Triadic coupling between hydride, acetylide and alkyne on the complex [WRe(η-C5Me5)O(CO)4( µ-H)(CCPh)]. Crystal structures of complexes containing a substituted cyclopentadienylidene ligand or a folded metallacyclopentadienyl fragment

Abstract

The reaction of the dinuclear oxoacetylide complex [WRe(η-C ₅ Me ₅ )O(CO) ₄ (µ-H)(µ- CCPh)] 1 with dimethyl acetylenedicarboxylate afforded the bis(alkylidene) complex [WRe(η-C ₅ Me ₅ )O(CO) ₃ (µ-CHPh) {µ-C ₅ (CO ₂ Me) ₄ }] 2, generated by formal co-ordination of two alkynes and cleavage of a C–C bond. In contrast, treatment of 1 with an excess of di-p-tolylacetylene in refluxing toluene gave three complexes [WRe(η-C ₅ Me ₅ )O(CO) ₃ {CH(Ph)CC (C ₆ H ₄ Me-p)CH(µ-η ² -C ₆ H ₃ Me)}] 3, [WRe(η-C ₅ Me ₅ )O(CO) ₃ {µ-C ₄ Ph[C ₂ H(C ₆ H ₄ Me-p) ₂ ](C ₆ H ₄ Me-p) ₂ }] 4 and [WRe(η-C ₅ Me ₅ )O(CO) ₃ {µ-C ₄ [C ₂ H(C ₆ H ₄ Me-p) ₂ ]Ph(C ₆ H ₄ Me-p) ₂ }] 5. Compounds 4 and 5, which possess a folded metallacyclopentadienyl fragment, are produced by hydride migration to alkyne, giving a cis-ditolylalkenyl substituent, followed by coupling with acetylide and a second ditolylacetylene molecule. Compound 3 is probably produced by a distinct sequence, involving initial formation of a C(C ₆ H ₄ Me-p)C(C ₆ H ₄ Me-p)CCHPh linkage, followed by orthometallation and hydrogen transfer. Single-crystal structural analyses of 2–5 have been performed and the possible reaction mechanisms leading to their isolation are presented.