Models for the homogeneous hydrodesulfurization of thiophenes: Manganese-mediated carbon-sulfur bond cleavage and hydrogenation reactions

Chemical reduction of a series of (eta(5)-thiophene)Mn(CO)(3)(+) complexes (3a-d) under an atmosphere of CO affords dimanganese metallathiacyclic complexes (4a-d), which have a Mn(CO)(4) moiety regioselectively inserted into a C-S bond. Reaction of 4 with H-2, the rate of which is strongly influenced by substituents on the thiophene ring, leads to hydrogenolysis of the Mn-C sigma-bond and formation of (OC)(3)Mn(mu-H)(mu-SCRCHCHCHR')Mn(CO)(3) (8; R, R' = H, Me), which contains bridging hydride and thiolate ligands and a Mn-Mn bond. The addition of PhMgBr to 3 occurs at the sulfur to give zwitterionic complexes (6a-c, 14), which undergo regioselective hydrogenolysis of a C-S bond and, in some cases, partial desulfurization with concomitant formation of (OC)(4)Mn(mu-H)(mu-SPh)Mn(CO)(4) (5a). Crystal structures are reported for complexes 4b,d, 5a, 8d, 10, 12c, and 14b,c. It is suggested that the reactions reported herein may be relevant to the general problem of hydrodesulfurization (HDS) of thiophenic molecules.