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Metal-Hydrogen Bond Cleavage Reactions of Transition Metal Hydrides: Hydrogen Atom, Hydride, and Proton Transfer Reactions

1991; Taylor & Francis; Volume: 12; Issue: 1 Linguagem: Inglês

10.1080/02603599108018617

1548-9574

R. Morris Bullock,

Carbon dioxide utilization in catalysis

Abstract Cleavage of the M-H bond of transition metal hydrides can result in delivery of a hydride (H−), hydrogen atom (H), or proton (H+) to an organic or organo-metallic substrate. Hydrogen atom transfer from a metal hydride to an olefin is an endothermic reaction; the rate at which different metal hydrides carry out this reaction is mainly dependent on the bond dissociation energy of the M-H bond. Hydrogen atom transfer from a metal hydride to a carbon-centered radical is an exothermic reaction in which the rate is largely determined by steric demands of the ligands of the metal hydride, with thermodynamics playing a less important role. Some neutral metal hydrides can function as hydride donors to carbocations. Anionic metal hydrides also exhibit hydridic reactivity, but in some cases the actual M-H bond cleavage step involves hydrogen atom transfer as a part of a radical chain reaction. Neutral metal hydrides can function as nucleophiles and as weakly coordinating ligands to coordinatively unsaturated metals.