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, gave rise to [Fe(2)(S(2)C(2)H(4))(mu CO)(CO)(3)(PMe(3))(3)](2+) (2) and [Fe(2)(S(2)C(2)H(4))(mu-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))(mu-CO)(CO)(2)(PMe(3)),(MeCN)](2+) (5) and [Fe(2)(S(2)C(2)H(4))(mu-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.