Muh-Mei Wei

Max García-Melchor

Jean-Claude Daran

Catherine Audin

Agustí Lledós

Rinaldo Poli

Eric Deydier

Eric Manoury

Coordination chemistry of new chiral P,N ferrocenyl ligands with half-sandwich Ruthenium(II), Rhodium(III) and Iridium(III) complexes

Keywords: Chiral PN ferrocenyl ligand, Hydrogen transfer, Rhodium, Ruthenium, Iridium, DFT calculations, Halfsandwich complexes, Metal chirality

New half-sandwich ruthenium(II), rhodium(III) and iridium(III) complexes (p-cymene)RuCl2L and Cp*MCl2L (M = Rh, Ir) where L is a planar chiral ferrocenyl tosylamine-phosphine ligand {1,2-(TosNRCH2)(PPh2)C5H3}FeCp (R = H, Me) coordinated in a monodendate fashion (κ 1 :P) have been synthesized and fully characterized both in solution (multinuclear NMR, mass spectrometry) and in the solid state (X-ray analysis on single crystals). Intra and inter molecular N-H•••Cl bonds were observed.

Variable temperature NMR shows equilibrium between different structures which have been discussed with the help of DFT calculations. Addition of triethylamine to the complexes with R = H allows removing the tosylamide acidic hydrogen giving rise to a ferrocenyl amidophosphine ligand coordinated in a bidendate fashion (κ 2 :P,N). All complexes have been fully characterized by multinuclear NMR and mass spectrometry. The structure of the iridium complex, determined by X-ray diffraction, shows a planar nitrogen atom and a stable metal-centered chirality. Only the most stable diastereoisomer, according to DFT calculations has been observed. A number of these complexes were assessed in the catalytic transfer hydrogenation and asymmetric transfer hydrogenation of acetophenone.

TABLE OF CONTENT GRAPHIC

Introduction

Homogenous asymmetric catalysis by transition metals has received considerable attention over the last few decades. Numerous chiral ligands and complexes allowing high efficiency reactions have been reported. In this area, chiral phosphines have played a significant role. 1,2 The possibility to easily modify their electronic and steric properties by a judicious choice of the substituents has proven extremely useful to successfully optimized catalytic reactions. In recent years, the use of diphosphine ligands (P,P ligands) and monophosphine ligands containing an additional donor atom (P,X ligands) with a different "hard" and "soft" character (according to Pearson's HSAB concept) have been widely investigated.

Among the numerous P,X ligands reported to date, chiral bidendate P,N ligands bearing a soft phosphine and a hard nitrogen provide interesting electronic and coordinating properties. 3 Their coordination with transition metals affords efficient catalysts for numerous asymmetric applications such as hydroformylation and hydrosilylation. 4 The nature of the nitrogen atom (sp 3 or sp 2 ), the electronic effects of its substituents (alkyl, aryl) and their steric hindrance allow to easily modulate the nitrogen donor atom lability. Hemilability is of particular interest in catalysis, as these ligands allow the formation of reactive sites while improving the catalyst stability. However, the ability of chiral ligands to undergo rapid association/dissociation processes may be a problem in asymmetric catalysis, when the reaction selectivity is controlled by the metal stereochemistry. This is particularly true when the metal is an additional center of chirality in the ligand associated form. Indeed, reaction of a pure R configurated bidendate ligand (RL) will conduct to two diastereoisomers (RLRM) and (RLSM) and the selective formation of one specific diastereoisomer may be a challenge. 5,6 One family of such chiral-at-metal complexes are the half sandwich complexes of ruthenium, rhodium and iridium, that have found efficient applications for instance in Asymmetric Transfer Hydrogenation (ATH). Ligands used for this reaction are mainly aminoalcohols or bidendate N,N ligands bearing a NH bond which is involved in the hydrogen transfer mechanism according to Noyori's proposal. [7][8][9][10][11] However, a few research groups have reported non "NH" P,N ligands active in Transfer Hydrogenation (TH). Among them, a few ferrocenyl phosphines have proven to be very efficient. Indeed, Stradiotto et al. recently reported ee's up to 95% in the ATH of sterically hindered ketones under mild conditions (40°C) using a P,N(sp 3 ) ligand bearing a NMe2 group and [IrCl(COD)]2 as a metal precursor (Chart 1, ligand 1). 12 A similar efficiency was also reported using ruthenium catalyst 2 (Chart 1) with a P,N(sp 2 ) ligand which involves a chiral oxazoline nitrogen atom donor. [13][14][15] These examples suggest the occurrence of a different mechanism in Transfer Hydrogenation and various experimental or/and computational studies have been carried out to better understand the coordination chemistry of P,N ligands and their role in TH. 12,[16][17][18][19][20] Chart 1

We have long been interested in the design and the synthesis of new chiral ferrocenyl ligands for exploring new asymmetric catalytic reactions or for improving the existing ones. [21][22][23][24][25][26] The important application of chiral ferrocene ligands in asymmetric catalysis is highlighted in recent reviews. 27,28 In the present paper we report the synthesis and the coordination chemistry of a new P,N chiral ferrocenyl ligand, bearing a TosNR fragment (R = H, Me), with ruthenium, rhodium and iridium half sandwich complexes. The facile H removal allows switching from a P-amino to a stronger P-amido donor. The ligand coordination and lability and the stereochemistry of the resulting complexes will be explored through both experimental and computational work. A preliminary evaluation of these complexes in ATH and asymmetric hydrogenation (AH) will also be presented.

Results and Discussion

1. Ligands Synthesis. 3) was chosen as starting material for this work. This compound can be prepared in multigram quantities and isolated as a racemic mixture or in a pure enantiomeric form, opening direct access to chiral ligands. 29 Moreover, the phosphino function is protected from oxidation by a sulfur atom allowing working in air. Ligands 5 and 5a were prepared in a two steps reaction by successive addition of HBF4 and tosylamide or methyltosylamide to a dichloromethane solution of 3 (Scheme 1) under the reaction conditions previously optimized for the synthesis of ferrocenyl phosphine. 30,31 After purification by flash chromatography on silicagel, compounds 4 and 4a were obtained as yellow powders in quantitative yields and fully characterized by mass spectroscopy and multinuclear NMR. Scheme 1. Synthesis of ligands 5 and 5a.

2-thiodiphenylphosphino(hydroxymethyl)ferrocene (

(i) CH2Cl2, HBF4, H2NSO2(C6H4)CH3 or HNMeSO2(C6H4)CH3; (j) reflux toluene, P(NMe2)3, overnight.

Compound 4 has been characterized by single-crystal X-ray diffraction. A view of the molecule is shown in Figure 1 and selected structural parameters are listed in Table 1. The sulfur atom is endo with respect to the Cp ring, being away from the ring plane by 1.013(3) Å, as observed in related ferrocenyl derivatives. The two Cp rings are roughly parallel (dihedral angle of 2.4(1)°) and nearly eclipsed (twist angle of 1.05( 12)°). The nitrogen atom is pyramidal (Σangles = 338.0(2)°) and endo with respect to the Cp ring with the hydrogen atom pointing to the sulfur atom S1 resulting in a intramolecular N-H•••S hydrogen bond (Table 2). All bonds lengths and angles in this structure are within expected range. 4) or Cl (6, 8, 10).

N1-H(Å) H•••X*(Å) N1•••X*(Å) N1-H•••X*(°)
Desulfurization was achieved with high efficiency using tris(dimethylamino)phosphine in refluxing toluene for 12 h under an argon atmosphere. Ligands 5 and 5a were recovered as yellow solids after flash chromatography (93% and 100% yield respectively) and fully characterized by mass spectrometry and multinuclear NMR. In all cases, the chloro-bridged dimer was cleaved by the phosphorus atom coordination while the nitrogen atom remains uncoordinated as shown by the X-ray structures. ORTEP views of the three geometries are presented in Figure 2. All three compounds adopt a roughly similar coordination environment with the phosphorus atom coordinated to the metal resulting in a "three-legged piano stool" geometry. A major difference is the presence of an intramolecular H-bond in the structure of 6, whereas those of compounds 8 and 10 feature an intermolecular H bonding network yielding infinite chains parallel to the [1 0 0] axis (Table 2). Compounds 8 and 10 are isomorphic in the polar P21 space group, whereas 6 crystallizes as a racemate in the centrosymmetric group P-1. Examination of selected geometric parameters shows that the three structures have an essentially identical geometry (Table 3). The main differences are a smaller Cl1-M-Cl2 angle and larger distances of the N1 and P1 atoms from the ferrocene Cp ring plane in compound 6. These differences might be related to the intramolecular N-H•••Cl1 hydrogen bond. Another difference of these structures is that the two Cp rings in compound 6 are nearly eclipsed with a twist angle of 4.0(2)°, whereas they are staggered in compounds 8 and 10 (Table 3). The hydrogen bond influences the M-Cl distance which is significantly longer in each compound relative to that of the free M-Cl bond. Similar observations were reported by Cowie et al. for half sandwich ruthenium complexes bearing a P,amine ligand. 32 The nitrogen atom in the structure of 6 is essentially planar with the sum of the angles equal to 359.4(2)° whereas a significant degree of pyramidalization is observed in the structures of compounds 8 and 10

(348.7(3)° and 351.1(4)° respectively). A closer look at tables 2 and 3 shows that the N•••Cl and N-S length in compound 6 are slightly shorter than in compounds 8 and 10. This result seems to suggest that the stronger H-bond in 6 increases the electron density on the sp 2 nitrogen, which is then partially transferred to the sulfur atom through a  interaction. 9(7) 135.8(3)  4.0(2) 26.6(3) 12.8(6) 25.8(4) In solution, the phosphorus atom coordination is easily followed by the downfield shift of the 31 P NMR signal. Upon coordination to the Ru atom in compound 6, the resonance of the free ligand at δ -24.2 is replaced by a sharp singlet at δ 14.6. The final product possesses two elements of chirality, namely the planar chiral ferrocenyl group and the metal atom. The latter is chiral because of the intramolecular hydrogen bond that involves one of the two Cl atoms. Thus, two diastereomeric pairs of enantiomers could in principle be obtained. The single resonance is presumably resulting from a rapid interconversion between the two diastereoisomers through the symmetric intermediate A (Scheme 3).

Scheme 3.

Proposed equilibrium between two diastereoisomers of compound 6.

