Zinc borylation and reduction by a diborane(4) species via B–O bond formation

Abstract

We report a convenient synthesis of the zinc–boryl complex (Nacnac^Mes)ZnBpin under mild conditions via formal disproportionation of bis(pinacolato)diboron(4), aided thermodynamically by B–O bond formation. This species can be isolated both base-free and as the DMAP adduct (Nacnac^Mes)Zn(DMAP)Bpin and crystallographically characterised in the latter form. Onward reactivity of the base free zinc boryl complex with CO₂ occurs reductively, yielding further B–O bonds as well as CO gas. The strength of this driving force can then be harnessed in the reaction between (Nacnac^Mes)ZnBpin and a Zn–O bonded species (Nacnac^Mes)ZnOB{(NDippCH)₂}, which yields the metal–metal bonded dimer [(Nacnac^Mes)Zn]₂, the overall formation of which utilizes a diboron(4) species as the stoichiometric reductant of Zn(II) to Zn(I).