Palladium/Phenanthrolines Catalyzed Carbonylation of Nitroarenes : the Key Role of the Nitrogen Ligand

Nitroarene carbonylation is the most direct alternative to the currently employed phosgene-based strategy for the industrial production of aryl isocyanates such as toluendiisocyanate (TDI) and 4,4'-methylendiphenyildiisocyanate (MDI). Despite the high toxicity of phosgene, several million tons of this product are still produced each year. Catalytic systems based on the palladium/phenanthroline combinations are by far the most promising for an industrial application of the carbonylation strategy. Phenantrolines are unique in their ability to stabilize the catalyst under the forcing conditions and, unlike phosphines, are not oxidized by nitroarenes.