Electron‐Rich Diferrous–Phosphane–Thiolates Relevant to Fe‐only Hydrogenase: Is Cyanide “Nature's Trimethylphosphane”?

The two‐step one‐pot oxidative decarbonylation of [Fe 2 (S 2 C 2 H 4 )(CO) 4 (PMe 3 ) 2 ] ( 1 ) with [FeCp 2 ]PF 6 , followed by addition of phosphane ligands, led to a series of diferrous dithiolato carbonyls 2 – 6 , containing three or four phosphane ligands. In situ measurements indicate efficient formation of 1 2+ as the initial intermediate of the oxidation of 1 , even when a deficiency of the oxidant was employed. Subsequent addition of PR 3 gave rise to [Fe 2 (S 2 C 2 H 4 )(μ‐CO)(CO) 3 (PMe 3 ) 3 ] 2+ ( 2 ) and [Fe 2 (S 2 C 2 H 4 )(μ‐CO)(CO) 2 (PMe 3 ) 2 (PR 3 ) 2 ] 2+ (R=Me 3 , OMe 4 ) as principal products. One terminal CO ligand in these complexes was readily substituted by MeCN, and [Fe 2 (S 2 C 2 H 4 )(μ‐CO)(CO) 2 (PMe 3 ) 3 (MeCN)] 2+ ( 5 ) and [Fe 2 (S 2 C 2 H 4 )(μ‐CO)(CO)(PMe 3 ) 4 (MeCN)] 2+ ( 6 ) were fully characterized. Relevant to the H red state of the active site of Fe‐only hydrogenases, the unsymmetrical derivatives 5 and 6 feature a semibridging CO ligand trans to a labile coordination site.