Palladium(II) based imines; synthesis, characterization, X-Ray structural analysis; DFT and catalytic hydrogenation study

Abstract

Based on the bridge alkyl chain length between the two azomethine linkages of the bis ortho naphtholimine ligands, two synthetic techniques were used to prepare a novel series of palladium(II) complexes. The molecular formulae of the isolated metal chelates were assigned based on thermal analysis (TGA and DTA) and analytical data. In addition comprehensive spectroscopic studies such as UV-Vis, IR, PXRD and X-ray single crystal have completed the structural formulations of the newly synthesized palladium(II) complexes in question. The best description of the overall molecular geometry of the palladium(II) center is the square planar as expected for the d8 center of palladium(II). DFT calculations were performed to correlate the structural properties of the present palladium(II) complexes with their catalytic activity towards the hydrogenation of cyclohexene. In addition, the optimized geometrical parameters deduced from the X-ray measurements for structural analysis are compared with the corresponding ones obtained by DFT calculations. Regarding complex 3, DFT calculations were carried out to decide the most appropriate molecular structure. The current square planar diimine palladium(II) complexes have been evaluated for the catalytic hydrogenation of mono olefin cyclohexene. The catalytic activity was studied in relation to the effect of catalyst structure, catalysis type, nature and amount of the solvents and co-solvents. The results obtained indicated that these complexes are pre-catalysts that efficiently catalyze hydrogenation of cyclohexene by H2 at mild conditions.