RELATIVE REACTIVITIES OF ANIONIC TRANSITION-METAL HYDRIDES - REDUCTION OF ALKYL-HALIDES
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A comparison of the second-order rate constants for halide displacement from n-BuBr by H- derived from anionic transition-metal hydrides established the following order of reactivity: cis-HW(CO)4P(OMe)3- > cis-HCr(CO)4P(OMe)3- > HW(CO)5- > CpV(CO)3H- > HCr(CO)5- > HRu(CO)4- HFe(CO)4- (no reaction). The lack of dependence of reactivity on degree of branching of the alkyl halide for HM(CO)5- (M = Cr, W) and a dramatic diminishing of reactivity for HM(CO)4P(OMe)3-, 1 2 > 3, resulted in a different order of reactivity on the basis of f-BuBr: HCr(CO)5- > HW(CO)5- > cis-HCr-(CO)4P(OMe)3- > CpV(CO)3H- > cis-HW(CO)4P(OMe)3- HFe(CO)4- (no reaction). Mechanistic probes were applied to reactions of HW(CO)5- and cis-HW(CO)4P-(OMe)3-, and preliminary results suggest the former to involve some radical character (single electron transfer) and the latter to react with considerable ionic character (H- transfer). 1984, American Chemical Society. All rights reserved.