Oxidation, coordination, and nickel-mediated deconstruction of a highly electron-rich diboron analogue of 1,3,5-hexatriene

The reductive coupling of an N-heterocyclic carbene (NHC) stabilized (dibromo)vinylborane yields a 1,2-divinyldiborene, which, although isoelectronic to a 1,3,5-triene, displays no extended $\pi$ conjugation because of twisting of the $C_2{B}_2{C}_2$ chain. While this divinyldiborene coordinates to copper(I) and platinum(0) in an ${\eta }^2$-$B_2$ and ${\eta }^4$-$C_2{B}_2$ fashion, respectively, it undergoes a complex rearrangement to an ${\eta }^4$-1,3-diborete upon complexation with nickel(0). (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA)