Chromium(III) derivatives of the tetradentate phenoxyamine ligand H 2 salan, where salan = the N,N 0 -dimethylated bis(aminophenoxide) ligand or the saturated version of the corresponding salen ligand, in the presence of 1 equiv of [PPN]N 3 (PPN=Ph 3 PdN þ dPPh 3 ) are shown to effectively catalyze the copolymerization of cyclohexene oxide and carbon dioxide. X-ray crystallographic analysis reveals the structure of the complex to be different from that of its salen analogue, with an all cis arrangement of the nitrogen and oxygen atoms. Although these catalysts are selective for copolymerizing propylene oxide and CO 2 at ambient temperature with a high degree of regioselectivity, the copolymerization of cyclohexene oxide and CO 2 requires higher temperatures (e.g., 60°C). Nevertheless, the random polymerization of cyclohexene oxide and propylene oxide with CO 2 at ambient temperature provides a terpolymer with a nearly statistical distribution of monomer units. In addition, these catalysts have been shown to be efficient at producing diblock copolymers of poly(propylene carbonate) and poly(cyclohexylene carbonate) as well as triblock copolymers of poly(propylene carbonate)/ poly(cyclohexylene carbonate)/poly(vinylcyclohexylene carbonate).

Cationic diimine Ru(II) complexes were synthesized and tested as catalysts for the formation of cyclic organic carbonates from CO 2 and liquid epoxides (propylene oxide, epichlorohydrine, 1,2-epoxybutane and styrene oxide) which served as both reactant and solvent. The reaction rates not only depended on the type of ligand, but also on reaction conditions such as temperature, pressure, base, the epoxide substrates and the use of an additional solvent. Reaction rates in terms of turnover frequencies up to 4050 mol product mol cat.−1 h −1 at 99% selectivity were achieved by optimizing the diimine ligand as well as the reaction temperature and CO 2 pressure. Consistent with CV measurements, the electron donating group on the p-position of the aryl ring accelerated the reaction rate.

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