Mechanistic Study of the Ru₃(CO)₁₂/Tetraalkylammonium Chloride Catalyzed Carbonylation Reactions of Nitroarenes to Carbamates and Ureas:  A Completely Revised Picture

The mechanism of the Ru3(CO)12/tetraalkylammonium halide catalyzed carbonylation of nitroarenes to carbamates has been investigated. A completely revised picture has emerged with respect to what was earlier believed. The carbonylation reaction of nitroarenes catalyzed by Ru3(CO)12 proceeds through 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 that 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 the chloride adduct may become important. [PPN][Ru3(CO)11(Cl)] also reacts with nitroarenes much more easily than Ru3(CO)12.