Mechanistic study of the Ru-3(CO)(12)/tetraalkylammonium chloride catalyzed carbonylation reactions of nitroarenes to carbamates and ureas: A completely revised picture

The mechanism of the Ru-3(CO)(12)/tetraalkylammonium halide catalyzed carbo nylation of nitroarenes to carbamates has been investigated. A completely r evised picture has emerged with respect to what was earlier believed. The c arbonylation reaction of nitroarenes catalyzed by Ru-3(CO)(12) proceeds thr ough the intermediate formation of aniline. Moreover, the active species is mononuclear and not a cluster. The effect of chloride is to accelerate the formation of Ru(CO)(5). This last complex forms an adduct with chloride th at reacts with nitroarenes at a much higher rate than Ru(CO)(5) itself, but this acceleration is not kinetically relevant during most of the reaction, as the initial nitroarene activation is not rate determining. Only toward the end of the reaction is a change in rds observed and the formation of th e chloride adduct may become important. [PPN] [Ru-3(CO)(11)(Cl)] also react s with nitroarenes much more easily than Ru-3(CO)(12).