Intermediates in the palladium-catalysed reaction of 1,3-dienes Part 8. The reaction of palladium-butadiene complexes with ethyl methylacetoacetate

Abstract The catalytic reaction of 1,3-butadiene with ethyl methylacetoacetate in the presence of (η 2 -1,3-butadiene)Pd(R 2 P(CH 2 ) n PR 2 ) compounds has been investigated. The product is a mixture of 1:1 adducts and the rate of reaction is highest when n 2, RPr i and in dichloromethane as solvent. Insight into the mechanism has been obtained by studying the stoichiometric reaction of (η 2 -1,3-butadiene)Pd(Pr i 2 PC 2 H 4 PPr i 2 ) with the ester using variable temperature NMR spectroscopy and it has been shown that initially an [(η 3 -1-MeC 3 H 4 )-Pd(Pr i 2 PC 2 H 4 Ppr i 2 )] + species is formed which reacts further to give (η 2 -alkene)Pd(Pr i 2 PC 2 H 4 Ppr i 2 ) compounds in which the product of the catalysis is complexed to the palladium atom. The crystal structures of three side products, viz. Pd 2 (Pr i 2 PCH 2 PPr i 2 ) 2 , [(η 1 ,η 3 -C 8 H 12 )Pd] 2 (Me 2 PC 2 H 4 PMe 2 ) and ClCH 2 Pd(Cy 2 PC 2 H 4 PCy 2 )Cl, have been determined by X-ray diffraction.