Synthesis, structural characterization and catalytic carbonylation of nitrobenzene 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 characterized by microanalysis, IR, UV/visible spectrometry, 1H and 13C [1H] NMR. 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 electron oxidation with Epa = + 0.96 V versus AgAgCl. Complex 1 along with a cocatalyst CuCl2 catalyzed the reductive carbonylation of nitrobenzene in methanol solvent at 200°C and 30 atm CO to give pheylurethane with a turnover (TOF) frequency of 4.5 mol of product per mol catalyst per h. Formation of palladium nitroso intermediate complex through deoxygenation of the -NO2 group via CO2 is proposed to be the rate determining step in the carbonylation of nitrobenzene. Based on the rate dependence studies rate law has been derived and thermodynamic activation parameters are calculated from the Arrhenius plot.