In order to probe the possible existence of isomers, variable temperature 31 P NMR investigations were carried out (Figure 3). Upon cooling, the δ 14.6 signal shifted upfield and broadened, reaching maximum linewidth at 213 K, followed by sharpening and further upfield shifting until a harp singlet was obtained at δ 11.3 at 183 K. Whereas a temperature-dependent chemical shift could result from a simple variation of the medium polarity (dichloromethane is known to have a strongly temperaturedependent dipole moment) and examples where this phenomenon occurs are common in 31 P NMR spectrometry, the broadening followed by sharpening unambiguously signals the presence of dynamic exchange phenomena. The single resonance observed at the slow exchange limit shows that one diastereoisomer is predominant with the minor isomer(s) remaining undetected. For the rhodium and iridium complexes 8 and 10, the 31 P{ 1 H} NMR spectra at room temperature gave broad signals at δ 24.2 and -7.0, respectively. For both complexes, the resonance further broadens upon cooling without a significant shift and then decoalesces to yield two signals of unequal intensity at 253 K for 8 or 233 K for 10 (Figure 3). Further cooling to 213K reveals the presence of at least three compounds. For complex 8, the spectrum at 213 K reveals a broad doublet at lower field around δ 28.8 Crystallization of 11 from a dichloromethane/hexane mixture gave suitable crystal for an X-ray diffraction analysis. A view of this compound is shown in Figure 4. The chelating P,N ligand and one chlorine atom complete the coordination sphere of the three-legged piano stool, as observed in related compounds published in the literature. [33][34][35] The distances and angles ( showing that the inversion of configuration at the metal is not a facile process. This last observation underlines the metal ability to preserve its absolute configuration which is an interesting point for asymmetric catalytic applications. The observation also indirectly shows that the 1:1 diastereomeric mixture of 11 is produced under kinetic control. 4) Cp(plane)-N1 -0.958( 8)

Cp(plane)-P1 -0.205( 6) Cp(plane)-Ir1 -0.342( 9)

DFT calculations.

In order to test the hypothesis outlined in Scheme 3 as the reason for the observed low-temperature NMR behavior, we have carried out a DFT computational study. Computational details (functional, basis sets, solvent model, etc.) are given in the Experimental part. The three compounds geometries were fully optimized, without any ligand simplification using the S planar chirality of the ferrocene ligand and starting from the geometry observed for compound 6 in the solid state. For the Rh and Ir complexes, analogous geometries adapted from that of 6 were built as starting points. Analogous starting structures were also generated for the other H-bonded diastereoisomers and for the open form.

The energetic results are shown in Table 5 and the optimized structures are available in the supporting information (Part 1). The calculated bonding parameters in the optimized structures are in good agreement with those determined by X-ray diffraction for the experimentally observed isomers (see comparison in the SI, Part 2). The most stable structure corresponds to the SM form for each metal, in agreement with observed geometry for the crystal structure of 6. This is true whether the comparison is made at the E of G level in the gas phase (Egas, Ggas) or in dichloromethane solution (Esol, Gsol), with the exception of compound 10 where the RIr structure is slightly more stable, but only at the Esol level. The form without hydrogen bond has the highest energy. Thus, the calculations suggest that the intramolecular hydrogen bond between a chlorine atom and the pendant sulfonamide hydrogen atom stabilizes the structure. The complex with the highest energy difference between the open and closed forms is 6 (7.7 and 5.1 kcal/mol at the Esol and Gsol levels, respectively), whereas this difference is of the order of 1-2 kcal/mol for compounds 8 and 10. This indicates that compound 6 forms a stronger H bond, in line with the X-ray structural results (Table 2). The two H-bonded isomers have very similar energy in the solvated model, the maximum difference being observed for 6 (3.9 and 2.0 kcal/mol at the Esol and Gsol levels, respectively). This difference appears large enough to provide only one observable isomer for 6 in NMR spectrum of 183 K, whereas the smaller energy differences for the isomers of (a) The symbol S or R in parentheses indicates the absolute configuration at the metal center, given that the absolute configuration used in the calculation for of the planar chiral ferrocene is S.

Coordination of ligand 5a.

Since the theoretical calculations do not support the explanation of the observed dynamic behavior for compounds 6, 8 and 10 as a result of H bond forming and breaking (Scheme 3) and in order to throw further light on this phenomenon, we have synthesized a new ligand, 5a, bearing one methyl group on the nitrogen atom (Scheme 1). This ligand cannot establish N-H•••Cl interactions. Addition of 5a to a dichloromethane solution of [Cp*RhCl2]2 afforded complex 8a in good yields (Scheme 2). This compound has been characterized by multinuclear NMR and mass spectrometries and by X-ray crystallography. It displays a structure roughly similar to those of 8 and 10, with the phosphorus atom coordinated to the metal and a dangling amine function, resulting again in a "three-legged piano stool" geometry. Selected geometric parameters for compound 8a are collected in Table 3. The main difference is that the ferrocene Cp rings in the structure of 8a form a dihedral angle midway between the eclipsed and staggered conformations. The room temperature 31 P{ 1 H} NMR spectrum of 8a shows a sharp doublet at δ 23.1 (JRh-P = 146 Hz) (Figure 3). However, decreasing the temperature leads to broadening and decoalescence in a qualitatively similar fashion and a similar temperature as compound 8. Two large signals are observed around δ 20 and 26 at 253 K. At 213K, the higher field signal becomes a relatively sharp doublet (JRh-P = 143 Hz), whereas the lower field signal disappears in the noise. From this spectrum, it seems that a third minor component may also be present near the high field doublet, as seen for the analogous compound 8, although the quality of the spectrum does not allow an unambiguous conclusion. Therefore, a fluxional behavior also exists for compound 8a. As no hydrogen bond is possible here, we are drawn to conclude that the structures observed at the slow exchange limit are not related to the establishment of H bonding at all, but probably result from different conformers related to each other by restricted rotation around the M-P and/or the P-C(Cp) bond. This hypothesis seems consistent with the minor effect of the H/Me substitution in the qualitative behavior of the NMR spectra of compounds 8 and 8a. Of course, it is not excluded that the H-bond seen for 6, 8 and 10 in the solid state is maintained in solution and contributes to the stabilization of the observed conformers.

Hydrogenation Catalysis.

As half sandwich complexes of ruthenium, rhodium or iridium bearing P,N ligands have shown efficiency in transfer hydrogenation and asymmetric transfer hydrogenation, we were prompted to investigate the activity of our compounds. Enantiomerically pure complexes 6, 8, 10 were synthesized as described above (Scheme 2) by coordination of the enantiomerically pure ligand 5 (R), which was accessed according to Scheme 1 from the optically pure alcohol 3. Acetophenone was the chosen model for our hydrogenation studies, the catalysis being carried out under standard conditions (Scheme 4). In basic media, one could expect the deprotonation of the acidic proton on the sulfonamide inducing the conversion of 6, 8 and 10 to 7, 9 and 11 respectively. Following initial exploratory experiments, carried out with complex 6 at 50°C under ATH conditions (no H2 pressure), which reached only 10% conversion after 4 days, subsequent experiments were carried out either in the presence of hydrogen or at a higher temperature (82°C) (the results are collected in Table 6). Under 30 bars of H2, significant conversion took place after 6 hours even at 50°C. The best conversion was observed with the ruthenium complex 6, although without any significant ee. Complexes 8 and 10, on the other hand, gave lower conversions and better albeit still rather low ee. The experiments carried out at 82°C under transfer hydrogenation conditions gave almost full conversions after 5 hours with either KOH or NaOH when using complex 6, once again without notable enantioselectivity. A kinetic study yielded a first order decay for the substrate (k = 0.650 min -1 ) with 96% conversion after 5 hours (Figure 5).

Scheme 4.

Catalytic hydrogenation of acetophenone. and first order plot (right).

Conclusions

We have reported herein the synthesis and coordination study of the new chiral ferrocenyl aminophosphines 5 and 5a. A series of half sandwich ruthenium (6), rhodium (8, 8a) and iridium (10) complexes bearing a monocoordinated neutral P,N ligand have been synthesized and fully characterized.

The variable temperature NMR studies show dynamic behavior that, because of the very similar behavior of 8 and 8a, cannot be attributed to the establishment of H bonds (N-H•••Cl) that are visible in the solid state. The DFT study, while confirming the possible existence of isomeric complexes that differ by the presence and location of the H bond, indicates that these isomers should interconvert too rapidly to be individually detected on the NMR timescale. By default, the phenomenon is attributed to restricted rotations around sterically crowded bonds. Deprotonation of complexes 6, 8 and 10 at the sulfonamide function gives rise to the new complexes 7, 9 and 11, where the P-amido ligand is bonded to the metal as a bidentate anionic ligand.

Complexes 6, 8 and 10 show moderate catalytic activity for the hydrogenation or transfer hydrogenation of acetophenone by H2 or iPrOH at 50°C. At higher temperature, complex 6 shows good catalytic activity in transfer hydrogenation. In both cases, the enationselectivity is poor. Although poor in terms of catalytic performance, these compounds may prove useful for mechanistic studies that are currently in progress. Coordination chemistry studies of these ligands on other catalytic platforms are also planned for the near future.

Experimental Section

General Considerations. All reactions were carried out using conventional Schlenk techniques under an inert atmosphere of argon. Thin layer chromatography and flash chromatography were carried out on Merck Kieselgel 60F254 precoated aluminum plates and Merck Kieselgel 60 respectively. Solvents were dried by conventional methods before use. Tetrafluoroboric acid diethylether complex (Sigma-Aldrich), p-toluenesulfonamide (Sigma-Aldrich) and tris(dimethylamino) phosphine (Alfa Aesar) were used as received without further purification. Racemic 2-thiodiphenylphosphino(hydroxymethyl)ferrocene, 1, was synthesized according to published procedure. [19] GC analyses were realized with an Agilent 5890 chromatograph equipped with FID detector and BETA DEX 225 chiral capillary column (30m/0.25mm/0.25μm). NMR analyses were performed on Bruker AV500 instruments. The spectra were referenced internally using the signal from the residual solvent for 1 H and 13 C, and externally using 85% H3PO4 for 31 P. Chemical shifts and coupling constants are given in ppm and Hertz respectively.

The following abbreviations are used: s: singlet; d: doublet; t: triplet; quint: quintuplet; m: multiplet; br: broad. Mass spectral analyses (GCT 1er Waters for DCI, CH4; UPLC Xevo G2 Q TOF (Waters) for ES + ) were performed by ''Service commun de spectrométrie de masse'' of the Université Paul-Sabatier, Toulouse (France).

Synthesis and caraterization of compound 4.

In a Schlenk tube, 3 (250 mg, 0.58 mmol) was dissolved in 5 mL of dry dichloromethane. A solution of tetrafluoroboric acid in ether (250 μL, 1.84 mmol) was then added. After 1 min of stirring, a solution of 1.98 g of p-toluenesulfonamide (12 mmol) in 14 mL of dry dichloromethane was added. After 1 min of stirring, the crude product was separated by chromatography on silica gel with pentane/ether (7/3 v/v) as eluent. After evaporation of the solvent, 260 mg of 4 were obtained (yellow solid, yield = 98%). 1 H{ 31

Catalysis experiments.

