Perfectly Alternating Copolymerization of Cyclic Anhydrides and Epoxides with Yttrium β-Diketiminate Complexes

Monometallic yttrium beta-diketiminate complexes are active and controlled catalysts for perfectly alternating ring-opening copolymerization of 1-butene oxide and phthalic anhydride under mild conditions. beta-Diketiminate ligands with pendant neutral donors were targeted to identify both the impact of donor strength and number of donors on rates of polymerization and the presence of undesirable side reactions. Initiating groups were also varied between alkyls, chlorides, and alkoxides. In the presence of a cocatalyst, the catalysts studied were active for polymerization with minimal side reactions, whereas lack of cocatalysts led to competing homopolymerization of epoxides. While a greater donor strength and a larger number of donors both increase the rate of polymerization, donor strength generally had a bigger impact when a cocatalyst was used. Additionally, alkoxide and chloride initiators proved to be the fastest, with alkyls being more sluggish. These subtle ligand changes significantly impacting polymerization activity lend promise to the facile tunability of rare earth metal complexes to be highly active for the target copolymerization, which renders further research in this area attractive and timely.

Automated summary

Monometallic yttrium beta-diketiminate complexes are active and controlled catalysts for the ring-opening copolymerization of 1-butene oxide and phthalic anhydride. The strength and number of pendant neutral donors in the beta-diketiminate ligands, as well as the choice of initiating groups, affect the polymerization rates and side reactions. The presence of a cocatalyst enhances the activity of the catalysts, while lack of cocatalysts leads to competing homopolymerization. The tunability of rare earth metal complexes in this copolymerization process makes further research in this area promising.