Unusual activation of 1-ethynyl-1-cyclohexanol by (RuCl(#eta#~5-C_9H_7)(PPh_3)_2): synthesis and reactivity of the allenylidene derivative (Ru{=C=C=C(C_(13)H_(20))}(#eta#~5-C_9H_7)(PPh_3)_2)(PF_6)

摘要

The reaction of[RuCl(#eta#~5-C_9H_7)(PPh_3)_2] with an excess of 1-ethynyl-1-cyclohexanol and NaPF_6 in refluxing methanol yielded the allenylidene complex[Ru{=C=C=C(C_(13)H_(20))}(#eta#~5-C_9H_7)(PPh_3)_2][PF_6] 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-C_9H_7)(PPh_3)_2][PF_6] 2 (R = 1-cyclohexenyl) with 1-ethynyl-1-cyclo-hexanol 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-C_9H_7)(PPh_3)_2][PF_6] (R = 1-cyclo-pentenyl, 1-cycloheptenyl or 1-cyclooctenyl) or allenylidene [Ru(=C=C=CR_2)(#eta#~5-C_9H_7)(PPh_3)_2][PF_6] (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-C_9H_7)(PPh_3)_2][PF_6] and [Ru(N ident to CMe)(#eta#~5-C_9H_7)(PPh_3)_2][PF_6], 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 deg C, to yield the neutral #sigma#-alkynyl derivatives [Ru{C ident to CC(C_(13)H_(20))R}(#eta#~5-C_9H_7)(PPh_3)_2] (R = C ident to N or OMe). Protonation of the R=CN derivative with HBF_4 centre dot Et_2O, in diethyl ether at -20 deg C, afforded the cationic vinylidene complex [Ru{=C=C(H)C(C_(13)H_(20))C ident to N}(#eta#~5-C_9H_7)(PPh_3)_2][BF_4]. In contrast, protonation with R = OMe gives back the starting allenylidene derivative 1.