Dimethyl Carbonate Synthesis from CO2 and Dimethoxytin(IV) Complexes: The Anatomy of the Alkylation Step Viewed from DFT Modeling

Carbon-Sulfur Bond Cleavage in Methanesulfonate on Diorganotin Quinaldate Platform - Synthesis and Characterization of [(n-Bu2SnL)2SO4]

The synthesis of mixed ligand di-n-butyltin complexes, [(n-Bu2SnL1-3)2SO4], 2-4 (HL1-3=2-quinoline/ 1-isoquinoline/ 4-methoxy-2-quinoline carboxylic acid) has been realized by reacting n-Bu2Sn(OMe)OSO2Me, 1 a with the corresponding quinaldic acid under solvothermal conditions. The observed transformation of methane sulfonate to sulfate anion represents a rare example of C-S bond cleavage on the organotin scaffolds, n-Bu2Sn(L1-3)OSO2Me, which have been identified as en route intermediates by NMR and X-ray crystallography. Analogous reaction when extended with Me2Sn(OMe)OSO2Me, 1 b and HL2 yields [(Me2Sn)2(L2)3(OSO2Me)], 5 as partially disproportionated product of Me2Sn(L2)OSO2Me. The solid-state structures of 2-5 reveal variable modes of coordination of the ligands to afford molecular and polymeric motifs.

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.

Sustainable Catalytic Synthesis of Diethyl Carbonate

New sustainable approaches should be developed to overcome equilibrium limitation of dialkyl carbonate synthesis from CO₂ and alcohols. Using tetraethyl orthosilicate (TEOS) and CO₂ with Zr catalysts, we report the first example of sustainable catalytic synthesis of diethyl carbonate (DEC). The disiloxane byproduct can be reverted to TEOS. Under the same conditions, DEC can be synthesized using a wide range of alkoxysilane substrates by investigating the effects of the number of ethoxy substituent in alkoxysilane substrates, alkyl chain, and unsaturated moiety on the fundamental property of this reaction. Mechanistic insights obtained by kinetic studies, labeling experiments, and spectroscopic investigations reveal that DEC is generated via nucleophilic ethoxylation of a CO₂ -inserted Zr catalyst and catalyst regeneration by TEOS. The unprecedented transformation offers a new approach toward a cleaner route for DEC synthesis using recyclable alkoxysilane.