Oxidatively induced abstraction reactions. A synthetic approach to low-coordinate and reactive early transition metal complexes containing metal-ligand multiple bonds

A library of low-coordinate titanium and vanadium complexes containing terminal metal-ligand multiply bonded functionalities such as alkylidenes, alkylidynes, and imides have been prepared by one-electron oxidatively induced alpha-hydrogen abstraction reactions. In the case of the alkylidene motif, the nucleophilic nature of the M-C multiple bond permits subsequent reactions such as alpha-hydrogen migration to generate other rare functionalities such as phosphinidene-alkyl and imide-alkyls. Identifying and fine-tuning of the supporting ancillary ligand on the metal has allowed the isolation of kinetically stable titanium alkylidene and phosphinidene systems. The former is a key functionality to generate transient titanium alkylidynes, which readily engage in intermolecular C-H activation reactions of arenes and alkanes, and the ring-opening metathesis of aromatic substrates such as pyridines. In this Account, we describe several synthetic strategies to achieve reactive functionalities, functionalities that were previously portrayed as incompatible or too kinetically reactive with 3d early transition metals.