Inner-sphere electron transfer in metal-cation chemistry

Bond activation of organic molecules by metal cations is usually rationaliz ed either in terms of the chemistry of Lewis acids or via oxidative additio n 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 re fer as inner-sphere electron transfer (ET). Thus, provided that certain con ditions are fulfilled, the insertion species R-M+-X may isomerize via ET to [R+ ... MX] structures with the positive charge located mostly at the orga nic 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 ex ists a transition structure between the two, that is, an ET-TS. Here, the r ole of inner sphere ET in organometallic gas-phase reactions and the possib le existence of ET-TSs are discussed for a series of examples investigated both computationally and experimentally. (C) 2000 Elsevier Science B.V.