Reactions of sixteen-electron bis(alkyne)-molybdenum and -tungsten complexes with phosphines and isocyanides; molecular and crystal structure of the insertion product [MoCF3(ButNC){(CF3)4C5NBut}(η-C5H5)]

Abstract

Diphenylacetylene reacts thermally, and but-2-yne on U.V. irradiation, with [Mo(COCF₃)(CO)₃(η-C₅H₅)] to give respectively, [Mo(CF₃)(CO)(η²-PhC₂Ph)(η-C₅H₅)] and [Mo(CF₃)(CO)(η²-MeC₂Me)(η-C₅H₅)]. In contrast, the corresponding reaction (u.v.) of hexafluorobut-2-yne or dimethyl acetylenedicarboxylate affords [Mo(CF₃)(η²-CF₃C₂CF₃)₂(η-C₅H₅)] and [Mo(CF₃){η²-C₂(CO₂Me)₂}₂(η-C₅H₅)]. Treatment of [Mo(CF₃)(CO)(η²-MeC₂Me)(η-C₅H₅)] with CF₃C₂CF₃ gives [Mo(CF₃)(η²-MeC₂Me)(η²-CF₃C₂CF₃)(η-C₅H₅)]. The co-ordinatively unsaturated bis(acetylene)complexes. and also [MCl(η²-CF₃C₂CF₃)₂(η-C₅H₅)](M = Mo or W), react with PMe₃ or PPh₃ to give the 18-electron species [MX(η²-RC₂R)₂L(η-C₅H₅)](M = MO or W; X = CF₃ or Cl: L = PMe₃ or PPh₃). These complexes exist in solution as equilibrating cis and trans isomers. An analogous reaction of [Mo(CF₃)(η²-CF₃C₂CF₃)₂(η-C₅H₅)] or [WCl(η²-CF₃C₂CF₃)₂(η-C₅H₅)] with Bu^tNC affords initially isostructural 1 : 1 adducts; however, excess of isocyanide gives cyclopentadienimine complexes. A single-crystal X-ray diffraction study has established the structure of [Mo(CF₃)(Bu^tNC){(CF₃)₄C₅NBu^t}(η-C₅H₅)]. Crystals are monoclinic, space group P2₁/a with a= 17.452(6), b= 35.410(18), and c= 9.182(4)Å, β= 95.91(3)°, Z= 8. The structure has been determined from the analysis of 7 900 data with I 1.0σ collected to 2θ 55.0°(MO-K_α, radiation) on a four-circle diffractometer, and refined by least squares to R 0.127. In contrast, excess of isocyanide reacts with [MoCl(η²-PhC₂Ph)₂(η-C₅H₅)] and with [MCl(η²-CF₃C₂CF₃)(η²-PhC₂Ph)(η-C₅H₅)](M = Mo or W) to give respectively, the cationic species [M(CNBu^t)₃(η²-RC₂R)(η-C₅H₅)]⁺(M = Mo or W; R = Ph or CF₃) isolated as Cl^– or [PF₆]^– salts. Oxygen reacts with [MX(CO)(η²-RC₂R)(η-C₅H₅)](M = Mo or W; X = Cl or CF₃; R = Ph or CF₃) to give the oxo-complexes [MoX(O)(η²-RC₂R)(η-C₅H₅)].