Selective Redox Activation of H2 or O2 in a [NiRu] Complex by Aromatic Ligand Effects

Identifying a Real Catalyst of [NiFe]-Hydrogenase Mimic for Exceptional H2 Photogeneration

Inspired by the natural [NiFe]-H₂ ase, we designed mimic 1, (dppe)Ni(μ-pdt)(μ-Cl)Ru(CO)₂ Cl to realize effective H₂ evolution under photocatalytic conditions. However, a new species 2 was captured in the course of photo-, electro-, and chemo- one-electron reduction. Experimental studies of in situ IR spectroscopy, EPR, NMR, X-ray absorption spectroscopy, and DFT calculations corroborated a dimeric structure of 2 as a closed-shell, symmetric structure with a Ru^I center. The isolated dimer 2 showed the real catalytic role in photocatalysis with a benchmark turnover frequency (TOF) of 1936 h^-1 for H₂ evolution, while mimic 1 worked as a pre-catalyst and evolved H₂ only after being reduced to 2. The remarkably catalytic activity and unique dimer structure of 2 operated in photocatalysis unveiled a broad research prospect in hydrogenases mimics for advanced H₂ evolution.

Homogeneous catalytic reduction of polyoxometalate by hydrogen gas with a hydrogenase model complex

Homogeneous catalytic reduction of polyoxometalates by hydrogen gas with a hydrogenase model complex was investigated for the first time.

Oxidation of Guanosine Monophosphate with O2 via a Ru-peroxo Complex in Water

Oxidative damage of DNA by reactive oxygen species (ROS) is responsible for aging and cancer. Although many studies of DNA damage by ROS have been conducted, there have been no reports of the oxidation of RNA components, such as guanosine monophosphate, by metal-based species in water. Here, we report the first case of oxidation of guanosine monophosphate to 8-oxoguanosine monophosphate by a metal-based oxygen bound species, derived from O₂ and in water.

Complexes of MN2S2·Fe(η5-C5R5)(CO) as platform for exploring cooperative heterobimetallic effects in HER electrocatalysis

The control of aggregation at sulfur by metallodithiolates (MN₂S₂) has made them prime candidates as building blocks for the synthesis of biomimetics of various bimetallic enzyme active sites, with reactivity consequences implicating redox control by both metal centers. Recent studies of MN₂S₂ (M = Ni²⁺, Fe(NO)²⁺) bound to [(η⁵-C₅H₅)Fe(CO)]⁺ as electrocatalysts for proton reduction, the hydrogen evolution reaction, demonstrated reduction-induced hemi-lability of the bridging cis-dithiolates as a key step in the electrochemical proton reduction process (Ding, et al., J. Am. Chem. Soc., 2016, 138, 12920-12927). The MN₂S₂·Fe(η⁵-C₅R₅)(CO) platform offers numerous possibilities for tuning the electronic character of the M(μ-S₂)Fe core. As well as modifying M within the metallodithiolate ligand, replacing H by CH₃ at the η⁵-C₅R₅ moiety increases the electron density at the Fe center, which might facilitate the reductive Fe-S bond cleavage. Although release of a free thiolate in these hemi-labile ligands creates a needed internal pendant base, this benefit might be countered by the increase in over-potential for addition of the first electron. Herein we report the preparation and characterization of four bimetallic aggregates with the (η⁵-C₅R₅)Fe(CO) (R = H, CH₃; Fe' or Fe*', respectively) or the dicarbonyl (η⁵-C₅R₅)Fe(CO)₂ scaffold (R = H, CH₃; Fe'' or Fe*'', respectively) bound to redox active MN₂S₂ ligands (M = Ni²⁺, Co(NO)²⁺; N₂S₂ = bismercaptoethane diazacycloheptane) Co-Fe*', Ni-Fe*', Co-Fe' and Co-Fe*'' complexes. The bidentate complexes were found to be electrocatalysts for proton reduction, although at high over-potential, especially for the derivatives of the electron-rich (η⁵-C₅(CH₃)₅)Fe(CO)⁺. The turnover (TON) and turnover frequencies (TOF) were determined and found to be comparable to the previously reported MN₂S₂·Fe(η⁵-C₅H₅)(CO)⁺ analogues.

A matrix of heterobimetallic complexes for interrogation of hydrogen evolution reaction electrocatalysts

Experimental and computational studies address key questions in a structure-function analysis of bioinspired electrocatalysts for the HER. Combinations of NiN2S2 or [(NO)Fe]N2S2 as donors to (η5-C5H5)Fe(CO)+ or [Fe(NO)2]+/0 generate a series of four bimetallics, gradually "softened" by increasing nitrosylation, from 0 to 3, by the non-innocent NO ligands. The nitrosylated NiFe complexes are isolated and structurally characterized in two redox levels, demonstrating required features of electrocatalysis. Computational modeling of experimental structures and likely transient intermediates that connect the electrochemical events find roles for electron delocalization by NO, as well as Fe-S bond dissociation that produce a terminal thiolate as pendant base well positioned to facilitate proton uptake and transfer. Dihydrogen formation is via proton/hydride coupling by internal S-H+···-H-Fe units of the "harder" bimetallic arrangements with more localized electron density, while softer units convert H-···H-via reductive elimination from two Fe-H deriving from the highly delocalized, doubly reduced [Fe2(NO)3]- derivative. Computational studies also account for the inactivity of a Ni2Fe complex resulting from entanglement of added H+ in a pinched -S δ-···H+··· δ-S- arrangement.

Hydrogenase Enzymes and Their Synthetic Models: The Role of Metal Hydrides

Hydrogenase enzymes efficiently process H2 and protons at organometallic FeFe, NiFe, or Fe active sites. Synthetic modeling of the many H2ase states has provided insight into H2ase structure and mechanism, as well as afforded catalysts for the H2 energy vector. Particularly important are hydride-bearing states, with synthetic hydride analogues now known for each hydrogenase class. These hydrides are typically prepared by protonation of low-valent cores. Examples of FeFe and NiFe hydrides derived from H2 have also been prepared. Such chemistry is more developed than mimicry of the redox-inactive monoFe enzyme, although functional models of the latter are now emerging. Advances in physical and theoretical characterization of H2ase enzymes and synthetic models have proven key to the study of hydrides in particular, and will guide modeling efforts toward more robust and active species optimized for practical applications.