Metal complexes of sulphur–nitrogen chelating agents. Part 10. The chemistry of palladium(II) complexes with some monoanionic tridentate ligands of the type SNN

Abstract

Complexes of the type [PdLX](X = Cl or Br) have been obtained with the tridentate ligands (HL) : methyl 2-(β-aminoethylamino)cyclopent-1-enedithiocarboxylate (HL¹), methyl 2-(β-aminopropylamino)cyclopent-1-enedithiocarboxylate (HL²), and methyl 2-(β-diethylaminoethylamino)cyclopent-1-enedithiocarboxylate (HL³). The reactions between [PdLX] and a stoicheiometric amount of silver perchlorate in acetonitrile and 99% methanol lead to the formation of the complexes [PdL(MeCN)]ClO₄ and [PdL(H₂O)]ClO₄ respectively. The co-ordinated solvents in these compounds can be easily substituted by other nucleophilic bases (B) and the corresponding complexes [PdL(B)]ClO₄ are obtained. Due to steric effects complexes of the type [PdL(py)]X (X = Cl, Br, or ClO₄; py = pyridine) cannot be prepared for the ligand HL³. In dry acetone the reaction between [PdLBr](L = L¹ or L²) and silver perchlorate in 2 : 1 molar ratio results in the formation of [Pd₂L₂Br]ClO₄. The same reaction in acidic medium (pH 2) affords [Pd(HL)Br]ClO₄. However, when the reactants are used in 1 : 1 molar proportion no stable product can be isolated. The heats of dissociation (ΔH) for the reaction [PdL¹(B)]Cl →[PdL¹Cl]+ B (B = pyridine, NH₂Et, or NHEt₂) have been compared with the analogous nickel(II) complexes, and the results show slightly greater bond strengths of Ni–B.