Anthracene-bridged dinuclear rhenium complexes are reported for electrocatalytic carbon dioxide (CO) reduction to carbon monoxide (CO). Related by hindered rotation of each rhenium active site to either side of the anthracene bridge, cis and trans conformers have been isolated and characterized. Electrochemical studies reveal distinct mechanisms, whereby the cis conformer operates via cooperative bimetallic CO activation and conversion and the trans conformer reduces CO through well-established single-site and bimolecular pathways analogous to Re(bpy)(CO)Cl. Higher turnover frequencies are observed for the cis conformer (35.3 s) relative to the trans conformer (22.9 s), with both outperforming Re(bpy)(CO)Cl (11.1 s). Notably, at low applied potentials, the cis conformer does not catalyze the reductive disproportionation of CO to CO and CO in contrast to the trans conformer and mononuclear catalyst, demonstrating that the orientation of active sites and structure of the dinuclear cis complex dictate an alternative catalytic pathway. Further, UV-vis spectroelectrochemical experiments demonstrate that the anthracene bridge prevents intramolecular formation of a deactivated Re-Re-bonded dimer. Indeed, the cis conformer also avoids intermolecular Re-Re bond formation.

One of the hallmark advances in our understanding of metalloprotein function is showcased in our ability to design new, non-native, catalytically active protein scaffolds. This review highlights progress and milestone achievements in the field of de novo metalloprotein design focused on reports from the past decade with special emphasis on de novo designs couched within common subfields of bioinorganic study: heme binding proteins, monometal- and dimetal-containing catalytic sites, and metal-containing electron transfer sites. Within each subfield, we highlight several of what we have identified as significant and important contributions to either our understanding of that subfield or de novo metalloprotein design as a discipline. These reports are placed in context both historically and scientifically. General suggestions for future directions that we feel will be important to advance our understanding or accelerate discovery are discussed.