Formation of sixteen-electron alkyne complexes by reaction of halogeno(tricarbonly)(η5-cyclopentadienyl)-molybdenum and -tungsten complexes with alkynes; crystal and molecular structure of [WCl(CF3C2CF3)2(η5-C5H5)]

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Abstract
Reaction of hexafluorobut-2-yne with [MoCl(CO)3(η5-C5H5)] affords the cyclopentadienone complex [MoCl(CO)(C8F12CO)(η5-C5H5)]. If the displaced carbon monoxide is removed, then the product is [MoCl(CF3C2CF3)2-(η-C5H5)] together with minior amonuts of [{MoCl(CF3C2CF3)(η5-C5H5)}2]. The reaction of CF3C2CF3 with [WCl(CO)3(η5-C5H5)] affords only [WCl(CF3C2CF3)2(η5-C5H5)](II), which was structurally identified by X-ray crystallography as an octahedral 16-electron species, in which the acetylene acts as a 2-electron donor. Treatment of [MoCl(CO)3(η5-C5H5)] with MeC⋮CMe affords either[MoCl(MeC2Me)2(η5-C5H5)] or [MoCl(CO){C4Me4(CO)2}(η5-C5H5)] depending on the reaction conditions. The latter compound is formulated as a duroqunione complex. U.v. irradiation of [WCl(CO)3(η5-C5H5)] and PhC⋮Cph gives [WCl(CO)(PhC2Ph)(η5-C5H5)]. In refluxing hexane, [MoCl(CO)3(η5-C5H5)] reacts with PhC2Ph to give [MoCl(CO)(PhC2Ph)(η5-C5H5)] and [MoCl(PhC2Ph)(η5-C5H5)]. The thermal reaction of MeC2Ph with [MoCl(CO)3(η5-C5H5)] gives initially [MoCl(CO)(PhC2Me)(η5-C5H5)] which reacts further to yield [MoCl(PhCMe)2(η5-C5H5)]. Treatment (60 °C) of [MoCl(CO)(PhC2Ph)(η5-C5H5)] with MeC2Me or CF3C2CF3 affords [MoCl(RC2R)2(η5-C5H5)] R = Me or CF3). At room temperature, [MoCl(CF3C2CF3)(PhC2Me)(η5-C5H5)] is formed. Similar reactions afforded the mixed acetylene complexes [MoCl(CF3C2CF3)(PhC2Me)(η5-C5H5)], [WCl(CF3C2CF3)(PhC2Ph)(η5-C5H5)], and (WCl(CF3C2H)(PhC2Ph)(η5-C5H5). Reaction of [MoCl(CO)(PhC2Ph)(η5-C5H5)] with CF3C⋮CH gives [MoCl(CF3C2H)2(η5-C5H5)]. The temperature-dependent dynamix behaviour of these complexes is discussed in terms of a propeller-type rotation of the acetylene.