Andrew D Phillips

Sandra Bolaño

Sylvain S Bosquain

Jean-Claude Daran

Raluca Malacea

Maurizio Peruzzini
email: mperuzzini@iccom.cnr.it

Rinaldo Poli
email: poli@lcc-toulouse.fr

Luca Gonsalvi
email: l.gonsalvi@iccom.cnr.it

A new class of rhodium(I) κ 1 -P and κ 2 -P,N complexes with rigid PTN(R) ligands (PTN = 7-phospha-3methyl-1,3,5-triazabicyclo[3.3.1]nonane)

INTRODUCTION

During the last decade, ligand design for homogeneous catalysts has advanced from simple bidentate diphosphines and diamines to mixed donor atom moieties, such as phosphino-ethers, phosphino-thioethers and aminophosphines. 1 These catalytic systems have been applied to hydroformylation, hydrogenation and hydrosilylation reactions. 2,3,4 Numerous configurations of phosphorus-nitrogen (P,N) ligands have been reported and can be generically divided into two categories, namely those based on structurally rigid sp 2 nitrogen centers, e.g. unsaturated pyridine [START_REF]For example: (a) Newkome[END_REF] and imine 6 groups or sp 3 nitrogen centers, which constitute saturated amine functionalities. 7,8 For sp 3 N-based ligands, rigidity is enforced either using a short (e.g. four atom) chain chelate, 8 or by usually inserting a phenyl, 9 pyridyl, 10 ferrocenyl 11 or other functionalities containing π-bonding into the ligand backbone. [START_REF] Stradiotto | For example, an interesting zwitterionic Indenide-Rh complex has been recently reported[END_REF] Among aminophosphine ligands, the neutral water-soluble phosphine 1-phospha-3,5,7triazaadamantane (PTA, 1), 13 was successfully used to prepare k 1 -P-coordinated rhodium catalysts capable of regioselective hydrogenation 14 and hydroformylation 15 of olefins in aqueous media.

Long-term catalyst stability and low activity are two of the most problematic aspects for systems based on PTA, 16 thus a shift from a monodentate to a bidentate hemilabile ligand system featuring similar stereoelectronic properties and water solubility could be of interest. On this basis we have considered the use of the bowl-shaped alkyl or aryl P-substituted 7-phospha-3-methyl-1,3,5triazabicyclo [3.3.1]nonanes abbreviated as PTN(R) (2), synthesized originally by Schmidbaur et al. 17 The bridgehead position of 2 anchors the ligand conformation, with the constrained curvature creating a preset bidentate capability. This structural feature is also advantageous in a non-chelating situation where the inflexible framework insures that the amine functionality remains always in close proximity of the transition metal center, a feature that has been suggested to facilitate the intramolecular based-assisted heterolytic cleavage of H 2 . 18 Other examples of chelated (κ 2 -P,N)-Rh complexes with aminophosphine (3), 19 aminophosphinite (4), 20 and aminophosphinite (5) 21 have been reported. The coordination chemistry of 2 has received so far scarce attention, including Au and Mo complexes (Chart 3). Depending on the nature of the ancillary substituent attached to Au, 2 adopts either a mono-or bi-dentate coordination mode, 22 and examples of both were obtained as, [κ 1 -P-AuCl{PTN(R)}] (6 R = Me, Ph), [κ 1 -P-AuCl{PTN(Me)} 2 ] (7), and [κ 2 -P,N-AuMe 2 {PTN(Me)}][AuCl 4 ] (8), the latter exhibiting high water solubility. A second group of PTN(R) complexes containing molybdenum have also been reported by Schmidbaur and coworkers. Although no crystals suitable for X-ray diffraction studies were obtained, in all cases, the In this article we report the synthesis, spectroscopic and structural data together with a computational analysis of 2 ligated to rhodium (I) centers, in both a mono-and bidentate coordination mode. The complexes were tested as catalysts for olefin hydroformylation and transfer hydrogenation of benzylidene acetone and acetophenone in organic and biphasic organic/water solvent systems and the results are reported.

RESULTS AND DISCUSSION

Syntheses and characterizations of Rh(I) complexes with PTN(R) ligands

PTN(R) ligands were first described by Schmidbaur and co-workers, and were obtained by reductive cleavage of P-functionalized PTA salts (see Scheme 1). 22,23 The choice of the substituent on P was limited to R = Me, Ph as negligible yields are obtained for R = benzyl, cyclohexyl, t-butyl due to non-selective and inefficient cleavage. The values for 2. 1 H-1 H COSY and 1 H- 13 C HETCOR experiments were used to provide definitive assignments of the CH 2 groups of 2 in 11a and 11b.

From the magnitudes of the n J PC it was possible to assign the CH 2 groups adjacent to phosphorus (Figure 1). For the resonances related to the CH and CH 2 groups of COD and 2, there are significant differences between 11a and 11b, reflecting the rigidity of the PTN(R) framework, as it is apparent from Figure 2.

H A H B N Me N H D H E H E H F H F H C H B H A N P H 3 C Rh H X H X H Y H Y H A H B N Me N H D H E H E H F H F H C H B H A N P Rh H X H X H Y H Y

X-ray crystal structure determinations

Suitable crystals of 10, 11 and 12 were grown and the corresponding X-ray crystal structure data were collected. Selected bond lengths and angles for all structures are provided in Table 3, while a the two sets of parameters refer to the crystallographically independent molecules in the unit cell. b due to a statistical disorder between the terminal P and N atoms in this structure, the corresponding distances and angle are less reliable.

All compounds feature a square planar geometry, two coordination positions being defined wither by the centers of the C-C bonds of cod or, in the case of 12, by iodide and CO ligands (Figure 3). Complex 10a shows intermolecular hydrogen bonding (3.045 Å) between the rhodium center and the N-methyl group of PTN(Me) moiety, the hydrogen assuming an axial position with respect to the Rh center. The Rh … N distances (see Table 3) are approximately 0.4-0.8 Å shorter than the sum of van der Waals radii for Rh and N (3.800 Å), suggesting the presence of a weak interactions between the Rh and N centers, due to the rigid ligand conformation and possibly shortened through crystal packing.

