Electron transfer within β-diketiminato nickel bromide and cobaltocene redox couples activating CO2

Abstract

Reduction of β-diketiminato nickel(II) complexes (L^tBuNi^II) to the corresponding nickel(I) compounds does not require alkali metal compounds but can also be performed with the milder cobaltocenes. L^tBuNiBr and Cp₂Co have rather similar redox potentials, so that the equilibrium with the corresponding electron transfer compound [L^tBuNi^IBr][Cp₂Co^III] (ETC) clearly lies on the side of the starting materials. Still, the ETC portion can be used to activate CO₂ yielding a mononuclear nickel(II) carbonate complex and ETC can be isolated almost quantitatively from the solutions through crystallisation. The more negative reduction potential of Cp*₂Co shifts the equilibrium formed with L^tBuNiBr strongly towards the ETC and accordingly the reaction of such solutions with CO₂ is much faster.