Fulvene-ruthenium and Cp-ruthenium complexes via [2 + 2 + 1] cyclotrimerization of phenylacetylene with [RuCl(Tp)(1,5-cod)]

The complex [RuCl(Tp)(1,5-cod)], which bears the labile 1,5-cod ligand, was prepared from a high-yielding route involving the reaction of [RuCl₂(1,5-cod)(CH₃CN)₂] with KTp (Tp = HB(pz)₃). The reaction of [RuCl(Tp)(1,5-cod)] with phenylacetylene in either ethanol or methanol gave anti-Markovnikov alkoxide-adduct complexes [Ru(Tp)(η⁶-C₅H₂Ph₂-CH(Ph)R)] (R = OMe, OEt). These adducts were formed by [2 + 2 + 1] cyclotrimerization reactions of phenylacetylene mediated by the precursor complex, [RuCl(Tp)(1,5-cod)]. The ruthenium(II)-fulvene complex, [Ru(Tp)(η⁶-C₅H₂Ph₂-CH(Ph))]⁺, involved in these transformations was successfully isolated in the presence of NH₄PF₆. These complexes were fully characterized by ¹H NMR, ¹³C NMR, DEPT, HSQC, IR, and ESI-MS spectroscopy. The molecular structures of [Ru(Tp)(η⁶-C₅H₂Ph₂-CH(Ph)R)] (R = OMe/OEt) and [Ru(Tp)(η⁶-C₅H₂Ph₂-CH(Ph))]PF₆ have been determined by X-ray single-crystal diffraction. These complexes have piano-stool structures around the ruthenium center where half of the coordination sites are occupied by the pyrazole ligand while the remaining sites are occupied by either the π-bonded cyclopentadiene (Cp) or fulvene ligand.