Understanding unprecedented reaction mechanisms and predicting catalytic pathways are touted as the virtues of computational chemistry in catalysis. Studies herein reported concentrate on analyzing the mechanism of new types of reactions based on electronic structure derived with DFT. This dissertation is mainly about a coinage field, manganese catalysis, and activation of N-heteroarene that is a building block for pharmaceutical compounds. The reactivity of manganese in mediating invaluable reactions such as C–H activation and CO2 conversion was recently reported, conferring a noble worth to mechanistic studies on manganese catalysis.