Skipping the one C–X one C–C bond rule in Kumada cross coupling reaction. Diarylation from an only B–I in metallacarboranes

• Mono Iodo-subsituted cobaltabisdicarbollide as substrate for metal catalyzed cross coupling reaction.
• Diarylation of cobaltabisdicarbollide starting with a single B–I bond by using Kumada type reaction.
• B–I and B–H activation by Pd for diarylation of cobaltabisdicarbollide using Bisphenyl Grignard reagent.

Typical Kumada cross-coupling reaction has always been associated with the formation of one C–C bond per each initial reactive C–I unit. This has also been the case for B–C cross-coupling starting from a single B–I. For the first time in this paper, diarylation in two distinct sites of a metallacarborane to generate two B–C bonds has been demonstrated, starting from a single B–I. The achievement has been possible by reacting Cs[3,3′-Co(8-I-1,2-C2B9H10) (1′,2′-C2B9H11)] with the 4-bromobiphenyl Grignard reagent in the presence of [PdCl2(PPh3)2] and CuI as co-catalyst. All experimental data including its X-ray crystal diffraction confirm the results.

First time reported diarylation on metallacarboranes starting with a single B–I bond has been achieved using Kumada reaction conditions. The geometry of the palladium catalyst helps in the activation of the B–H and B–I bonds to couple more than one organomagnesium compound with the metallacarborane, something never seen in classic organic chemistry.Figure optionsDownload as PowerPoint slide