 5	C 5 H 11	C 5 H 11		H 11 C 5	H 11 C 5	C 5 H 11	C 5 H 11
				47							49				50					51
	Entry R 1 CH=CH 2		R 2 CH=CH 2		Ligand (L/Rh)	Hydrogenated products (%) R 1 CH 2 CH 3 /R 2 CH 2 CH 3
	1															47 (1:1)		13.5 / 2.5 = 5.4
	2															47 (1:2)		100 / 100 = 1.0
	3															47 (2:1)		33.6 / 22.0 = 1.5
	4															49 (2:1)		35.3 / 19.5 = 1.8
	5 b															50 (2:1)		26.2 / 20.3 = 1.3
	6 c															51 (1:1)		36.4 / 22.6 = 1.3
	7															no ligand		94.8 / 83.6 = 1.1

Acknowledgments

We acknowledge financial support from the Institut d'Etudes Avancées de l'Université de Strasbourg (USIAS), The International Center for Frontier Research in Chemistry (icFRC), and The Indo-French Centre for the Promotion of Advanced Research (IFCPAR) (Project No 5005-1).

Keywords: Resorcinarenes