Natural inspirations for metal–ligand cooperative catalysis

In conventional homogeneous catalysis, supporting ligands act as spectators that do not interact directly with substrates. However, in metal–ligand cooperative catalysis, ligands are involved in facilitating reaction pathways that would be less favourable were they to occur solely at the metal centre. This catalysis paradigm has been known for some time, in part because it is at play in enzyme catalysis. For example, studies of hydrogenative and dehydrogenative enzymes have revealed striking details of metal–ligand cooperative catalysis that involve functional groups proximal to metal active sites. In addition to the more well-known [FeFe]-hydrogenase and [NiFe]-hydrogenase enzymes, [Fe]-hydrogenase, lactate racemase and alcohol dehydrogenase each makes use of cooperative catalysis. This Perspective highlights these enzymatic examples of metal–ligand cooperative catalysis and describes functional bioinspired molecular catalysts that also make use of these motifs. Although progress has been made in developing molecular catalysts, considerable challenges will need to be addressed before we have synthetic catalysts of practical value. Metal–ligand cooperative catalysis involves both the metal and the ligand moieties present in a complex interacting with substrates. Cooperative catalysis is central to the mechanisms of hydrogenases, lactate racemase and alcohol dehydrogenase. This Perspective describes these enzymes, as well as the small-molecule mimics inspired by these elaborate natural catalysts.