Chemistry of Iron Thiolate Complexes with CN^-and CO. Models for the [Fe(CO)(CN)₂] Structural Unit in Ni−Fe Hydrogenase Enzymes

Hydrogenase enzymes: Recent structural studies and active site models

“…When the infrared spectra of this cyclopentadienyl complex in various oxidation states were carefully studied (including 13 C and 15 N labels), excellent agreement with the IR spectra of the Ni/Fe enzyme active site was observed [59]. An iron phosphine trithiolate complex with CN À and CO ligands which exhibits a reversible Fe(II)/Fe(III) redox couple at À476 mV has been suggested as a model for the iron moiety in the Ni/Fe active site [60]. Based on the 100 cm À1 shifts in CO stretching frequencies observed in this model complex upon oxidation from Fe(II) to Fe(III), it is suggested that the oxidation state of the iron in the Ni/Fe enzymes remains unchanged upon redox cycling of the enzyme.…”

Carbon Monoxide and Cyanide Ligands in a Classical Organometallic Complex Model for Fe-Only Hydrogenase

“…[19] Furthermore, the [(h 5 -C 5 H 5 )Fe II (CO)(CN) 2 ] À ion provided a precise match of n(CO) and n(CN) in the oxidized form of [NiFe]H 2 ase, confirming the proposed oxidation state of Fe II in the [(SCys) 2 Ni III (m-SCys) 2 Fe II (CO)(CN) 2 ] site. [5] A highly asymmetric model complex which contains {Fe II -(m-SR) 3 -Fe II (CO) 2 } shows n(CO) bands at 2011 and 1957 cm À1 , considerably higher than the average n(CO) band of the reduced Fe-only H 2 ase enzyme.…”

Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

“…Perfect TBP geometry does not permit a diamagnetic ground state for a d 6 metal, but the observed distorted geometry is consistent with the S = 0 ground state. 36,37 It is also worth noting that the coordination geometry may be different in solution. Despite the metal coordination geometry differences, the Fe-C and C-O bond lengths of 1 and 2 are very similar to each other.…”