Synthesis, reactivity, and theoretical studies of the eta(2)(4e)-bonded phosphaalkyne complex [CpMo{P(OMe)(3)}(2){eta(2)(4e)-P CBut}][B(C6F5)(4)] and the molybdenum-mediated cyclocotrimerization of alkyne and phosphaalkyne Ligands

Whereas the cations [CpMo{P(OMe)(3)}(2){eta(2)(4e)-alkyne}](+) do not react with alkynes or P=CBut, the newly synthesized isostructural phosphaalkyne complex [CpMo{P(OMe)(3)}(2){eta(2)(4e)-P=CBut}][B(C6F5)(4)], which is unreactive towards PhC2Ph, readily reacts via an associative stepwise process with P=CBut to give [CpMo{P(OMe)(3)}(2){eta(4)-1,3-P2C2Bu2t}][B(C6F5)(4)]. A further interesting difference in alkyne and phosphaalkyne chemistry was observed when it was found that CpMoCl(CO){eta(2)(4e)-PhC2Ph} reacts with TlPF6 and P=CBut to give the unusual 16-electron cyclocotrimerization product [CpMo{=C(Bu-t)PC(Bu-t)=PC(Ph)=C(Ph)}(CO)][PF6], identified by single-crystal X-ray crystallography.