Nuclear magnetic resonance studies in coordination chemistry IV. Reactions of π-allypalladium complexes as influenced by various phosphorus ligands

Abstract

It is shown that in π-allylpalladium complexes, e.g. (π-C 4H 7)PdClL (L = AsPh 3, PPh 3) and substituted π-methallyl compounds, so called “πσ” reactions may occur, i.e. reversible interconversions from the π-allyl to a short-lived σ-allyl form with interchange of the syn- and anti-protons. These interchanges are caused either by reactions of the monomeric complex with excess free ligand L or by reactions of the complex with dimeric π-allylpalladium chloride compounds. In the case of these dimer-dependent “πσ” reactions it was found that at low temperatures syn- and anti-protons interchange on one side of the allyl group, whereas at higher temperatures interchange occurs on both sides of the allyl group of the monometer. The interchange on one side was studied in particular for various phosphine compounds. It proved to be first order in the monomer and first order in the dimer complex for L =P(n-C 4H 9) 3. Additional information about “πσ” reactions in general was further obtained for dimethyl-substituted π-methallylpalladium compounds. Also included are the results of NMR measurements on the formation and ligand exchange reactions of ionic complexes [(π-C 4H 7)Pd(PR 3) 2] +Cl − for various phosphines.