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)­CrIIIX/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)­CrIIIX/cocatalyst system (tmtaa = tetramethyltetraazaannulene) shows polymer
selectivity close to 90% with three times the activity (TOF = 20–30
h–1). With the use of a bifunctional (salen)­CrIII 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.