Nitrogen ligands effects in the palladium-catalyzed carbonylation reaction of nitrobenzene to give N-methyl phenylcarbamate

We previously reported an enhancement in the catalytic activity of a palladium-phenanthroline system towards the carbonylation of nitroarenes to N-methyl arylcarbamates when non-symmetric phenanthrolines were used as ligands. In particular, best results were obtained when an electron donating group was present on just one of the pyridinic rings of the ligand. Here we report the effect of stronger donor groups on the catalytic activity and on the selectivity of the system, even in the presence of different phosphorus acids used as promoters. High catalytic activities were reached but the high basicity of the ligands can negatively affect the product selectivity. The presence of steric hindrance near one or both the nitrogen donor atoms was shown to be detrimental for the activity of the system both with phenanthroline ligands and a quinoline–guanidine hybrid ligand.