Cooperative redox and spin activity from three redox congeners of sulfur-bridged iron nitrosyl and nickel dithiolene complexes.

The synthesis of sulfur-bridged Fe-Ni heterobimetallics was inspired by Nature's strategies to "trick" abundant first row transition metals into enabling 2-electron processes: redox-active ligands (including pendant iron-sulfur clusters) and proximal metals. Our design to have redox-active ligands on each metal, NO on iron and dithiolene on nickel, resulted in the observation of unexpectedly intricate physical properties. The metallodithiolate, (NO)Fe(NS), reacts with a labile ligand derivative of [Ni(SCPh)], Ni, yielding the expected S-bridged neutral adduct, , containing a doublet {Fe(NO)}.

Self-Assembled Nickel-4 Supramolecular Squares and Assays for HER Electrocatalysts Derived Therefrom.

Solid-state structures find a self-assembled tetrameric nickel cage with carboxylate linkages, [Ni(NS'O)I(CHCN)] ([]), resulting from sulfur acetylation by sodium iodoacetate of an [NiNS] dimer in acetonitrile. Various synthetic routes to the tetramer, best described from XRD as a molecular square, were discovered to generate the hexacoordinate nickel units ligated by NS, iodide, and two carboxylate oxygens, one of which is the bridge from the adjacent nickel unit in []. Removal of the four iodides by silver ion precipitation yields an analogous species but with an additional vacant coordination site, [], a cation but with coordinated solvent molecules.

Synthetic Metallodithiolato Ligands as Pendant Bases in [FeFe], [Fe[Fe(NO)]], and [(μ-H)FeFe] Complexes.

The development of ligands with specific stereo- and electrochemical requirements that are necessary for catalyst design challenges synthetic chemists in academia and industry. The crucial aza-dithiolate linker in the active site of [FeFe]-Hase has inspired the development of synthetic analogues that utilize ligands which serve as conventional σ donors with pendant base features for H binding and delivery. Several MNS complexes (M = Ni, [Fe(NO)], [Co(NO)], etc.

Controlling O Reactivity in Synthetic Analogues of [NiFeS]- and [NiFeSe]-Hydrogenase Active Sites.

Strategies for limiting, or reversing, the degradation of air-sensitive, base metal catalysts for the hydrogen evolution/oxidation reaction on contact with adventitious O are guided by nature's design of hydrogenase active sites. The affinity of oxygen for sulfur and selenium, in [NiFeS]- and [NiFeSe]-Hase, yields oxygenated chalcogens under aerobic conditions, and delays irreversible oxygen damage at the metals by maintaining the NiFe core structures. To identify the controlling features of S-site oxygen uptake, related (μ-E)(μ-S') (E = S or Se, = (η-CH)Fe(CO)) complexes were electronically tuned by the para-substituent on μ-EPhX (X = CF, Cl, H, OMe, NMe) and compared in aspects of communication between Ni and Fe.

Oxygen uptake in complexes related to [NiFeS]- and [NiFeSe]-hydrogenase active sites.

A biomimetic study for S/Se oxygenation in Ni(μ-EPh)(μ-SN)Fe, (E = S or Se; SN = Me-diazacycloheptane-CHCHS); Fe = (η-CH)Fe(CO) complexes related to the oxygen-damaged active sites of [NiFeS]/[NiFeSe]-Hases is described. Mono- and di-oxygenates (major and minor species, respectively) of the chalcogens result from exposure of the heterobimetallics to O; one was isolated and structurally characterized to have Ni-O-Se-Fe-S connectivity within a 5-membered ring. A compositionally analogous mono-oxy species was implicated by (CO) IR spectroscopy to be the corresponding Ni-O-S-Fe-S complex; treatment with O-abstraction agents such as P(-tolyl) or PMe remediated the O damage.