Theoretical Study On Reaction Mechanism Of Nickel Catalyzed Selective Insertion Of Unsaturated Hydrocarbons Into C-C Bond

The cleavage of C-C bonds is the fundamental issue in organic chemistry, and one of the most efficient approaches to C-C bonds activation is the use of transition metal as catalysts. Chemists have developed a variety of transition-metal catalysts for C-C bond functionalization, such as, ruthenium, rhodium, palladium, iron, copper, nickel, iridium, tungsten, rhenium, osmium, and gold. These transition-metal catalysts have showed high efficiency in accomplishing many fascinating transformations of the unsaturated hydrocarbon ?alkynes or olefins? insertion into C-C bond, to achieve the conversion of function group or ring-enlargement reaction. As a novel strategy, the application of synergistic effects of metal-metal, metal-organic, and organic-organic combined catalysts have received much attention. What's more, an efficient cooperation of the lewis acid ?LA? with the transition-metal complex is expected to be a powerful tool in C-C ?-bond cleavage. In experiments, catalyst design and optimization requires a great amount of tests. It is an efficient approach to model the catalysis using computational programmes for exploring catalytic mechanisms. With these in hand, it helps to compare the effect on reactions from different catalysts and further improve the catalysts and design new catalysts. Theoretical investigations of transition metal catalytic mechanisms are important instructive supports for catalyst design and synthesis currently. In this paper, we mainly explored the reaction mechanism of transition-metal catalyzed unsaturated hydrocarbon insertion into C-C bond and compared with the results of experiment, so that it can contribute to provide theoretical basis for the design of more efficient catalysts. The results of the study are as follows:1. Theoretical study on reaction mechanism of nickel/Lewis acid ?BPh₃? catalyzed alkyne insertion into C-CN bond of 2,3,5,6-tetrafluorobenzonnitrile. The mechanism of but-2-yne with 2,3,5,6-tetrafluorobenzonnitrile catalyzed by Ni?0?/BPh₃ was studied in detail. The results show that the cocatalyst BPh₃ did not change the mechanism, with or without BPh₃, complete cycle include the migration, oxidative addition, alkyne insertion and reductive elimination, where alkyne insertion ??G°???=21.9 kcal/mol? is the rate-determining step. In addition, it was found that BPh₃ can reduce the activation barriers of the migration, oxidative addition and alkyne insertion and the reaction energy barrier of the Ni migration step was reduced by 3.4 kcal/mol, which is consistent with the experimental fact. In addition, we also discussed the regioselectivity of the oxidation addition process and interpreted the reason of selective C-CN bond activation. Finally, we predicted that the Ni?PPh₃??AL? catalyst would have a better catalytic activity for this reaction system, the ?G°??? is 10.0 kcal/mol in alkyne insertion, which can provide a new direction for the experimental synthesis.2. Theoretical study on reaction mechanism of nickel-catalyzed cycloaddition of 1, 3-diene and 1-Boc-3-azetidone. Two possible reaction mechanisms of nickel-catalyzed 1, 3-butadiene insertion 1-Boc-3-azetidone including ?-carbon elimination pathway and oxidative addition pathway have been investigated in detail by DFT method. The results show that the energy barrier of the cleavage of C-C bonds is up to 48.0 kcal/mol, which indicate that the reaction mechanism is not the traditional ?-carbon elimination pathway. Furthermore, the oxidative addition pathway includes oxidative addition, diene insertion and reduction elimination steps, where the diene insertion is the rate-determining step ?AG°???= 32.2 kcal/mol?. It indicates that the reaction is carried out by an oxidative addition reaction mechanism. This study would help to better understand the mechanism of this kind of reaction, and provide a theoretical basis to design a more effective catalyst to reduce the activation barrier of rate-determining step.