Cyclopalladated complexes with N-(benzoyl)-N′-(2,4-dimethoxybenzylidene)hydrazine:: syntheses, characterization and structural studies

Cyclopalladated complexes with the Schiff base N-(benzoyl)-N'-(2,4-dimethoxybenzylidene)hydrazine (H2L, 1) have been described. The reaction of 1 with Li-2[PdCl4] in methanol yields the complex [Pd(HL)Cl] (2). [Pd(HL)(CH3CN)Cl] (3) has been prepared by dissolving 2 in acetonitrile. In methanol-acetonitrile mixture, treatment of 2 with two mole equivalents of PPh3 produces [PdL(PPh3)] (4) and that with one mole equivalent of PPh3 produces [Pd(HL)(PPh3)Cl] (5). Crystallization of 2 from dmso-d(6) results into isolation of [Pd(HL)((CD3)(2)SO)Cl] (6). In 2, the monoanionic ligand (HL-) is C,N,O-donor and the Cl-atom is trans to the azomethine N-atom. In 3, 5 and 6, HL- is C,N-donor and the Cl-atom is trans to the metallated C-atom. The remaining fourth coordination site is occupied by the N-atom of CH3CN, the P-atom of PPh3 and the S-atom of (CD3)(2)SO in 3, 5 and 6, respectively. Thus on dissolution in acetonitrile and dmso and in reaction with stoichiometric PPh3 the incoming ligand imposes a rearrangement of the coordinating atoms on the palladium centre. On the other hand, in presence of excess PPh3 deprotonation of the amide functionality in 2 occurs and the Cl-atom is replaced by the P-atom of PPh3 to form 4. Here the dianionic ligand (L2-) remains C,N,O-donor as in 2. The compounds have been characterized with the help of elemental analysis (C, H, N), infrared, H-1 NMR and electronic absorption spectroscopy. Molecular structures of 3, 4, and 6 have been determined by X-ray crystallography. (C) 2003 Elsevier B.V. All rights reserved.