The hydroboration of pyridine with pinacolborane (HBpin) catalyzed by (C₅Me₅)₂ThMe₂ and [(C₅Me₅)₂Th(H)(μ-H)]₂, which was reported efficient and 1,2-regioselective, was theoretically investigated in details by using B3PW91 functional combined with mixed basis sets. Based on the calculations, the necessity of using catalyst and the reactive species of the above pre-catalysts were confirmed, the most plausible mechanisms of direct and catalyzed 1,2- and 1,4-hydroboration of pyridine were determined, and the regioselectivity and the substituent effect of pyridine were discussed. The main conclusions were drawn as follows.

Firstly, the mechanisms of direct 1,2- and 1,4-hydroboration of pyridine with HBpin were studied, which were found difficult to occur owing to the high Gibbs free energy barriers of 48.8 and 57.0 kcal/mol even the barriers could be lowered by about 15 kcal/mol with a HBpin assisting the hydrogen migration. Therefore, suitable catalyst is necessary.

Secondly, the calculated results showed that the sigma bond metathesis between the second HBpin and Th-C bond has lower rate-determining Gibbs free energy barrier of 19.1 kcal/mol compared with 22.3 kcal/mol for the corresponding process between the first HBpin and another Th-C bond. That means CAT1 prefers to react with two HBpins to give rise to Cp*₂ThH₂（RC1）but not to react with one HBpin to produce Cp*₂ThHMe（RC）in the presence of excess HBpin. Namely, it is Cp*₂ThH₂, but not Cp*₂ThHMe which was thought to be active catalyst, that actually catalyzed the hydroboration of pyridine.

Thirdly, among the four possible mechanisms of the 1,2-hydroboration of pyridine catalyzed by RC1 considered here, mechanisms 2A and 2B were plausible with low and comparable rate-determining Gibbs free energy barriers which well agreed with the experimental activation energy, suggesting the reaction could smoothly occur under mild conditions. Mechanism 2A was supported by the experimentally detected intermediate 2A-INT1, but did not match the kinetic isotopic effect of KH/KD = 2.75. Mechanism 2B was in excellent agreement with the kinetic isotopic effect, while not including the experimental intermediate. It was found that the mechanism was depending on the adding mode of regents. Mechanism 2A was followed when consequently adding CAT1 and pyridine and HBpin, while mecnanism 2B was preferred when adopting one-pot technique.

Fourthly, compared with mechanism 4A, mechanisms 4B, 4C and 4D were not competitive for the 1,4-hydroboration of pyridine catalyzed by RC1 because of high free energy barriers. Mechanism 4A contained four steps including pyridine hydrogenation, coordination adjustment, B-N coupling, and hydrogen migration, in which pyridine hydrogenation was rate-determining with the free energy barrier of 28.5 kcal/mol, suggesting that 1,4-hydroboration of pyridine was less probable under the experimental condition.

Fifthly, the results indicated that the 1,4-hydroboration could not compete with the 1,4-hydroboration considering the about 8 kcal/mol higher rate-determining free energy barrier than that of 1,2-hydroboration and the comparable exothermicity. This was accordant with the experimental findings that the reaction was highly 1,2-regioselective which was mainly attributed to electronic effect .

Finally，the studies on the 1,2-hydroboration of substituted pyridines based on mechanism 2B showed that ortho-substitued pyridines were not reactive owing to the high free energy barriers, and meta-substitued pyridines only gave rise to the 3-substitued but not 5-substitued 1,2-products which were controlled by thermodynamics, and the order of yields of para-substitued pyridines was in line with the thermodynamic stability of products.

In a word, the mechanisms of the hydroboration of pyridine catalyzed by thorium complex were detailedly investigated in the present thesis. Not only was the uncommon mechanism 2B for 1,2-hydroboration confirmed, but the dependence of mechanisms 2A and 2B on the adding mode of regents was found. This study is very helpful to better understand the mechanisms of hydroboration of pyridine even of other compounds, and may provide a theoretical basis for the rational design of new catalysts in experimental research.