Insertion of BH<sub>3</sub> into a Cobalt–Aryl Bond: Synthetic Routes to Arylborohydride and Borane-Amino Hydride Complexes
Shengnan Zhang, Xiaofang Zhai, Yike Song, Lei Feng, Chen‐Ho Tung, Wenguang Wang
Abstract
We report a new method to synthesize cobalt arylborohydrides and incorporate the borane-amine unit into the coordination sphere of a half-sandwich cobalt system based on activation of primary amines. Insertion of BH3 into the Co(II)–C(aryl) bond of the phosphinoaryl cobalt compound Cp*Co(2-C6H4PPh2) (1) provided the cobalt arylborohydride Cp*Co(κ3-H,H,P-H3BC6H4PPh2) (2), which was oxidized to the cationic cobalt(III) arylborohydride (2+). Complex 2+ can be synthesized alternatively by oxidation of the cobalt(II) aryl compound (1), followed by BH3 insertion into the Co(III)-C(aryl) unit. This cationic borohydride enables alkyl amines activation. As exemplified by the reaction with cyclohexylamine, the phosphinoborohydride moiety in 2+ undergoes B–N bond coupling with the two amine molecules by release of 2 equiv of H2, leading to the borane-amino cobalt(III) hydride (3) featuring a phosphinoborane-diamine ligand, 1,2-Ph2PC6H4B(NHCy)2.