Metal Hydride Catalysis Oxygen Containing Carbon Double Bond Material In Theoretical Research

The level of atmospheric carbon dioxide has increased rapidly inreceng years due to humanactivities. It has resulted in the problem greenhouse effect and global warming. So the transitionof carbon dioxide into useful chemicals has become an important research topic. Formic acidcould serve as a hydrogen storage material, a precursor methanol, or a fuel. The investigation onthe mechansim of the reduction reactions of carbon dioxide by transition metal hydrid complexescan provide theoretical guide for the development of new high-efficiency catalysts.As Bu3SnH has some merits, including mild reaction conditions, strong operatibility, it hasbeen very attractive in the field of organic synthesis.Our work focus on the following aspects:（1） A detailed mechanism for the electrocatalytic reduction of CO2to formate by an iridiumdihydride pincer complex has been systematically investigated by performing DFT calculations.The calculated results indicate that the catalytic cycle includes three steps. The first step is theformation of Ir-formate intermediate. This step is achieved through hydride transferring from anIr-H bond to CO2. In the second step, formate anion releases from Ir-formate intermediate, whichcan lead to the formation of cationic hydride [（POCOP）-IrH（MeCN）₂]+. Solvent plays animportant role in the formation of formate anion, which cannot be generated in the gas phase.The reaction of CO2transforming to HCOO is driven by H2O hydrogen bonding to formate.The third step is catalyst regeneration. The formation of a non-classical hydrogen bond isresponsible for the regeneration of Ir-Cat, which is supported by natural bond orbital （NBO）analysis. The present theoretical results have rationalized the experimental observations well. Wehope these findings will be meaningful in the design of useful electrocatalysts for the reductionof CO2to formate or formic acid.（2） The reaction mechanism for catalytic reduction of CO2to formate by Iron dihydride pincercomplex is studied using density functional theory （DFT）. The reaction pathways areinvestigated in detail. The results suggest that the reaction proceeds in three steps: insertion ofcarbon dioxide into the Iron pincer dihydride, elimination of formate ligand from the[（tBu-PNP）Fe（H）（CO）（η1-OOCH）] complex, and catalyst regeneration. The solvent efect ofwater on the reaction is explored. The results indicate that water has an important efect on Elimination of formate ligand from [（tBu-PNP）Fe（H）（CO）（η1-OOCH）] complex. In addition, italso plays a critical role for regeneration of the catalyst via dearomatization and subsequentproton migration.（3） We have theoretically studied the mechanism on rotation of the N-alkenyl bond ofN-cycloalkenyl-N-benzyl acetamide and5-endo radical cyclization reaction catalyzed byBu3SnH. The calculated results suggest that rotating tautomerism can impact reaction processesof all channels, and eventually affects selectivity and yield of the products. If rotation barrier ishigher than the free energy barrier of the following reactions, interconvert reaction is unlikely tooccur. On the contrary, if rotation barrier is lower than the activation energy of the followingreactions, the rotating velocity is greater than the reaction rate. So a single bond rotation canoccur and have important influence on selectivity and the yield of the reaction. In addition,according to our calculation, there are two competitive reactions （cyclization, bimoleculartrapping） in this system. Cyclization reaction is more competitive than bimolecular trappingreaction due to its low free energy barrier. What’s more, cyclization reaction of2b should be themost dominant. The occurring possibility of all paths should obey the order: cycb>cyca>bim（cyc: cyclization, bim: bimolecular trapping）.