Reductive elimination of η 3-allyl(aryl)palladium complexes promoted by allyl halides

Abstract

Comparison between the reactivity patterns of the reactions of η 3-allyl(aryl)palladium complexes with allyl chlorides and those with styrene, allylbenzene, methyl iodide and benzyl chloride suggested the dual role of allyl chloride in enhancing the reductive elimination of these complexes, namely coordination to Pd through the CC bond and removal of the electron density via oxidative addition. The product distribution pattern in the reductive elimination of Pd(η 3-CH 2CHCH 2)(Ar)(EPh 3) ( 1) (E = P, As; Ar = C 6H 3Cl 2-2,5) accelerated by CH 2CMeCH 2Cl (reaction A) and that of Pd(η 3-CH 2CMeCH 2(Ar)(EPh 3) ( 2) accelerated by CH 2CHCH 2Cl (reaction B) has been determined. For the reaction of the AsPh 3 complexes both A and B carried out in toluene dichloromethane afforded, at the early stages, only the coupling product (allylbenzene derivative) associated with the allyl unit of the original complex itself. At the later stages the product derived from the substrate chloride increased owing to facile ligand exchange (allyl-methallyl and/or aryl-Cl) between 1 and 2 and the η 3-allyl(chloro)palladium complex which is another product of the reductive elimination. Consistent with the oxidative addition of the allyl chlorides, the reaction of the PPh 3 complexes in dichloromethane and 1,2-di-chloroethane gave a greater quantity of the product derived from the substrate chloride than that from the complex even at the early stages.