Preparation of methyl hydride and dimethyl complexes of osmium and iron:: reaction of M(CO)2(PMe3)2CH3I and [M(CO)3(PMe3)2CH3]+BPh4- (M = Os, Fe) with borohydrides and lithium methyl

cis,trans-Os(CO)(2)(PMe3)(2)CH3I (1) and fac-[Os(CO)(3)(PMe3)(2)CH3](+) BPh4- (3) react with borohydrides (NaBH4, NBu4BH4, LiBEt3H) in diethyl ether to form the methyl hydride complex Os(CO)(3)(PMe3)(2)(CH3)H (7). Similarly the monosubstituted fac-Os(CO)(3)(PMe3)CH3I (9) reacts with borohydrides to give fac-Os(CO)(3)(PMe3)(CH3)H (10). The isoelectronic complexes of iron cis,trans-Fe(CO)(2)(PMe3)(2)CH3I (2) and fac-[Fe(CO)(3)(PMe3)(2)CH3]BPh4 (4) give instead the dihydride complex cis,transFe(CO)(2)(PMe3)(2)H-2 (8). Complexes (1)-(4) react with lithium methyl to form the dimethyl complexes cis,trans-M(CO)(2)(PMe3)(2)(CH,), [M = Os (5), Fe (6)1. The structures of the complexes are studied by IR and H-1-, C-13{H-1)-, P-31{H-1}-NMR spectroscopies. The different results are explained on the basis of a fast reductive elimination reaction in the case of iron and a fast decarbonylation reaction in the case of osmium. (C) 2001 Elsevier Science B.V. All rights reserved.