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)]

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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 ButNC 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)(ButNC){(CF3)4C5NBut}(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-Kα, 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(CNBut)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)].