Five-coordinate [RuCl(P-P*)(2)]+ complexes containing chiral diphosphines:Application in the asymmetric cyclopropanation and epoxidation of olefins

The six-coordinate complexes trans-[RuCl2(P-P*)(2)] (P-P* = (S,S)-1,2-bis(1 -naphthylphenylphosphino)ethane (bnpe), 2a; (S,S)-2,3-bis(diphenylphosphino )butane (chiraphos), 2b) have been prepared and structurally characterized. The X-ray studies of 2a,b show non-C-2-symmetric conformations of the subs tituents at the PPh2 groups in a highly crowded octahedral environment. Com plexes 2a,b react with Tl[PF6] in CH2Cl2 to give the corresponding monochlo ro, cationic derivatives [RuCl(P-P*)(2)]PF6 (P-P*:= bnpe, 3a; chiraphos, 3b ). The bnpe derivative 3a is five-coordinate both in the solid state (by X- ray investigation) and in solution (by P-31 NMR spectroscopy). The chirapho s analogue 3b apparently dimerizes in solution, depending on the solvent (C DCl3 or CD2Cl2) and on the concentration. Complexes 3a,b catalyze the decom position of ethyl diazoacetate to give, in the presence of styrene, the cor responding cyclopropanation products with enantioselectivity up to 35% ee a nd E/Z ratios of about 55:45. Complexes 3a,b also catalyze the epoxidation of unfunctionalized olefins with iodosyl benzene as the primary oxidant. Hi gh olefin conversions and fair selectivity for the epoxide are observed, bu t both 3a and 3b give racemic epoxide.