In 10b, the majority of substituent orientations are identical among the two isomers present. The primary difference is in the rotation of the phenyl group, with Rh-P-C ipso -C ortho torsion angle at -12.09(5)° vs -29.40(5)°; in the former the phenyl group is almost coplanar with the bridgehead C, P and terminal N atoms, while for the second conformer it is almost eclipsed with the P-C bond of 2b.

An analysis of the crystal structure apparently showed no indications of disorder. The presence of the two different conformers is likely due to a small energy rotation barrier for the C(Ph)-P bond.

The crystal packing forms a pseudo polymer (see Figure 4) where the units are sequentially linked through chloride-PTN interactions ranging from 2.734 to 2.910 Å. The different number of Cl ... H (of the PTN fragment) interactions between units results in a variation in Rh-Cl bond length and phenyl group orientation within the individual conformers.

The Rh … N distances in 10a and 10b are significantly shorter than the distance between Rh and the dangling NEt 2 group in the [RhCl(CO){Ph 2 PCH(o-C 6 H 4 NMe 2 )CH(Ph)NHPh}] complex (3.66 Å). 18 The ligand is oriented such that it lies with the P,N vector orthogonal to the plane defined by the Rh, Å). 29 The stronger π-back donation to COD indicates that the PTN(R) ligand is a stronger donor than PPh 3 .

In 11 the cation and anion fragments are well separated from each other, the closest interactions being between H(PTN(R)) ... F(BAr F 4 ) at 2.449 Å for both R = Me, Ph. The formation of the Rh-N bond is accompanied by a shorter Rh-P bond (see The HOMO of free 2a consists of an out-of-phase combination of lone pairs associated with the three N atoms and a major contribution from the phosphorus lone pair (Figure 6). As in the case of the tightly constrained PTA, the intra-atomic repulsions between the two internal N centers and the terminal nitrogen and phosphorus centers are caused by the rigidly pinned structure of 2a, thus resulting in a unusually higher energy expected for the HOMO. [START_REF] Phillips | Book of Abstrats[END_REF] This is in line wih tthe experimental observation that PTN is methylated at phosphorus rather than at nitrogen, as expected based on pure hard-soft rules. 22 A single point calculation consisting of only the PTN(Me) fragment with the geometry fixed in the coordinating position observed in complexes 13 and 14 shows a 1.74 and 11.27 kcal mol -1 difference in total energy from that of 2a. Moreover, the energy of HOMO increased by 7.31 and 10.92 kcal mol -1 respectively. A large portion of this energy change can be associated with an increase in bond strain when the internal framework of the ligand is stretched for metal coordination, especially high in the κ 2 -P,N chelating mode.

Mayer bond indices [START_REF] Mayer | [END_REF] are particularly useful for measuring bond strain energy rather than bond lengths which in the case of the PTN(Me)-chelated complexes are unreliable due to site disorder between the coordinating P and N centers. Using the free 2a as a reference point, continuing to Pcoordination and finally to the P,N-chelate mode, the differences between 2a and the 13, 14 and 15 are presented in Table 4. It can be noticed that the P-coordination of PTN(Me) in 13 induces an overall bond strengthening within the ligand which can be attributed mainly to a substantial reduction in internal inter-atomic repulsion between P and N centers. In contrast, upon P,Nchelation in the cationic Rh complex 14, a bond strength reduction occurs particularly for P-CH 2 and In summary, the DFT studies reveal significant changes to the PTN ligand on passing from the P-mono-to the P,N-chelating-coordination mode. Overall, it is evident that the PTN ligand has a preference for maintaining P-coordination to Rh. In contrast, a higher energy cost, in terms of bond strain, is associated with P,N-chelation which suggests that the ligand may show hemilabile behavior in the presence of polar solvents or other types of nucleophiles. Comparison of the Mayer bond indices for Rh-P and Rh-N bonds in cationic (14) and neutral (15) Rh(I) complex. indicates a stronger interaction with PTN in the latter complex, implying a higher tendency for hemilabile behavior for 14.

N t -CH

Olefin hydroformylation tests

Complexes 10, 11 and 12 were tested as catalysts for styrene and 1-hexene hydroformylation and transfer hydrogenation of benzylideneacetone (BZA) and acetophenone using HCO 2 Na/H 2 O or KOH/Pr i OH. The catalytic tests were carried out either using complexes formed in situ by addition of the ligands to either [RhCl(cod)] 2 or [Rh(acac)(cod)], 33 or by introducing the preformed complexes in the reaction mixture. It is well known that [RhCl(cod)] 2 and Cl-containing phosphine adducts are a less suitable precatalysts than other Rh salts, because of the generation of strong acidity (HCl) under catalytic conditions. 2 However, the presence of external bases such as amines is often an efficient remedy and the use of hemilabile aminophosphine ligands has recently received considerable attention. 18,34 The positive effect of the nitrogen donor basicity and proximity to the metal center has been demonstrated. 34b Therefore, a comparison of the activity for the Cl -and acac - precursors in the presence of ligands 2 was considered of interest.

Under mild hydroformylation conditions (CO/H 2 600 psi; CHCl 3 , 100 ml; 55 o C), using the complexes made in situ, the COD ligand will likely be replaced by CO. The runs were monitored by sampling the reaction mixtures and the conversion profiles are shown in Figure 7. The systems tested showed comparable efficiency (complete conversion after 8h), chemoselectivity (ca. 90% total aldehyde yield), and regioselectivity (b/l ratio ca. 91:9), without detectable traces of ethylbenzene among the (unidentified) by-products. No induction period was observed for the conversion of styrene. The conversion profiles are very similar, suggesting that the active species must be very close in nature for all the systems tested (Figure 7). Conversely, a blank test carried out with [RhCl(cod)] 2 without 2 under identical experimental conditions showed that an induction period is required for aldehyde formation. These results are significant when compared with those recently reported in the presence of similar P,N ligands under essentially identical conditions, which showed no activity (TOF < 1 h -1 ) with PPh 3 from the chloride precursor. 34b That study has demonstrated that the TOF is sensitive to the distance between the N and P functions for amines of comparable basicity, proving that the proximity of the basic amine to the catalytic center has a beneficial role in the catalytic rate determining step. Only with ligand Ph 2 PCH 2 NMe 2 having the most basic amine in closest proximity to the phosphine donor was a similar activity observed for the chloride and acac catalytic precursors, 34b as observed in the present case for ligands 2. Styrene hydroformylation tests were then repeated in the presence of the preformed aminophosphine complexes and the final conversion and yields (no sampling) are reported in Table 5, both under strictly homogeneous (chloroform) and biphasic (n-octane/water) conditions. High conversions and chemoselectivity to the branched aldehydes (>94%) were achieved as expected for rhodium complexes and only traces of hydrogenated product (ethylbenzene, <0.5%) were determined. Control runs with [Rh(cod)Cl 2 ] 2 showed that in CHCl 3 at 55°C a slightly higher l/b ratio is obtained at complete conversion (0.11, corresponding to 88.9% branched and 9.9% linear aldehyde), whereas in water/octane at 60 °C a higher amount of ethylbenzene is produced (5.9% against 0.1 in CHCl 3 ) accompanied by a small increase in regioselectivity (l/b 0.08).

