Electron-Rich Diferrous-Phosphane-Thiolates Relevant to Fe-only Hydrogenase: Is Cyanide 'Nature's Trimethylphosphane'?

摘要

The two-step one-pot oxida-tive decarbonylation of [Fe_2-(S_2C_2H_4)(CO)_4(PMe_3)_2] (1) with [FeCp_2]PF_6,followed by addition of phosphane ligands,led to a series of di-ferrous 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_2C_2H_4)(mu-CO)(CO)_3(PMe_3)_3]~(2+) (2) and [Fe_2-(S_2C_2H_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_2C_2H_4)(mu-CO)(CO)_2-(PMe_3)_3(MeCN)]~(2+) (5) and [Fe_2-(S_2C_2H_4)(mu-CO)(CO)(PMe_3)_4(MeCN)]~(2+) (6) were fully characterized.Relevant to the H_(rcd) state of the active site of Fe-only hydrogenases,the unsymmetri-cal derivatives 5 and 6 feature a semi-bridging CO ligand trans to a labile coordination site.