Transition metal boryl complex explained

In chemistry, a transition metal boryl complex is a molecular species with a formally anionic boron center coordinated to a transition metal.^[1] They have the formula L_nM-BR₂ or L_nM-(BR₂LB) (L = ligand, R = H, organic substituent, LB = Lewis base). One example is (C₅Me₅)Mn(CO)₂(BH₂PMe₃) (Me = methyl).^[2] Such compounds, especially those derived from catecholborane and the related pinacolborane, are intermediates in transition metal-catalyzed borylation reactions.

Synthesis

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.^[3]

C₆H₄O₂BH + Pt(PR₃)₂ → C₆H₄O₂B Pt(PR₃)₂H

Addition of diboron tetrafluoride to Vaska's complex gives the triboryl iridium(III) derivative:

2B₂F₄ + IrCl(CO)(PPh₃)₂ → Ir(BF₂)₃(CO)(PPh₃)₂ + ClBF₂

References

1. Transition Metal−Boryl Compounds: Synthesis, Reactivity, and Structure. Geoffrey J. Irvine. M. J. Gerald Lesley. Todd B. Marder. Nicholas C. Norman. Craig R. Rice. Edward G. Robins. Warren R. Roper. George R. Whittell. L. James Wright. Chem. Rev.. 98. 2685–2722. 1998. 8. 10.1021/cr9500085. 11848976.
2. Staubitz, A.. Robertson, A. P. M.. Sloan, M. E.. Manners, I.. Amine− and Phosphine−Borane Adducts: New Interest in Old Molecules. Chem. Rev.. 2010. 110. 7. 4023–4078. 10.1021/cr100105a. 20672859.
3. 10.1021/acs.chemrev.6b00193. Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse. 2016. Neeve. Emily C.. Geier. Stephen J.. Mkhalid. Ibraheem A. I.. Westcott. Stephen A.. Marder. Todd B.. Chemical Reviews. 116. 16. 9091–9161. 27434758. free. 1807/78811. free.