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A study has been made of the asymmetric hydrosilylation of acetophenone by diphenylsilane under the influence of rhodium complexes with chiral phosphites. The enantioselective nature of the reaction depends on the phosphite structure, the acetophenone/rhodium and ligana/rhodium ratios, and the temperature. The maximum optical yield (24%) is attainod on the complex [Rh(COD)Cl]2/(S, S)-2-ethoxy-4,5-dicarbisopropoxy-1,3-2-dioxophiospholane.

The binuclear structure of complex (IIa) is indicated by the finding of a mass spectral peak with m/z 971 and IR absorption band for the bridging bond VRh_Cl = 294 cm -I. X-ray photoelectron spectroscopy showed bidentate coordination for ligand (IIa). The increase in the energy of the bond energies of the 2p electrons of phosphorus and is electrons of nitrogen upon going from the free ligand (131.0 and 398.6 eV) to the coordinated ligand (132.6 and 400.6 eV) indicates the formation of Rh-P and Rh-N bonds in the solid samples of complex (IIa). The lack of resolution in the iH and 31p NMR spectra of solutions of (IIa) at 20~ and the appearance of a doublet in the 31p NMR spectrum of this complex in CH2CI 2 at -80~ (6P = 33.9 ppm, iJP,Rh = 151.1 Hz) is evidence for rapid dissociation and formation of the Rh-N bond. Analysis of the IH NMR spectrum of complex (IIb) (splittihg of the doublet for the protons of the methyl group bound to the CH group and broadening of the signai for the protons of the methyl groups at the nitrogen atom) and its ~ip NMR spectrum (doublet, 5P = 20.5 ppm, IJP,Rh = 168.0 Hz) suggests coordination of the phosphorus and nitrogen atoms by rhodium'and the existence of two conformers of this complex (IIb) [2].

Ligand L I was obtained by the reaction of the diisopropyl ester of (+)-tartaric acid with P(NMe2)2OEt in i:i mole ratio at 120~ Ligand L 2 was obtained by the reaction of the (-)-menthol with di(o,o-di-tert-butyl-p-methyl)phenyl chlorophosphite in absolute benzene at 0~ Both these compounds were characterized by IH, 13C, and 31p NMR and IR spectroscopy and physicochemical indices. Catalysts were obtained in situ from [Rh(COD)CI]z and [RH(CO)2CI]z with L I and L 2. The experiments were carried out in a reactor maintained at constant temperature in an argon atmosphere. The experiment indicated by an asterisk was carried out in CCI 4. The other reactions were carried out without solvent. As shown previously, the reaction temperature and acetophenone:rhodium (AP/Rh) and ligand:rhodium (L*/Rh) ratios affect the enantioselectivity of the catalyst [2]. The results are given in Fig. I. l-Phenylethanol was obtained when the reaction was carried out with the rhodium complexes with L I in optical yield up to 23%. This is the first example of the successful use of phosphite complexes in asymmetric hydrosilylation.