Synergy between metals for small molecule activation: Enzymes and bio-inspired complexes

Abstract Transition metal-driven small molecule activation is essential for the production of fuels and chemicals or energy supply. The use of multimetallic catalysts, where two or more metal centers act in synergy to activate and transform the substrate(s), is widespread both in nature (metalloenzymes) and (bio)inorganic chemistry. Benefits of this strategy in terms of catalytic performances result from cooperation between different metals (i) to bind and activate a single substrate, (ii) to activate different substrates reacting together (typically one per metal), or (iii) with one “assisting” metal tuning the reactivity of the “active” metal center. In this review, we discuss multimetallic active sites of enzymes and multimetallic synthetic bio-inspired complexes, for which the cooperation between metal centers is critical for the activation of small molecules. The following processes are considered: (i) H2 production(/oxidation) ([FeFe]- and [NiFe]-hydrogenases); (ii) O2 reduction (cytochrome c oxidase); (iii) CO2 reduction and formation of C–C bonds (NiFe- and MoCu-dependent CO dehydrogenases and acetyl-CoA synthase); (iv) N2 reduction (Mo-dependent nitrogenase); and (v) N2O reduction (N2O reductase). This overview is expected to contribute to understand the role of metal-metal synergy in enzymes and model complexes and its impact on reactivity. This background, in combination with ligand design, can be exploited for the development of the next generation of bio-inspired multinuclear catalysts with optimized performances.