Chemical fixation of carbon dioxide and other heterocumulenes: The development of catalysts for the reaction of epoxides and carbon dioxide/heterocumulenes

CrIII(salen) complexes were found to be excellent catalysts for the coupling of terminal epoxides with CO2 when used in conjunction with a Lewis base co-catalyst (DMAP). We optimized the catalyst systems activity by modifying the structure of the catalyst and co-catalyst as well as tuning other reaction parameters. This lead to the development of a catalyst system which cleanly affords the product cyclic carbonates in high yield under mild reaction conditions and is applicable to a variety of terminal epoxides.;CoIII(porphyrin) and CoIII(salen) complexes were also demonstrated to be efficient catalysts for the coupling of CO 2 and epoxides. As was the case for the CrIII(salen) complex, these Lewis acids also required the presence of a Lewis base co-catalyst. These CoIII complexes were found to be highly active catalysts for the synthesis of the cyclic carbonate products from a variety of terminal mono- and disubstituted epoxides affording high yield and selectivity. 1,2-Disubstituted internal epoxides were also investigated as substrates and found to react with very high stereospecificity. A chiral CoIII(salen) complex was found to be more selective than the analogous chiral CrIII(salen) complex in the kinetic resolution of propylene oxide with CO2. We discovered that the enantioselectivity could be further improved with modifications of the sterics and electronics of the co-catalysts, attaining a maximum selectivity factor of 5.6.;We also investigated the extension of our CrIII(salen)/Lewis base catalyst system to the coupling of epoxides with isocyanates. In contrast to the coupling reaction of CO2 and epoxides, the optimal catalyst system for this transformation required a weak Lewis base. Under optimal reaction parameters, this catalyst system was active for the production of a variety of 5-substituted oxazolidinones in high yield and selectivity. In addition, this catalyst system was shown to catalyze the transformation of chiral epoxides to chiral oxazolidinones with no loss in chirality.