A DFT Study of the Conversion of CO2 in Dimethylcarbonate Catalyzed by Sn(IV) Alkoxides

作者:de Souto Renata C; Rosenbach Nilton Jr; Mota Claudio J A*
来源:Journal of the Brazilian Chemical Society, 2014, 25(12): 2322-2328.
DOI:10.5935/0103-5053.20140240

摘要

Foram realizados calculos de teoria do funcional da densidade (DFT) de intermediarios e estados de transicao da reacao entre o CO2 e metanol sobre catalisadores do tipo R2Sn(OCH3)(2). A interacao da molecula de CO2 com o catalisador de estanho e controlada pelo termo entropico, sendo desfavorecida a temperatura ambiente e pressao atmosferica. Por outro lado, a insercao da molecula de CO2 na ligacao Sn-OCH3 e termodinamicamente favorecida para todos os catalisadores estudados. A energia livre de ativacao calculada varia com a natureza do substituinte R. Grupos fenila apresentam a menor barreira, enquanto que os atomos de halogenio, as mais elevadas. Os grupos alquila apresentam barreiras intermediarias. Os calculos estao de acordo com resultados experimentais recentes, que indicaram uma maior frequencia de rotacao da reacao (TON) para a formacao de dimetil carbonato (DMC) quando Ph2SnO foi usado como catalisador. O esquema mecanistico completo foi calculado para os substituintes fenila e metila, considerando uma especie de estanho dimerica. %26lt;br%26gt;Density functional theory (DFT) calculations of intermediates and transition states of the reaction between CO2 and methanol over different R2Sn(OCH3) 2 catalysts (R = alkyl, phenyl and halogens) were carried out. The interaction of the CO2 molecule with the tin catalyst was controlled by the entropic term, being disfavored at room temperature and atmospheric pressure. On the other hand, the insertion of the CO2 molecule into the Sn-OCH3 bond is thermodynamic favorable for all the catalysts studied. The computed free-energy of activation varied with the nature of the substituent R. Phenyl groups exhibit the smallest barrier, whereas halogen atoms the highest. Alkyl groups present intermediate barriers. The results are in agreement with recent experimental results that indicated a higher turnover number (TON) for dimethylcarbonate (DMC) formation when Ph2SnO was used as catalyst. The whole mechanistic scheme was then computed for phenyl and methyl as substituents, considering a dimer tin species.

  • 出版日期2014-12