A [FeIIFeII] dithiolate complex containing acyl and carbonyl ligands was synthesized. The diiron complex reacted with phosphine, cyanide, isocyanide, and CO to give monomeric FeII complexes reproducing the first coordination sphere of the active site of [Fe]-hydrogenase (H2-forming methylene-tetrahydromethanopterin dehydrogenase, Hmd) in various states. All the acyl and carbonyl carbons in the diiron complex underwent facile isotopic exchange with 13CO via monomeric Fe tricarbonyl intermediates.