Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 69. Reactions of [MoW(CC6H4Me-4)(CO)7(η-C5H5)] with but-2-yne; crystal structures of [MoW{µ-C(C6H4Me-4)C(Me)C(Me)}(CO)3(η-MeC2Me)2(η-C5H5)] and [MoW{µ-C(C6H4Me-4)C(CH2)C(H)MeC(O)}(CO)6(η-C5H5)]·0.5CH2Cl2

Abstract

Treatment of [MoW(CC₆H₄Me-4)(CO)₇(η-C₅H₅)] with but-2-yne in refluxing thf (tetrahydrofuran) affords the compounds [MoW{µ-C(C₆H₄Me-4)C(Me)C(Me)}(CO)₃(η-MeC₂Me)₂(η-C₅H₅)]. In contrast, at room temperature in thf these reagents yield the complex [MoW{µ-C(C₆H₄Me-4)C(CH₂)C(H)MeC(O)}(CO)₆(η-C₅H₅)]. The structures of both products have been established by X-ray diffraction. That of [MoW{µ-C(C₆H₄Me-4)C(Me)C(Me)}(CO)₃(η-MeC₂Me)₂(η-C₅H₅)] has a Mo–W bond [2.971(2)Å] spanned by the µ-C(C₆H₄Me-4)C(Me)C(Me) group. The molybdenum atom carries a cyclopentadienyl and two carbonyl groups, while the tungsten atom is ligated by a carbonyl and two MeCCMe groups. In the other dimetal compound the Mo–W bond [3.131(1)Å] is bridged by a novel C₄ fragment in such a manner that there is a [graphic omitted](O) ring system, the C(C₆H₄Me-4)CCH₂ moiety of which is η³-co-ordinated to the tungsten. The latter carries four essentially orthogonal carbonyl groups, and the molybdenum centre is ligated by two carbonyl groups and the C₅H₅ ring. The ¹H and ¹³C-{¹H} n.m.r. spectra of the new compounds are reported and discussed, as are their possible modes of formation. Reaction between [MoW{µ-C(C₆H₄Me-4)C(Me)C(Me)}(CO)₃(η-MeC₂Me)₂(η-C₅H₅)] and PMe₃ affords a simple substitution product containing a W(PMe₃)(η-MeC₂Me)₂ fragment.