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)(+) compl exes (3a-d) under an atmosphere of CO affords dimanganese metallathiac yclic 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 i s 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), w hich 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 comp lexes 4b,d, 5a, 8d, 10, 12c, and 14b,c. It is suggested that the react ions reported herein may be relevant to the general problem of hydrode sulfurization (HDS) of thiophenic molecules.