Enhancing the Catalytic Performance of Group I, II Metal Halides in the Cycloaddition of CO2 to Epoxides under Atmospheric Conditions by Cooperation with Homogeneous and Heterogeneous Highly Nucleophilic Aminopyridines: Experimental and Theoretical Study.

Compared to metal-organic complexes and transition-metal halides, group I metal halides are attractive catalysts for the crucial cycloaddition reaction of CO2 to epoxides as they are ubiquitously available and inexpensive, have a low molecular weight, and are not based on (potentially) endangered metals, especially for the case of sodium and potassium. Nevertheless, given their low intrinsic catalytic efficiency, they require the assistance of additional catalytic moieties. In this work, we show that by exploiting the high nucleophilicity of opportunely designed aminopyridines, catalytic systems based on alkaline metals can be formed, which allow the cycloaddition of CO2 to epoxides to proceed under atmospheric pressure at moderate temperatures. Importantly, the aminopyridine nucleophiles can be applied in their heterogenized form, leading to a recyclable catalytic system. An investigation of the reaction mechanism by density functional theory calculations shows that metal halide complexes and nucleophilic pyridines can work as a dual cooperative catalytic system where the use of aminopyridines leads to lower energy barriers for the opening of the epoxide ring, and halide-adducts are involved in the subsequent steps of CO2 insertion and ring closure.

Do Carbon Nano-onions Behave as Nanoscopic Faraday Cages? A Comparison of the Reactivity of C60 , C240 , C60 @C240 , Li+ @C60 , Li+ @C240 , and Li+ @C60 @C240.

From the analysis of the polarizability of carbon nano-onions (CNOs), it was concluded that CNOs behave as near perfect nanoscopic Faraday cages. If CNOs behave as ideal Faraday cages, the reactivity of the C240 cage should be the same in Li+ @C240 and Li+ @C60 @C240 . In this work, the Diels-Alder reaction of cyclopentadiene to the free C240 cage and the C60 @C240 CNO together with their Li+ -doped counterparts were analyzed using DFT. It was found that in all cases the preferred cycloaddition is on bond [6,6] of type B of C240 . Encapsulation of Li+ results in lower enthalpy barriers due to the decrease of the energy of the LUMO orbital of the C240 cage. When the Li+ is placed inside the CNO C60 @C240 , the decrease in enthalpy barrier is similar to that of Li+ @C240 . However, the location of Li+ in Li+ @C240 (off-centered) and Li+ @C60 @C240 (centered) is quite different. When Li+ was placed in the center of the C240 cage in Li+ @C240 , the barriers increased significantly. Taking into account this effect, the barriers in Li+ @C240 and Li+ @C60 @C240 differ by about 4 kcal mol-1 . This result can be attributed to the shielding effect of C60 in Li+ @C60 @C240 . As a result, we conclude that this CNO does not act as a perfect Faraday cage.