A model for the CO-inhibited form of [NiFe] hydrogenase: synthesis of (CO)3Fe(μ-StBu)3Ni{SC6H3-2, 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(mu-(SBu)-Bu-t)(3)Ni(SDmp), 1 (Dmp = C6H3-2; 6-(mesityl)(2)), was synthesized from the reaction of the tetranuclear Fe-Ni-Ni-Fe complex [(CO)(3)Fe(mu-(SBu)-Bu-t)(3)Ni](2)(mu-Br)(2), 2 with NaSDmp at -40 degrees C. The nickel site of complex 1 was found to add CO or (CNBu)-Bu-t at -40 degrees C to give (CO)(3)Fe((SBu)-Bu-t)(mu-(SBu)-Bu-t)(2)Ni(CO) (SDmp), 3, or (CO)(3)Fe((SBu)-Bu-t)(mu-(SBu)-Bu-t)(2)Ni((CNBu)-Bu-t)(SDmp), 4, respectively. One of the CO bands of 3, appearing at 2055cm(-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 CNtBu adduct 4 is more robust.