SYNTHESIS, STRUCTURAL CHARACTERIZATION AND CATALYTIC CARBONYLATION OFNITROBENZENE AND AMINES BY MONONUCLEAR PALLADIUM(II) COMPLEXES CONTAINING SUBSTITUTED PYRIDINE LIGANDS

Reaction of 2,6-lutidine and 3-picoline with pd(CH3COO)(2) in dry benz ene gave diacetato-bis-2,6-lutidine palladium(II) (1) and diacetato bi s-3-picoline palladium(II) (2) respectively. The complexes 1 and 2 wer e characterized by spectroscopic (IR, UV-Vis,H-1, C-13[H-1] NMR) and s tructural determination by single crystal X-ray methods. Both the comp lexes are nearly perfect square planar (trans) complexes, the coordina tion valencies being provided by one of the oxygens of two acetate lig ands and the nitrogen of the pyridine. The structure of complex 1 is h eld by van der Waal's contacts only and the structure of complex 2 is held in space by intermolecular hydrogen bonding. The near identical b ond length of Pd-O and Pd-N show that the acetate groups are labile, w hich may be a principle factor for the catalytic activity of the compl exes. Cyclic voltametry studies exhibit an irreversible one electron o xidation with Delta E(pa) = +0.93 and +0.86 V vs Ag/AgCl. The complexe s 1 and 2 with cocatalysts FeCl3 or CuCl2 were found to be active homo geneous catalysts in the carbonylation of nitrobenzene to phenyluretha ne and carbonylation of aromatic and aliphatic amines to diureas respe ctively in the temperature range 150-200 degrees C and 40 atm. CO, res pectively. The catalytic studies indicated that complex 2 was more act ive than 1 in carbonylation of nitrobenzene and of amines under the re action conditions studied. In the case of amines, the activities of co mplex 1 and 2 were decreased in the order n-butylamine > diethylamine > benzylaime > cyclohexylamine. However, both complexes were inactive in carbonylation of triethylamine.