Molybdenum-mediated methoxycarbonylation of propargyl halides: molecular and crystal structure of the vinylmolybdenum(II) complex [Mo(bipy)(CO)2(C5H7O2)(py)]BF4

Abstract

Treatment of a methanolic suspension of [PPh₄][Mo(bipy)(CO)₃X](bipy = 2,2′-bipyridine, X = Cl or Br) held at –17 °C with propargyl (prop-2-ynyl) chloride or bromide yields the cis-dicarbonylmolybdenum complexes [Mo(bipy)(CO)₂(C₅H₇O₂)X][X = Cl (1) or Br (2)], which are believed to contain an η³-oxacyclobutenyl ligand formed by methoxycarbonylation of the propargyl moiety. Reaction of complex (1) or (2) with Na(O₂CC₂F₅), or with AgBF₄ in acetone followed by pyridine, yields [Mo(bipy)(CO)₂(C₅H₇O₂)(O₂CC₂F₅)](3) and [Mo(bipy)(CO)₂(C₅H₇O₂)(py)]BF₄(4)(py = pyridine) respectively, in which the mode of bonding of the C₅H₇O₂ ligand has changed from η³-alkyl to σ-vinyl. Crystal structure analysis shows that in the molecule (4) the molybdenum atom is seven-co-ordinate being bonded to bipy [2.241 (7), 2.164(7)Å], pyridine [2.275(8)Å], two carbonyl groups [1.936(10), 1.983(11)Å], and the bidentate C₅H₇O₂ ligand [Mo–O 2.164(6) and Mo–C 2.155(10)Å].