Two heterodinuclear NiFe-based sulfenate complexes mimicking an S-oxygenated intermediate of an O2-tolerant [NiFe]-H2ase: synthesis, structures, and reactivity

Abstract

The synthetic modelling of the S-oxygenated intermediate of an O₂-tolerant [NiFe]-H₂ase has proven to be greatly challenging. Treatment of 1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptane with Ni(acac)₂ gave dithiolate complex [1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptanato]nickel(II) or (bmmp-dach)Ni (1) and further treatment of complex 1 with 37% aqueous H₂O₂ afforded sulfenate complex [1-(2-mercapto-2-methylpropyl)-4-(2-sulfeno-2-methylpropyl)-1,4-diazacycloheptanato]nickel(II) or (mmp-sulfeno-dach)Ni (2) and sulfinate complex [1-(2-mercapto-2-methylpropyl)-4-(2-sulfino-2-methylpropyl)-1,4-diazacycloheptanato]nickel(II) or (mmp-sulfino-dach)Ni (3). More interestingly, treatment of complex 2 with FeI₂ afforded the unexpected dithiolate/diiodine complex [(bmmp-dach)Ni][2I₂] (4), while complex 2 reacted with Fe₂(CO)₉ or CpFe(CO)₂(BF₄) to give dinuclear Ni(II)Fe(0) and Ni(II)Fe(II) complexes [(mmp-sulfeno-dach)Ni][Fe(CO)₄] (5) and [(mmp-sulfeno-dach)Ni][Fe(CO)₂Cp(BF₄)] (6), respectively. Further reactivity studies demonstrated that (i) the reaction of complex 5 or 6 with decarbonylating agent Me₃NO produced complex 2, and (ii) the reaction of complex 5 with organometallic oxidant FcBF₄ afforded trinuclear Ni dithiolate complex [(bmmp-dach)Ni]₂[Ni(BF₄)₂] (7), unexpectedly. All the new complexes 1–7 were fully characterized by elemental analysis and various spectroscopic methods, and particularly the molecular structures of complexes 2–5 and 7 were further confirmed by X-ray crystallography.