Preliminary mechanistic [START_REF] Phillips | Book of Abstrats[END_REF] P HPNMR studies in sapphire tube conditions showed that all phosphorus species are present in solution as doublets due to coupling with Rh during and after exposing CHCl 3 solutions of the complexes to CO/H 2 pressure (600 psi) and prolonged heating to 55 °C, regardless from the presence of styrene. 35 Further hydroformylation studies were carried out using 1-hexene as substrate, and the results are summarized in Table 6. As expected, the linear aldehyde is the favored product, with l/b ratio ranging from 1.35 (10b in CHCl 3 , 4 h) to 3.13 (10a in THF, 1 h). The best conversion was achieved with 10b (99%), although a larger amount of isomerized alkenes were found by GC analysis of the reaction mixture after the run. The composition of the syngas mixture has only a slight effect on the final conversion and yields, both being higher in the presence of CO/H 2 1:1 mixture. The yield of isomerization is not largely affected by this variable. Remarkably, our systems afford very little amounts of hydrogenation products, except in the case when CHCl 3 is used as solvent at 55 °C instead of THF at 60 °C, where alcohols were also accounted for among the products. The previously reported hydroformylation of 1-hexene with [Rh(acac)(CO)(PTA)] complex, 36 carried out in water, resulted in l/b ratio and TON in the same range as our set of catalysts. The catalytic styrene hydroformylation results are comparable with those reported by Andrieu et al. 18,34b using Ph 2 PCH(o-C 6 H 4 CH 2 NHPh) (γ-P,N) as ligand, for which HPNMR studies showed that under catalytic conditions it behaves as a monodentate phosphine, and this may imply a hemilabile nature of the PTN ligands in these reactions.

Transfer hydrogenation tests

The catalytic activity of Rh complexes in transfer hydrogenation reactions is well documented. 37 Complexes 10 and 11 were tested in the transfer hydrogenation of benzylideneacetone (BZA) and acetophenone. Very high chemoselectivity to C=C bond hydrogenation was obtained with all complexes in the transfer reduction of BZA using NaHCO 2 as hydrogen source in water (Table 7).

Interestingly, a ligand effect was observed on the conversion of BZA using 2a instead of 2b, regardless from the coordination mode of the ligand. The highest conversions (>95%) were observed in the presence of 2b. Hydrogen transfer reduction of acetophenone was achieved using the KOH/Pr i OH protocol (Table 7). Interestingly, good conversions (57-69%) were achieved using the monocoordinated Rh(I) neutral complexes 10 while moderate conversions were obtained with the cationic κ 2 -P,N chelated complexes 11. At higher substrate/catalyst ratio (1000), hydrogen transfer to acetophenone still occurred albeit with lower conversion (20 %, TON 198). Cationic complexes 11 generally displayed TON values similar to the cationic aminophosphine rhodium precatalyst described by Gao et al. 38 Control experiments using [Rh(cod)Cl 2 ] 2 showed that BZA conversion was negligible under reaction conditions described in Table 7.

CONCLUSIONS

In summary, a new class of Rh(I) neutral and cationic complexes bearing the water soluble aminophosphine cage ligand PTN have been synthesized, showing both κ 1 -P and κ 2 -P,N coordination modes. All the new PTN complexes were fully characterized by conventional spectroscopic methods in solution and by x-ray diffractometry in the solid state. The geometry of the ligand was correlated to the stability of chelation mode vs monocoordination by DFT calculations, suggesting that the straining constrains imposed by the rigid PTN ligand favors κ 1 -P coordination to Rh. The PTN ligand may behave as hemilabile under forcing olefin hydroformylation conditions and keep their κ 1 -P or κ 2 -P,N coordination mode during milder transfer hydrogenation of activated olefins and ketones. Mechanistic studies are currently in progress to verify this hypothesis.

Manipulations of all products and reagents were carried under a purified N 2 or Ar atmosphere with standard Schlenk techniques. All glassware was pre-dried overnight and subsequently several purge/refill cycles were performed before the introduction of solvents or reagents. Toluene and npentane were dried by reflux over sodium, while dichloromethane was refluxed with CaH 2 . All solvents were degassed prior to use. Styrene was purified by washing three times with 10% aqueous solution of NaOH followed by three washing with distilled water. After drying and filtration with MgSO 4 , the styrene was twice trap to trap distilled under static vacuum and degassed for 30 minutes with a stream of argon. [RhCl(cod)] 2 39 and [Rh 2 I 2 (CO) 4 ] 40 were prepared in accordance with standard literature procedures. The aminophosphines 2a,b were synthesized with a slightly modified procedure to that reported in the literature. [START_REF] Assmann | [END_REF]22 NaBAr F 4 was synthesized as described by Brookhart et al. 25

X-ray Structure Determinations.

