Study On The Mechanism Of Nickel-Catalyzed Carboxylation Of Aryl Zinc Reagent With CO₂

VI Climate change caused by carbon dioxide?CO₂?in the atmosphere has become a hot topic of political,scientific and media discussion.As the most abundant carbon source after biomass and natural gas,carbon dioxide can be used to produce chemical products with high value and commercial benefits.Although the activation and transformation of CO₂ molecules are difficult due to their chemical inertness,it can be activated by transition metal catalysts.One of the important topics to reduce CO₂ in the atmosphere is to activate CO₂ by environmentally friendly chemical methods.Among many methods,catalytic activation of CO₂ with transition metal complexes has become one of the most attractive methods.At present,researchers have found all kinds of non-oxidized and low-valent transition metal catalysts for catalyzing CO₂,but the understanding of their catalytic mechanism is not deep enough.Computational chemistry,as an effective research method,can overcome the disadvantage that it is difficult to detect intermediates in experiments,provide a new understanding of the reaction mechanism of catalysts at the molecular level,and provide theoretical guidance for the design and development of new catalysts.In this work,we use a combination of theoretical and experimental methods to explore the detail reaction mechanism of 1,1'-bis?diphenylphosphino?ferrocene?dppf?and tricyclohexylphosphine?PCy₃?and aryl zinc reagents,which catalyze the activation of CO₂ to form carboxylic acid compounds through cross-coupling reaction.According to the calculation results of B3 LYP density functional theory?DFT?,the free energy barrier of the rate-limiting step with?dppf?Ni is only 1.64 kcal mol^-1 higher than the barrier with?PCy₃?₂Ni.The former is the best reaction path in the two reaction mechanisms of stepwise and concerted.The catalytic performance of?dppf?Ni catalyst is better.In addition,during the experiment,it is found that the yield of?PCy₃?₂Ni catalyst is higher,which prompt us to conduct further theoretical research.It is found that the reason for the low yield of?dppf?Ni catalyst is its weak ability to capture CO₂ molecules.In order to further understand the effect of other ligands on the whole catalytic cycle mechanism,we considered the other two ligands 1,2-bis?diphenylphosphino?ethane?dppe?and 1,4-bis?diphenylphosphino?butane?dppb?.A series of theoretical calculations show that the ligand effect will not affect the catalytic activation mechanism of transition metal complexes for CO₂ and?dppf?Ni complexes in the theoretical level is still an excellent performance comparison of the catalyst.