Remote functionalization of C-H and C-C bonds by "naked" transition-metal ions (Cosi Fan Tutte)

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Gas-phase experiments with naked transition-metal ions offer a unique opportunity to probe, in the absence of any solvation, ion-pairing, and/or ligand effects, the intrinsic properties of reactive organometallic species and to evaluate the potential role these remarkable transients play in the initial steps of the activation of C-H and C-C bonds. Not surprisingly, this topic is of fundamental interest in catalysis and has attracted considerable attention in the last decade. The authors and later others, have recently demonstrated that remote functionalization can be achieved in the gas phase for quite a variety of flexible substrates including aliphatic nitriles, isonitriles, amines, alcohols, ketones, alkynes, and allenes, respectively. Specifically, we have shown that the C-H bond of a terminal methyl group of an alkyl chain can be oxidatively added to the anchored transition-metal ion M{sup +} (Scheme II). The insertion is followed by a {beta}-hydrogen shift (5 {yields} 6) or {beta}-cleavage of the C-C bond (5 {yields} 7) to generate intermediates from which eventually reductive elimination of H{sub 2} of ligand detachment occurs. This discussion will be confined to recent results from our laboratory. While most of the data will be concerned with the chemistry of aliphatic nitriles, the reactions of alkynesmore » with bare transition-metal ions will be briefly mentioned.« less