Abstract
The five‐coordinate compounds [MHCl(CO)(P__i__Pr~3~)~2~] (where 1a: M = Ru; 1b: M = Os) react with P__i__Pr~2~R* [where R* = CH(Me)Ph] to give the octahedral complexes mer‐[MHCl(CO)(P__i__Pr~2~R*)~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 C~2~(CO~2~Me)~2~, which afford the substitution products [MHCl(CO)(L)(P__i__Pr~2~R*)~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)(P__i__Pr~3~)(Chiraphos)] (15, 16) and [MHCl(CO)(P__i__Pr~3~)(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)(P__i__Pr~3~)(dppe)] (14) was obtained from 1b and 1,2‐C~2~H~4~(PPh~2~)~2~ (dppe). The hydrido(tetrahydroboranato) compounds [MH(κ^2^‐H~2~BH~2~)(CO)(P__i__Pr~3~)~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 [{OsH~2~(CO)(P__i__Pr~3~)~2~}~2~(μ‐Diop)] (22). The molecular structure of 22 was determined crystallographically. Treatment of [OsH~2~Cl~2~(P__i__Pr~3~)~2~] (23) with two equivalents of (S,S)‐Chiraphos afforded stepwise [OsH~2~Cl~2~(P__i__Pr~3~)(Chiraphos)] (25) and, after reductive elimination of HCl and displacement of P__i__Pr~3~, trans‐[OsHCl(Chiraphos)~2~] (24). Both 24 and [OsH~2~(Chiraphos)~2~] (27), which was prepared from 24 and NaBH~4~/MeOH, were transformed with HBF~4~ in diethyl ether into the dihydrogen complexes [OsCl(H~2~)(Chiraphos)~2~]BF~4~ (28) and [OsH(H~2~)(Chiraphos)~2~]BF~4~ (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)