Copolymerization of CO₂ and Cyclohexene Oxide Mediated by Yb(salen)-Based Complexes

New catalysts based on Yb­(salen) complexes active for the copolymerization of cyclohexene oxide (CHO) and CO₂ to give poly­(cyclo­hexene)­carbonate (PCHC) are reported. In combination with cocatalytic, nucleophilic chloride additives these new (binary) catalysts provided good conversion and selectivity for PCHC formation with average turnover frequencies of up to 35 h^–1 and narrow molecular weight distributions. The best results were obtained with the binary catalyst system 1 (0.1 mol %)/NBu₄Cl (0.05 mol %); at 90 °C a conversion of 57% was reached after 18 h with a TOF of 31 h^–1, and the polycarbonate had an M_n of 10.2 kg/mol and a PDI of 1.54. Comparative catalysis studies have also been performed with a series of literature systems based on transition metal/lanthanide salen complexes, and the newly presented catalysts show comparatively good activity as well as copolymerization selectivity. MALDI-ToF mass spectrometric analysis revealed that trace water contamination and/or traces of 1,2-cyclo­hexanediol were responsible for chain transfer effects limiting to some extent the maximum molecular weights that can be achieved in the current reactor setup.