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Reactions of Li2[PdCl4] with N-(aroyl)-N′-(2,4-dimethoxybenzylidene)hydrazines (H2L = (4-R–C6H4)C( O)NHN CH(2,4-(CH3O)2C6H3)) in presence of PPh3 have provided cyclopalladated complexes having the general formula [PdL(PPh3)] (1, 2 and 3 where R = OCH3, CH3 and Cl, respectively) and a coordination complex trans-[Pd(HL)(PPh3)2Cl] (4 where R = NO2). The complexes have been characterized by elemental analysis, infrared, 1H NMR and electronic absorption spectroscopy. X-ray structures of all the complexes have been determined. In 1, 2 and 3, the C,N,O-donor dianionic ligand (L2−) forms two fused five-membered chelate rings at the metal centre. On the other hand, the monoanionic ligand (HL−) acts as deprotonated amide N-donor in 4. The strong electron withdrawing effect of the nitro group on the aroyl fragment is possibly responsible for the monodentate amide N-coordinating behavior of HL− in 4. The orientation of the 4-methoxy group in 1 is different than that in 2 and 3 due to intramolecular C–H⋯π interaction in the last two complexes. The structure of 4 shows an apical C–H⋯Pd interaction involving the azomethine (–CH N–) group of HL−. In the crystal lattice of all the structures, various types of intermolecular non-covalent interactions are present. The self-assembly of the molecules of 1, 2 and 3 leads to two-dimensional networks. The same network observed for 2 and 3 reflects the interchangeability of the chloro and methyl groups due to their similar volumes. In the case of 4, the complex and the water molecules present in the crystal lattice form parallel homo-chiral helices and finally interhelical interactions lead to a three-dimensional network.

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.