Activation of Alkynols by [Cp*RuCl(PEt3)2]: New Intermediates and Alternative Dehydration Products. X-ray Crystal Structures of [Cp*Ru{CCHC(CH2)Ph}(PEt3)2][BPh4], [Cp*Ru(CCCPh2)(PEt3)2][BPh4], and [Cp*Ru{C⋮CC(PEt3)Me2}(PEt3)2][BPh4]

The full sequence of species involved in the activation of alkynols by the fragment [Cp*Ru(PEt 3 ) 2 ] + was determined. The complex [Cp*RuCl(PEt 3 ) 2 ] (Cp* = C 5 Me 5 ) reacts with 2-propyn-1-ol derivatives in the presence of NaBPh 4, yielding the metastable 3-hydroxyalkynyl hydrido complexes [Cp*Ru(H){C⋮CC(OH)RR‘}(PEt 3 ) 2 ][BPh 4 ], intermediates in the formation of the corresponding 3-hydroxyvinylidene complexes [Cp*Ru{ C CHC(OH)RR‘}(PEt 3 ) 2 ][BPh 4 ], to which these compounds rearrange both in solution and in the solid state. η 2 -Alkynol derivatives have been detected by 31 P{ 1 H} NMR at −40 °C as the first species involved in the reaction of alkynols with [Cp*Ru(N 2 )(PEt 3 ) 2 ][BPh 4 ]. Dehydration of 3-hydroxyalkynyl hydrido and 3-hydroxyvinylidene complexes may be spontaneous or forced, leading to vinylvinylidene, allenylidene, or the novel enynyl hydrido species. The unstable allenylidene led to the formation of an alkynylphosphonio compound without an external source of phosphine.