Diiron azadithiolate models with bulky bridgehead moiety: Synthesis, structure and electrochemistry

Abstract

To further explore the function of azadithiolate (ADT) bridges in diiron complexes and to develop new biomimics for the active site of [FeFe]-H2ases, here a new model complex [Fe2{(μ-SCH2)2NCHPh2}(CO)6] (1), featuring a bulky bridgehead (CHPh2) was prepared by condensation reaction of [Fe2(μ-SCH2OH)2(CO)6] and NH2CHPh2. The corresponding monophosphine-substituted diiron azadithiolate complexes, [Fe2{(μ-SCH2)2NCHPh2}(CO)5 L] (2–7) [L = PPh3, PPh2(2-C5H4N), PPh2(C6H11), P(C6H4–4-CH3)3, P(C6H4–4–OCH3)3, P(2-C4H3O)3], were prepared via the one-pot method that involves [Fe2(μ-SCH2OH)2(CO)6], phosphine ligand and NH2CHPh2. The diphosphine-substituted complexes, [Fe2{(μ-SCH2)2NCHPh2}(CO)5(κ1-dppm)] [dppm = CH2(PPh2)2] (8), [Fe2{(μ-SCH2)2NCHPh2} (CO)4{(κ2-Ph2P)2NCH2C6H5}] (9), [Fe2{(μ-SCH2)2NCHPh2}(CO)4(μ-dppm)] (10) and [Fe2{(μ-SCH2)2NCHPh2}(CO)4{(μ-Ph2P)2NCH2Ph}] (11) were synthesized using either Me3NO-assisted oxidative decarbonylation reaction or thermal reaction. All the new complexes were fully structurally characterized by elemental analysis, spectroscopies, and particularly for 2–10 by X-ray crystallography. Furthermore, the electrochemical and electrocatalytic properties of these model complexes were investigated by cyclic voltammetry, demonstrating their ability to catalyze the reduction of protons to produce H2 when acetic acid was used as the proton source.