Formation of cationic molybdenum η2-vinyl complexes; structural evidence for the coupling of η2-vinyl and alkyne ligands

Abstract

Protonation (HBF₄·Et₂O) of [MoX(η²-MeC₂Me)₂L](X = Cl, Br, I; L =η-C₅H₅ or η⁵-C₉H₇) affords the cations [X[graphic omitted]HMe(η²-MeC₂Me)L][BF₄], which react with LiX to give [X₂[graphic omitted]HMe(η²-MeC₂Me)L] or with PR₃(R = Me, or OMe) to give the C–C coupled products [XMoC(Me)-η³-{C(Me)C(Me)CHMe}(PR₃)(L)][BF₄], the latter being structurally identified by X-ray crystallography; carbon–carbon coupling also occurs on reduction of [Br₂[graphic omitted]HMe(η²-MeC₂Me)(η-C₅H₅)] with Mg/Hg in the presence of CO to form [MoBr(CO){η⁴-CHMeC(Me)·C(Me)CHMe}(η-C₅H₅)], and treatment of the phosphine promoted coupled products with Li[N(SiMe₃)₂] leads to reversible deprotonation reactions affording [MoX{η⁴-CHMeC(Me)·C(Me)CCH₂}(PR₃)L].