Biomimetic Transition Metal Cluster Complexes: Synthetic Studies and Applications in the Reduction of Inert Small Molecules

Abstract

Abstract Transition metal cluster complexes, particularly those containing iron and sulfur, are used as catalysts for the biological reduction of inert small molecules such as N2 and CO2. The structures of these biological clusters are complicated and the protein backbones around the clusters often play important roles in catalysis, hence reproducing or mimicking the enzymatic functions with synthetic cluster complexes remains a challenge. Appropriate assumptions and hypotheses on the relationships between the structures and functions of biological clusters are needed to develop synthetic molecular catalysts inspired by enzymes. This account reviews recent studies by the author and his coworkers on iron-containing biomimetic cluster complexes. Cubic Mo-Fe-S clusters supported by bulky cyclopentadienyl ligands on molybdenum were designed and synthesized, and their Fe sites captured and catalytically converted N2 under reducing conditions. Iron-hydride clusters, which are relevant to the active species of biological and industrial nitrogen fixation, also served as catalysts for the reduction of N2. Furthermore, various metal-sulfur clusters, ranging from a structural mimic of the complex active site of the N2-reducing enzyme to a simple and cubic [Fe4S4] cluster, were found to catalyze the biologically inaccessible direct conversion of CO2 to short-chain hydrocarbons. These studies have demonstrated the potential utility of biomimetic approaches to the catalytic reduction of inert small molecules, through the rational design and synthesis of simple yet appropriate iron-containing cluster complexes.