Kinetic Studies of Copolymerization of Cyclohexene Oxide with CO2 by a Diamino-bis(phenolate) Chromium(III) Complex

A diamino-bis(phenolate) chromium(III) complex, CrCl(THF)[L], 1, where [L] = dimethylaminoethylamino-N,N-bis(2-methylene-4,6-tert-butylphenolate), has been synthesized in high yield and characterized by MALDI-TOF mass spectrometry, elemental analysis, UV-vis spectroscopy and single crystal X-ray diffraction. This complex combined with 4-dimethylaminopyridine (DMAP) or bis(triphenylphosphoranylidene)ammonium chloride or azide salts (PPNCl or PPNN3) shows improved activity over previously reported amine-bis(phenolate) chromium(III) complexes for copolymerization of cyclohexene oxide (CHO) and CO2 to yield poly(cyclohexene) carbonate (PCHC). Kinetic studies of the complex/DMAP system showed the activation energy for polycarbonate formation to be 62 kJ/mol. End group analysis of resulting polycarbonates by MALDI-TOF MS reveals either the chloride of the Cr(III) complex or the external nucleophile initiates the copolymerization reaction.