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Palladacycles with C,N-bidentate and N,C,N′-tridentate ligands: Structures, spectral study and catalytic methanolysis of Pdes

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Title: Palladacycles with C,N-bidentate and N,C,N′-tridentate ligands: Structures, spectral study and catalytic methanolysis of Pdes
Authors: Lu, Zhong-Lin1 luzl@bnu.edu.cn, Wang, Xue-Rui1, Liu, Bian-Bian1, Wang, Rui-Yao2
Source: Journal of Organometallic Chemistry. Sep2010, Vol. 695 Issue 19/20, p2191-2200. 10p.
Subjects: Organopalladium compounds, Ligands (Chemistry), Molecular structure, Palladium catalysts, Nuclear magnetic resonance spectroscopy, Chemical kinetics, Pyridine, Pesticides
Abstract: 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,C1,N′-](aqua)palladium(II) triflate (2), (N,N-dimethylaminobenzyl-C1,N)(4-trifluoromethylpyridine)(aqua)palladium(II) triflate (3), and (N,N-dimethylaminobenzyl-C1,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 Pdes. 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 Pde 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. [ABSTRACT FROM AUTHOR]
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Abstract: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,C1,N′-](aqua)palladium(II) triflate (2), (N,N-dimethylaminobenzyl-C1,N)(4-trifluoromethylpyridine)(aqua)palladium(II) triflate (3), and (N,N-dimethylaminobenzyl-C1,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 Pdes. 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 Pde 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. [ABSTRACT FROM AUTHOR]
ISSN:0022328X
DOI:10.1016/j.jorganchem.2010.06.002