Cyclopalladation of indole-3-carboxaldehyde aroylhydrazones

Reactions of PdCl2, LiCl, indole-3-carboxaldehyde 4-R-benzoylhydrazones (H2Ln; n = 1, 2, 3 and 4 for R = H, Cl, OMe and NMe2, respectively) and CH3COONa·3H2O in 1:2:1:1 mol ratio in methanol produce the cyclopalladated species of general formula [Pd(HLn)Cl] in 65–85% yields. The complexes have been characterized with the help of elemental analysis and spectroscopic (infrared, electronic and NMR) measurements. The proton NMR spectra of the complexes suggest palladation at the peri position of the indole moiety in (HLn)−. Molecular structure of a representative complex determined by X-ray crystallography confirms the peri-palladation and formation of a distorted CNOCl square-plane around the metal centre by the tridentate (HLn)− and the chloride.