Palladacycles with C, N-bidentate and N, C, N′-tridentate ligands: Structures, spectral study and catalytic methanolysis of P [dbnd]S pesticides

Abstract

Palladacycles 2– 4 with C, N-bidentate and N, C, N′-tridentate ligands were prepared and characterized. The X-ray crystal structures of [2,6-bis( N,N-dimethylaminomethyl)phenyl-N,C 1,N′-](aqua)palladium(II) triflate ( 2), ( N, N-dimethylaminobenzyl-C 1,N)(4-trifluoromethylpyridine)(aqua)palladium(II) triflate ( 3), and ( N, N-dimethylaminobenzyl-C 1,N)(4- N, N-dimethylaminopyridine)(aqua)palladium(II) triflate ( 4), were determined. While 2 is much less active, 3 and 4 effectively catalyze the methanolysis of the P S pesticides. The catalytic activities were higher with the trifluoromethylpyridine co-ligand as compared to palladacycles containing 4- N, N-dimethylaminopyridine and pyridine co-ligands. 1H NMR spectra and the catalytic kinetic dependences on concentration and pH revealed that the active species was a palladacycle containing one methoxide and one pyridine in the coordination sphere. A plot of the catalytic activity vs. free [pyridine] indicated the participation of a common species. The proposed catalytic mechanism involves a pre-equilibrium binding of the P S pesticide to palladium(II) center followed by dissociation of the pyridine and subsequent cleavage of the P–OAr unit through the intramolecular displacement on phosphorus by the adjacent Pd-coordinated methoxide.