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.