Theoretical Study Of The Properties And Formation Mechanism Of Carbenes In Ionic Liquids

In the last decade an explosive development has been observed in the fields of both ionic liquids (ILs) as potential chemically inert solvents with many possible technical applications, and carbenes as catalysts with superb performance. Since the cations of many ILs can be deprotonated by strong bases yielding carbenes, these two fields are inherently connected. And this possibility is not merely a possible decomposition mechanism for ILs but also an opportunity to unite the advantageous properties of these two groups of compounds into a novel and powerful chemistry. Apart from the most popular and most investigated classes, imidazole-2-ylidenes, the formation of other highly reactive neutral species ("abnormal carbenes," e.g. pyridine-ylidenes) is feasible in highly basic ionic liquids. However, as an active intermediate, the time to survive in the system of carbene is a split second, a general analysis methods can not detect the existence of it. Therefore, it is difficult to capture this kind of intermediate and make a characterization of it in experiment, including the formation mechanism from the ionic liquid. It is an important method to solve this problem by using quantum chemistry calculation.In this paper, we got a high accuracy and more efficient calculation condition for carbenes from 44 DFT methods and 3 common basis sets:M05/aug-CC-pVDZ, based on five carbenes:H2C:, C12C:, F2C:, HC1C:, HFC, of which the ?ES-T experimental value was known and by comparing the precision G3MP2. We made optimization on structure and energy of different types of carbenes through the use of Gaussian09 software package. The wave function of electronic information of carbenes were got and characterized by using two wave function analysis software packages:AIM2000 and Multiwfn. Summarizes the diffirences between the two two, low-lying electronic states of carbene:singlet and triplet, as well as the effects of substitution and heterocyclic structure on electron donating ability and stability of carbenes. Combining with partition function and transition state theory, the relationship between the enthalpy (H) and entropy (S) value of the system abtained by gaussian09 and the activation energy(Ea) was established. Then we found the calculated Ea was more accuracy to describe the reaction energy barrier than the energy difference (AE), which was used to by most literatures. For the first time the graphene network was introduced into the IL-Carbene system, and confirmed that the introduced graphene network was beneficial to the formation of the carbene in the system, and found the hydrogen atoms on the graphene edge layer can be further reduced the energy barrier of transformation process from ion pair to the carbene by the edge effect of the adsorption process. This work can provide guidance for future molecular design of ILs-Carbene systems and experimental synthesis.