The iron-iron hydrogenase enzyme, as well as some of its structural and functional models, have been shown to catalyze the reversible oxidation of molecular hydrogen. In nature, the enzymatic activity is inhibited by carbon monoxide, and this inhibition is reversible by light. The active site of the enzyme consists of a diiron core, with a disulfide bridge and varying CO and CN ligands. This has led us to make structural and functional models of the active site with the general formula [Fe2L6] (m-Rdt). We use light to make reactive intermediates from these models that might be important in the catalytic process and study these photoproducts with small molecules and possible substrates. Photolysis of the model, [Fe(CO3]2 (m-pdt), (1), was done in different solvents with varying concentrations of CO, and the thermal regeneration was studied using temperature dependent kinetics to obtain rate constants and entropy of activation. This thermodynamic parameter assesses whether reactions occur through an associative type mechanism or a dissociative type mechanism. Our results show a strong solvent dependence for the rate of reaction, with rate constants ranging from 3 x 10-5 M-1 s-1 in acetonitrile 0.92 M-1 s-1 in THF to 1.0 x 108 M-1 s-1 in hexane. This strong solvent dependence suggests that substitution occurs through a dissociative type mechanism, but preliminary temperature dependent studies indicate a possible difference in mechanism based on solvent. Synthesis of other models with varying bridge heads and ligands may produce derivatives that show difference in their photochemistry and thermal reactivity. Furthermore, quantum yield of 1 has been determined to 0.17.

Temperature and solvent dependent kinetics and quantum yields of [Fe-Fe] hydrogenase model complexes

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.