Unusual activation of 1-ethynyl-1-cyclohexanol by [RuCl(eta(5)-C9H7)-(PPh3)(2)]: synthesis and reactivity of the allenylidene derivative [Ru{= C = C = C(C13H20)}(eta(5)-C9H7)(PPh3)(2)][PF6]

The reaction of [RuCl(eta(5)-C9H7)(PPh3)(2)] with an excess of 1-ethynyl-1- cyclohexanol and NaPF6 in refluxing methanol yielded the allenylidene compl ex [Ru{=C=C=C(C13H20)}(eta(5)-C9H7)(PPh3)(2)][PF6] 1 via an unprecedented c oupling of two molecules of the propargyl (prop-2-ynyl) alcohol derivative. Complex 1 can also be obtained by reaction of the vinylvinylidene derivati ve [Ru{=C=C(H)R}(eta(5)-C9H7)(PPh3)(2)][PF6] 2 (R = 1-cyclohexenyl) with 1- ethynyl-1-cyclohexanol or 1-ethynylcyclohexene in refluxing methanol. The b ehaviour of 2 towards other 1-alkyn-3-ols has been studied but only the rep lacement of the vinylidene moiety by the propargyl alcohols, via an eta(1)- vinylidene-eta(2)-alkyne tautomerization process, to generate both vinylvin ylidene [Ru{=C=C(H)R}(eta(5)-C9H7)(PPh3)(2)][PF6] (R = 1-cyclopentenyl, 1-c ycloheptenyl or 1-cyclooctenyl) or allenylidene [Ru(=C=C=CR2)(eta(5)-C9H7)( PPh3)(2)][PF6] (R = Ph or R-2 = 2,2'-biphenyldiyl) complexes along with 1-e thynylcyclohexene was observed. A similar 1,3-enyne elimination also takes place in the reaction of 2 with phenylacetylene or acetonitrile to afford [ Ru{=C=C(H)Ph}(eta(5)-C9H7)(PPh3)(2)][PF6] and [Ru(N=CMe)(eta(5)-C9H7)(PPh3) (2)][PF6], respectively. On the basis of these observations a mechanism for the formation of 1 is proposed. The allenylidene complex 1 regioselectivel y reacts with NaR, in THF at -20 degrees C, to yield the neutral sigma-alky nyl derivatives [Ru{C=CC(C13H20)R}(eta(5)-C9H7)(PPh3)(2)] (R = C=N or OMe). Protonation of the R = CN derivative with HBF4. Et2O, in diethyl ether at -20 degrees C, afforded the cationic vinylidene complex [Ru{=C=C(H)C(C13H20 )C=N}(eta(5)-C9H7)(PPh3)(2)][BF4]. In contrast, protonation with R = OMe gi ves back the starting allenylidene derivative 1.