Large transparent yellow crystals suitable for single X-ray diffraction were obtained under air and moisture free conditions by slow diffusion of a layer of dry and degassed pentane into a saturated solution of dry and degassed solvents, toluene for 10a and 10b or dichloromethane for 11a, 11b and 12. A single crystal of each compound was mounted under inert perfluoropolyether on the tip of glass fiber and cooled in the cryostream of an Oxford-Diffraction XCALIBUR CCD diffractometer for 10a, 10b, 11a and 12 or a Stoe IPDS diffractometer for 11b. Data were collected using the monochromatic MoK α radiation (λ = 0.71073). The structures were solved by direct methods (SIR97 [START_REF] Altomare | SIR97 a program for automatic solution of crystal structures by direct methods[END_REF] or SHELXS-97 [START_REF] Sheldrick | SHELX97[END_REF] ) and refined by least-squares procedures on F 2 using SHELXL-97. [START_REF] Sheldrick | SHELX97[END_REF] In 11a and 11b some CF 3 groups displayed very large anisotropic displacement parameters for the F atoms and they were then treated as disordered over two positions using the tools available in SHELXL-97. It is interesting to note that in compound 11a, the isotropic thermal parameters for the P and N atoms coordinated to the rhodium displayed unrealistic differences thus indicating that the coordination sites are partially occupied either by P or N atoms. The P and N atoms were considered as sharing the same site and free refinement of the occupancy factors led to a P/N ratio of 90:10 on one site and 10:90 on the other site. All H atoms attached to carbon were introduced in idealized positions and treated as riding models. The drawing of the molecules was realized with the help of ORTEP3. [START_REF] Farrugia | ORTEP3 for Windows[END_REF] Crystal data and refinement parameters are shown in a two crystallographically independent molecules are present in the unit cell.

DFT Calculations

Geometry optimizations, Mayer bond indexes and energies were calculated with density functional theory using the Gaussian 03 suite of programs. [START_REF] Frisch | Gaussian Inc[END_REF] The three parameter hybrid gradient-corrected functional (B3P86) as developed by Becke [START_REF] Becke | [END_REF] with the non-local correlation of Perdew 46 was used.

For each step of the geometry optimizations, self-consistent iterations were performed until a convergence criterion of 10 -8 was achieved. A double zeta gaussian-type basis set 47 was augmented with polarization functions 48 and with an additional set of d-orbitals for C, N and P and an additional p-orbital for hydrogen (6-31+G(d,p)). Rhodium was modeled with the LAN2DZ basis set of double zeta quality, substituting the core electron wave-functions with an effective potential. 49 Optimized structures were verified to be stationary minima as indicated by the absence of imaginary frequencies, expect in the case of transition state (one imaginary was observed). Frequencies Simulated infrared spectra and reported frequencies values were corrected using a standard correction factor based on the level of theory and basis sets employed.

κ 2 -

 2 P,N coordination mode of 2 in [Mo(CO) 4 {PTN(R)}] (9, R = Me, Ph) is inferred from the number and intensity of IR active CO stretching frequencies.22

22

 22

1 2 Complex 3

 123 Scheme 1

Figure 1 :

 1 Figure 1: Labeling scheme of protons in the [Rh(COD)(PTN(R)] + complexes 11a and 11b. The ring current effects of the phenyl group in 11b significant alter the 1 H chemical shifts of H A , H B , H C and

Figure 2 :

 2 Figure 2: Comparison of the 1 H NMR spectra of 11a and 11b demonstrating the effects of the phenyl group in 11b.

Compounds 10 12 Figure 3 :

 10123 Figure 3: ORTEP diagrams of complexes RhCl(COD)(PTN(R)) (R = Me, 10a; Ph, 10b), the cationic fragments, [Rh(COD)(PTN(R))] + (R = Me, 11a; Ph, 11b) and the neutral complex

Figure 4 :

 4 Figure 4: Left: Packing diagram (section) of 10b highlighting the intermolecular interactions

Figure 5 .

 5 In general, the optimized geometric parameters of 13, 14 and 15 accurately represent the corresponding values experimentally observed for 10a, 11a and 12 within experimental error, especially those pertaining to the ethylene groups, 2a, the P-Rh-Cl angle (for 13), the P-Rh-N bite angle (for 14) and the torsion angle of N-P-Rh-Cl. Minor over-estimations were observed for the Rh-P and Rh-Cl bonds (+0.02 and +0.01 Å respectively). A large variation, up to 7°, is noted with the C-Rh-C bond angles, probably caused by the replacement of the cyclic COD by two less constrained ethylene ligands.The optimization of 14 in Cs symmetry, with the ethylene groups bisected by the N-Rh-P plane, yielded a saddle point with a corresponding single imaginary frequency of -60.2 cm -1 . Reoptimization in C 1 resulted in a skewing of the ethylene groups within the square planar coordination geometry by 11.2°, as observed in the crystal structure of 11a, yielding a stable minimum. Hence the distortion has an electronic origin related to rhodium coordination and does not result from the COD.The skewing energy is trivial and was calculated to be only 0.3 kcal mol -1 , which is in agreement with the fluxional behavior observed in solution. Indeed, the 1 H NMR spectra of 11 show only a single resonance for H X and H Y . Model 15 was optimized with Cs symmetry analogous to the crystal structure 12, no imaginary frequencies were observed.

Figure 5 :

 5 Figure 5: DFT Calculated geometries for 13, 14 (representing simpler models of 10a and 11b) and

Figure 6 :

 6 Figure 6: Left, The HOMO of PTN(Me) 2a demonstrating the anti-bonding repulsions between the phosphorus and nitrogen atoms. Right, SHOMO of RhPTN(Me), 13 showing the orbital interaction between Rh d xy and the σ*(P-C) of the PTN ligand which is partially responsible for weakening the P-C bonds. The other metal-ligand bonds have been omitted for clarity.

Figure 7 :

 7 Figure 7: Reaction profiles for styrene hydroformylation in CHCl 3 at 55 °C. Run 1 (□),

b

  Conditions: catalyst:acetophenone:KOH (1:500:5); Pr i OH (10 ml); 80 °C, 6 h.

c

  GC values based on pure samples. A = 4-phenyl-2-butanone; B = 4-phenyl-3-buten-2-ol; C = 1-phenyethanol.

3 .

