Probing the mechanistic aspects of the chromium salen catalyzed carbon dioxide/epoxide copolymerization process using in situ ATR/FTIR

Studies of the copolymerization of CO2 and epoxides have been the staple of our groupʹs research program for the better part of a decade now. During that time, the incorporation of attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy has greatly enhanced the kinetic and mechanistic investigations performed. However helpful, there are some difficulties, e.g., phase partitioning, that we have discovered and overcome in that same time period. The greatest step forward was achieved by the incorporation of 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (TMSO) as an epoxide for performing accurate kinetic studies. Herein, we discuss the development of this technique into one of the mainstays within our laboratories, highlighted by our most recent catalyst system that utilizes (salen)CrIIIX/cocatalyst where salen: N,N′-bis(salicylidene)-1,2-ethylenediimine, X: Cl− or N3− and cocatalyst: N-methylimidazole, phosphines and PPN+ salts. Through altering the cocatalyst, ligand architecture and initiator, this catalyst system has proven to be one of the most industrially viable catalysts currently being studied.