Synthesis, Molecular Structure and Catalytic Activity of Six‐Coordinate Chloro(hydrido)‐ and Dihydridoruthenium(II) and ‐osmium(II) Complexes with the Chiral Ligands PiPr2NH(Me)Ph, (S,S)‐Chiraphos and (S,S,)‐Diop

Abstract

AbstractThe five‐coordinate compounds [MHCl(CO)(PiPr3)2] (where 1a: M = Ru; 1b: M = Os) react with PiPr2R* [where R* = CH(Me)Ph] to give the octahedral complexes mer‐[MHCl(CO)(PiPr2R*)3] (6 and 7). The lability of the phosphane trans to the hydride is illustrated by the replacement reactions with CO, P(OMe)3 and C2(CO2Me)2, which afford the substitution products [MHCl(CO)(L)(PiPr2R*)2] (8−12) in high yields. The reactions of 1a and 1b with (S,S)‐Chiraphos and (S,S)‐Diop lead to one or two diastereoisomers of the chelate complexes [MHCl(CO)(PiPr3)(Chiraphos)] (15, 16) and [MHCl(CO)(PiPr3)(Diop)] (17, 18); the ratio of the diastereoisomers is dependent on the metal, the bidentate ligand and the reaction conditions. The racemate of [OsHCl(CO)(PiPr3)(dppe)] (14) was obtained from 1b and 1,2‐C2H4(PPh2)2 (dppe). The hydrido(tetrahydroboranato) compounds [MH(κ2‐H2BH2)(CO)(PiPr3)2] (where 2a: M = Ru; 2b: M = Os) also react with (S,S)‐Chiraphos and (S,S)‐Diop to give either the mononuclear, octahedral, chelate complexes 19−21 or, for M = Os and (S,S)‐Diop, the dinuclear compound [{OsH2(CO)(PiPr3)2}2(μ‐Diop)] (22). The molecular structure of 22 was determined crystallographically. Treatment of [OsH2Cl2(PiPr3)2] (23) with two equivalents of (S,S)‐Chiraphos afforded stepwise [OsH2Cl2(PiPr3)(Chiraphos)] (25) and, after reductive elimination of HCl and displacement of PiPr3, trans‐[OsHCl(Chiraphos)2] (24). Both 24 and [OsH2(Chiraphos)2] (27), which was prepared from 24 and NaBH4/MeOH, were transformed with HBF4 in diethyl ether into the dihydrogen complexes [OsCl(H2)(Chiraphos)2]BF4 (28) and [OsH(H2)(Chiraphos)2]BF4 (29) in excellent yields. The catalytic activity of the chloro(hydrido)‐ and dihydridometal derivatives in the asymmetric transfer hydrogenation of acetophenone with 2‐propanol was investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)