 3 74 (m, 1H, 2 J HH = 8.6 Hz, N-CHH-N), 3.78 (m, 1H, 2 J HH = 8.6 Hz, N-CHH-N), 4.04 (m, 2H a +2H b , P-CH a H b -N), 4.39 (d, 2H, 3 J HH = 13.0 Hz, N-CHH-NMe). 13 C NMR (100.63 MHz, 25 °C, CD 2 Cl 2 ) δ(ppm) = 29.68 (s, N-CH 3 ), (d, 1 J PC = 22.5 Hz, P-CH 3 ), 56.25 (d, 1 J PC = 30.2 Hz, P-CH 2 -N), 70.79 (d, 3 J PC = 9.1 Hz, N-CH 2 -N), 79.42 (s, N-CH 2 -NMe) 189.91 (CO) 31 P NMR (121.42 MHz, 25 °C, CD 2 Cl 2 ) δ(ppm) = -25.98 (d, 1 J RhP = 154.0 Hz). IR: ν CO (cm -1 ) = 1974 (KBr), 1989 (CH 2 Cl 2 ).

  31 P{ 1 H} NMR chemical shifts for 10-12 are summarized in Table 1, in the normal range of other four-coordinate Rh complexes of the type RhX 2 L 2 .

[START_REF] Verkade | Chapter 13 in Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis[END_REF]

For 12,

[START_REF] Phillips | Book of Abstrats[END_REF]

P NMR shows a chemical shift of -26.0 ppm in CD 2 Cl 2 , which is the highest field signal for all Rh-PTN(R) compounds reported.

Table 1 :

 1 Solution 31 P NMR data for 2, 10, 11 and 12. All signals are referenced with respect to 85% aqueous H 3 PO 4 .

	Compound	δ (ppm)	1 J RhP (Hz)	Solvent
	2a 2b 10a 10b 11a 11b 12	-91.8 a -77.1 a -48.2 b -43.9 b -40.2 b -37.4 b -26.5 b	--151.2 b 152.3 b 143.5 b 142.3 b 154.4 b	C 6 D 6 CDCl 3 C 6 D 6 C 6 D 6 CD 2 Cl 2 CD 2 Cl 2 CD 2 Cl 2
	a Reference 23.

b

This work.

1

H NMR chemical shifts are summarized in Table

Table 2 :

 2 Solution 1 H NMR data (δ, ppm, TMS referenced) for 2

, 10, 11 and 12.

	Figure 1) is shifted extremely upfield, δ( 1 H Y ) = 3.559 ppm (c.f. δ( 1 H X ) = 5.303 ppm) and δ( 13 C) =
	70.95 (c.f. 109.12) ppm. These effects are attributed to ring current generated by the π-system of the
	phenyl substituent and its direct face-on positioning with respect to (CH) Y group of COD, which is
	evident from the crystal structure of 11b (vide infra). The chemical shift of the P-CH 2 groups of 2
	(H A and H B ) are less affected (and H c to an even lesser extent) as observed by a different orientation
	from the phenyl group.
			11a		11b
	Compound CH 2 (COD)	CH(COD) CH 3 -N CH 2 (PTN(R))	R-P ( 3 J PH , Hz)
	2a a	n/a	n/a	1.97 s	3.36-4.02	0.93d (5.40)
	2b a	n/a	n/a	2.23 s	3.65-4.05	7.33-7.67
	10a b	1.95-2.34	5.73 br s	2.22 s	3.02-4.26	1.14dd (6.60, 2.40 c )
	11a a	2.25-2.57	5.26 br s	2.39 s	3.77-4.53	1.16d (9.90)
	12 a	n/a	n/a	2.86 s	3.65-4.40	1.50 dd (10.46, 2.55 c )
	10b b	1.89-2.32	5.77 br s	2.42 s	3.43-4.550	7.31-8.19
	11b a	2.09-2.56	5.30 br s	2.45 s	3.56-4.65	7.28-7.60
			3.56 br s
	a In CD 2 Cl 2 solution. b In C 6 D 6 solution. c 4 J RhH
	In 11b, the CH 2 signals of COD (protons H X and H Y , Figure 1) show a complicated splitting
	pattern. Both the 1 H and 13 C NMR show that one set of the CH groups belonging to COD (H Y ,

Table 8 (

 8 Experimental Section) summarizes the main crystallographic data.

Table 3 :

 3 Selected bond lengths (Å) and angles (°) for compounds

10, 11 and 12.

	C=C	1.409(3)	1.407(6)	1.407(6)	1.376(7)	1.406(6)
	(trans to Cl or N)
	Rh-C(O)						1.803(5)
	Rh(C)-O						1.138(5)
	P-Cexo	1.829(2)	1.829(4)	1.828(4)	1.775(5) b	1.813(4)
	P-Cendo	1.875(2)	1.870(4)	1.873(4)	1.800(5) b	1.844(4)	1.844(4)
		1.863(2)	1.864(4)	1.864(4)	1.805(5) b	1.853(4)	1.840(5)
	N-Cexo	1.455(2)	1.465(4)	1.452(4)	1.525(6) b	1.498(5)	1.481(5)
	N-Cendo	1.474(2)	1.475(4)	1.466(4)	1.570(6) b	1.512(5)	1.510(5)
		1.465(2)	1.472(4)	1.452(4)	1.577(6) b	1.517(5)	1.521(5)
	Cl-Rh-P	87.58(2)	90.22(4)	89.07(4)	-	-
	I-Rh-N						98.7(1)
	P-Rh-C(O)						90.6(2)
	N-Rh-P	80.99(2)	62.65(4)	60.35(4)	83.3(1) b	84.1(1)	84.1(1)
	Cl-Rh-N	95.05(2)	81.69(4)	60.33(4)	-	-
	C-Rh-C	81.7(2)	81.1(2)	81.9(2)	80.0(2)	80.5(1)
		81.3(2)	81.8(2)	80.8(2)	79.9(2)	80.5(1)
	Cl-Rh-P-N	-97.6(2)	-80.5(1)	-81.7(1)	-	-
	Cl-Rh-C-P exo	82.2(2)	93.1(1)	98.8(1)	-	-
	Parameter	10a		10b a	11a	11b	12
	Rh-P	2.3073(5)	2.323(1)	2.334(1)	2.229(2) b	2.239(1)	2.206(1)
	Rh-Cl	2.3739(5)	2.394(1)	2.368(1)	-	-
	Rh-I						2.711(5)
	Rh-N	3.401(2)	3.055(2)	3.226(2)	2.204(3) b	2.213(3)	2.219(3)
	Rh-C	2.206(2)	2.189(4)	2.191(4)	2.229(5)	2.226(4)
	(trans to P)	2.199(2)	2.179(4)	2.179(4)	2.230(5)	2.280(4)
	Rh-C	2.108(2)	2.107(4)	2.116(4)	2.146(5)	2.155(3)
	(trans to Cl or N)	2.107(2)	2.106(4)	2.098(4)	2.132(5)	2.130(3)
	C=C	1.374(3)	1.385(6)	1.368(6)	1.353(8)	1.352(6)
	(trans to P)