For the kinetic study: the catalyst (0.005 mmol) and acetophenone (0.5 mmol) were dissolved in distilled iPrOH (4.75 mL). After adding a 0.1 M NaOH solution in iPrOH (0.25 mL, 0.025 mmol), the mixture was stirred at 82°C. At various times, aliquots were withdrawn from the sample and passed through a short silica gel column before being analyzed by GC on a chiral column. For the transfer hydrogenation studies: the catalyst (0.005 mmol) and acetophenone (0.5 mmol) were dissolved in distilled iPrOH (1.25 mL). After introducing a 0.1 M base (NaOH or KOH) solution in iPrOH (0.25 mL, 0.025 mmol), the mixture was stirred at 82°C. After 5 hours, the mixture was passed through a short silica gel column before being analyzed by GC on a chiral column. For the hydrogenation studies: the catalyst (0.005 mmol) and acetophenone (0.5 mmol) were dissolved in distilled iPrOH (1.25 mL) in an autoclave. After addition of a 0.1 M NaOH solution in iPrOH (0.25mL, 0.025 mmol), the autoclave was pressurized by H2 (30 bar). The mixture was then stirred at 50°C. After 6 hours, the autoclave was cooled and vented and the recovered mixture was passed through a short silica gel column before being analyzed by GC on a chiral column.

X-ray structural analyses.

A single crystal of each compound was mounted under inert perfluoropolyether at the tip of a glass fiber and cooled in the cryostream of either an Oxford-Diffraction XCALIBUR CCD diffractometer for 4 and 6, or an Agilent Technologies GEMINI EOS diffractometer for 8, 8a, 10 and 11. The structures were solved by direct methods (SIR97) 36 and refined by least-squares procedures on F 2 using SHELXL-97. 37 All H atoms attached to carbon atoms were introduced in the calculation at idealised positions and treated as riding models. In compound 8a, owing to the poor quality of the data, some residual electron density was difficult to model. Therefore, the SQUEEZE function of PLATON 38 was used to eliminate the contribution of the electron density in the solvent region from the intensity data, and the solvent-free model was employed for the final refinement. There are two large cavities of 769 Å 3 per unit cell. PLATON estimated that each cavity contains about 138 electrons which may correspond to a mixture of dichloromethane and diethyl ether in the ratio one to two. Both solvents were used to crystallize the compound. The drawing of the molecules was realised with the help of ORTEP32 39 or PLATON. 38 Crystal data and refinement parameters are available in the Supporting Information (Part 6).

Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-6893066 ( 4), CCDC-6893067 ( 6), CCDC-6893068 ( 8), CCDC-6893069 (8a), CCDC-6893070 (10), and CCDC-6893071 (11). Copies of the data can be obtained free of charge on application to CCDC, 12

Union Road, Cambridge CB2 IEZ, UK [Fax: int. Code +44(1223)336-033; E-mail: deposit@ccdc.cam.ac.uk].

Computational details. All calculations were carried out at the DFT level by means of the dispersion-corrected functional M06 as implemented in the Gaussian09 program package. [START_REF] Frisch | Revision A.01[END_REF] Ir, Fe, Rh and Ru atoms were described using the LANL2DZ effective core potential [START_REF] Hay | [END_REF]42 for the inner electrons and its associated double-ζ basis set for the outer ones. Additionally, f-polarization shells (exponents = 0.938, 2.462, 1.350, 1.235, respectively) 43 were also added for these metal atoms. For C, O, S, P, H and the Cl and N atoms the 6-31G (d,p) and the 6-31+G(d) basis sets were used, respectively. Geometries of all the metal complexes were fully optimized without any symmetry constraint. Harmonic force constants were computed at the optimized geometries confirming the nature of these stationary points as minima. Solvent effects (CH2Cl2, ε = 8.930) were introduced through single point calculations at optimized gas-phase geometries by means of a continuum method, the SMD solvation model 44 implemented in Gaussian09. The relative Gibbs energies in dichloromethane (ΔGsol) were obtained by employing the following scheme: ΔGsol = ΔEsol + (ΔGgas -ΔEgas)

The energies presented in this work are given in kcal/mol.

Figure 1 .

 1 Figure 1. Molecular view of compound 4 with the atom labeling scheme. Ellipsoids are drawn at the

2. Coordination of ligand 5 .Scheme 2 .

 52 Scheme 2. Synthesis of complexes 6, 7, 8, 8a, 9, 10, 11

Figure 2 .

 2 Figure 2. ORTEP views of compounds 6, 8, 8a and 10 with the atom labeling scheme. Ellipsoids are

Figure 3 .

 3 Figure 3. 31 P{ 1 H} NMR variable temperature analysis of compounds 6 (extreme left), 8 (middle left),

(

  JRh-P = 141 Hz) as the major component, plus two higher field sharp doublets at δ 20.6 (JRh-P = 144 Hz, intermediate intensity) and20.4 (JRh-P = 144 Hz, minor intensity). Complex 10 exibits a similar behavior, a broad signal (major) being observed around δ -1.8 plus two higher field sharper singlets at δ -9.0 (minor) and -10.1 (intermediate). These observations would appear consistent with the equilibration hypothesis formulated for compound 6 in Scheme 3. Even though compounds 8 and 10 reveal an intermolecular H bonding in the solid state, their structure in solution could involve, like that observed for 6 in the solid state, an intramolecular H bond. Further investigations of this issue by DFT calculations will be shown later in section 4.3. P,amido complexes synthesis.Addition of five equivalents of triethylamine to dichloromethane solutions of complexes 6, 8 and 10 yielded the P,amido complexes 7, 9 and 11, respectively, where the anionic nature of the amido ligand favors the ligand coordination in a κ 2 :P,N fashion with the concomitant replacement of a chlorido ligand (Scheme 2). All of these complexes have been fully characterized by multinuclear NMR and mass spectrometries. Unlike their precursors 6, 8 and 10, these complexes present sharp signals in the 1 H and 31 P{ 1 H} NMR spectra. The latter exhibits two signals with similar intensities: two singlets at δ18.3 and 26.6 for the ruthenium complex 7, two doublets at δ 19.6 (JRhP = 147 Hz) and 30.9 (JRhP = 142 Hz) for the rhodium complex 9, and two singlets at δ -0.9 and -10.1 for the iridium complex 11. The simultaneous P and N coordination creates a non labile chiral center at the metal atom, giving rise to two possible diastereoisomers (SL,SM and RL,RM) and (SL,RM and RL,SM).

Figure 4 .

 4 Figure 4. ORTEP view of compound 11 with the atom labeling scheme. Displacement ellipsoids are

compounds 8

 8 and 10 would seem consistent with the observation of three resonances at low temperature for these compounds. On the other hand, the small energy difference associated with breaking and forming the H bond should in principle insure a very rapid equilibration on the NMR timescale for all compounds, leading to the expectation of only one average resonance at all temperatures (an exchange rate of 2.47•10 3 s -1 is calculated for the Eyring equation for a barrier of 7.7 kcal/mol at 183 K). Hence, the computational investigation suggests that the forming and breaking of the H bond (Scheme 3) is unlikely to be the cause of the slow exchange phenomena observed by low-temperature NMR for compounds 6, 8 and 10.DFT calculations were also carried out on compound 11 in order to verify the relative energy between the two possible diastereoisomeric forms. The optimized geometries are shown in the SI (Part 3). The geometry of the experimentally observed RL,RIr/SL,SIr diastereoisomer is in close agreement with that determined by X-ray diffraction (comparison available in the SI, Part 4). According to the theoretical calculations, the crystallographically characterized RL,RIr/SL,SIr diastereoisomer is 11.7 kcal/mol more stable at the Egas level than the RL,SIr/SL,RIr diastereoisomer. Inspection of the two optimized geometries, however, does not reveal any obvious reason for the lower stability of the RL,SIr/SL,RIr diastereoisomer.

Figure 5 .

 5 Figure 5. Kinetics investigation of the reaction of acetophenone (0.5 mmol) in 5 mL iPrOH with 1% of

Table 1 .

 1 Selected bond distances (Å) and bond angles (°) for compound 4.

	Distances
	Fe-Ct1	1.6406(7)
	Fe-Ct2	1.6521(9)
	P1-C1	1.7943(15)
	P1-S1	1.9532(5)
	C2-C21	1.497(2)
	C21-N1	1.466(2)
	N1-S2	1.6255(13)
	S1-O1	1.4327(12)
	S1-O2	1.4276(12)
	Angles
	*Ct1-Fe-Ct2	177.55(7)
	C21-N1-S2	115.78(10)
	C21-N1-H1A	112.51(14)
	S2-N1-H1A	109.78(11)

*Ct1 and Ct2 are the centroids of the Cp rings

Table 2 .

 2 Hydrogen bond parameters for compounds 4, 6, 8 and 10.

Table 3 .

 3 Selected geometric parameters (distances in Å, angles in °) for compounds 6

, 8, 8a and 10. 6 8 8a 10

	Cl1-M1-Cl2	87.46(2)	91.96(3)	92.91(8)	89.28(4)
	Cl1-M1-P1	91.89(2)	93.19(3)	92.19(8)	93.41(4)
	Cl2-M1-P1	88.09(2)	86.51(3)	87.25(7)	86.87(4)
	C21-N1-S1	123.63(15)	119.92(24)	118.8(6)	119.9(3)
	C21-N1-R1	120.21(20)	118.60(29)	114.9(7)	120.3(4)
	S1-N1-R1	115.59(17)	110.20(24)	117.3(7)	110.9(3)
	C2-C21-N1-S1 -130.35(17)	-135.21(27)	-128.
	Distances
	Fe-Ct1	1.6502(9)	1.644(2)	1.649(4)	1.643(2)
	Fe-Ct2	1.6555(12)	1.657(2)	1.653(4)	1.663(2)
	M1-P1	2.3644(5)	2.3656(8)	2.355(2)	2.3375(11)
	M1-Ct3	1.6973(8)	1.8295(4)	1.827(4)	1.833(2)
	M1-Cl1	2.4123(5)	2.4008(9)	2.388(2)	2.4059(12)
	M1-Cl2	2.4087(5)	2.4094(8)	2.394(2)	2.4114(11)
	P1-C1	1.8085(19)	1.818(3)	1.799(8)	1.808(4)
	C2-C21	1.496(3)	1.500(5)	1.515(11) 1.496(6)
	C21-N1	1.457(3)	1.464(4)	1.462(11) 1.468(6)
	N1-S1	1.5903(18)	1.614(3)	1.627(7)	1.615(4)
	S1-O1	1.4294(17)	1.429(3)	1.440(7)	1.428(4)
	S1-O2	1.4307(17)	1.427(3)	1.425(7)	1.429(4)
	P1•••Cp(plane)	0.447(3)	0.235(6)	0.266(12) -0.241(7)
	C21•••Cp(plane) -0.015(3)	-0.008(6)	-0.022(15) 0.017(8)
	N1•••Cp(plane) 1.349(4)	-0.595(7)	0.00(2)	0.595(8)
	M1•••Cp(plane) 2.731(3)	0.249(8)	0.212(18) -0.249(10)
	Angles
	Ct1-Fe-Ct2	174.32(5)	176.03(9)	176.9(2)	175.93(13)
	Ct3-M1-Cl1	123.90(3)	122.10(6)	119.07(14) 119.84(7)
	Ct3-M1-Cl2	124.98(3)	119.54(6)	121.74(16) 122.59(7)
	Ct3-M1-P1	128.50(3)	132.69(6)	133.14(16) 133.04(7)

Table 4 )

 4 are in the normal range when compared to the related compounds. The structure presented corresponds to the SL,SIr diastereoisomer but as the space group is centrosymmetric the RL,RIr enantiomer is also present within the crystal. The solid state 31 P{ 1 H} NMR spectrum of the crystals gave only one signal at δ -7.7 and redissolution of the crystallized sample in CDCl3 give back only the signal at δ -10.1, confirming the selective crystallization of the RL,RIr/SL,SIr diastereoisomer. Consequently, the other 31 P{ 1 H} NMR signal observed at δ -0.9 can be attributed to the RL,SIr/SL,RIr diastereoisomer. Moreover, no conversion of RL,RIr/SL,SIr to RL,SIr/SL,RIr was observed in solution by NMR in 4 hours at room temperature,

Table 4 .

