Synthesis of molybdenum carbene complexes of thiophene derivatives

Dinuclear molybdenum biscarbone complexes, [M(CO)(5)-C(OEt)spacerC(OEt)M(CO)(5)], were synthesized employing the classical Fischer method, The connecting spacer unit in each case was a heterocyclic thiophene derivative and included deprotonated thiophene (HTH) 2, 2,'-bithiophene (HT-TH) 5, 3,6-dimethylthieno[3,2-b]thiophene (HT'T'H) 8 as well as dithieno[3,2-b;2',3'-d]-thiophene (HTTTH) 11. In each of the cases the particular monocarbene complex [Mo(CO)(5)C(OEt)TH](1), [Mo(CO)(5)C(OEt)T-TH] (4), [Mo(CO)(5)C(OEt)T'T'H] (7) or [Mo(CO)(5)C(OEt)TTTH] (10) was obtained as a byproduct of the reaction. The more reactive biscarbene complexes of thiophene, [Mo(CO)(5)C(OEt)TC(OEt)-Mo(CO)(5)](2), 2,2'-bithiophene, [Mo(CO)(5)(OEt)T-TC(OEt)-Mo(CO)(5)](5), and 3,6-dimethylthieno[3,2-b]thiophene, [Mo(CO)(5)-C(OEt)T'T'C(OEt)Mo(CO)(5)] (8), yielded, upon exposure to trace amounts of water or oxygen, modified monocarbene products, complexes [Mo(CO)(5)C(OEt)TC(O)OEt] (3), [Mo(CO)(5)C(OEt)-T-TC(O)OEt] (6) and [Mo(CO)(5)(OEt)T'T'C(O)OEt] (9) respectively, in which one metal moiety was replaced by an oxygen group, In the case of the more stable dithieno[3,2-b;2',3'-d]thiophene biscarbene Complex [Mo(CO)(5)C(OEt)TTTC(OEt)Mo(CO)(5)] (11), this product was absent. Instead, a biscarbene product [Mo(CO)(5)C-(OEt)TTTC(OEt)C(OEt)TTTC(OEt)Mo(CO)(5)] (12) was yielded that contained an extended conjugated bridging ligand, resulting from a carbene-carbene coupling reaction.