SYNTHESIS, STRUCTURAL CHARACTERIZATION AND CATALYTIC CARBONYLATION OFNITROBENZENE TO PHENYLURETHANE USING PALLADIUM(II) 1,10-PHENANTHROLINE DIACETATO COMPLEX

Four coordinate complexes of Pd(II) of the type [PdLX2] where L = 1,10 -phenanthroline and X = acetato group were synthesized and characteriz ed by microanalysis, IR, UV/visible spectrometry, H-1 and C-13 [H-1] N MR. Structural determinations were carried out by single crystal X-ray diffraction method. The complex was found to be nearly square planar by geometry, the coordination valencies being provided by oxygens (one from each acetato group) and two nitrogens of the 1,10-phenanthroline moiety. Cyclic voltammetric studies exhibit an irreversible one elect ron oxidation with E-pa = +0.96 V Versus Ag/AgCl. Complex 1 along with a cocatalyst CuCl2 catalyzed the reductive carbonylation of nitrobenz ene in methanol solvent at 200 degrees C and 30 atm CO to give pheylur ethane with a turnover (TOF) frequency of 4.5 mol of product per mol c atalyst per h. Formation of palladium nitroso intermediate complex thr ough deoxygenation of the -NO2 group via CO2 is proposed to be the rat e determining step in the carbonylation of nitrobenzene. Based on the rate dependence studies rate law has been derived and thermodynamic ac tivation parameters are calculated from the Arrhenius plot. (C) 1997 E lsevier Science B.V.