The employment of a hydrophilic tris(morpholino)phosphine ligand in diiron propane-1,3-dithiolate complexes for potentially water-soluble iron-only hydrogenase active-site mimics

A tris(morpholino) phosphine (TMP) ligand was introduced into the diiron dithiolate complexes in order to improve the hydro-and protophilicity of the iron-only hydrogenase active site models. Mono-and di-TMP substituted diiron complexes, (mu-pdt)[Fe(CO)(3)][Fe(CO)(2)(TMP)] (2, pdt = 1,3-propanedithiolato) and (mu-pdt) [Fe(CO)(2)(TMP)](2) (3), were synthesized and spectroscopically characterized. The coordination configuration of 3 was determined by single X-ray analysis. Temperature-dependent H-1 and P-31 NMR spectroscopy studies provided insight into the interconversion of the irondithiacyclohexane ring and the rotation of the [Fe(CO)(2)PR3] moieties for 2 and 3 in solution. The electrochemical properties of 2 and 3 were investigated in pure CH3CN and CH3CN-H2O mixtures in the absence and presence of acetic acid. Hydrogen production and the dependence of current on acid concentration indicated that complexes 2 and 3 exhibited electrocatalytic activities for proton reduction in both pure and H2O-containing CH3CN solutions. The current sensitivities, i.e., electrocatalytic activities, were demonstrated to be greater in CH3CN-H2O mixtures than in pure CH3CN. The most effective electrocatalytic activities of 2 and 3 were observed with 10% added water.