 4 Selected

	Distances
	Fe-Ct1	1.645(2)	P1-C1	1.807(4)

geometric parameters for compound 11. Bond distances (Å), bond angles (°), torsion angles (°).

Table 5 .

 5 Relative energies (in kcal/mol) computed for the different isomers of compounds 6 (Scheme 3), 8 and 10.

		Isomer a	Egas	Ggas	Esol	Gsol
		NH … Cl1(S) 0.0	0.0	0.0	0.0
	6	NH … Cl2(R) 4.9	3.0	3.9	2.0
		No H bond 7.9	5.2	7.7	5.1
		NH … Cl1(S) 0.0	0.0	0.0	0.0
	8	NH … Cl2(R) 0.8	3.0	0.4	2.5
		No H bond 1.6	1.4	2.0	1.7
		NH … Cl1(S) 0.0	0.0	0.0	0.0
	10 NH … Cl2(R) 0.1	0.9	-0.3	0.4
		No H bond 1.3	1.3	1.3	1.3
		RL,RIr/SL,SIr 0.0	0.0	0.0	0.0
	11 RL,SIr/SL,RIr 11.7	10.5	7.1	5.9

  .05 (JCP = 84.8 Hz, quat, PPh2), 132.74 (JCP = 84.8 Hz, quat, PPh2), 131.97 (JCP = 10.6 Hz, PPh2), 131.72 (JCP = 10.2 Hz, PPh2), 131.57 (JCP = 3.6 Hz, PPh2), 131.39 (JCP = 3.6 Hz, PPh2), 129.52 (SO2PhCH3), 128.53 (JCP = 11.9 Hz, PPh2), 128.16 (JCP = 11.9 Hz, PPh2), 127.08 (SO2PhCH3), 88.71 (JCP = 11.8 Hz, quat, subst Cp), 74.88 (JCP = 12.9 Hz, subst Cp), 74.67 (JCP = 12.9 Hz, subst Cp), 73.94 In a Schlenk tube, 260 mg of 4 (0.46 mmol) were dissolved in 9.16 mL of dry toluene together with 0.5 mL of tris(dimethylamino)phosphine(2.75 mmol). The solution was kept at reflux overnight under argon. After cooling back to room temperature, the solution was evaporated under reduced pressure. The crude residue was purified under argon by flash chromatography on silica gel with dichloromethane as eluent. After evaporation of the solvent, 236.76 mg of 5 were obtained (yellow solid, yield = 93%). 1 H{31 P} NMR (500 MHz, CDCl3) δ (ppm) : In a Schlenk tube, 200 mg of 3 (0.46 mmol) were dissolved in 4 mL of dry dichloromethane. A solution of tetrafluoroboric acid in ether (200 μL, 1.47 mmol) was then added. After 1 min of stirring, a solution of 1.7 g of N-methyl-p-toluenesulfonamide(9.26 mmol) in 10 mL of dry dichloromethane was added. After 1 min of stirring, the crude product was J = 7.9 Hz, SO2PhCH3), 7.24 (1H, t, J = 5.9 Hz, PPh2), 7.23 (2H, m, PPh2),7.18 (2H, m , (JCP = 38.2 Hz, quat, subst Cp), 76.10 (JCP = 14.3 Hz, subst Cp), 73.31 (JCP = 7.2 Hz, subst Cp), 71.03 (Cp), 70.22 (JCP = 8.3 Hz, subst Cp), 40.85 (CH2NH), 30.10 (CH/Cym), 22.23 (CHCH3/Cym), 21.55(SO2PhCH3), 21.17 (CHCH3/Cym), 17.18 (PhCH3/Cym). 31 P{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): 14.60. HR/MS (ES + ) m/e: 824.0756 (M-Cl, 70%) (calc. M-Cl: 824.0755).

	P} NMR (500 MHz, CDCl3) δ (ppm) : 7.81 (2H, m, PPh2), 7.65 (2H, m, SO2PhCH3), 7.58 (1H, m ,PPh2), 7.54 (2H, m, PPh2), 7.52 (2H, m, PPh2), 7.47 (1H, m, PPh2), 7.39 (2H, m, PPh2), 7.27 (2H, m, SO2PhCH3), 5.23 (1H, t, J = 6.7 Hz, subst (JCP = 83.9 Hz, quat, subst Cp), 70.75 (Cp), 69.28 (JCP = 10.4 Hz, subst Cp), 41.08 (CH2NH), 21.53 (SO2PhCH3). 31 P{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): 41.10. HR/MS (DCI, CH4) m/e: 585.0649 (M, 19%) (calc. M: 585.0648). Synthesis and caraterization of compound 5. 7.55 (2H, m, SO2PhCH3), 7.47 (2H, m, PPh2), 7.40 (2H, m, PPh2), 7.39 (1H, m ,PPh2), 7.31 (2H, m, PPh2), 7.31 (1H, m, PPh2), 7.25 (2H, m, SO2PhCH3), 7.11 (2H, m, PPh2), 4.43 (1H, dd, J = 4.3 Hz, 2.4 Hz, subst Cp), 4.27 (1H, t, J = 2.5 Hz, subst Cp), 4.22 (1H, t, J = 6.1 Hz, NH), 4.07 (5H, s, Cp), 4.00 (1H, dd, J = 13.2 Hz, 6.5 Hz, CH2NH), 3.98 (1H, dd, J = 13.3 Hz, 5.1 Hz, CH2NH), 3.71 (1H, dd, J = 2.3 Hz, 1.1 Hz, subst Cp), 2.44 (3H, s, SO2PhCH3). 13 C{ 1 H} NMR (500 MHz, CDCl3) δ (ppm) : 143.17 (quat, SO2PhCH3), 139.14 (JCP = 10.4 Hz, quat, PPh2), 136.77 (quat, SO2PhCH3), 136.31 (JCP = 8 Hz, quat, PPh2), 134.61 (JCP = 20.6 Hz, PPh2), 132.48 (JCP = 18.8 Hz, PPh2), 129.59 (SO2PhCH3), 129.30 (PPh2), 128.62 (PPh2), 128.57 (JCP = 6.3 Hz, PPh2), 128.29 (JCP = 8 Hz, PPh2), 127.03 (SO2PhCH3), 87.93 (JCP = 24.2 Hz, quat, subst Cp), 76.29 (JCP = 7.0 Hz, quat, subst Cp), 72.07 (JCP = 2.9 Hz, subst Cp), 71.62 (JCP = 2.9 Hz, subst Cp), 69.73 (Cp), 69.70 (subst Cp), 41.82 (CH2NH), 21.55 (SO2PhCH3). 31 P{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): -24.24. HR/MS (DCI, CH4) m/e: 554.1006 (M+1, 100%) (calc. M+1: 554.0927) Hz, subst Cp), 67.81 (JCP = 6.6 Hz, subst Cp), 45.16 (CH2N), 21.38 (SO2PhCH3), 8.68 (CCH3/Cp*). 31 P{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): -10.13 (s). Second diastereoisomer. 1 H{ 31 P} NMR (500 MHz, CDCl3) δ (ppm) : 8.37 (2H, m, PPh2), 7.78 (2H, m, SO2PhCH3), 7.73 (2H, m, PPh2), 7.69 (2H, m, PPh2), 7.61 (1H, m, PPh2), 7.36 (1H, m, PPh2), 7.33 (2H, m, PPh2), 7.23 (2H, m, SO2PhCH3), 4.61 (1H, Synthesis and caraterization of compound 4a. separated by chromatography on silica gel with pentane/ether (7/3 v/v) as eluent. After evaporation of the solvent, 275.8 mg of 4a were obtained (yellow solid, yield = 100%). 1 H{ 31 P} NMR (500 MHz, CDCl3) δ (ppm) : 7.84 (2H, m, PPh2), 7.62 (2H, m, PPh2), 7.61 (2H, m, SO2PhCH3), 7.55 (1H, m, PPh2), 7.50 (1H, m, PPh2), 7.45 (2H, m, PPh2), 7.37 (2H, m , PPh2), 7.30 (2H, m, SO2PhCH3), 4.95 (1H, m, subst Cp), 4.37 (1H, t, J = 2.4 Hz, subst Cp), 4.69 (1H, d, J = 15.5 Hz CH2N), 4.35 (5H, s, Cp), 4.29 (1H, d, J = 15.5 Hz, CH2N), 3.78 (1H, br, subst Cp), 2.44 (3H, s, SO2PhCH3). 2.38 (3H, s, NCH3). 13 C{ 1 H} NMR (500 MHz, CDCl3) δ (ppm) : 143.16 (quat, SO2PhCH3), 134.63 (JCP = 85.6 Hz, quat, PPh2), 133.14 (JCP = 85.6 Hz, quat, PPh2), 132.05 (JCP = 10.4 Hz, PPh2), 134.86 (quat, SO2PhCH3), 131.99 (JCP = 10.4 Hz, PPh2), 129.65 (SO2PhCH3), 131.41 (JCP = 3.0 Hz, PPh2), 131.33 (JCP = 3.0 Hz, PPh2), 128.32 (JCP = 11.9 Hz, PPh2), 128.08 (JCP = 11.9 Hz, PPh2), 127.38 (SO2PhCH3), 88.58 (JCP = 11.5 Hz, quat, subst Cp), 73.77 (JCP = 92.2 Hz, quat, subst Cp), 74.79 (JCP = 8.9 Hz, subst Cp), 74.49 (JCP = 12.1 Hz, subst Cp), 69.58 (JCP = 10.4 Hz, subst Cp), 71.07 (Cp), 48.71 (CH2N), 35.55 (NCH3), 21.50 (SO2PhCH3). 31 P{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): 41.07. HR/MS (ES + ) m/e: 599.0820 (M, 30%) (calc. M: 599.0805); 622.0718 (M+Na, 100%) (calc. M+Na: 622.0703). Synthesis and caraterization of compound 5a. In a Schlenk tube, 300 mg of 4a (0.50 mmol) were dissolved in 9.8 mL of dry toluene together with 0.46 mL of tris(dimethylamino)phosphine (2.51 mmol). The solution was kept at reflux overnight under argon. After cooling back to room temperature, the solution was evaporated in vacuo. The crude residue was purified under argon by flash chromatography on silica gel with dichloromethane as eluent. After evaporation of the solvent, 283.8 mg of 5a were obtained (yellow solid, yield = 100%). 1 H{ 31 P} NMR (500 MHz, CDCl3) δ (ppm) : 7.64 (2H, d, J = 8.0 Hz, SO2PhCH3), 7.58 (2H, m, PPh2), 7.41 (2H, m, PPh2), 7.40 (1H, t, J = 4.9 Hz ,PPh2), mg, 0.018 mmol) was dissolved in dry dichloromethane (2 mL) and then triethylamine (12.54 µl, 0.09 mmol) was added. The reaction was carried under at 40°C for 1.5 hour. The solvent was evaporated and the resulting red solid was washed by dry pentane. After evaporation of the solvent, 11.87 mg of 7 were obtained (yield = 80%). First diastereoisomer 1 H{ 31 P} NMR (500 MHz, CDCl3) δ (ppm) : 8.50-7.20 (10H, m, PPh2), 7.81 (2H, m, SO2PhCH3), 7.31 (2H, m, SO2PhCH3), 5.79 (1H, m, Ph/Cym), 5.21 (1H, d, J = 15.3 Hz, CH2N), 5.15 (1H, m, Ph/Cym), 4.89 (1H, m, Ph/Cym), 4.74 (1H, m, Ph/Cym), 4.39 (1H, Hz, CH(CH3)2), 1.24 (3H, d, J = 6.2 Hz, CH(CH3)2), 0.56 (3H, s, PhCH3/Cym). 13 C{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): 143.09 (quat, SO2PhCH3), 140.59 (quat, SO2PhCH3), 138.80 (JCP = 49.1 Hz, quat, PPh2), 132.52 (JCP = 8 Hz, PPh2), 131.07 (PPh2), 129.60 (PPh2), 129.49 (JCP = 13.2 Hz, PPh2), 129.49 (SO2PhCH3), 128.07 (JCP = 10.4 Hz, PPh2), 127.3 (JCP = 8.9 Hz, PPh2), 126.55 (SO2PhCH3), 124.88 (quat, Ph/Cym), 98.94 (JCP = 13.6 Hz, quat, subst Cp), 98.53 (Ph/Cym), 92.78 (quat, Ph/Cym), 85.45 (Ph/Cym), 83.18 (Ph/Cym), 75.11 (Ph/Cym), 70.54(Cp), 70.1 (JCP = 49.2 Hz, subst Cp), 69.09 (JCP = 7.7 Hz, subst Cp), 68.13 (subst Cp), 44.81 (CH2N), 31.13 (CH/Cym), 23.70 (CHCH3/Cym), 21.68 (SO2PhCH3), 12.61 (PhCH3/Cym). 31 P{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): 18.31. Second diastereoisomer 1 H{ 31 P} NMR (500 MHz, CDCl3) δ (ppm) : 8.50-7.20 (10H, m, PPh2), 7.89 (2H, m, SO2PhCH3), 7.31 (2H, m, SO2PhCH3), 5.57 (1H, m, Ph/Cym), 5.24 (1H, m, Ph/Cym), 4.59 (1H, m, d, J=15.2 Hz, CH2N), 4.17 (1H, br, subst Cp), 4.09 (1H, t, J = 2.2 Hz, subst Cp), 3.92 (1H, br, subst Cp), 3.88 (1H, d, J = 15.0 Hz, CH2N), 3.58 (5H, s, Cp), 2.40 (3H, s, SO2PhCH3), 1.21 (15H, s, Cp*). 13 C{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): 143.90 (quat, SO2PhCH3), 140.36 (quat, SO2PhCH3), 136.40 (JCP = 13.0 Hz, PPh2), 133.98 (JCP = 8.0 Hz, PPh2), 133.12 (JCP = 57.5 Hz, quat, PPh2), 132.51 (JCP = 59.6 Hz, quat, PPh2), 131.41 (PPh2), 130.10 (PPh2), 129.14 (SO2PhCH3), 128.13 (JCP = 11.3 Hz, PPh2), 126.72 (JCP = 9.6 Hz, PPh2), 126.55 (SO2PhCH3), 95.07 (JCP = 12.5 Hz, quat, subst Cp), 93.98 (JCP = 2.8 Hz, quat, CCH3/Cp*), 75.52 (JCP = 60 Hz, quat, subst Cp), 70.77 (subst Cp), 70.39(Cp), 67.62 (JCP = 7.6 Hz, subst Cp), 65.88 (JCP = 8.2 Hz, subst Cp), 46.98 (CH2N), 21.38 (SO2PhCH3), 8.92 7.30 (2H, d, Synthesis and caraterization of compound 7. In a Schlenk tube under argon, compound 6 (15.47 (CCH3/Cp*).

