ControllingO 2 Reactivity in SyntheticAnalogues 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 O2 are guided by Nature’s design of hydrogenase active sites. The affinity of oxygen for sulfur, in [NiFeS]-H2ase, and selenium, in [NiFeSe]-H2ase, yields oxygenated chalcogens under aerobic conditions, and delays irreversible oxygen damage at the metals by maintenance of the NiFe core structure of active sites. In attempts to identify the controlling features of S-site oxygen uptake, related Ni(µ-EPhX)(µ-S’N2)Fe (E = S or Se, Fe = (η5-C5H5)FeII(CO)) complexes were electronically tuned by the para substituent on the phenyl ring (X = CF3, Cl, H, OMe, NMe2) and compared in aspects of communication between Ni and Fe, redox potentials, and chemical reactivities. Studies of S- and Se-oxygenation by O2 found both single and double O-atom uptake at the chalcogens that led to the conversion of the 4-membered core, Ni(µ-EPhX)(µ-S’N2)Fe, to a 5-memb...