Trinuclear [NiFe] Clusters as Structural Models for [NiFe] Hydrogenase Active Sites

[Fe(CH 3 COCH=CHPh)(CO) 3 ] reacts with [Ni(‘S 4 ’)] x ( x = 1, 2) or [Ni(‘S 4 C 3 Me 2 ’)] [‘S 4 ’ 2− = 1,2‐bis(2‐mercaptophenylthio)ethane(2‐),‘S 4 C 3 Me 2 ’ 2− = 1,3‐bis(2‐mercaptophenylthio)‐2,2‐dimethylpropane(2‐)] to afford trinuclear [NiFe] clusters [Ni(‘S 4 ’){Fe(CO) 3 } 2 ] ( 1 ) and [Ni(‘S 4 C 3 Me 2 ’){Fe(CO) 3 } 2 ] ( 2 ) and the dinuclear Fe II Fe 0 complex [Fe(CO)(‘S 4 C 3 Me 2 ’)Fe(CO) 3 ] ( 3 ). Clusters 1 and 2 have Ni−Fe bond lengths similar to those of active or reduced states of [NiFe] hydrogenases, a sulfur‐dominated coordination sphere of Ni and iron‐bound CO. Therefore, 1 and 2 may serve as structural model complexes for the [NiFe] hydrogenase active site. Combination of the ‘S 4 C 3 Me 2 ’ ligand with FeCl 2 ·4H 2 O yielded [Fe(‘S 4 C 3 Me 2 ’)] 2 ( 4 ), the dinuclearity of which suggests that the ‘S 4 C 3 Me 2 ’ ligand is less flexible than its ethylene‐bridged derivative, which affords a tetrameric [Fe(‘S 4 ’)] 4 complex reported earlier. Compound 4 reacts with 2 equiv. of CO to give [Fe(CO)(‘S 4 C 3 Me 2 ’)] 2 ( 5 ), which like 4 is only sparingly soluble in all common organic solvents. Complex 5 easily loses CO even if stored in the solid state. [Fe(CH 3 COCH=CHPh)(CO) 3 ] reacts with 5 to afford 3 as the only product. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)