(377e) Mechanistic Understanding of “Pd Cycle” Using Reaction Progress Analysis: An Insight into Understanding the Formation of Homo-Coupled Biaryl (impurity) Vs Hetro-Coupled Biaryl (desired product) Using Reaction Kinetics in the Catalytic Cycle

Cross coupling of unsaturated aryl triflates (or aryl halides) with boronic acid using Pd as catalyst (Suzuki coupling) have become increasingly attractive for making the hetro-coupled product (Ar-Ar'). However, most Pd cycle reactions produce some homo-coupled impurity. This is a major concern when the impurities are Poly Chloro Biphenyls (PCBs). PCBs are toxic and hazardous to humans and environment. They need to be controlled at very low levels (<50 ppm) for most processing plants in USA (unless they are registered producer of PCB's). To understand and control the impurity formation was the most important challenge. This presentation demonstrates how reaction kinetic profiles along with mathematical modeling can be used to gain an understanding of reaction mechanism, and thereby provide an insight on how to reduce the amount of PCBs generated with limited number of experiments (typically three). The principles of reaction progress analysis developed by Prof Donna Blackmond proved to be very useful in understanding and finding ways to reduce PCB in the reaction. Fundamental questions that needs to be answered when performing catalyst reaction, such as, stability of catalyst, catalyst poisoning, inhibition, reaction mechanism can also be answered with these limited number of experiments.