The Importance of the Bite Angle of Metal(III) Salen Catalysts in the Sequestration of CO2 with Epoxides in Mild Conditions

Abstract

The search for environmentally sustainable and economically affordable catalysts is incessant in the world of chemistry, especially when it comes to reduce polluting gases such as CO2. Capture and sequestration of CO2 are very interesting research fields, although it seems clear that the efforts must be routed towards the potential use of CO2 as an economical feedstock. In this sense, the CO2 cycloaddition to epoxides to give rise to cyclic carbonates has attracted much attention. Here the results for the formation of cyclic organic carbonates catalyzed by metal-salen complexes, previously achieved with yttrium and scandium, are compared with those of analogous complexes containing metals from the first transition series, such as cobalt or chromium. DFT calculations allow to determine whether this switch of metals will be feasible and provide the basis for instigating future experimental efforts in this regard. The calculations analyzing the structure and electronics of the catalysts allow us to give not only a clear picture of whether these catalysts will be efficient, but also allow to assess which metal center is the most convenient and/or whether the catalytic reaction will occur under mild conditions. Advanced buried volume calculations with the SambVca packages shed light on the different catalytic pockets of monometallic first row transition metals versus group III salen complexes. Our results show that the bite O-M-O angle plays an essential role in the catalysis