A model for the CO-inhibited form of [NiFe] hydrogenase: synthesis of (CO) 3 Fe( μ -S t Bu) 3 Ni{SC 6 H 3 -2,6-(mesityl) 2 } and reversible CO addition at the Ni site

A [NiFe] hydrogenase model compound having a distorted trigonal-pyramidal nickel center, (CO)3 Fe(μ -St Bu)3 Ni(SDmp), 1 (Dmp = C6 H3 -2,6-(mesityl)2 ), was synthesized from the reaction of the tetranuclear Fe-Ni-Ni-Fe complex [(CO)3 Fe(μ -St Bu)3 Ni]2 (μ -Br)2 , 2 with NaSDmp at -40 °C. The nickel site of complex 1 was found to add CO or CNt Bu at -40 °C to give (CO)3 Fe(St Bu)(μ -St Bu)2 Ni(CO)(SDmp), 3, or (CO)3 Fe(St Bu)(μ -St Bu)2 Ni(CNt Bu)(SDmp), 4, respectively. One of the CO bands of 3, appearing at 2055 cm-1 in the infrared spectrum, was assigned as the Ni-CO band, and this frequency is comparable to those observed for the CO-inhibited forms of [NiFe] hydrogenase. Like the CO-inhibited forms of [NiFe] hydrogenase, the coordination of CO at the nickel site of 1 is reversible, while the CNt Bu adduct 4 is more robust.