Benzoate-functionalized diiron propanedithiolate complexes with mono- and di-phosphine ligands as catalysts for reduction of protons

Abstract

Reaction of the diiron propanedithiolate complex [μ-(SCH2)2CHO2CC6H5]Fe2(CO)6 (A) with triphenylphosphine (PPh3) or cis-1,2-bis(diphenylphosphine)ethylene (cis-dppv) in the presence of one equivalent of Me3NO·2H2O yielded a mono-substituted complex [μ-(SCH2)2CHO2CC6H5]Fe2(CO)5(PPh3) (1) or an asymmetrically substituted complex [(μ-SCH2)2CHO2CC6H5]Fe2(CO)4(κ2-dppv) (2), respectively. The structures of both complexes were characterized by spectroscopic methods and X-ray crystallography. In the solid state, the PPh3 ligand in 1 occupies an apical position of the square pyramidal geometries of the Fe2, while the cis-dppv in 2 coordinates Fe2 in an apical-basal manner. The electrochemistry of both complexes was investigated. The electron-withdrawing benzoate functionality on the bridgehead carbon of the propanedithiolate bridge shifts the oxidation and reduction potentials of 1 or 2 slightly. Both complexes can catalyze the reduction of protons from CF3COOH but with a higher efficiency for 2.