Methoxycarbonylation of olefins catalyzed by palladium complexes bearing P,N-donor ligands.
The methoxycarbonylation of alkenes catalyzed by palladium(II) complexes with P,N-donor ligands, 2-(diphenylphosphinoamino)pyridine (Ph2PNHpy), 2-[(diphenylphosphino)methyl]pyridine (Ph2PCH2py), and 2-(diphenylphosphino)quinoline (Ph2Pqn) 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(PPh3)L]Cl (L = Ph2PCH2py and Ph2Pqn) show lower activity in the methoxycarbonylation of styrene than that of the 2-(diphenylphosphinoamino)pyridine ligand. Replacement of the last ligand by (diphenylphosphino)phenylamine (Ph2PNHPh) or 2-(diphenylphosphinoaminomethyl)pyridine (Ph2PNMepy) also reduces significantly the activity of the catalyst, indicating that both the presence of the pyridine fragment as well as the NH group, are required to achieve a high performing catalyst. Isotopic labeling experiments using MeOD are consistent with a hydride mechanism for the [PdCl(PPh3)(Ph2PNHpy)]Cl catalyst.
Aguirre
Pedro A
PA
Universidad de Chile, Facultad de Ciencias Químicas y Farmacéuticas, Departamento de Inorgánica y Analítica, Casilla 233 Santiago 1, Chile. paguirre@ciq.uchi le.cl
Lagos
Carolina A
CA
Moya
Sergio A
SA
Zúñiga
César
C
Vera-Oyarce
Cristian
C
Sola
Eduardo
E
Peris
Gabriel
G
Bayón
J Carles
JC
D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D004952:Esters / Q000138:chemical synthesis*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry; D010165:Palladium / Q000737:chemistry*; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry*
D000475:Alkenes; D004952:Esters; D009942:Organometallic Compounds; D011725:Pyridines; D010165:Palladium