An investigaiton of the zinc based coupling of carbon dioxide and epoxides to form polycarbonates/cyclic carbonates

The utilization of simple Lewis base adducts of metal halide complexes for the coupling of CO₂ and epoxides has been achieved. Complexes of the type ZnX₂L₂ and ZnX₆L₄, where L is a substituted pyridine ligand, have been synthesized and characterized. These complexes exhibit a large range of activities towards coupling CO ₂ and epoxides as well as in the amount of ether in the resultant polymer. As such, the ether content of the polymer can be controlled to an extent from ∼35% to ∼0% by variation of the catalyst used and/or reaction conditions. These complexes are also seen to be very effective at the production of cyclic carbonate, the amount of which varies largely with the catalyst and monomer used. This behavior has been explored by kinetic measurements using in situ infrared spectroscopy. Employment of phosphines as the Lewis base for zinc and cadmium metal centers has also been investigated and correlated to the previous work.; Investigations into the activity of various novel epoxides towards ring opening polymerization have also been explored. These new epoxides are shown to bind to cadmium phenoxides and the relative binding affinities are monitored via 113Cd NMR spectroscopy. The cadmium phenoxide dimer Cd ₂(O-tBu₂C₆H₃)₄ has been utilized to indicate epoxide binding by the disruption of the dimeric catalyst by the epoxide. The activity of these epoxides towards ring opening and the subsequent polymerization will be discussed along with computational studies of the energetics for the ring opening process.