Synthesis and comparison of nickel, palladium, and platinum bis(N-heterocyclic carbene) pincer complexes for electrocatalytic CO2 reduction

Abstract

A valence isoelectronic and isostructural series of charged bis(N-heterocyclic carbene) pincer complexes [M(bC^N^bC)X]OTf and [M(bC^N^bC)CH₃CN](OTf)₂ (where M = Ni, Pd, and Pt, bC^N^bC = 1,1′-(pyridine-2,6-diylbis(methylene))bis(3-butylbenzo[d]imidazol-2-ylidene)) were synthesized, characterized, modelled by density functional theory calculations, and compared for their electrochemical properties and reactivity with CO₂. Although the electrochemical response of each complex is altered by the presence of CO₂, controlled potential electrolysis experiments demonstrated the superior ability of [Pd] to reduce CO₂ to CO in faradaic efficiencies up to 58% in the presence of trifluoroacetic acid, compared to [Pt] and [Ni] which showed only marginal production of CO, giving the trend [Pd] ≫ [Pt] > [Ni] for this series.