A theoretician’s view of the Ce+ mediated activation of the NH bond in ammonia

The insertion reaction of Ce+(4H, 4f15d2) into the NH bond of ammonia on the doublet and quartet potential energy surfaces has been investigated at the density functional theory using the hybrid exchange correlation functional B3LYP level. Crossing points between the potential energy surfaces are located using different methods, and possible spin inversion processes are discussed by means of spin–orbit coupling (SOC) calculations. As a result, there is a crossing point between the doublet and the quartet state surfaces. The reacting system will start in the quartet ground state, the change of the spin state probably occurring immediately after the formation of the electrostatic complex intermediate, leading to a significant decrease in the barrier height of 4TS12 from 17.3 to 2.5 kcal/mol, and then move on the doublet potential energy surface as the reaction proceeds. The minimum energy crossing point (2/4MECP) is located by using the methods of Harvey et al. On the basis of the calculated SOC value and potential energy surfaces, the estimated probability of ISC (PISC) at 2/4MECP is approximate 0.214. Additionally, the natural bond orbital (NBO) and natural resonance theory (NRT) analyses have been used to characterize the nature of the bonds for all of the minima and transition states along the optimal reaction paths. On the basis of the obtained results, it is possible to conclude that for the molecules considered the reaction is a spin-forbidden process, this is a typical two-state reactivity (TSR) reaction. These conclusions are consistent with the experimental observations.