DFT MECHANISTIC STUDIES FOR A Pd-CATALYZED GREEN SYNTHESIS OF ISOCYANATES

Isocyanates are critical intermediates for the synthesis of several industrial products, and they are traditionally produced employing the toxic phosgene at one of the stages. An alternative synthesis involves the direct carbonylation of nitroarenes catalyzed by Pd/phenanthroline complexes in the presence of an acid . Very recently, we reported how the change of several experimental variables in this synthesis affects the turnover number and the selectivity of the reaction. Although these studies gave indications on the presence of key intermediates, the full reaction mechanism remained unexplored. Herein, we discuss the outcomes of an extensive DFT study for the whole reaction mechanism involving the Pd/phenanthroline catalytic system. The TOF determining intermediate and transition state have been located and experimental findings rationalized. Special attention has been devoted to the role of acid and how its nature would affect the rate determining barriers. The study has been also extended to different substituted phenanthrolines, explaining experimental outcomes and presenting a ligand rational design in the attempt to improve the catalytic performances.