REACTIONS OF CP-STAR-IR(2,5-DIMETHYLTHIOPHENE) WITH IRON CARBONYLS - A NEW MECHANISM FOR THIOPHENE HYDRODESULFURIZATION

Reactions of the isomers Cp*Ir(eta-4-2,5-Me2T) (1) and Cp*Ir(C,S-2,5-Me2T) (2), where Cp* = eta-5-C5Me5 and 2,5-Me2T = 2,5-dimethylthiophene, with iron carbonyls (Fe(CO)5, Fe2(CO)9, and Fe3(CO)12) give eight different products, 3-10. Two of them, Cp*Ir(eta-4-2,5-Me2T.Fe(CO)4) (3) and Cp*Ir(eta-4-2,5-Me2T.Fe2(CO)7) (7), retain the eta-4-2,5-Me2T coordination to the Ir but are also bonded through the sulfur to the Fe atom(s). Both 1 and 2 react with Fe3(CO)12 to give 8 in which all of the elements of 2,5-Me2T are present but the sulfur has been removed from the thiophene ring. Reaction of 8 with CO (1 atm) [GRAPHICS] gives the totally desulfurized 9. A new mechanism is proposed for thiophene hydrodesulfurization (HDS) based on the C-S bond cleavage reactions which occur when 1 rearranges to 2 and 2 is converted to 8. Structures of 3, 7, 8, and 9 were established by X-ray diffraction studies.