Cp),

4.61 (1H, br, subst Cp), 4.33 (1H, s, NH), 4.30 (5H, s, Cp)

,

3.89 (1H, dd, J = 14.1 Hz, 6.7 Hz, CH2NH), 3.86 (1H, dd, J = 14.1 Hz, 6.7 Hz, CH2NH), 3.77 (1H, br, subst Cp), 2.44 (3H, s, SO2PhCH3)

. 135br, subst Cp), 4.10 (1H, br, subst Cp), 4.09 (1H, d, J = 17.8 Hz, CH2N), 3.99 (1H, br, subst Cp), 3.67 (5H, s, Cp), 2.95 (1H, heptuplet, J = 7.2 Hz, CH(CH3)2), 2.45 (3H, s, SO2PhCH3), 1.27 (3H, d, J = 6.2 Ph/Cym), 4.44 (1H, d, J = 23 Hz, CH2N), 4.36 (1H, d, J = 38.8 Hz, CH2N), 4.22 (1H, m, Ph/Cym), 4.16 (1H, t, J = 2.5 Hz, subst Cp), 4.10 (1H, br, subst Cp), 4.04 (1H, br, subst Cp), 3.53 (5H, s, Cp), 2.63 (1H, heptuplet, J = 7.4 Hz, CH(CH3)2), 2.45 (3H, s, SO2PhCH3), 1.91 (3H, s, PhCH3/Cym), 0.98 (3H, d, 31 P{ 1 H} NMR (500 MHz, CDCl3) δ (ppm): -0.89 (s). HR/MS (DCI, CH4): 880.1653 (M-Cl, 33%) (calc. M-Cl: 880.1652).

  Figures of optimized structures, tables of X-ray data, tables of selected bond distances and angles, Figures of NMR and HR mass spectra for all new compounds, table of Cartesian coordinates for all optimized structures(35 pages). This material is available free of charge via the Internet at http://pubs.acs.org.

ASSOCIATED CONTENT

Supporting Information.

Centre National de la Recherche Scientifique (CNRS) and Institut Universitaire de France (IUF).

ACKNOWLEDGMENT

We gratefully acknowledge financial support from the Centre National de la Recherche Scientifique (CNRS), from the Institut Universitaire de France and the funding of Laboratoire Européen Associé « Laboratoire Trans-Pyrénéen: de la Molécule aux Matériaux » for the DFT calculation at Universitat Autònoma de Barcelona.

AUTHOR INFORMATION

Corresponding Author E-mail addresses: eric.deydier@iut-tlse3.fr, eric.manoury@lcc-toulouse.fr.

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Funding Sources


Ekaterina M Kozinets

Oleksandr Koniev

Oleg A Filippov

Jean-Claude Daran

Rinaldo Poli

Elena V Shubina

Natalia V Belkova

Eric Manoury

Elena S Shubina

Sr = Cpfe

Coordination chemistry of diphenylphosphinoferrocenylthioethers on cyclooctadiene and norbornadiene rhodium(i) platforms

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Since the development by Noyori and coworkers of efficient catalytic systems for the asymmetric hydrogenation of non functionalized ketones [1][2][3] , much effort has been devoted to the asymmetric hydrogenation of polar substrates, 4 ketones 5 but also imines [START_REF] Tang | Chemical Reviews[END_REF][START_REF] Nugent | [END_REF][8][9] or heteroarenes, 10 because of their great scientific and practical importance, which includes industrial applications. 11,12 Most of the catalysts used so far are based on ruthenium, rhodium and iridium with phosphorus and nitrogen-containing ligands.

Our group has worked extensively on the chiral ligand platform built around the planar chirality of ferrocene, mostly with asymmetric 1,2 substitution, but also 1,2,3 trisubstitution and 1,2,3,1' tetrasubstitution. [13][14][15][16][17] Our interest in recent years has focused on chiral ligands based on P and S donor atoms with the development of the 1,2-substituted ferrocenes (P,SR) shown in Scheme 1. [18][19][20][START_REF] Malacea | Phosphorus Ligands in Asymmetric Catalysis[END_REF][START_REF] Lam | [END_REF] The use of these ligands (particularly for R = Et, Ph, Bz and tBu) has led to a number of catalytic applications in asymmetric allylic substitution 23,24 asymmetric methoxycarbonylation 25 and asymmetric hydrogenation. 26 Although other kinds of ligands based on P and S donor atoms have already been used in C=C hydrogenations, [27][28][29][30] we reported the first application of these types of ligands, to the best of our knowledge, to the hydrogenation of ketones, promising results being obtained in the ionic hydrogenation of various acetophenones. 26 In combination with [IrCl(COD)]2 (COD = 1,5-cyclooctadiene), these ligands have yielded the corresponding IrCl(COD)(P,SR) adducts, of which those with R = Et, Ph and Bz adopt a 5-coordinate square pyramidal geometry (axial Cl) in the solid state and in solution, whereas the tBu derivative is square planar with a dangling thioether function. 31 These iridium complexes were shown to be excellent precatalysts for the hydrogenation of aromatic ketones in the presence of a strong base such as NaOMe in methanol and other alcohols, leading to quantitative hydrogenations in less than two hours at room temperatures under 30 bar of H2 and with only 0.05% of catalyst loading and with enantiomeric excesses that reached >99% (at 0°C) for selected substrates. 26 55 Scheme 1. General structure of the (P,SR) ligands used in this study. Specific stoichiometric investigations of the precatalyst hydrogenation in methanol, yielding partial hydrogenation of the cyclooctadiene to cyclooctene (experimentally observed by GC-MS) and presumably leading at least initially to 60 Ir(P,SR)(OMe)(MeOH), have not so far allowed the isolation or spectroscopic observation of a catalytically active species. It is known from elegant work by Heller et al. that the hydrogenation of diene ligands in complexes such as [M(diene)(L2)] + (L2 being typically a diphosphine ligand a M = Rh) in methanol yields 65 [M(L2)(MeOH)2] + adducts and that such derivatives are less easily generated and less stable when M = Ir. [32][33][34][35] With the goal of generating more stable model complexes of the above mentioned iridium catalysts, we have therefore turned out attention to analogous Rh complexes. We report in this contribution the 70 synthesis and characterization of a variety of adducts of the (P,SR) ligands in Scheme 1 with [RhCl(COD)]2 and [RhCl(NBD)]2 (NBD = norbornadiene). This includes an IR study and a DFT investigation to elucidate the structure of the compound in the solid state and in solution. Related cationic 75 complexes [Rh(COD)(P,SR)] + and [Rh(NBD)(P,SR)] + have also been isolated and structurally characterized. We also report preliminary investigations of acetophenone hydrogenation using these rhodium complexes as precatalysts. It will be shown that, albeit the catalytic activity is lower, these complexes are good 80 structural and functional models of the corresponding Ir precatalysts.

