Electronic and geometric effects of phosphatriazaadamantane ligands on the catalytic activity of an [FeFe] hydrogenase inspired complex

Abstract

The [FeFe] hydrogenase enzyme active site inspired complexes [Fe₂(μ-C₆H₄S₂)(CO)₅PTA] (1PTA) and [Fe₂(μ-C₆H₄S₂)(CO)₄PTA₂] (1PTA₂) (PTA = 1,3,5-triaza-7-phosphaadamantane) were synthesized and characterized. The ability of 1PTA and 1PTA₂ to catalytically produce molecular hydrogen in solution from the weak acid acetic acid was examined electrochemically and compared to previous studies on the all carbonyl containing analogue [Fe₂(μ-C₆H₄S₂)(CO)₆] (1). Computational methods and cyclic voltammograms indicated that the substitution of CO ligands by PTA in 1 resulted in markedly different reduction chemistry. Both 1PTA and 1PTA₂ catalytically produce molecular hydrogen from acetic acid, however, the mechanism by which 1 and 1PTA and 1PTA₂ catalyze hydrogen differ in the initial reductive processes.