The versatile organometallic type active sites in biology that harbor intact metallo-sulfur units are key The versatile organometallic type active sites in biology that harbor intact metallo-sulfur units are key inspirations for synthetic biomimetic studies. Salient features of such active sites, viz., the propitious positioning of the pendant amine-base over the distal iron in the H-cluster of [FeFe]-Hv2ase, are 'design-directives' in the development of small molecule catalysts. The Dubois catalyst, featuring such a pendant amine, achieves turnovers over 100,000 vs^-1 and serves as a testament to the success of such systems. Although the active site of [NiFe]-Hv2ase is devoid of such a pendant amine, it uses terminal cysteinyl-thiolates in this capacity. As a synthetic chemist, I used several MNv2Sv2 metallodithiolates, as intact metoalloligands, to bind [Cp^RFe(CO)]^+ or {Fe(NO)v2}^9/10 receiver units, via bridging thiolates. These mono- and bidentate hetero/homobimetallic complexes emulate core features of [NiFe]-Hv2ase active site. Despite lack of terminal thiolates or pendant amine, the bidentate complexes showed H^+ reduction electrocatalysis to produce Hv2. Hence the obvious question was how did these electrocatalysts work? Extensive collaborations with Prof. M. B. Hall and co-worker Dr. Shengda Ding, suggested e-/H^+ induced rearrangement of S-bridged bimetallics that allowed HER. Thus, these stable bidentate complexes undergo bidentate/monodentate hemi-lability to develop in situ pendant base features, reminiscent of the enzyme active sites. The free thiolate in the monodentate bound bimetallics displayed stoichiometric binding of protons and Phv3Pau^+ (as a proton analogue), and other electrophiles to support the claim. The versatility of the metallodithiolates ligands, as surrogates of conventional phosphines and carbenes, was also shown in their monodentate binding capabilities with [Fe^Ife^I], [Fe^I[Fe(NO)]^II] and [(u-H)Fe^IIFe^II] systems, as [FeFe]-Hv2ase bioinspired trimetallics.
