Inner-sphere electron transfer in metal-cation chemistry

Abstract

Bond activation of organic molecules by metal cations is usually rationalized either in terms of the chemistry of Lewis acids or via oxidative addition of metal fragments to RX bonds, that is, R X+ M +→ R M + X→ products. In most of these mechanisms, the positive charge is assumed to be located on the metal center. Here, we propose an alternative mechanism, to which we refer as inner-sphere electron transfer (ET). Thus, provided that certain conditions are fulfilled, the insertion species RM +X may isomerize via ET to [ R +⋯ MX] structures with the positive charge located mostly at the organic residue R. If RM +X and [ R +⋯ MX] are not just resonance structures but distinct minima on the related potential-energy surfaces, there also exists a transition structure between the two, that is, an ET-TS. Here, the role of inner sphere ET in organometallic gas-phase reactions and the possible existence of ET-TSs are discussed for a series of examples investigated both computationally and experimentally.