Unusual activation of 1-ethynyl-1-cyclohexanol by [RuCl(η5-C9H7)-(PPh3)2]:: synthesis and reactivity of the allenylidene derivative [Ru{=C=C=C(C13H20)}(η5-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 complex [Ru{=C=C=C(C13H20)}(eta(5)-C9H7)(PPh3)(2)][PF6] 1 via an unprecedented coupling of two molecules of the propargyl (prop-2-ynyl) alcohol derivative. Complex 1 can also be obtained by reaction of the vinylvinylidene derivative [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 behaviour of 2 towards other 1-alkyn-3-ols has been studied but only the replacement of the vinylidene moiety by the propargyl alcohols, via an eta(1)-vinylidene-eta(2)-alkyne tautomerization process, to generate both vinylvinylidene [Ru{=C=C(H)R}(eta(5)-C9H7)(PPh3)(2)][PF6] (R = 1-cyclopentenyl, 1-cycloheptenyl 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-ethynylcyclohexene 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 regioselectively reacts with NaR, in THF at -20 degrees C, to yield the neutral sigma-alkynyl 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 gives back the starting allenylidene derivative 1.