Chemometric optimization of the ruthenium carbonyl catalyzed cyclization of 2-nitrostilbene to 2-phenylindole

A chemometric optimization of the Ru3(CO)12 catalysed deoxygenation of 2-nitrostilbene to 2-phenylindole was carried out. The effects of temperature, CO pressure, amounts of catalyst and substrate on conversion and selectivity were examined by factorial design/response surface methods. The conversion was found to increase on increasing the temperature and decreasing the CO pressure, it assumed a minimum value for medium amounts of catalyst and was almost independent of the amount of substrate. These results were also confirmed using a learning system and were used to develop a mechanism for the reaction. The data suggest two different mechanisms: one based on a Ru(CO)5 catalysed process and another one based on a Ru3(CO)12 catalysed process, which are first and zero order with respect to the substrate, respectively