A Computational Study On The Mechanism Of Intermolecular C-H Amination With Electrophilic Nitrogen Source Catalyzed By Palladium And Nucleus-Independent Chemical Shift Analysis Of The Electronic States Of The（CX）₄（X=O,S,Se） Molecules

Compounds containing C-N bond are widely found in nature and industrial chemical products closely related to our daily life. Accordingly, it has been one of the hot topics in the field of organic chemistry to seek a simple, efficient and environmentally friendly method for the construction of C-N bonds, which has important scientific significance and application value. Recently, the direct amination reaction of C-H bonds catalyzed by transition metals has become a hot research topic because of its simplicity and high efficiency. Among direct amination reactions, on the reaction of constructing C-N bonds with electrophilic amination reagent as nitrogen source, the intermolecular C-H amination reactions involved with O-benzoyl-N-alkyl hydroxylamine derivatives catalyzed by palladium have achieved very good results, but the detailed mechanism is not clear. In this work, the mechanism of the Pd-catalyzed C-H amination reactions was studied in detail by DFT methods. Computational results indicated that the reaction catalyzed by Pd（OAc）2 followed an uncommon Pd（II）-Pd（IV）-Pd（II） pattern. The key steps included: 1) the deprotonated N-aryl benzamides coordinated with Pd（II） catalyst and C-H bond activated by the ligand of acetate to afford the cyclic Pd（II） intermediate; 2) the Pd（II） intermediate was oxidized to the Pd（IV） species by the potential oxidant R1R2NOBz; 3) the Pd（IV） species subsequently underwent reductive elimination to afford the desired product. It is worth noting that Pd（0） underwent the same catalytic model with Pd（II）: 1) oxidative addition of the N-O bond onto Pd（0） could take place to yield Pd（II） species and coordinate with the deprotonated N-aryl benzamides; 2) the activation of C-H bond is performed by the amino group; 3) the yielded key intermediate is identical with that in the Pd（II） catalyzed mechanism and the subsequent routes leading to the desired amination product follow the feasible Pd（II） catalyzed mechanism proposed previously.（CX）n（X = O, S, Se） molecules and related dianion（CX） _n^2-（X = O, S, Se） have attracted considerable researchinterests recently due to their special structures. Early studies have suggested these molecules with Dnh symmetry should be aromatic. Then the nucleus independent chemical shift（NICS） as the most effective criterion of aromaticity is applied in the studies on aromaticity of（CO） _n^2-,（CS） _n^2- dianions and related singlet neutral（CO）n and（CS）n molecules. However, subsequent calculations and experiments showed that（CO）4 has a triplet ground state, and those calculations on（CO）4 were carried out on an excited singlet state. Herein, we decided to conduct a further NICS analysis on the low-lying electronic states（CO）4,（CS）4 and（CSe）4. The NICS（1） analysis results on the 8π and 10π singlet states and the 9π triplet state of（CO）4,（CS）4, and（CSe）4 indicate: 1) the 10π, excited, singlet states of these molecules are more “aromatic” than the lower energy 8π singlet states. The NICS（1） values for the 9π triplet states are intermediate between those for the two singlet states. The NICS（1） values in all three molecules largely depend on the number of electrons that occupy the a2 u π MO. 2) transferring electrons from the b2 g σ MO into the a2 u π MO decreases the NICS（1） value, suggesting an increase in diamagnetic ring current. In addition, the decreases of NICS（1） values are larger in（CO）4 than in（CS）4 or（CSe）4, which attributed to coefficients of the carbons in the a2 u π MO much larger in（CO）4 than in（CS）4 or（CSe）4.