Carbon Dioxide Copolymerization Study with a Sterically Encumbering Naphthalene-Derived Oxide

Poly(1,4-dihydronaphthalene carbonate) has been prepared via the catalytic coupling of carbon dioxide and 1,4-dihydronaphthalene oxide using chromium(III) catalysts. The copolymer formation is found to be greatly dependent on the steric environment around the metal center. Traditional (salen)(CrX)-X-III/cocatalyst systems bearing bulky t-butyl groups hinder the approach of the large monomer, significantly diminishing polymer chain growth and providing the entropically favored cyclic byproduct in excess. In contrast, employing the sterically unencumbered azaannulene-derived catalyst, (tmtaa)(CrX)-X-III/cocatalyst system (tmtaa = tetramethyl-tetraazaannulene) shows polymer selectivity close to 90% with three times the activity (TOF = 20-30 h(-1)). With the use of a bifunctional (salen)Cr-III catalyst, even higher polymer selectivity (>90%) can be observed. The complete synthesis of a new bifunctional tetraazaannulene ligand for a more effective catalyst is also described herein.