Nickel–iron dithiolates related to the deactivated [NiFe]-hydrogenases

Abstract

Described herein are preparations of synthetic models for the deactivated Ni(II)Fe(II) states of the [NiFe]-hydrogenases. Iodination of the S = ½ species [(dppe)Ni(pdt)Fe(CO)₃]⁺ afforded the diamagnetic iodo complex [(dppe)Ni(pdt)IFe(CO)₃]⁺. Crystallographic analysis of this species confirmed the presence of square-pyramidal Ni linked to an octahedral Fe centre. The Ni⋯Fe separation of 3.018 Å indicated the absence of metal–metal bonding. This complex could be reduced to give (dppe)Ni(pdt)Fe(CO)₃ and, in the presence of iodide, decarbonylated to afford (dppe)Ni(pdt)FeI₂. Derivatives of the type [(diphosphine)Ni(dithiolate)XFe(CO)₂L]⁺ (X = Cl, Br, I) were prepared by halogenation of mixed-valence precursors [(diphosphine)Ni(dithiolate)Fe(CO)₂L]⁺ (diphosphine = dppe, dcpe; L = tertiary phosphine or CO). The Fe(CO)₂(PR₃)-containing derivatives are more robust than the related tricarbonyl derivatives. Exploiting this greater stability, we characterised examples of chloride and bromide derivatives. Related fluorides could be prepared by F⁻ abstraction from BF₄⁻. Spectroscopic evidence is presented for the hydroperoxide [(dppe)Ni(pdt)(OOH)Fe(CO)₂L]⁺, which represents a model for the Ni-SU state.