Comments on the catalytic alkoxycarbonylation of alkynes

Abstract

The alkoxycarbonyl complexes Pd(Ph₂Ppy)₂(CO₂R)(OAc) where Ph₂Ppy is 2-pyridyldiphenylphosphine and R = Me 1, Et 2, i-Pr 3 have been prepared from Pd(OAc)₂ and Ph₂Ppy in ethanol solution under an atmosphere of CO. Increasing the CO pressure favours the formation of palladium carbonyl species. In the presence of 2 mol equivalents of CF₃CO₂H, the complex Pd(Ph₂Ppy)₂(CO₂CH₃)(CF₃CO₂) 4 is isolated from methanol. Pd(Ph₂Ppy)₂(CO₂CH₃)Cl 5 has been obtained by the reaction of Pd(Ph₂Ppy)₂Cl₂ with NaOCH₃ in the presence of CO. 1 and 5 have been crystallographicaly characterised as trans isomers, a geometry confirmed for all the complexes by ¹³C NMR. The reactivity of the complexes toward alkynes and propadiene has been investigated and the π-allyl complex [Pd(Ph₂Ppy)₂{η³-C₃H₄C(CH₃)CH₂}][O₂CCF₃] 8 isolated and structurally characterised.