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

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{C6H4CH=N(CH2)(2)(2,6-Cl2C6H3)}(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{C6H4CH=N(CH2)(2)(2,6-Cl2C6H3)}(mu-Cl)](2) (3) in 88 % yield. Compounds 2 and 3 reacted with an excess of [D-5]pyridine or a stoichiometric amount of PPh3 to give the mononuclear compounds trans-N,L-[Pd{C6H4CH=N(CH2)(2)(2,6-Cl2C6H3)}(X)(L)] (4: X = OAc, L = [D-5]py; 5: X = Cl, L = [D-5]py; 6: X = OAc, L = PPh3; 7: X = Cl, L = PPh3). Compounds 4 and 5 were prepared in a CDCl3/[D-5]py solution and studied by H-1 and C-13{H-1) 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{C6H4CH=N(CH2)(2)(2,6-Cl2C6H3)}Cl)(2){mu-L-2}] {8: L-2 = Ph2PCH2CH2PPh2; 9: L-2 = trans-Ph2PCH=CHPPh2; 10: L-2 = 4,4'-bipyridine; 11: L-2 = NH2CH2CH2OCH2CH2OCH2CH2NH2; 12: L-2 = NH2CH2(CHOH)CH2NH2)] 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 H-1 and C-13{H-1} 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 CHCl3 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, NH3 or PH3.