Synthesis of cyclopalladated derivatives of (E)-N-Benzylidene-2-(2,6- dichlorophenyl)ethanamine and their reactivity towards monodentate and symmetric bidentate lewis bases

Article abstract of DOI:10.1002/ejic.201100293

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 °C under nitrogen produced the corresponding acetato-bridged endo five-membered ortho-cyclopalladated dimer [Pd{C₆H ₄CH=N(CH₂)₂ (2,6-Cl₂C ₆H₃)}(μ-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 ₆H₄CH=N(CH₂)2(2,6-Cl₂C ₆H₃)}(μ-Cl)]₂ (3)in 88% yield. Compounds 2 and 3 reacted with an excess of [D5]pyridine or a stoichiometric amount of PPh₃ to give the mononuclear compounds trans-N,L-[Pd{C ₆H₄CH=N(CH₂)₂-(2,6-Cl ₂C₆H₃)}(X)(L)] (4:X=OAc,L=[D₅]py; 5:X=Cl,L=[D₅]py; 6: X = OAc, L = PPh₃; 7:X=Cl,L=PPh ₃). Compounds 4 and 5 were prepared in a CDCl₃/[D ₅]py solution and studied by ¹H and ¹³C{ ¹H} 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 ₆H₄CH=N(CH₂)₂ (2,6-Cl ₂C₆H₃)}Cl) ₂{μ-L₂}] [8:L₂ =Ph₂-PCH₂CH₂PPh₂; 9:L₂ = trans-Ph₂PCH=CHPPh₂; 10:L₂ = 4,4'-bipyridine; 11:L₂ =NH₂CH₂CH ₂OCH₂CH₂OCH₂CH₂NH ₂; 12:L₂ =NH₂CH₂ (CHOH)CH ₂NH₂)] 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 ¹H and 13C{ ¹H} NMR spectroscopy. In addition, the crystal structures of 2, 8·2CH₂Cl₂, 10·4CHCl₃ and 11·2CH₂Cl₂ 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 fivemembered ortho-cyclopalladated imine, X is OAc, Cl, Br or I and L is py, NH₃ or PH₃.