Synthesis of Cyclopalladated Derivatives of (E)-N2 Benzylidene-2-(2,6-dichlorophenyl)ethanamine and Their Reactivity towards Monodentate andSymmetric Bidentate Lewis Bases

Abstract

Treatment of the monoimine (E)-N-benzylidene-2-(2,6-dichlorophenyl)ethanamine (1) with a stoichiometric amount of Pd(OAc)(2) in acetic acid at 60 degrees C under nitrogen produced the corresponding acetato-bridged endo five-membered ortho-cyclopalladated dimer [Pd{C(6)H(4)CH=N(CH(2))(2)(2,6-Cl(2)C(6)H(3))}(mu-OAc)](2) (2), which was isolated in pure form in 80% yield. Reaction of 2 with an excess of LiCl in acetone gave rise to the corresponding chlorido-bridged cyclopalladated dimer [Pd{C(6)H(4)CH=N(CH(2))(2)(2,6-Cl(2)C(6)H(3))}(mu-Cl)](2) (3) in 88 % yield. Compounds 2 and 3 reacted with an excess of [D(5)]pyridine or a stoichiometric amount of PPh(3) to give the mononuclear compounds trans-N,L-[Pd{C(6)H(4)CH=N(CH(2))(2)(2,6-Cl(2)C(6)H(3))}(X)(L)] (4: X = OAc, L = [D(5)]py; 5: X = Cl, L = [D(5)]py; 6: X = OAc, L = PPh(3); 7: X = Cl, L = PPh(3)). Compounds 4 and 5 were prepared in a CDCl(3)/[D(5)]py solution and studied by (1)H and (13)C{(1)H) NMR spectroscopy, but they were not isolated. Compound 3 was treated with different types of symmetric bidentate Lewis bases in a 1:1 molar ratio to give high yields of the dinuclear compounds trans-N,L-[(Pd{C(6)H(4)CH=N(CH(2))(2)(2,6-Cl(2)C(6)H(3))}Cl)(2){mu-L(2)}] {8: L(2) = Ph(2)PCH(2)CH(2)PPh(2); 9: L(2) = trans-Ph(2)PCH=CHPPh(2); 10: L(2) = 4,4'-bipyridine; 11: L(2) = NH(2)CH(2)CH(2)OCH(2)CH(2)OCH(2)CH(2)NH(2); 12: L(2) = NH(2)CH(2)(CHOH)CH(2)NH(2))] in which the symmetric bidentate Lewis base bridged two identical cyclopalladated units. Compounds 1-3 and 6-12 were fully characterized by elemental analysis, mass spectrometry, IR and (1)H and (13)C{(1)H} NMR spectroscopy. In addition, the crystal structures of 2, 8 center dot 2CH(2)Cl(2), 10 center dot 4CHCl(3) and 11 center dot 2CH(2)Cl(2) were determined by single-crystal X-ray diffraction analysis. Also reported is the theoretical study of the differences in the absolute Gibbs free energies in acetone or CHCl(3) solution between the cis- and trans-N,L stereoisomers of compounds [Pd(C-N)(X)(L)] in which Pd(C-N) is a model of an endo five-membered ortho-cyclopalladated imine, X is OAc, Cl, Br or I and L is py, NH(3) or PH(3).