Table 3

 3 This result is consistent with the stronger ligand coordination characteristic of cationic rhodium(I) complexes.The P-Rh-N bite angle for 11a and 11b (ca. 84°), is midway between the six (86.7°) and five membered systems (82.8°). A comparison of 10a and 11a with [Au{PTN(Me)}Me 2 ][AuMe 2 Cl 2 ] reveals the P-M-N bond angles are identical22 within experimental error at a value of 82.7(5)°.Due to the statistical disorder of the chelating P and N atoms within 11a (described in the X-ray Structure Determination section), it is inconclusive whether the P-Rh and N-Rh distances are different from those of 11b. The phenyl plane in 11b is orthogonal to the plane defined by P, Rh and N and it is faced towards one side of COD. This observation is consistent with the NMR analysis Figure4). A related example was reported in the cis-[PdCl 2 (PTA) 2 ] structure where two strong Pd … H(CH) axial interactions (2.86 Å) form a dimeric unit.[START_REF] Desiraju | The Weak Hydrogen Bond[END_REF] -P,N chelation. The complete 2a ligand was optimized in Cs symmetry in the lowest energy configuration with exo-substituents on both P and N, which is the most suitable conformer for coordination. The energy-minimized model exactly matches the

	Computational Analysis
	A density functional theory investigation on 2a and model complexes of 10a and 11a was
	performed in order to elucidate the electronic effects associated with P-coordination to Rh including
	the changes induced through κ 2

), i.e. approximately 0.1 Å shorter than that of the parent compounds 10.

showing downfield chemical shift and distributed resonances associated with COD and PTN(R) susbstituents (see above). This demonstrates that the phenyl group is maintained in an identical fixed position for the solution and in the solid state. Another interesting aspect of the structures of 11 is the significant increase in the P-C endo and N-C endo bonds (see Table

3

) suggesting that 2 has been stretched in order to accommodate a chelating coordination mode. Analogous for compounds 10a and 10b, the Rh-C bonds are longer and the C=C bond is longer for the atoms of the COD ligand located trans to phosphorus.

In contrast to 11a, 12 does not have disordering of P, N donor sites due the specific influences of the trans-effects caused by CO and I. Thus, the structure of 12 is significantly more reliable in terms of metric parameters associated with the chelated PTN ligand than 11a. However, as a general observation, 11a features shorter Rh-P and Rh-N bond lengths than 12, which is consistent with stronger bonding associated with a cationic Rh center in the former. In comparison to RhCl(CO) complexes with 5, 12 has both a longer Rh-P and Rh-N bond length, combined with a slightly wider P-Rh-N bond angle, moreover, the Rh-C(O) distance is shorter in 12 than in RhCl(CO) complexes with 5. This suggests that 2 is a weaker ligand than 5, and, probably, more hemi-labile. The internal PTN framework of 12 demonstrates some shortening in the P-C endo and N-C endo bonds, which is unresolved in the COD analog. The packing of the unit cell is similar to the other Rh-PTN complexes, containing weak intermolecular contacts between hydrogens of 2. The most interesting property is an axial interaction between Rh and H3A (2.920 Å), which is continuously repeated as an extended polymeric structure (exo,exo-geometry observed in the disordered crystal structure reported by Schmidbaur and coworkers.

22

Complexes of 10a and 11a were simplified by replacing COD by two ethylene groups, yielding the model complexes [RhCl(C 2 H 4 ) 2 {PTN(Me)}], 13, and [Rh(C 2 H 4 ) 2 {PTN(Me)}] + , 14.

Complex 12 was modelled (15) without any simplifications, and is shown in

Table 4 :

 4 Comparison of Mayer Bond Indices for the PTN(Me) ligand, free (2a) and ligated as through P-coordination 13, and P,N-chelation 14, 15. For nitrogen labeling see Figure5.

	Parameter	2a	13	14	15
	P-CH 3	0.698	0.997	1.075	1.009
	P-CH 2	0.721	0.880	0.634	0.738
			0.868	0.693
	P-CH 2 -N i	0.828	0.945	0.908	0.881
			0.926	0.911

Table 5 :

 5 Styrene hydroformylation under homogeneous a and biphasic conditions b .

	Complex	Conv. (%) Branched (%)	Linear (%)	l/b	EtPh (%)
	10a a	99.3	95.4	3.7	0.039	0.2
	10a b	57.7	52.9	2.3	0.043	1.9
	10b a	88.4	84.5	3.7	0.044	0.2
	10b b	71.0	66.9	3.2	0.047	0.9
	11a a	80.8	74.7	5.5	0.074	0.5
	11b b	99.9	95.3	4.7	0.049	0.0
	12 b	40.6	39.5	0.1	0.003	1.0

a styrene: 2.5 mmol; cat: 0.01 mmol; H 2 :CO (1:1), 600 psi; CH 3 Cl: 40ml; 55 °C; 6 h. b as above, except H 2 O/n-octane (2/1), 60 °C.

Table 6 :

 6 1-hexene hydroformylation under homogeneous conditions a .

	Catalyst	Conv. % (h) Linear % Branched % l/b Isom % Hydrog %
	10a	20.2(1)	12.2	3.9	3.13	4.0	0.1
	10a	61.5(4)	31.9	13.4	2.38	16.1	0.1
	10a b	83.0(4)	43.5	20.9	2.08	18.4	0.2
	10a c	92.5(4)	50.7	26.2	1.94	15.5	0.1
	10b	63.4(1)	33.6	12.3	2.73	17.4	0.1
	10b	99.3(4)	48.3	26.1	1.85	20.9	4.0
	10b c	82.5(4)	33.5	24.9	1.35	19.9	4.2 d
	11a	27.4(1)	14.8	5.5	2.69	7.0	0.1
	11a	70.0(4)	35.8	15.8	2.27	17.6	0.8
	11b	52.6(1)	29.8	11.3	2.64	11.3	0.2

a 1-hexene: 2.5 mmol; cat 0.01 mmol; H 2 :CO (2:1), 600 psi; THF: 30 ml; 60 °C; 4 h.

b CO/H 2 (1:1) 600 psi.

c CHCl 3 30 ml, 55 °C, CO/H 2 (1:1) 600 psi. d including alcohols.

