Quaterpyridine-bridged binuclear manganese(I) carbonyl complexes: comparison of electrocatalytic H2 evolution with mononuclear analogues

Abstract

The hydrogen evolution reaction, which reduces protons to molecular hydrogen, has attracted significant attention as an efficient method for hydrogen production. In this context, manganese(I) carbonyl complexes have been studied as electrochemical proton reduction catalysts because of their low cost and structural similarity to the active sites of iron–iron hydrogenases. In this work, binuclear manganese(I) carbonyl complexes bridged by quaterpyridine (containing two 2,2’-bipyridyl frameworks) were synthesized and their structure–reactivity relationships were investigated. The proton nuclear magnetic resonance spectroscopy and structural determination suggested that the primary coordination spheres of these dimers possess identical geometries in both solid and solution states. Additionally, electrochemical measurements were performed in the presence of protons using a solvent-coordinated dimer and its corresponding monomer to investigate the catalytic activity for proton reduction. The mono- and binuclear complexes exhibited different redox properties: the dimer exhibited inferior catalytic parameters for proton reduction compared with the corresponding monomer. These results suggest that the stability of the reduced species greatly affects the catalytic activity, and that multinucleation does not necessarily lead to improved catalytic performance. This work therefore provides essential information that should assist the design of novel manganese(I) catalysts for the proton reduction reaction.