Pd(Ii)-Complexes of Telluro-Substituted Schiff Base Ligands: Effect of the Pendant Alkyl Group on Suzuki and Heck Coupling Through in Situ Generated Palladium Nanoparticles

Abstract

Two telluro-substituted Schiff bases L1/L2 having different pendant carbon chains (−Me in L1 and −C10H21 in L2) and their corresponding square planar Pd(II)-complexes (1/2) have been synthesized and their structural characterization has been carried out using multinuclear NMR and elemental analysis. The ligand L2 showed a Smectic liquid crystalline phase and melts at 81 °C into isotropic liquid whereas L1 and complexes (1/2) did not show any liquid crystalline property. The square planer Pd(II)-complexes (1/2) have been formed through the coordination of ligands (L1/L2) respectively in mono-anionic tridentate mode (Te,N,O−) and the fourth coordination sphere at the palladium center is occupied with Cl− ion. Both complexes 1/2 (1 to 2 mol%) have been examined as a catalyst for Suzuki and Heck coupling reactions and their activity depends significantly on the length pendant alkyl chain. The results obtained from Hg-/PPh3-poisoning and three phase test on Suzuki-Miyaura coupling indicate the participation of both homogeneous as well as heterogeneous palladium species protected with the ligand or its fragment.

Keywords: Palladium complex, Organotellurium ligand, Carbon-Carbon coupling, Effect of the pendant alkyl chain, Homogenous or heterogenous catalysis