C-and O-metallation of N-benzylideneamines by palladium (II). Synthesis and X-ray crystal structure of [Pd(2-{CH=N-(CH2)2-4′-(MeO)C6H4}-4,5-(MeO)2C6H2)Br(PPh3)]

Article abstract of DOI:10.1016/0022-328X(96)06182-7

The action of Pd(AcO)₂ on the imines 3,4-(MeO)₂C₆H₃CH=N(CH₂)_nC₆H₄R has been studied. Five-membered endo metallacycles were obtained from the imines la (R = H, n = 0), 1b (R = 2-MeO, n = 0), 1c (R = 4-MeO, n = 1) and 1d (R = 4-MeO, n = 2) by activation of the less hindered C(aromatic)-H bond. A six-membered metallacycle, containing a Pd-O bond, was obtained from the imine 1e, 2,4,6-(MeO)₃C₆H₂CH=NC₆H₅, by activation of one of the ortho O-CH₃ bonds. All these results show the strong tendency of imines to form endocyclic compounds and the importance of steric factors in the process. Complexes [PdBr(C-N)(PPh₃)] or even [Pd(AcO)(C-N)(PPh₃)], in which the acetate acts as a monodentated ligand, can be obtained by the action of PPh₃ on the new cyclometallated compounds. [Pd(2-{CH=N-(CH₂)₂-4′-(MeO)C₆H₄}-4,5-(MeO)₂C₆H₂)Br(PPh₃)] crystallizes in the triclinic space group P1 with a = 18.388(3), b = 10.167(2), c = 9.858(2) A, α = 69.00(2), β = 76.79(2), γ = 78.80(3)° and Z = 2.