Transition metal boryl complex

Structure of boryl ligands in metal complexes.

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.

Structure of (PMe₃)₄RhB(pinacolate).^[3] (color code: pink=B, blue green=Rh, red=O, orange=P).

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.^[4]

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

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

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

References

^ 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 (1998). "Transition Metal−Boryl Compounds: Synthesis, Reactivity, and Structure". Chem. Rev. 98: 2685–2722. doi:10.1021/cr9500085.
^ Staubitz, A.; Robertson, A. P. M.; Sloan, M. E.; Manners, I. (2010). "Amine− and Phosphine−Borane Adducts: New Interest in Old Molecules". Chem. Rev. 110: 4023–4078. doi:10.1021/cr100105a.
^ C.Borner; K.Brandhorst; C.Kleeberg (2015). "Selective B–B bond activation in an unsymmetrical diborane(4) by [(Me₃P)₄Rh–X] (X = Me, OtBu): a switch of mechanism?". Dalton Trans. 44: 8600. doi:10.1039/C5DT00618J.
^ Neeve, Emily C.; Geier, Stephen J.; Mkhalid, Ibraheem A. I.; Westcott, Stephen A.; Marder, Todd B. (2016). "Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse". Chemical Reviews. 116 (16): 9091–9161. doi:10.1021/acs.chemrev.6b00193. PMID 27434758.

[1] 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 (1998). "Transition Metal−Boryl Compounds: Synthesis, Reactivity, and Structure". Chem. Rev. 98: 2685–2722. doi:10.1021/cr9500085.

[2] Staubitz, A.; Robertson, A. P. M.; Sloan, M. E.; Manners, I. (2010). "Amine− and Phosphine−Borane Adducts: New Interest in Old Molecules". Chem. Rev. 110: 4023–4078. doi:10.1021/cr100105a.

[3] C.Borner; K.Brandhorst; C.Kleeberg (2015). "Selective B–B bond activation in an unsymmetrical diborane(4) by [(Me₃P)₄Rh–X] (X = Me, OtBu): a switch of mechanism?". Dalton Trans. 44: 8600. doi:10.1039/C5DT00618J.

[4] Neeve, Emily C.; Geier, Stephen J.; Mkhalid, Ibraheem A. I.; Westcott, Stephen A.; Marder, Todd B. (2016). "Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse". Chemical Reviews. 116 (16): 9091–9161. doi:10.1021/acs.chemrev.6b00193. PMID 27434758.

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