Reductive carbonylation of nitrobenzene to phenylurethane catalyzed by Ru(III)-Schiff base complexes

Abstract

Ruthenium complexes containing Schiff bases with N2O2, N4 and N5 donor groups with the general formula [Ru(III)(X)Cl 1 or 2], where X = Schiff base such as bis(salicylaldehyde)-o-phenylenediimine (salen), bis (salicylaldehyde) ethylenediimine (salen), bis(picolaldehyde)ethylenediimine (picen), bis(picolaldehyde)-o-phenylenediimine (pic-dien), bis(picolaldehyde)- diethylenetriimine (pic-dien), were tested for their catalytic activity towards the reductive carbonylation of nitrobenzene in ethanol to give phenylurethane. The five Ru(III) complexes tested towards reductive carbonylation showed different catalytic activities in the range 160 - 200“C and CO partial pressure of 15 atm. Among the complexes tested, [Ru(saloph)Cl2] showed the highest catalytic activity with a turnover rate greater than 80 mol product per mol catalyst per hour at 160“C and 15 atm CO. [Ru(pic-en)Cl2]Cl and [Ru(pic-opd)Cl2]Cl complexes with N4 donor systems were found to be less active towards carbonylation of nitrobenzene, as indicated by their turnover rates of 20 and 15 mol product per mol catalyst per hour, respectively, at 200“C and 15 atm CO. The complex [Ru(pic-dien)Cl]Cl2N5 donor system was completely inactive even at 200“C and 15 atm CO, and no conversion of nitrobenzene was seen even after 12 h contact time.