Synthesis of Molybdenum Carbene Complexes of Thiophene Derivatives

Abstract

Dinuclear molybdenum biscarbene complexes, [M(CO)5C(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, 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)5C(OEt)TH](1), [Mo(CO)5C(OEt)T-TH] (4), [Mo(CO)5C(OEt)T'T'H] (7) or [Mo(CO)5C(OEt)TTTH] (10) was obtained as a byproduct of the reaction. The more reactive biscarbene complexes of thiophene, [Mo(CO)5C(OEt)TC(OEt)Mo(CO)5](2), 2, 2'-bithiophene, [Mo(CO)5C(OEt)T-TC(OEt)Mo(CO)5](5), and 3, 6-dimethylthieno[3, 2-b]thiophene, [Mo(CO)5C(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)5C(OEt)TC(O)OEt] (3), [Mo(CO)5C(OEt)T-TC(O)OEt] (6) and [Mo(CO)5C(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 bis carbene complex [Mo(CO)5C(OEt)TTTC(OEt)Mo(CO)5] (11), this product was absent. Instead, a biscarbene product [Mo(CO)5C (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. Die Synthese von Molybdan Carbenkomplexen von Thiophen Derivaten Die Synthese und Eigenschaften der neuen Dimolybdan-dicarben-Komplexe, [M(CO)5C(OEt)-Spacer-C(OEt)M (CO)5], (Spacer (Brucke) = Thienylen(2), 2, 2'-Bithienylen(5), 3, 6-Dimethylthieno[3, 2-b]thienylen(8), Dithieno[3, 2-b;2', 3'-d]thienylen (11) werdern beschrieben. Nebenprodukte der Dilithiumthienyle ergaben auserdem die neuen Monocarbenkomplexe, [M(CO)5 C(OEt)-Spacer-H] (1, 4, 7, 10), die vollstandig charakterisiert wurden. Die Biscarben-Komplexe 2, 5 und 8 reagieren in polaren Losungsmitteln mit Sauerstoff oder Wasser zu den entsprechenden [M(CO)5C(OEt)-Spacer-C(O)OEt]-Komplexen 3, 6 und 9. Der Biscarben-Komplex 11 liefert in geringer Ausbeute den neuen Biscarben-Komplex 12, was auf eine Carben-Carben-Kupplungsreaktion hinweist.