A journey into metal–carbon bond homolysis

Abstract

This article surveys the current knowledge in metal alkyl complexes with homolytically weak metal–carbon bonds, therefore prone to thermally produce alkyl radicals. It outlines the role of a metal complex as a moderator to control the radical reactivity (“persistent radical effect”). It describes the methods that have been used so far (as well as others that are potentially available) to investigate the metal–carbon bond cleavage thermodynamic and kinetic parameters, including their caveats and limitations. A number of systems scrutinized in the author’s own laboratory and in those of collaborators are presented and discussed. These investigations have combined metal complexes and alkyl radicals, with guidance and understanding provided by DFT calculations, to achieve higher performance in the controlled radical polymerization of challenging monomers (vinyl acetate, vinylidene fluoride) and in olefin radical cross-coupling, and have brought to light mechanistic questions of more general relevance.

Keywords

• Metal–carbon bond
• Homolytic cleavage
• Bond dissociation enthalpy
• Persistent radical effect
• Metal-mediated radical reactivity