Theoretical Study On Catalytic Synthesis Of New Carbon - Carbon Bond By Transition Metal (Pd, Rh)

In this work, we have studied the mechanisms of the two projects, one at the B3 LYP level of DFT and the other at the M06 level of DFT. Frequency calculations at the same level of theory were also conducted to verify all the stationary points as minima or transition states and to provide free energies at 298.15 K. The intrinsic reaction coordinate analysis was carried out to confirm that all stationary points are smoothly connected to each other. The lanl2 dz basis set was used for Pd and Rh atom and the 6-31g(d,p) basis set was used for other atoms. We aim to present the favorable mechanisms, explain the experimental results, and offer guidance for further study of related reactions.(1) The reaction mechanism for the palladium(II)-catalyzed cross-coupling of N-tosylhydrazone S1 with alkene S2 has been studied with the help of density functional calculations. The acetate present in the catalyst was found to directly participate in the reaction. The tBu O- group that was added excessively into the reaction system plays an important role for forming the new C=C double bond. In addition, whether in the absence or presence of water, the hydrogen addition process is found to be rate-determining. In the former case the overall barrier is 34.1 kcal/mol, corresponding to the fact that only trace amount of product P was detected. In the latter case the overall barrier is lowered to 29.8 kcal/mol, corresponding to the fact that product P was obtained with a yield of 75%.We clarified how water plays an assistant role to promote the catalytic reaction studied.(2) A mechanistic study of the substituent-dependent ring formations in RhIII-catalyzed C-H activation/cycloaddition of benzamide and diazo compounds was carried out by using DFT calculations. The results indicated that the decomposition of the diazo compound is facilitated upon the formation of the five-membered rhodacycle, in which the RhIII center is more electrophilic. The insertion of carbenoid into Rh-C(phenyl) bond occurs readily and forms a 6-membered rhodacycle. However, the following C-N bond formation is difficult both kinetically and thermodynamically by reductive elimination from the RhIII species. Instead, the Rhv-nitrenoid intermediate could be formed by migration of the pivalate from N to Rh, which undergoes the heterocyclization much more easily and complementary ring-formations could be modulated by the nature of the substituent at the a-carbon. For this reaction, mechanistic experiments insisted that acyloxy is turnover-limiting and irreversible. However,our theoretical and computational study prove that the migration of the OPiv is the turnover-limiting rather than the C-H activation.