Mechanism Insight into the Csp3-H Amination Catalyzed by the Metal Phthalocyanine

Possible mechanisms and the selectivity of Z- and E-substrates for the Csp(3)-H amination catalyzed by the metal phthalocyanines have been explored by DFT calculations. Here the whole amination reaction includes the preformation of iminoiodinane and the intramolecular C-H amination through a metallonitrene intermediate, and the former experiences relatively high free energy barriers of 27-30 kcal/mol. The present results show that the quintet-state pathway catalyzed by the Mn(III)-phthalocyanine is responsible for the low-energy C-H amination with a free energy barrier of 20.5 kcal/mol for the initial C-H activation to yield a carbon-centered radical intermediate. For the Zn- and Mg-phthalocyanine catalysts, the free energy barriers range from 10.3 to 12.6 kcal/mol for the partially rate-determining C-H cleavage, exhibiting higher catalytic activity than the Mn(III)-phthalocyanine. The triplet-singlet spin flip in the C-H cleaved intermediate is predicted to be involved in the C-N bond coupling and the E-conformer is more favorable than the Z-substrate in the Zn- and Mg-catalyzed C-H aminations.