Diiron Proton Reduction Catalysts Possessing Electron‐Rich and Electron‐Poor Naphthalene‐1,8‐dithiolate Ligands

Abstract The diiron complexes [Fe 2 (CO) 6 (1,8‐S 2 ‐2,4,5,7‐Cl 4 C 10 H 2 )] ( 3 ), [Fe 2 (CO) 6 (1,8‐S 2 C 10 H 6 )] ( 4 ), and [Fe 2 (CO) 6 (1,8‐S 2 ‐2,7‐ t Bu 2 C 10 H 4 )] ( 5 ) were synthesized in moderate yield from naphthalene‐1,8‐dithiols and [Fe 3 (CO) 12 ]. They were characterized by IR, 1 H and 13 C NMR spectroscopy and 3 and 4 were characterized by X‐ray crystallography. They contain a butterfly Fe 2 S 2 core with Fe–Fe distances of 2.529(1) ( 3 ) and 2.506(1) Å ( 4 ). Cyclic voltammetry (CH 2 Cl 2 / n Bu 4 PF 6 ) revealed two one‐electron reductions, at potentials more positive than those for the related [Fe 2 (CO) 6 (S(CH 2 ) 3 S)] ( 1 ), and one one‐electron oxidation. The first reduction of the electron poor 3 (−1.60 V vs Fc/Fc + ) is 240 mV more positive than the first reduction of the electron rich 5 (−1.84 V). Electrochemical studies revealed that 3 – 5 facilitate the proton reduction of p ‐toluenesulfonic acid. The rates of catalysis, with a 95 % confidence limit, are 2.4±0.8 ( 1 ), 5.2±0.8 ( 3 ), 3.1±1.1 ( 4 ), 2.9±0.6 ( 5 ), and 4.5±0.2 h −1 for the related [Fe 2 (CO) 6 (1,2‐S 2 C 6 H 4 )]. The rates were determined by bulk electrolysis at −1.70 V (Fc/Fc + ), which correspond to an overpotential of 1.05 V for p ‐toluenesulfonic acid.