(Tetramethyltetraazaannulene)chromium Chloride: A Highly Active Catalyst for the Alternating Copolymerization of Epoxides and Carbon Dioxide

A tetramethyltetraazaannulene complex incorporating a chromium(III) metal center has been shown to be highly active toward the
copolymerization of cyclohexene oxide and carbon dioxide to afford
poly(cyclohexene carbonate) in the presence of [PPN]N3 [PPN+
= bis(triphenylphosphoranylidene)ammonium] as a cocatalyst. An
asymptotical rate increase was observed, leveling at 2 equiv of
cocatalyst with a maximum turnover frequency of 1300 h-1 at
80 °C. A benefit of this new catalyst system over that of the
previously studied less-active (salen)CrX system is that the (tmtaa)CrCl catalyst has a much lower propensity toward the formation
of a cyclic carbonate byproduct throughout the copolymerization
reaction.