Experimental Section

2|

General. All reactions were carried out under an argon atmosphere using standard Schlenk techniques. Solvents were carefully dried by conventional methods and distilled under argon before use. The (R/S)-2-diphenylphosphanyl-(R-thiomethyl)ferrocene ligands (R = Et, tBu, Ph, Bz) were prepared according to a published procedure from racemic 2-(diphenylthiophosphanylferrocenyl)methanol. 36 Compounds [RhCl(COD)]2, [RhCl(NBD)]2 and [Rh(COD)2]BF4 were purchased from Strem Chemicals and used as received. 1 H, 13 C{ 1 H} and 31 P{ 1 H} NMR spectra were recorded with a Bruker Avance 500 FT-NMR spectrometer. The resonances were calibrated relative to the residual solvent peaks and are reported with positive values downfield from TMS. For all characterized compounds, the peak assignments in the 1 H and 13 C NMR spectra were based on COSY, HSQC and HMBC 2D experiments. HRMS were obtained from dichloromethane solutions with a Xevo G2 Q TOF spectrometer by the electrospray method. IR spectra were recorded at room temperature with a Nicolet 6700 spectrometer in the solid state (as nujol mulls) using polyethylene cells for the low frequency region. The optical purity and the conversions for 20 the hydrogenation experiments were determined by chiral GC (Supelco BETA DEX TM 225).

General procedure for the synthesis of RhCl(NBD)(P,SR), 1. In a Schlenk tube, under nitrogen, ligand (P,SR) (0.793 mmol) was dissolved in dichloromethane (5 mL) and [RhCl(NBD)]2 (183 mg, 0.396 mmol) was added. The solution was stirred for 4 h at room temperature and 15 mL of pentane was then added to yield a yellow precipitate. The precipitate was filtered under argon and washed with pentane to give RhCl(NBD)(P,SR).

RhCl(NBD)(P,StBu) (1 tBu , yield: 97%). Essential spectroscopic parameters for the other compounds: R = Ph: δ 28.0 (d, JP-Rh = 166 Hz). R = Bz: δ 31.1 (d, JP-Rh = 170 Hz). R = Et: δ22.8 (d, JP-Rh = 144 Hz).

General procedure for the synthesis of [Rh(COD)(P,SR)]BF4, 4. In a Schlenk tube, under nitrogen, ligand (P,SR) (0.305 mmol) was dissolved in dichloromethane (5 mL) and [Rh(COD)2]BF4 (124 mg, 0.305 mmol) was added. The solution was stirred for 30 min at room temperature and 15 mL of pentane was then added to yield a yellow precipitate. The precipitate was filtered under argon and washed with pentane to 15.0 (CH3). 31 P{ 1 H} NMR (500 202MHz, CDCl3): δ 22.9 (d, JP-Rh = 144 Hz). MS (ESI) m/e: 655,081 (M-BF4 -, 100 %).

X-ray crystallography. A single crystal of each compound was mounted under inert perfluoropolyether on the tip of a cryoloop and cooled in the cryostream of either an Oxford-20 Diffraction XCALIBUR SAPPHIRE-I CCD diffractometer or an Agilent Technologies GEMINI EOS CCD diffractometer. Data were collected using the monochromatic MoK radiation (= 0.71073). The structures were solved by direct methods (SIR97) 37 and refined by least-squares procedures on F 2 using 25 SHELXL-97. 38 All H atoms attached to carbon were introduced in idealised positions and treated as riding on their parent atoms in the calculations. The drawing of the molecules was realised with the help of ORTEP3. [START_REF] Burnett | ORTEPIII[END_REF][START_REF] Farrugia | [END_REF] polarization functions (SDD(f)) 48 were applied for the Rh, Ir and Fe atoms. Geometry optimizations were performed for the neutral NBD and COD complexes 1 and 3 with R = Ph and tBu without any ligand simplification. Calculations were also carried out on the isolated cation of 2 Ph and on the iridium analogue

IrCl(COD)(P,StBu).

No scaling factors were applied to the calculated low-frequency vibrations. Since the inclusion of anharmonicity effects in the case of 3 tBu did not lead to any significant change in the Rh-Cl frequency values (see Supporting Information, Table S1), this method was not applied to the other calculations.

General procedure of asymmetric hydrogenation Solution of 6.4*10 -3 mmol of catalyst, 3.2*10 -2 mmol of CH3ONa (5 equivs.) and 3.2 mmol of acetophenone (500 equivs.) in 2 ml of isopropanol was transferred into a 5-ml glass vial which was then placed under argon into a stainless steel autoclave. The reaction vessel was pressurized to the 30 bar of H2 pressure and stirred with magnetic bar for 1 hour at room temperature. The reaction was stopped by release of pressure. The crude materials were obtained by purification reaction mixture by chromatography on silica using dichloromethane as an eluent. The product was finally analyzed by chiral GC.

Results and Discussion. (a) Syntheses

The addition of the (P,SR) ligand (1 equiv per Rh atom) to a dichloromethane solution of [RhCl(NBD)]2 or [RhCl(COD)]2 yielded the corresponding adducts RhCl(NBD)(P,SR), 1 R , and RhCl(COD)(P,SR), 3 R , see Scheme 2. For the NBD reagent, the complete series with R = tBu, Ph, Bz and Et was obtained as pure derivatives as shown by the NMR and HRMS analyses.

Concerning the COD series, although all compounds could be obtained in solution as shown by the spectroscopic analyses, only the tBu derivative 3 tBu could be isolated as a pure product. Starting from 1 tBu , addition of NaBF4 in dichloromethane led to the precipitation of NaCl and formation of [Rh(NBD)(P,StBu)]BF4, 2 tBu , in sufficient purity. The complete series of the BF4 salts containing the COD ligand, [Rh(COD)(P,SR)]BF4, 4 R , on the other hand, was more conveniently obtained by addition of (P,SR) to a solution of compound [Rh(COD)2]BF4. All these were isolated in a pure state.

(b) Characterization of the [Rh(diene)(P,SR)] + salts 2 and 4

We begin the characterization section with the salts 2 and 4, for which the analysis is more straightforward. The NMR spectra show standard 1 H, 13 C and 31 P chemical shifts and coupling patterns for the expected square planar coordination around the Rh I center. In particular, Rh coupling is visible for selected 13 C resonances of the diene ligand and for the phosphine 31 P resonance (the latter is collected in The molecular geometry of compounds 2 tBu , 4 Ph and 4 Bz was confirmed by single crystal X-ray diffraction. Whereas compound 2 tBu contains only the cation and the anion in the crystal, compounds 4 Ph and 4 Bz crystallize with one molecule of dichloromethane per ion pair. Views of the three cations are 60 shown in Figure 1 and relevant bond distances and angles for the three compounds are compared in Table 3. The geometry is typical of [Rh(diene)(L 1 L 2 )] + complexes where L 1 L 2 is a chelating ligand, of which over 1000 are reported in the literature. The two midpoints of the donating ene functions and the P and S 65 donor atoms define an approximate square planar configuration, which is quite typical of d 8 Rh I . As a matter of fact, the geometry is nearly for 4 Ph , with trans angles quite close to 180° (P-Rh-X1 and S-Rh-X2 = 178.6(3) and 174.69(6)°, respectively; X = midpoints of the C=C bonds, see Table 3), whereas it is more 70 distorted for 4 Bz . A close inspection of the structure of 4 Bz shows that this distortion is related to a twist of the COD ligand, which is caused by a van der Waals repulsion between one of the COD CH=CH donating groups (C11-C12) and the CH2 group of the benzyl substituent on sulfur (C22). A similar van der Waals 75 repulsion, namely a 2.16Å contact between theH atoms on one of the tBu methyl groups (C23) and on atom C12 of the NBD ligand, explains the even larger distortion observed in 2 tBu (P-Rh-X1 and S-Rh-X2 = 163.54(4) and 166.20(4)°, respectively; see Table 3). As expected, the X1-Rh-X2 angle is much smaller for 80 the NBD ligand with a value of 69.943(11)°, similar to the angle observed in related compound. 29 Another peculiar geometrical feature is that the sulfur substituent is placed anti relative to the CpFe moiety of the ferrocene group for the three complexes. Upon coordination, the sulfur atom becomes chiral and therefore 85 two different diastereoisomers could be obtained in principle, with the sulfur substituent either syn or anti to the CpFe moiety.

6|

Like for all previously reported complexes containing ligands of this family, without exception, 31, 49-51 a single compound is obtained in solution and the sulphur substituent is placed on the side opposite (anti) to the FeCp group with respect to the S-C-C-C-P chelate. Consequently, the observed diastereomer has the configuration (Sfc, SS) or (Rfc, RS) for 2 tBu and for 4 Ph and(Rfc, SS) or (Sfc, RS) for 4 Bz . The two Cp rings are roughly eclipsed with the largest twist angle, , 7.5(4)° for 4 Bz . A few other [Rh(diene)(P,S)] n+ complexes of d 8 Rh I have been previously described, some being cationic with a phosphinethioether 28,29,[52][53][54][55] or phosphine-phosphine sulfide 56, 57 ligand, others being neutral with a phosphine-thiolato ligand, 56,58,59 but the Rh-S distance does not appear to be too sensitive to this modification. The Rh-P and Rh-S distances found for 4 Ph and 4 Bz (see Table 3) compare quite well with the average in the above 20 mentioned examples (Rh-P: 2.29(3) Å and Rh-S: 2.36(3) Å). Whereas the Rh-P distances are quite similar for the three compounds, the Rh-S distance is significantly shorter in 4 Bz , suggesting a better binding ability of the benzyl derivative, and longer in 2 tBu , probably reflecting the greater steric bulk of the 25 sulphur substituent which is also responsible for the greater geometry distortion (vide supra). There are no reasons to doubt that the solution structures of the other 4 R compounds are identical to the solid state structure found for 4 Ph and 4 Bz .

