Université de Lyon, Université Lyon 1 et CNRS, Sciences Analytiques-Laboratoire de Chimie Physique Théorique, 43 bd du 11 novembre 1918, 69622 Villeurbanne cedex, France.
Phys Chem Chem Phys. 2011 Feb 14;13(6):2401-8. doi: 10.1039/c0cp02089c. Epub 2010 Nov 22.
The formation of dimethyl carbonate (DMC) from CO(2) and methanol with the dimer n-Bu(2)Sn(OCH(3))(2) was investigated by experimental kinetics in support of DFT calculations. Under the reaction conditions (357-423 K, 10-20 MPa), identical initial rates are observed with three different reacting mixtures, CO(2)/toluene, supercritical CO(2), and CO(2)/methanol, and are consistent with the formation of monomeric di-n-butyltin(iv) species. An intramolecular mechanism is, therefore, proposed with an Arrhenius activation energy amounting to 104 ± 10 kJ mol(-1) for DMC synthesis. DFT calculations on the (CH(3))(2)Sn(OCH(3))(2)/CO(2) system show that the exothermic insertion of CO(2) into the Sn-OCH(3) bond occurs by a concerted Lewis acid-base interaction involving the tin center and the oxygen atom of the methoxy ligand. The Gibbs energy diagrams highlight that, under the reaction conditions, the dimer-monomer equilibrium is significantly shifted towards monomeric species, in agreement with the experimental kinetics. Importantly, the two Sn-OCH(3) bonds are prompt to insert CO(2). These results provide new insight into the reaction mechanism and catalyst design to enhance the turnover numbers.
采用实验动力学和密度泛函理论（DFT）计算相结合的方法研究了二氧化碳（CO2）和甲醇与二聚体[n-Bu2Sn（OCH3）2]2（2）反应生成碳酸二甲酯（DMC）的反应。在反应条件（357-423 K，10-20 MPa）下，三种不同的反应混合物（CO2/甲苯、超临界 CO2 和 CO2/甲醇）均表现出相同的初始反应速率，与单体二丁基锡（iv）物种的形成一致。因此，提出了一种分子内反应机理，其 DMC 合成的阿伦尼乌斯活化能为 104±10 kJ mol-1。对[(CH3)2Sn（OCH3）2]2/CO2 体系的 DFT 计算表明，CO2 与 Sn-OCH3 键的放热插入是通过涉及锡中心和甲氧基配体氧原子的协同路易斯酸碱相互作用发生的。吉布斯能图表明，在反应条件下，二聚体-单体平衡明显向单体物种移动，这与实验动力学一致。重要的是，两个 Sn-OCH3 键能够迅速插入 CO2。这些结果为反应机理和催化剂设计提供了新的见解，以提高转化率。
