A Nitrogenase Cluster Model [Fe₈S₆O] with an Oxygen Unsymmetrically Bridging Two Proto-Fe₄S₃ Cubes: Relevancy to the Substrate Binding Mode of the FeMo Cofactor

An oxygen-encapsulated iron sulfido cluster, [(DmpS)­Fe4S3O]­[(DmpS)­Fe4S3]­(μ-SDmp)2(μ-OCPh3) (2; Dmp = 2,6-(mesityl)2C6H3), has been synthesized by the reaction of the preformed dinuclear iron thiolate/alkoxide [(Ph3CO)­Fe]2(μ-SDmp)2 (1) with 1/8S8 and 1/4H2O in toluene. In the [Fe8S6O] core, the oxygen atom bridges unsymmetrically two incomplete Fe4S3 cubes, and two coordinatively unsaturated iron atoms are weakly bound to mesityl rings. Relevance of the cluster structure of 2 to the nitrogenase FeMo cofactor and its substrate binding mode is discussed.