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 Li2[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-d6 results into isolation of [Pd(HL)((CD3)2SO)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)2SO 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, 1H NMR and electronic absorption spectroscopy. Molecular structures of 3, 4, and 6 have been determined by X-ray crystallography.