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

Abstract

AbstractTreatment 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‐memberedortho‐cyclopalladated dimer [Pd{C6H4CH=N(CH2)2(2,6‐Cl2C6H3)}(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{C6H4CH=N(CH2)2(2,6‐Cl2C6H3)}(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{C6H4CH=N(CH2)2(2,6‐Cl2C6H3)}(X)(L)] (4: X = OAc, L = [D5]py; 5: X = Cl, L = [D5]py; 6: X = OAc, L = PPh3; 7: X = Cl, L = PPh3). Compounds 4 and 5 were prepared in a CDCl3/[D5]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{C6H4CH=N(CH2)2(2,6‐Cl2C6H3)}Cl)2{μ‐L2}] [8: L2 = Ph2PCH2CH2PPh2; 9: L2 = trans‐Ph2PCH=CHPPh2; 10: L2 = 4,4′‐bipyridine; 11: L2 = NH2CH2CH2OCH2CH2OCH2CH2NH2; 12: L2 = 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 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 five‐membered ortho‐cyclopalladated imine, X is OAc, Cl, Br or I and L is py, NH3 or PH3.