Methoxycarbonylation of olefins catalyzed by palladium complexes bearing P,N-donor ligands

Abstract

The methoxycarbonylation of alkenes catalyzed by palladium(ii) complexes with P,N-donor ligands, 2-(diphenylphosphinoamino)pyridine (Ph 2PNHpy), 2-[(diphenylphosphino)methyl]pyridine (Ph 2PCH2py), and 2-(diphenylphosphino)quinoline (Ph 2Pqn) has been investigated. The results show that the complex [PdCl(PPh3)(Ph2PNHpy)]Cl or an equimolar mixture of [PdCl2(Ph2PNHpy)] and PPh3, in the presence of p-toluensulfonic acid (TsOH), is an efficient catalyst for this reaction. This catalytic system promotes the conversion of styrene into methyl 2-phenylpropanoate and methyl 3-phenylpropanoate with nearly complete chemoselectivity, 98% regioselectivity in the branched isomer, and high turnover frequency, even at alkene/Pd molar ratios of 1000. Best results were obtained in toluene-MeOH (3: 1) solvent. The Pd/Ph2PNHpy catalyst is also efficient in the methoxycarbonylation of cyclohexene and 1-hexene, although with lower rates than with styrene. Related palladium complexes [PdCl(PPh 3)L]Cl (L = Ph2