Catalytic activity of PdCl2 complexes with pyridines in nitrobenzene carbonylation

Synthesis of square planar palladium(II) complexes of general structure PdCl2(XnPy)2 (where: Py = pyridine; XnPy = 2-MePy; 3-MePy; 4-MePy; 2,4-Me2Py; 2,6-Me2Py; 2-ClPy; 3-ClPy and 3,5-Cl2Py) has been performed in order to study activity of these complexes as catalysts of nitrobenzene (NB) carbonylation – a process of industrial importance leading to production of ethyl N-phenylcarbamate (EPC). Electron withdrawing/electron donating properties of XnPy ligands (described by experimentally determined acidity parameter pKa) have been correlated with activities of PdCl2(XnPy)2 complexes during NB carbonylation in presence of catalytic system PdCl2(XnPy)2/Fe/I2/XnPy. We observed that conversions of substrates and yields of EPC increase within increasing basicity of XnPy ligand (for not sterically hindered XnPy's). On the basis of current work and our previous studies a detailed mechanism of catalytic carbonylation of NB is proposed.

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► Carbonylation of nitrobenzene and nitrobenzene/aniline catalyzed by PdCl2(XnPy)2 complexes is investigated.
► The substituent effect in XnPy on catalytic activity of PdCl2(XnPy)2 is studied.
► A detailed mechanism of catalytic carbonylation of nitrobenzene is proposed.