Table 7 :

 7 Hydrogen transfer tests for the reduction of BZA a and acetophenone b .

	selectivity

  All other reagents (technical grade) were purchased from commercial sources and used as received. The NMR spectra were recorded using a Bruker AC-200 operating at 200 MHz, a VARIAN VXR instrument operating at 300 MHz or a Bruker Avance DRX operating at 400 MHz. Deuterated dichloromethane was dried with activated 4 Å molecular sieves and C 6 D 6 with stirring over Na-K alloy. Both solvents were degassed prior to sample preparation. Chemicals shifts for 1 H After 1 h of stirring at room temperature, the volume of the solution was reduced to 5 mL under reduced pressure. Addition of 8 mL of n-pentane resulted in the formation of a yellow powder, which was collected by decanting off the mother liquor, washed with three 2 mL portions of n-pentane and dried overnight under vacuum. Me ), 5.72 (br s, 4H, CH 2 (COD)). 13 C NMR (75.43 MHz, 25 °C, C 6 D 6 ) δ(ppm) = 28.95 (s, CH 2 (COD)), 33.43 (s, CH 2 (COD)), 38.86 (s, N-CH 3 ), 50.45 (d, 1 J PC = 14.6 Hz, P-CH 3 ), 66.96 (d, 1 J PC = 13.6 Hz, P-CH 2 -N), 70.71 (d, 3 J PC = 10.8 Hz, N-CH 2 -N), 76.47 (s, N-CH 2 -N Me ), 98.98 (s, CH(COD)). 31 P NMR (121.42 MHz, 25 °C, C 6 D 6 ) δ(ppm) = -48.21 (d, 1 J RhP = 151.2 Hz). MS (EI): -,m-C 6 H 5 ), 7.65 (s, 4H, p-C 6 H 3 (CF 3 ) 2 ), 7.85 (s, 8H, o-C 6 H 3 (CF 3 ) 2 )). 13 C NMR (75.43 MHz, 25 °C, C 6 D 6 ) δ(ppm) = 29.74 (s, CH 2 (C 8 H 12 )), 32.40 (s, CH 2 (COD)), 46.97 (s, N-CH 3 ), 51.29 (d, 1 J PC = 16.6 Hz, P-CH 2 -N), 70.95 (s, CH(COD)), 75.60 (d, 3 J PC = 11.8 Hz, N-CH 2 -N), 80.80 (s, N-CH 2 -N Me ), 109.12 (s, CH(C 8 H 12 )), 118.38 (s, p-C 6 H 3 (CF 3 ) 2 ), 132.71 (s, p-C 6 H 5 ), 124.96 (d, 1 J PC = 37.1Hz, i-C 6 H 5 ), 125.49 (q, 1 J FC = 272.5 Hz, CF 3 ), 129.75 (q, 2 J FC = 32.2 Hz, m-C 6 H 3 (CF 3 ) 2 ), 130.46(d, 3 J PC = 9.8 Hz, o-C 6 H 5 ), 130.71 (d, 2 J PC = 7.8 Hz, m-C 6 H 5 ), 135.69 (s, o-C 6 H 3 (CF 3 ) 2 ), 162.64 (non binomial q, 1 J CB = 49.79 Hz, i-C 6 H 3 (CF 3 ) 2 ).[START_REF] Phillips | Book of Abstrats[END_REF] P NMR (121.42 MHz, 25 °C, CD 2 Cl 2 ) δ(ppm) = -To a dry and N 2 purged 50 mL Schlenk flask, 57 mg (0.1 mmol) of [Rh 2 I 2 (CO) 4 ] was dissolved with 5 mL of dry and degassed toluene. To this solution,

