Synthetic and structural studies on new diiron azadithiolate (ADT)-type model compounds for active site of [FeFe]hydrogenases

Abstract

A series of new diiron azadithiolate (ADT) complexes (1–8), which could be regarded as the active site models of [FeFe]hydrogenases, have been synthesized starting from parent complex [(μ-SCH₂)₂NCH₂CH₂OH]Fe₂(CO)₆ (A). Treatment of A with ethyl malonyl chloride or malonyl dichloride in the presence of pyridine afforded the malonyl-containing complexes [(μ-SCH₂)₂NCH₂CH₂O₂CCH₂CO₂Et]Fe₂(CO)₆ (1) and [Fe₂(CO)₆(μ-SCH₂)₂NCH₂CH₂O₂C]₂CH₂ (2). Further treatment of 1 and 2 with PPh₃ under different conditions produced the PPh₃-substituted complexes [(μ-SCH₂)₂NCH₂CH₂O₂CCH₂CO₂Et]Fe₂(CO)₅(PPh₃) (3), [(μ-SCH₂)₂NCH₂CH₂O₂CCH₂CO₂Et]Fe₂(CO)₄(PPh₃)₂ (4), and [Fe₂(CO)₅(PPh₃)(μ-SCH₂)₂NCH₂CH₂O₂C]₂CH₂ (5). More interestingly, complexes 1–3 could react with C₆₀ in the presence of CBr₄ and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) via Bingel–Hirsch reaction to give the C₆₀-containing complexes [(μ-SCH₂)₂NCH₂CH₂O₂CC(C₆₀)CO₂Et]Fe₂(CO)₆ (6), [Fe₂(CO)₆(μ-SCH₂)₂NCH₂CH₂O₂C]₂C(C₆₀) (7), and [(μ-SCH₂)₂NCH₂CH₂O₂CC(C₆₀)CO₂Et]Fe₂(CO)₅(PPh₃) (8). The new ADT-type models 1–8 were characterized by elemental analysis and spectroscopy, whereas 2–4 were further studied by X-ray crystallography and 6–8 investigated in detail by DFT methods.