ABSTRACT
Hydroboration and hydrogenation reductions of CO2 catalyzed by a porphyrinoid-based dimagnesium(I) electride (Mg2EP) were investigated by density functional theory calculations. Herein, the presence of potentially excess electrons located at the Mg-Mg bond endows Mg2EP with the ability to activate small molecules such as CO2, HBpin, and H2, thus opening up the possibility for further CO2 conversion. The Mg2EP-catalyzed hydroboration of CO2 to HCOOBpin is predicted to have relatively higher activity in comparison to the hydrogenation reduction to formic acid (HCOOH). Interestingly, the common solvent molecule tetrahydrofuran as an auxiliary can coordinate with the Mg center to effectively weaken the bonding interaction between the dimagnesium center and the intermediate species from the CO2 conversion, thereby promoting the catalytic cycle for the CO2 hydroboration. The present results suggest that the electride Mg2EP is promising for the molecular catalyst in the CO2 transformation.
ABSTRACT
Methane is the simplest alkane and can be used as an alternative energy source for oil and coal, but the greenhouse effect caused by its leakage into the air is not negligible, and its conversion into liquid methanol not only facilitates transportation, but also contributes to carbon neutrality. In order to find an efficient method for converting methane to methanol, CH4 oxidation catalyzed by Fe(IV)-Oxo-corrolazine (Fe(IV)-Oxo-Cz) and its reaction mechanism regulation by oriented external electric fields (OEEFs) are systematically studied by density functional calculations. The calculations show that Fe(IV)-Oxo-Cz can abstract one H atom from CH4 to form the intermediate with OH group connecting on the corrolazine ring, with the energy barrier of 25.44 kcal mol-1. And then the product methanol is formed through the following rebound reaction. Moreover, the energy barrier can be reduced to 20.72 kcal mol-1 through a two-state reaction pathway. Furthermore, the effect of OEEFs on the reaction is investigated. We found that OEEFs can effectively regulate the reaction by adjusting the stability of the reactant and the transition state through the interaction of electric field-molecular dipole moment. When the electric field is negative, the energy barrier of the reaction decreases with the increase of electric intensity. Moreover, the OEEF aligned along the intrinsic FeâO reaction axis can effectively regulate the ability of forming the OH on the corrolazine ring by adjusting the charges of O and H atoms. When the electric field intensity is -0.010 a.u., the OH can be directly rebounded to the CH3· before it is connecting on the corrolazine ring, thus forming the product directly from the transition state without passing through the intermediate with only an energy barrier of 17.34 kcal mol-1, which greatly improves the selectivity of the reaction.
ABSTRACT
The degradation of BaP into hydroxybenzo[a]pyrene by Mn-corrolazine and its regulation by an oriented external electronic field (OEEF) were systematically studied using first-principle calculations. Extensive density function calculations showed that the degradation of BaP into hydroxybenzo[a]pyrene by Mn-corrolazine occurs via a three-step process in the absence of OEEF, in which a more toxic and stable epoxide intermediate is generated. However, upon application of OEEF along the intrinsic Mn-O reaction axis, the degradation of BaP into hydroxybenzo[a]pyrene is greatly simplified. The negative charge on the terminal O atom of Mn-OO corrolazine increases with an increase in the OEEF intensity. As the intensity of the OEEF increases over 0.004 a.u., the negatively charged terminal O atom has the ability to directly abstract the positively charged H atom of BaP and the degradation of BaP into hydroxybenzo[a]pyrene can be completed via a one-step process, avoiding the production of more toxic epoxide intermediates.
