Nitrene group transfer catalyzed by a transition metal, such as Co, is an attractive synthetic methodology for forming C–N bonds in isocyanates1. Lee et al. reported a novel ligand-assisted strategy for isocyanate generation, where a nitrene is inserted into a Co–Si bond and selectively delivered to CO2. In their study, they proposed a catalytic cycle for the transformation of alkyl azide and CO into isocyanate using photolysis. Furthermore, they presented a proposed catalytic mechanism and corresponding reaction energies based on density functional theory (DFT) calculations. The present research extends their findings by performing DFT calculations to investigate the entire catalytic cycle and the detailed reaction mechanism of nitrene group transfer catalyzed by a Co complex in both low-spin singlet and high-spin triplet states. Our calculations indicate that the singlet surface is generally more stable than the triplet surface. Differences were observed between the singlet and triplet pathways, which are discussed in detail herein.