Synthesis, Reactivity, and Theoretical Studies of the η²(4e)-Bonded Phosphaalkyne Complex [CpMo{P(OMe)₃}₂{η²(4e)-P⋮CBu^t}][B(C₆F₅)₄] and the Molybdenum-Mediated Cyclocotrimerization of Alkyne and Phosphaalkyne Ligands

Abstract

Whereas the cations [CpMo{P(OMe) 3 } 2 {η 2 (4e)-alkyne}] + do not react with alkynes or P⋮CBu t, the newly synthesized isostructural phosphaalkyne complex [CpMo{P(OMe) 3 } 2 {η 2 (4e)-P⋮CBu t }][B(C 6 F 5 ) 4 ], which is unreactive towards PhC 2 Ph, readily reacts via an associative stepwise process with P⋮CBu t to give [CpMo{P(OMe) 3 } 2 {η 4 -1,3-P 2 C 2 Bu t 2 }][B(C 6 F 5 ) 4 ]. A further interesting difference in alkyne and phosphaalkyne chemistry was observed when it was found that CpMoCl(CO){η 2 (4e)-PhC 2 Ph} reacts with TlPF 6 and P⋮CBu t to give the unusual 16-electron cyclocotrimerization product identified by single-crystal X-ray crystallography.