Vavasori Andrea, Ronchin Lucio, Pietrobon Luca, Bravo Sara
Department of Molecular Science and Nanosystems, Ca' Foscari University of Venice, Scientific Campus via Torino n° 155, 30172 Venezia, Italy.
Molecules. 2025 May 2;30(9):2027. doi: 10.3390/molecules30092027.
Currently, the most promising alternative to the use of the phosgenation reaction, for large-scale production of isocyanates, ureas, and carbamates, appears to be the Pd-catalyzed oxidative carbonylation of arylamines. During the reaction, the Pd(II) catalytic species are reduced to Pd(0) and the addition of sacrificial oxidizing agents is usually necessary to restart the catalytic cycle. Among these oxidizing agents, molecular oxygen is undoubtedly the more appealing, from an economical and green point of view, but it is not so efficient, whereas several metal salts (named cocatalysts) can be used, able to form redox couples with Pd(0) or to act as electron transfer mediators with oxygen itself. Testing several Pd(II) complexes, metal cocatalysts, and promoters, we have found that the [PdCl(dppf)]/FeCl/LiBr = 1/1200/200 (mol/mol) system efficiently catalyzes the carbonylation of aniline to form 1,3-diphenylurea selectively (100%) with a TOF of ca. 1177 h. On the other hand, the addition of oxygen to such a system strongly increases the aniline conversion (0.3 MPa of O increases the TOF at ca. 3930 h), but it moves the selectivity towards the phenyl isocyanate (65%, mol/mol).
目前，对于大规模生产异氰酸酯、脲和氨基甲酸酯而言，光气法最有前景的替代方法似乎是钯催化的芳胺氧化羰基化反应。在反应过程中，钯（II）催化物种被还原为钯（0），通常需要添加牺牲性氧化剂来重启催化循环。在这些氧化剂中，从经济和绿色的角度来看，分子氧无疑更具吸引力，但它的效率不高，而几种金属盐（称为助催化剂）可以使用，它们能够与钯（0）形成氧化还原对，或与氧本身作为电子转移介质。通过测试几种钯（II）配合物、金属助催化剂和促进剂，我们发现[PdCl(dppf)]/FeCl/LiBr = 1/1200/200（摩尔/摩尔）体系能有效催化苯胺的羰基化反应，以约1177 h的时空产率选择性地（100%）生成1,3 - 二苯基脲。另一方面，向该体系中添加氧气会显著提高苯胺转化率（0.3 MPa的氧气将时空产率提高到约3930 h），但会使选择性转向苯基异氰酸酯（65%，摩尔/摩尔）。
