METHOXYCARBONYLATION OF STYRENE BY PALLADIUM(II) COMPLEX CONTAINING THE DIPHENYLPHOSPHINOCYRHETRENE LIGAND

Abstract

ABSTRACT The palladium-catalyzed methoxycarbonylation of vinylarenes has been investigated for the first time using phosphinocyrhetrene [(η 5 -C 5 H 4 PPh 2 )Re(CO) 3 ] a non-metallocenic organometallic ligand. The catalytic system trans-[(η 5 -C 5 H 4 PPh 2 )Re(CO) 3 ]PdCl 2 (NCMe)/PPh 3 (1:2 ratio), carbon monoxide and methanol, in the presence of HCl as acidic promoter, showed good catalytic activity, excellent regioselectivity to the branched products and chemoselectivity up to 94%. Keywords: Methoxycarbonylation, phosphinocyrhetrene ligand, vinylarenes. 1.- INTRODUCTION Palladium-catalyzed hydroesterification reaction (Reppe carbonylation) is a powerful synthetic strategy for the preparation of linear and branched esters from easily available unsaturated substrates. 1,2 It has been established that the regioselectivity of carboxylation products is strongly dependent on the ligands bound to a transition metal and the reaction conditions. The most common catalytic system involve Pd(II) and mono- and bidentate aromatic phosphines. Catalysts containing bidentate diphosphine ligands have been more frequently used for this reaction, but they have the disadvantage to produce branched product in low regio- and enantioselectivity, although a few successful examples have been reported recently.