DFT/B3LYP geometry optimizations were carried out for the Concerning the neutral chlorido complexes, the solution and solid state structures cannot be assigned as easily because of the presence of five potentially coordinating ligands. We were unfortunately unable to obtain single crystals for any of these structure I in Scheme 3), whereas the compounds with R = Et, Ph and Bz prefer a pentacoordinated square pyramidal geometry with a loosely bonded axial Cl ligand (structure II). These structural motifs seem to be maintained in solution, according to 55 observed differences in the NMR properties, notably the 31 P resonance. 31 The Rh complexes 1 R and 3 R could also conceivably adopt structure I or II, but a third possibility (III) with a chelating (P,S) ligand and an outer sphere chloride ion, related to those observed for 2 tBu , 4 Ph and 4 Bz by simple replacement of the 60 BF4 -ion with Cl -, can also be imagined. Inspection of the previously published X-ray structures of related rhodium complexes suggests that III is unlikely but cannot be totally excluded, because a handful of compounds with the RhX(diene)(L 1 L 2 ) stoichiometry feature indeed a free halide 65 anion. In these structures, the cationic complex is characterized by strongly binding neutral ligands such as two monodentate Nheterocyclic carbenes (NHC), 60 a bidentatebis-NHC, 61-63 a 2,2'bipyridine, 64 or a 2,2'-dipyridylmethane. 65 All the other structures of this type contain, like those of 4 Ph and 4 Bz , non coordinating X - 70 anion (mostly PF6 -, BF4 -, CF3SO3 -and ClO4 -). A 5-coordinate geometry of type II also appears unlikely because it is much less common for Rh I than for Ir I , but again it cannot be excluded. Rare examples of 5-coordinate RhX(diene)(L 1 L 2 ), with COD or NBD and including a halide ligand in the coordination geometry are 75 limited to complexes where L 1 L 2 is bipyridine, 64 64 2-pyridylimines, 66 or an NHC-oxazoline. [67][68][69] It is also relevant to compare pairs of related [Rh(diene)(L 1 L 2 )] + X - and RhY(diene)(L 1 L 2 ) structures (X = non coordinating anion, Y = halide), where the weaker partner of the chelating L 1 L 2 donor set dissociates to let the halide enter the coordination sphere on going from the former to the latter. Examples of this situation include bidentate ligands L 1 L 2 such as phosphine-amines, 70,71 phosphine-ethers, 72 or phosphine-phosphine oxides. 73,74 Clearly, all these examples involve a relatively strong donor (e.g. a phosphine) and a weaker one (N or O donor) giving the bidentate ligand a pronounced hemilability character. Apparently, examples of this type for phosphine-thioethers have not yet been described. Since no suitable single crystals for a diffraction analysis could be obtained for any of compounds 1 and 3, their structure was addressed by a combination of spectroscopic techniques (IR, NMR) and DFT calculations. As shown in Table 2, the 31 P chemical shift and Rh coupling for compounds 1 and 3 do not greatly differ from those of the BF4 -salts 2 and 4. This is an expected occurrence if the chloride complexes adopted structure III. It should be remarked that the 31 Another useful comparison comes from the detailed analysis of the 1 H spectra. Most protons (i.e. diene, PPh2) are not expected to greatly respond to the structural type. The FcCH2S protons, on 40 the other hand, may be sensitive to the thioether coordination, namely discriminate between I and II/III. The two protons of this group, whether the S atom is coordinated or not, are diastereotopic and therefore always give rise to an AB pattern. This feature was also observed for the free ligands and for the 45 sulfur-protected version of the free ligand, (S=P,SR), 23 the 1 H and 13 C resonances of which are collected in Table 4 together with those of the isolated compounds 1-4. It can be noted that the two doublets of the AB pattern in the 1 H NMR are very close to each other in the (P,SR) and (S=P,SR) molecules (Δδ< 0.4 ppm). This 50 difference is systematically much greater for the cationic complexes in the BF4 -salts where the S atom is coordinated to the Rh centre (0.83 ppm in 4 Bz and > 1 ppm for all other examples). It can be argued that the enantioselective sulfur coordination makes a further magnetic discrimination of the two CH2 protons, 55 thereby increasing their chemical shift difference. Considering now the chlorido derivatives, we note that three of them exhibit a small chemical shift difference (0.13 for 1 Bz , 0.31 for 1 Et , ca. 0.3 for 3 tBu ), whereas the Δδ values are much greater for the other a Data from ref. 23 .

2-phenyl- (a) (b) (c) |7 azopyridine,
two compounds (1.22 for 1 tBu , 1.09 for 1 Ph ) and comparable to those of the cationic complexes. These results would tend to suggest that the thioether function is not coordinated to the Rh center in complexes 1 Bz , 1 Et and 3 tBu (e.g. structure I), whereas coordination might occur for the other two derivatives. Analysis of the FcCH2S 13 C chemical shift does not bring any additional clarification, since this resonance appears to be very little sensitive to the chemical environment as shown in Table 4.

Since the NMR analysis does not allow an unambiguous assignment of the chemical structure for the chlorido derivatives, additional studies were carried out by solid state IR spectroscopy, although limited to the COD-(P,S tBu ) and NBD-(P,S tBu ) derivatives. Spectra in the lower fingerprint region (600-250 cm -1 ) were measured for 1 tBu , 2 tBu , 3 tBu , 4 tBu and IrCl(COD)(P,StBu) in the solid state and the results are reported in Figure 2. The M-Cl stretching region shows various bands, the most intense one having a higher frequency for the iridium compound IrCl(COD)(P,StBu) (295 cm -1 ) than for the rhodium compounds 1 tBu and 3 tBu (271 and 288 cm -1 , respectively). The assignment of these bands to the Ir-Cl and Rh-Cl stretching vibrations, respectively, was confirmed by the calculations (vide infra). On going to the tetrafluoroborate salts 2 tBu and 4 tBu , the major band disappears in agreement with the removal of the Cl - ligand from the metal coordination sphere. These observations are in favor of a coordination geometry of type I or II (Scheme 3).

Geometry optimizations for all three types of structures were carried out at the same computational level as for the cationic complexes described above. The calculations were carried out for complexes 1 R and 3 R for R = tBu and Ph in order to evaluate the effect of the R substituent and the diene ligand. The geometry of the iridium analogue IrCl(COD)(P,StBu) was also optimized and was found to agree quite well with that obtained experimentally in the solid state. 31 A table with the most significant metric parameters for all optimized structures is reported in the Supporting Information (Table S2). All attempts to optimize the geometry of [Rh(diene)(P,SR)] + with Cl -as a counteranion (e.g. a geometry of type III in Scheme 3) led to the dissociation of the thioether arm to allow formation of the rhodium-chloride bond (i.e. an optimized geometry of type I in Scheme 3). The geometry of the only local energy minimum obtained for 3 tBu is quite similar to that of the iridium analogue, with the sulfur atom far away from the Rh center (5.556 Å). 31 Similar optimized geometries are also adopted by the other complexes (1 Ph , 1 tBu , 3 Ph ). Replacement of the S atom in the coordination sphere of 2 R or 4 R by the Cl atom in 1 R or 3 R systematically lengthens the M-P bond by ca. 0.05 Å (cf. Table 3 and Table S2). A second, higher energy minimum was also found for complexes 1 Ph , 1 tBu and 3 Ph . In these structures, the sulfur donor 55 function has rearranged to place itself along the z direction perpendicularly to the square plane defined by the other four ligands, loosely interacting with the metal center, defining a pseudo pentacoordinated square-pyramidal geometry like that of II in Scheme 3, except that the axial coordination position of the 60 square pyramid is occupied by the sulfur atom instead of the Cl atom (type II'). An example is shown in Figure 3 for compound 1 tBu (all other optimized geometries are available in the Supporting Information section, Figure S2). The Rh-S distance is too long to be considered an interaction for compound 3 Ph (3.674 65 Å), whereas it signals a genuine 5-coordinate geometry for 1 Ph (2.824 Å) and 1 tBu (2.702 Å), when considering that the axial interaction for 5-coordinate square pyramidal d 8 complexes is lengthened by the dz2 electron pair. The shorter Rh-S separation for the tBu derivative may be related to the greater donating 70 power of the StBu donor function. On the other hand, this geometry is more destabilized relative to the square planar global minimum for 1 tBu (by 8.2 kcal/mol) than for 1 Ph (3.1 kcal/mol). The greater steric bulk of the tBu group may be responsible for this difference. All attempts to optimize a type II geometry led to 75 one of the above mentioned minima. Therefore, the geometry optimizations are in favor of a structure of type I for compounds 1 and 3, irrespective of the nature of the R substituent (at least for Ph and tBu). It is now of interest to analyze the calculated IR spectrum of 5 the observed minima and compare it with the experimental ones reported in Figure 2. The M-Cl stretching vibration is coupled with M-(diene) stretches in all rhodium complexes and contributes mostly to two intense bands, which exhibit a greater frequency difference in the COD series. The analysis is rather simple for the COD compound 3 tBu and for the iridium analogue, since only a minimum of type I was optimized. The computed spectra for these two compounds, as well as for the salt 4 tBu , are shown in Figure 4. These spectra match rather closely those experimentally observed, confirming the Type I structure. The calculated maximum absorption for the strongest M-Cl stretching band is at 279 cm -1 for the Ir complex and at 277 cm -1 for the Rh complex 3 tBu , whereas the spectrum of 4 tBu does not show any strong band in this region. The adoption of a structure of type I by compound 3 tBu is also in line with the suggestion of the 1 H NMR 20 spectrum (AB pattern of the CH2StBu moiety, vide supra). The calculated spectra for the type I and type II' minima of 25 compounds 1 tBu and 1 Ph are shown in Figure 5. It can be seen that the Rh-Cl stretching band for the type I minima is very similar to that of compound 3 tBu (286 and 273 cm -1 for the strongest absorption). On the other hand, the Rh-Cl vibration is shifted to much lower frequencies in the type II' minima of 1 Ph (247 cm -1 ), and especially of 1 tBu (208 cm -1 ). This effect can obviously be attributed to the coordination of the sulfur atom, which provides additional electron density to the metal center and labilizes the Rh-Cl bond, an effect which is stronger for the tBu derivative where the Rh-S distance is shorter. In agreement with this 35 argument, the Rh-Cl distance is shorter for the type I minima of compounds 1 tBu and 1 Ph (2.382 and 2.390 Å, respectively) and longer for the type II' geometries of 1 Ph (2.459 Å) and particularly 1 tBu (2.572 Å). The difference between the calculated Rh-Cl frequencies for the type I and II' minima (Δν) is 78 cm -1 40 for 1 tBu and 26 cm -1 for 1 Ph . On the other hand, the experimental Rh-Cl stretching frequency in 1 tBu is only 17 cm -1 lower than that of compound 3 tBu . Therefore, we conclude that the structure adopted by compound 1 tBu is most likely of type I in the solid state, like that of compound 3 tBu . However, the large chemical

(d) Catalytic studies

Because iridium complexes of diphenylphosphinoferrocenyl thioether ligands were shown to be excellent precatalysts for the hydrogenation of acetophenone in the presence of NaOMe in isopropanol at room temperature under 30 bar of H2 and with 65 only 0.2% of catalyst, we decided to study the catalytic properties of corresponding rhodium complexes in the same conditions and compare the activity of the complexes (Scheme 4). For these preliminary investigations, we selected only the complexes with t-butyl substituent on sulfur. The results are shown in Table 5. that the rhodium complexes are not only structural but also functional models of the iridium analogues. All these rhodium complexes exhibit a rather similar catalytic activity, which is however significantly lower than that of the corresponding iridium complex IrCl(COD)(P,StBu), whereas their enantio-10 selectivities are only slightly lower. A full description of the catalytic performance of these complexes, including the effect of the sulphur substituent, reaction temperature, and substrate, which is currently being investigated, will be reported in due course.

