Metallacyclopentatriene-butadienyl carbene rearrangement in the oxidative coupling of alkynes mediated by [RuCp(SbR3)(CH3CN)2]+ (R = Ph, n-Bu)

The oxidative coupling of alkynes is investigated as promoted by the half-sandwich compound [RuCp(SbR3)(CH3CN)(2)]PF6 (R = Ph, n-Bu). There are various ways by which the initially formed electrophilic metallacyclopentatriene complex rearranges to a stable product. In the case where the alkyne disposes of an alpha-alkyl substituent, intramolecular 1,2 hydrogen migration leads to a butadienyl carbene complex as obtained by using 2,8-decadiyne or HCequivalent toCCH(2)R' (R' = n-Pr, Ph, OH). A conceivable mechanism for this reaction sequence is established by means of DFT/B3LYP calculations. In line with experiment, the existence of two isomeric butadienyl carbene complexes is proposed. In the case of R' = Ph and OH the butadienyl carbene is not the final product but rearranges to give eta(3)-allyl-vinyl and eta(3)-allylacyl complexes. In the absence of an alpha-alkyl substituent as for HCequivalent toCC(6)H(9), HCequivalent toCC(6)H(10)-OH, and HCequivalent toCCMe(2)OH, eta(3)-butadienyl-vinyl complexes are formed. Finally, from the alkynes HCequivalent toCPh, HCequivalent toCBu(t), and HCequivalent toCSiMe(3) no tractable materials are obtained.