Away from phosgene: reductive carbonylation of nitroarenes and oxidative carbonylation of amines, understanding the mechanism to improve performance

Abstract

Recent progress, with some emphasis on the author's own work, on the understanding of the mechanism of the reductive carbonylation of nitroarenes and of the oxidative carbonylation of amines is discussed, highlighting the close connection between the two reactions and trying to unify scattered data in the literature. Isocyanates, carbamates and ureas can be obtained by either procedure, without the need for the use of the toxic and corrosive phosgene.

Phosgene-free synthesis of 1,3-diphenylurea via catalyzed reductive carbonylation of nitrobenzene

“…Initially, in the presence of CO and of the catalyst, the nitro compound generates a metallacycle 1 [26][27][28][29][30]64]. This intermediate undergoes decarboxylation, leaving the nitroso group 2 bonds to the metal.…”

“…The catalytic reductive carbonylation of the aromatic nitro compounds appears to be a convenient alternative phosgene-free route. In this process the nitro group reacts directly with CO under the influence of a catalyst to form isocyanate or, in the presence of an alcohol, the derived carbamate (Scheme 1) [25][26][27][28][29][30].…”

Catalytic Activity of Supported Rhodium(I) Complex for the Carbonylation of Nitrobenzene: Mechanism for Carbamate Formation

“…35 Though we have isolated the substrate coordinated rhodium species (designated as complex 3), we are not sure of its real existence or formation in the high CO pressure, high temperature catalytic run in DMF solution. Since nitrosobenzene and phenyl nitrine intermediates have been predicted for the palladium and ruthenium complexes by various groups, 2 we speculated Scheme 2 for the initial stages of our catalytic carbonylation reactions. This could best explain the isolation of intermediates from the starting complex and the formation of aniline as an associated product in all cases.…”

“…As per the recently published review, 2 it is clear that deeper understanding of the reaction mechanism of the carbonylation system is required to gain better insight into the selectivity factor. In the present paper we have investigated the reductive carbonylation reaction of nitrobenzene to carbamates using a polystyrene anchored rhodium complex and made an attempt to find the catalytic pathway based on the isolation and characterization of key reactive intermediates from its soluble analogue.…”

“…Many important compounds such as ureas, carbamates, azo and azoxyarenes, oximes and several heterocyclic compounds can be selectively obtained by either reductive carbonylation of nitroaromatics [1][2][3][4][5][6][7][8][9][10] or oxidative carbonylation of anilines. [11][12][13][14] Isocyanates, carbamates and ureas can now be obtained by either procedure without the use of the toxic and corrosive phosgene.…”