Copolymerization of cyclohexene oxide and carbon dioxide using (salen)Co(III) complexes: synthesis and characterization of syndiotactic poly(cyclohexene carbonate)

Synthetic routes to a series of new (salen) CoX (salen = N, N'-bis(salicylidene)-1,2-diaminoalkane; X = halide or carboxylate) species are described and the X-ray crystal structures of two (salen-1) CoX (salen-1 = N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminocyclohexane; X = Cl, I) complexes are presented. (R, R)-(salen- 1) CoX (X = Cl, Br, I, OAc, pentafluorobenzoate (OBzF(5))) catalysts are active for the copolymerization of cyclohexene oxide (CHO) and CO2, yielding syndiotactic poly(cyclohexene carbonate) (PCHC), a previously unreported PCHC microstructure. Variation of the salen ligand and reaction conditions, as well as the inclusion of [PPN] Cl ([PPN] Cl = bis( triphenylphosphine) iminium chloride) cocatalysts, has dramatic effects on the polymerization rate and the resultant PCHC tacticity. Catalysts rac-(salen- 6) CoX (salen- 6 = N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminopropane; X = Br, OBzF(5)) have high activities for CHO/CO2 copolymerization, yielding syndiotactic PCHCs with up to 81% r-centered tetrads. Using Bernoullian statistical methods, PCHC tetrad and triad sequences were assigned in the C-13 NMR spectra of these polymers in the carbonyl and methylene regions, respectively.