Conclusions

Rhodium complexes associating chiral ferrocenyl phosphinethioethers and diene (COD or NBD) ligands have been synthesized and fully characterized. For the neutral chlorido complexes, for which X-ray structural analyses could not be 20 carried out, combination of NMR and IR spectroscopy and DFT calculations indicates that they adopt a square planar geometry with a dangling thioether function. A second, pentacoordinated structure with a square pyramidal geometry and the thioether function placed in the axial position is however easily accessible.

25

The cationic complexes, on the other hand adopt a standard square planar bis-chelated structure. These rhodium complexes are not only good structural models for our previously published iridium-based hydrogenation catalysts but have also been tested in the asymmetric hydrogenation of acetophenones and proved to 30 be efficient precatalysts.

RechercheInternationale) "Homogeneous catalysis for Sustainable Development" and a France-Russia (RFBR -CNRS) bilateral grant. We are also grateful to the IUF (InstitutUniversitaire de France) for additional funding and to the CINES(Centre Informatique National de 40 l'EnseignementSupérieur) and the CICT (Centre Interuniversitaire de Calcul de Toulouse, project CALMIP) for granting free computational time. EMK thanks the Embassy of France in Moscow for a Ph.D. grant.

Notes and references

Figure 1 .

 1 Figure 1. Molecular views of the cationic complexes in compounds 2 tBu 10

30 cations of 2 R and 4 R

 304 with R = tBu and Ph. The results are also reported in Table3. For compounds 2 tBu and 4 Ph , the optimized geometry reproduced quite well the experimentally observed one, except for a slight overestimation of the Rh-P, Rh-S and Rh-C distances (by 0.08 Å on average for Rh-S and Rh-P, 0.04 Å for 35 Rh-C). Whereas the calculated Rh-P distance is essentially the same in all four compounds, the Rh-S distance increases from Ph to the more bulky tBu substituent, in agreement with the experimental evidence. Views of all optimized geometries are provided in the Supporting Information, FigureS1. 40 (c) Characterization of the chloride complexes 1 and 3

45 compounds,

 45 preventing us to determine the solid state structure. Interestingly, the structure adopted by the related iridium complexes IrCl(COD){CpFe[1,2-C5H3(PPh2)(CH2SR)]} depends on the nature of the thioether substituent.31 For R = tBu, the molecule adopts a square planar geometry with a (COD)ClP 50 coordination environment and a dangling thioether function (i.e.

Scheme 3 .

 3 Scheme 3. Possible molecular geometries for MCl(diene)(L 1 L 2 ) complexes (M = Rh, Ir).

  P chemical shift in the [IrCl(COD)(P,SR)] and [Ir(COD)(P,SR)] + compounds was found diagnostic for 25 discriminating structures of type I (δ -4.2 for R = Ph and -3.1 for R = Et), II (δ 15.7 for R = tBu) and III (δ 11.0 for R = Ph and 14.5 for R = tBu).31 In particular, the 31 P resonance is rather similar for the Ir complexes of type II and III and different relative to those with structure I. Therefore, the similarity 30 between the resonances of the chloride complexes 1 and 3 with those of the BF4 salts 2 and 4 that are known to adopt structure III would appear to point to a structure of type II or III for the chloride complexes. This argument, however, can in no way be considered conclusive because the metal nature may have a 35 different effect on the chemical shift of the different structural types.

50 Figure 2 .

 502 Figure 2. Solid state IR spectra (lower fingerprint region) of 3 tBu (red line), 4 tBu (blue line), 1 tBu (pink line), 2 tBu (cyan line) and IrCl(COD)(P,StBu) (green line).

Figure 3 .

 3 Figure 3. DFT(B3LYP) optimized geometries of 1 Ph with relative energies in parentheses in kcal/mol. Hydrogen atoms are omitted for clarity.

Figure 4 .

 4 Figure 4. Calculated IR spectra (lower fingerprint region) of 3 tBu (red line), 4 tBu (blue line) and IrCl(COD)(P,StBu) (green line).

45 shiftFigure 5 .

 455 Figure 5. Calculated IR spectra (lower fingerprint region) of 1 tBu type I (green line), 1 Ph type I (red line), 1 tBu type II' (pink line) and 1 Ph type II' (blue line).

60

 60

70 Scheme 4 .

 704 Scheme 4. Asymmetric hydrogenation of acetophenone.

Table 1 .

 1 Crystal data and structure refinement parameters.

				Crystal data and refinement
	30	parameters	are	shown	in

Table 2 .

 2 Table 2 for all compounds). 31 P NMR data for the Rh complexes (δ in ppm with the 2 JPRh in Hertz in parentheses).

	50
	Scheme 2. Summary of the synthetic work and compounds numbering
			scheme.
		1 R	2 R	3 R	4 R
	R = tBu	23.6 (159)	26.1 (158)	21.0 (148)	23.8 (143)
	R = Ph	23.8 (154)		28.0 (166)	22.1 (144)
	R = Bz	20.3 (147)		31.1 (170)	21.8 (144)
	R = Et	21.3 (148)		22.8 (144)	22.9 (144)
	55

Table 3 .

 3 Selected experimental (from X-ray diffraction) and computed (by DFT optimizations) bond lengths [Å] and angles [°] in compounds 2 R and 4 R .

		2 tBu		2 Ph	4 tBu	4 Ph		4 Bz
		X-ray	DFT	DFT	DFT	X-ray	DFT	X-ray
	Distances a
	Rh-P	2.2587(13)	2.331	2.343	2.354	2.2858(15)	2.354	2.2796(10)
	Rh-S	2.3641(13)	2.452	2.402	2.508	2.3378(11)	2.421	2.3194(10)
	Rh-X1	2.1231(3)	2.165	2.145	2.179	2.119(2)	2.184	2.1198(3)
	Rh-X2	2.0066(4)	2.032	2.047	2.062	2.040(5)	2.069	2.0199(3)
	Rh-C11	2.229(5)	2.263	2.260	2.302	2.227(4)	2.310	2.210(4)
	Rh-C12	2.229(5)	2.283	2.248	2.270	2.227(4)	2.271	2.240(4)
	Rh-C15	2.118(5)	2.159	2.169	2.173	2.169(4)	2.182	2.127(5)
	Rh-C16	2.127(5)	2.141	2.159	2.183	2.142(4)	2.188	2.142(5)
	C11-C12	1.358(8)	1.409	1.404	1.408	1.368(8)	1.404	1.352(8)
	C15-C16	1.384(8)	1.383	1.385	1.384	1.391(7)	1.385	1.380(11)
	Angles a
	P-Rh-S	92.64(5)	92.2	92.6	90.3	92.30(3)	90.9	93.24(4)
	P-Rh-X1	163.54(4)	165.6	168.8	175.8	178.6(3)	177.2	168.29(3)
	P-Rh-X2	93.84(13)	97.6	99.6	92.5	93.01(6)	93.5	91.59(3)
	S-Rh-X1	103.01(3)	102.0	98.5	93.1	88.83(12)	91.0	90.95(3)
	S-Rh-X2	166.20(4)	163.5	166.1	171.6	174.69(6)	172.6	168.21(3)
	X1-Rh-X2	69.943(11)	69.2	69.6	84.4	85.87(17)	84.9	86.423(13)

a X1 and X2 are the midpoints of the coordinating COD C=C functions, C11-C12 and C14-C15 (for the NBD complexes) or C15-C16 (for the COD complexes), respectively.

|8

Table 4 .

 4 Selected 1 H (Δδ in parentheses) and13 C NMR (in italics) data for the FcCH2S group in complexes 1-4 (δ in ppm).

		1 R	2 R	3 R	4 R	(P,SR) a	(S=P,SR) a
	R = tBu	5.06, 3.84 (1.22) 28.8	3.96, 2.81 (1.15) 29.1	ca. 4.2, 3.91 (ca. 0.3) 28.6	ca. 4.0, 2.69(ca. 1.3) 29.2	3.80, 3.63 (0.17) 27.4	3.99, 3.96 (0.04) 26.7
	R = Ph	5.37, 4.2 (1.09) 34.1			4.17, 3.04(1.15) 37.9	4.17, 4.09 (0.08) 34.2	4.42, 4.35 (0.07) 33.3
	R = Bz	4.13, 4.00 (0.13) 31.3			3.50, 2.67 (0.83) 31.5	3.72, 3.65 (0.07) 31.1	4.14, 3.77 (0.37) 30.5
	R = Et	4.37, 4.06 (0.31) 30.8			ca. 4.0, 2.70 (ca. 1.3) 30.3	3.74, 3.74 (0.00) 30.9	4.09, 3.87 (0.22) 30.3

to but not central to the matter under discussion, limited experimental and spectral data, and crystallographic data.

Acknowledgement

We are grateful to the CNRS (Centre National de la RechercheScientifique) and the RFBR (Russian Foundation for Basic Research) for support through the GDRI (Groupe de

Computational details. Calculations were performed with the Gaussian09 package [START_REF] Frisch | Gaussian 09, Revision A.02[END_REF] using the B3LYP hybrid functional [START_REF] Becke | [END_REF]43 under the DFT approach, since it performs better in frequency calculations. All carbon and hydrogen atoms were described with 45 the 6-31G(d,p) basis set, whereas the 6-31++G(d,p) basis set was applied to the P, S, B, F and Cl atoms. Effective core potentials (ECP) and its associated SDD basis set [44][45][46][47]