In chemistry, a transition metal boryl complex is a molecular species with a formally anionic boron center coordinated to a transition metal. They have the formula L<sub>n</sub>M-BR<sub>2</sub> or L<sub>n</sub>M-(BR<sub>2</sub>LB) (L = ligand, R = H, organic substituent, LB = Lewis base). One example is (C<sub>5</sub>Me<sub>5</sub>)Mn(CO)<sub>2</sub>(BH<sub>2</sub>PMe<sub>3</sub>) (Me = methyl). Such compounds, especially those derived from catecholborane and the related pinacolborane, are intermediates in transition metal-catalyzed borylation reactions.
Oxidative addition is the main route to metal boryl complexes. Both B-H and B-B bonds add to low-valent metal complexes. For example, catecholborane oxidatively adds to Pt(0) to give the boryl hydride.
Addition of diboron tetrafluoride to Vaska's complex gives the triboryl iridium(III) derivative: