Synthetic Active Site Model of the [NiFeSe] Hydrogenase

A dinuclear synthetic model of the [NiFeSe] hydrogenase active site and a structural, spectroscopic and electrochemical analysis of this complex is reported. [NiFe(‘S(2)Se(2)’)(CO)(3)] (H(2)‘S(2)Se(2)’=1,2-bis(2-thiabutyl-3,3-dimethyl-4-selenol)benzene) has been synthesized by reacting the nickel selenolate complex [Ni(‘S(2)Se(2)’)] with [Fe(CO)(3)bda] (bda=benzylideneacetone). X-ray crystal structure analysis confirms that [NiFe(‘S(2)Se(2)’)(CO)(3)] mimics the key structural features of the enzyme active site, including a doubly bridged heterobimetallic nickel and iron center with a selenolate terminally coordinated to the nickel center. Comparison of [NiFe(‘S(2)Se(2)’)(CO)(3)] with the previously reported thiolate analogue [NiFe(‘S(4)’)(CO)(3)] (H(2)‘S(4)’=H(2)xbsms=1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene) showed that the selenolate groups in [NiFe(‘S(2)Se(2)’)(CO)(3)] give lower carbonyl stretching frequencies in the IR spectrum. Electrochemical studies of [NiFe(‘S(2)Se(2)’)(CO)(3)] and [NiFe(‘S(4)’)(CO)(3)] demonstrated that both complexes do not operate as homogenous H(2) evolution catalysts, but are precursors to a solid deposit on an electrode surface for H(2) evolution catalysis in organic and aqueous solution.