	30 minutes. R = Me (10a). Yield 0.748 g (93 %). Anal. Calcd. (found) for C 15 H 28 N 3 PRh: C, 42.92 (43.02); H,
	6.72 (6.32); N, 10.01 (9.70). Melting point (decomposition): 172 ºC. 1 H NMR (299.96 MHz, 25 °C,
	C 6 D 6 ) δ(ppm) = 1.14 (dd, 3H, 3 J PH = 6.6 Hz, 4 J RhH = 2.4 Hz, P-CH 3 ), 1.94 (m, 4H, CH 2 (COD)), 2.22
	and 13 C are referenced with respect to external TMS and 31 P was referenced to external aqueoaus 85% H 3 PO 4 . FTIR spectra were measured on a Perkin Elmer Spectrum BX instrument using KBr pellets or solution cells. Elemental combustion microanalyses (C, H, N) were obtained using a Perkin-Elmer 2400 series II elemental analyzer. Mass spectra were obtained with a Nermag R10-10 mass spectrometer with the electron-impact technique. GC analyses were performed on a Shimadzu GC-14 A gas chromatograph equipped with a flame ionisation detector and a 30 m (0.25 mm i.d., 0.25 µm) film thickness) SPB-1 Supelco fused silica capillary column. GC/MS analyses were performed on a Shimadzu QP 5000 apparatus equipped with a column identical with that used for GC analysis. (s, 3H, N-CH 3 ), 2.34 (br s, 4H, CH 2 (COD)), 3.04 (m, 2H, P-CHH-N), 3.08 (m, 2H, , N-CHH-N), 3.56 (m, 1H, N-CHH-N), 3.85 (m, 1H, N-CHH-N), 3.92 (m, 2H, P-CHH-N), 4.23 (m, 2H, N-CHH-N m/z 419 (M + , 14.3%), 311 (M + -COD, 28.8%), 268 (M + -COD-CH 2 NCH 3 , 11.6%), 232 (M + -COD-CH 2 NCH 3 -HCl, 10.3%). R = Ph (10b). Yield 0.863 g (89.6 %). Anal. Calcd. (found) for C 20 H 30 N 3 PRh: C, 49.86 (49.82); H, 6.28 (6.12); N, 8.72 (8.31). Melting point (decomposition): 173 ºC. 1 H NMR (299.96 MHz, 25 °C, C 6 D 6 ) δ(ppm) = 1.90 (m, 4H, CH 2 (COD)), 2.34 (br s, 4H, CH 2 (COD)), 2.42 (s, 3H, N-CH 3 ), 3.44 (m, 2H, P-CHH-N), 3.92 (m, 1H, N-CHH-N), 4.13 (m, 2H, P-CHH-N), 4.53 (m, 2H, N-CHH-N Me ), 5.77 (br s, 4H, CH 2 (COD)), 7.34 (m, 4H, o-,m-C 6 H 5 ), 8.16 (t, 3 J HH = 7.8 Hz, 1H, p-C 6 H 5 ). 13 C NMR (75.43 MHz, 25 °C, C 6 D 6 ) δ(ppm) = 29.01 (s, CH 2 (COD)), 33.17 (s, CH 2 (COD)), 39.39 (s, N-CH 3 ), 49.32 (d, 1 J PC = 10.71 Hz, P-CH 2 -N), 68.05 (s, CH(COD)), 71.08 (d, 3 J PC = 9.60 Hz, N-CH 2 -N), 76.10 (s, N-CH 2 -N Me ), 97.77 (s, CH(COD)), 129.53 (s, p-C 6 H 5 ), 131.42 (d, 1 J PC = 85.01 Hz, i-C 6 H 5 ), 132.75 (d, 3 J PC = 9.81 Hz, m-C 6 H 5 ), 139.56 (d, 2 J PC = 15.61 Hz, o-C 6 H 5 ). 31 P NMR (121.42 MHz, 25 4 anion [m/z 796 (BAr F 4 -CF 3 +2H, 0.058%), 777 (796-F, 0.033%), 727 (796-CF 3 , 0.037%), 650 (BAr F 3 + , 1.01%), 631 (650-F, 0.92%)], plus two fragments deriving from the cationic rhodium complex [1055 (M + -PTN(Ph)-F, 0.023%); 861 (1055-Ar F -F, 0.048%)]. 36.7 g (0.21 mmol) of PTN(Me) in 5 mL of toluene was slowly added, and after 1 h stirring at ambient temperature, an orange precipitate was obtained. After removal of the mother liquor, the remaining solid was washed with three 2 mL portions of pentane and dried under reduced vacuum overnight. Yield 0.055 g (64%). Anal. Calcd. (found) for C 8 H 16 N 3 OIPRh: C, 22.29 (22.45); H, 3.74 (3.89); N, 9.75 (9.70). 1 H NMR (400.13 MHz, 25 °C, CD 2 Cl 2 ) δ(ppm) = 1.56 (dd, 3H, 2 J PH = 10.5 °C, C 6 D 37.36 (d, 1 J RhP = 142.3 Hz). The MS (EI) spectrum shows fragments deriving from the BAr F Hz, 3 J RhH = 2. 6 Hz, P-CH 3 ), 2.86 (s, 3H, N-CH 3 ), 3.67 (br d, 2H, 2 J HH = 12.8 Hz, N-CHH-NMe),
	Synthesis of [RhCl(cod){PTN(R)}] (10). In a dry and N 2 purged 50 mL Schlenk flask were
	introduced 0.493 g (1.00 mmol) of [RhCl(cod)] 2 and 5 mL of toluene. After 5 min of stirring, 2.00
	mmol (2a, 0.346 g; 2b, 0.471g) dissolved in 10 mL of toluene were added dropwise over a period of

6 ) δ(ppm) = -43.90 (d, 1 J RhP = 152.3 Hz). MS (EI): m/z 481 (M + , 0.85%), 373 (M + -COD, 10.1%), 330 (M + -COD-CH 2 NCH 3 , 9.8%), 294 (M + -COD-CH 2 NCH 3 -HCl, 12.2%). oSynthesis of [RhI(CO){PTN(Me)}] (12).

Table 8 .

 8 Crystallographic data (excluding structure factors) have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC ****. Copies of the data can be obtained free of charge on application to the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44) 1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).

Table 8 :

 8 Selected crystallographic data for Rh(PTN(R))Cl(cod) (R = Me, 10a; R = Ph, 10b), PRh C 40 H 60 Cl 2 N 6 P 2 Rh 2 C 48 H 42 BF 24 N 3 PRh C 52 H 42 BF 24 N 3 PRh C 8 H 16 N 3 OPRhI fw, g mol -1

	Rh(cod)(PTN(R))][B(3,5-(CF 3 ) 2 C 6 H 3 ) 4 ] (R = Me, 11a; R = Ph, 11b) and RhI(PTN(Me))CO, 12.
		10a	10b a	11a	11b	12
	formula	C 15 H 28 ClN 3 419.73	963.60	1332.44	1309.58	431.02
	colour, habit	yellow, needle	yellow, prism	yellow, prism	yellow cube	orange prism
	cryst syst	P bca	P 2 1 /c	P -1	P -1	Pbca
	space group	orthorhombic	monoclinic	triclinic	triclinic	orthorhombic
	a, Å	15.3268(7)	9.9872(6)	13.3739(16)	12.2076(13)	12.5944(12)

ACKNOWLEDGEMENTS:

We thank the EC for promoting this scientific activity with financial support including grants through the Marie Curie Research Training Network "Hydrochem" (contract HPRN-CT-2002-00176). Drs P. Barbaro, C. Mealli, (ICCOM-CNR) and Dr. E. Manoury (LCC) are gratefully acknowledged for extra NMR experiments and useful discussions regarding computational studies and catalysis. Dr C. Giannelli (University of Florence) is kindly acknowledged for supplementary GC analysis. Thanks are expressed to "FIRENZE HYDROLAB", a project sponsored by Ente Cassa di Risparmio di Firenze, for supporting this research activity.

SUPPORTING INFORMATION

Crystallographic information files (CIF) for 10a, 10b, 11a, 11b and 12; coordinates for optimized models 2a, 13, 14 and 15; full author list for Ref 47; experimental details for catalytic tests. This material is available free of charge via the Internet at http://pubs.acs.org.

EXPERIMENTAL SECTION