Kinetics and Thermodynamics of the Monomer−Dimer Equilibria of Dialkoxydibutylstannanes

Formation of Dimethyl Carbonate from CO2 and Methanol Catalyzed by Me2SnO: A Density Functional Theory Approach

The conversion of CO₂ into dimethyl carbonate (DMC) is an environmental and industrial appealing topic because it contributes to reduce the emissions of CO₂ and to increase its use as raw material. In the present study we employed the CAM-B3LYP/def2-SVP DFT approach to evaluate the thermodynamic and kinetic parameters for the catalytic conversion of CO₂ and methanol into DMC. Starting with the activation of four methanol molecules by the [Me₂SnO]₂ dimer, we computed all the stationary points along the pathway to convert CO₂ and methanol into the DMC. The capture of two CO₂ molecules is promoted by an alkoxitin intermediate, in an exothermic process, with low activation energy. Formation of a first DMC occurs after an intramolecular rerrangement involving a tetrahedral intermediate. The formation of a second DMC may occur either in a process similar to the first one or by dimerization of the hemicarbonate formed after releasing the first DMC. In this pathway, the [Me₂(OH)SnO(OMe)SnMe₂]₂ complex is formed. This complex is less reactive than [Me₂Sn(OMe)₂]₂ but still conserves the catalytic activity. Identification of this mechanism suggests that the catalytic action of Me₂SnO can be improved by modulating the formation of the final [Me₂(OH)SnO(OMe)SnMe₂]₂ complex.

Synthesis of Fluorinated Dialkyl Carbonates from Carbon Dioxide as a Carbonyl Source

Fluorinated dialkyl carbonates (DACs), which serve as environmentally benign phosgene substitutes, were produced successfully from carbon dioxide either directly or indirectly. Nucleophilic addition of 2,2,2-trifluoroethanol to carbon dioxide and subsequent reaction with 2,2,2-trifluoroethyltriflate (3 a) afforded bis(2,2,2-trifluoroethyl) carbonate (1) in up to 79 % yield. Additionally, carbonate 1 was obtained through the stoichiometric reaction of 3 a and cesium carbonate. Although bis(1,1,1,3,3,3-hexafluoro-2-propyl) carbonate (4) was difficult to obtain by either of the above two methods, it could be synthesized through the transesterification of carbonate 1.

Spectroscopic and thermal properties of stannadithiane compounds bearing endocyclic ether and lactone groups

Four related stannadithiane compounds containing different endocyclic functional groups -including ether (1), diether (2), lactone (3), and spirolactone (4)- were prepared. The conformational landscape has been fully determined for the 8-membered representative (compound 1) resulting in a distorted crown form with the butyl chains adopting an extended conformation. The infrared and Raman spectra of stannadithiane species have been measured and interpreted, aided by quantum chemical calculations and potential energy surface analysis. Special attention has been devoted to the analysis of the vibrational features of the heterocyclic moieties. The characteristic ν_as(SnS) and ν_s(SnS) stretching modes of the SnS₂endo-cyclic group were clearly observed in the Raman spectra at around 340 and 315 cm^-1, respectively. The exo-cyclic ν(SnC) stretching modes were found near 590 and 565 cm^-1 for the antisymmetric and symmetric motions, respectively. Thermal behavior for compounds 2-4 has been determined by thermogravimetric methods.