C-Br versus C-H bond activation in palladium (II) cyclopalladated compounds. Crystal and molecular structure of [Pd{C6H4C(H)=NCy}(MeCOCHCOMe)]

Article abstract of DOI:10.1016/S0022-328X(02)01882-X

Treatment of N-(2-bromobenzylidene)cyclohexylamine, 2-BrC₆H₄C(H)=NCy (a), with tris(dibenzylideneacetone) palladium(0) in refluxing benzene gave the cyclometallated compound [Pd{C₆H₄C(H)=NCy}(Br)]₂ (1). Treatment of 1 with thallium acetylacetonate gave the mononuclear cyclometallated compound [Pd{C₆H₄C(H)=NCy}(MeCOCHCOMe)] (2). Reaction of a with palladium(II) acetate in refluxing acetic acid gave the dinuclear Pd(II) compound [Pd{2-BrC₆H₃C(H)= NCy}(O₂CMe)]₂ (3). Treatment of 3 with aqueous sodium chloride gave the dimer complex [Pd{2- BrC₆H₃C(H)=NCy}(Cl)]₂ (4). Reaction of 4 with tertiary phosphines gave the cyclometallated complexes [Pd{2-BrC₆H₃C(H)=NCy}(L)] (5: L = PPh₃; 6: L = PEtPh₂; 7: L = PMePh₂), with the phosphine ligand trans to the imine nitrogen atom. Treatment of 2-Br=4,5- tris(dibenzylideneacetone)palladium(0) gave [Pd{4,5-(MeO)₂C₆H₂C(H)=NCH₂ CH₂NMe₂}(X)] (8: X = Cl; 16: X = Br, respectively) and with the ligand as [C, N, N] terdentate. Treatment of 8 with tertiary phosphines gave [Pd{4,5-(MeO)₂C₆H₂ C(H)=NCH₂CH₂NMe₂}(Cl)(L)] (9: L = PPh3; 10: L = PEtPh₂; 11: L = PMePh₂). Reaction of 1,4-{2-Br-4,5-(MeO)₂C₆H₂C(H)-N} ₂C₆H₄ (c), with PdCl₂, Li₂[PdCl₄] or K₂[PdCl₄] gave the tetranuclear compound [1,4-{Pd[4,5-(MeO)₂C₆ H₂C(H)=N](Cl)}₂C₆H₄] ₂ (12), which when treated with tertiary phosphines gave the dinuclear species 13-15. The molecular structure of 2 has been determined by X-ray crystallography.