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)2CH3I (1) and fac-[Os(CO)3(PMe3)2CH3]+BPh4− (3) react with borohydrides (NaBH4, NBu4BH4, LiBEt3H) in diethyl ether to form the methyl hydride complex Os(CO)2(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)2CH3I (2) and fac-[Fe(CO)3(PMe3)2CH3]BPh4 (4) give instead the dihydride complex cis,trans-Fe(CO)2(PMe3)2H2 (8). Complexes (1)–(4) react with lithium methyl to form the dimethyl complexes cis,trans-M(CO)2(PMe3)2(CH3)2 [M=Os (5), Fe (6)]. The structures of the complexes are studied by IR and 1H-, 13C{1H}-, 31P{1H}-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.