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

Possible mechanisms and the selectivity of Z- and E-substrates for the Csp3–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.