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)]

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.