Quantum Chemical Investigation of the Transition States and Intermediates for the Reaction of the Nitrosonium Ion with the Pentaammineazidocobalt(III) Ion.

The water exchange reaction on Co(NH3)5OH23+ was investigated with various density functionals and basis sets. A Gibbs activation energy (ΔG⧧) agreeing with experiment was obtained with the long-range-corrected functionals ωB97X-D3 and LC-BOP-LRD, SMD hydration, and modified Karlsruhe def2-TZVP basis sets. This computational technique was then applied to the reaction of NO+ with Co(NH3)5N32+. All of the possible pathways were investigated, NO+ attack at the terminal N of Co(NH3)5N32+ via the E and the Z isomers of the transition states, and NO+ attack at the bound N of azide, also via both isomers. The most favorable pathway proceeds via the attack at the bound N via the Z isomer. This leads to the intermediate with an oxatetrazole ligand bound to Co(III) at the N in the 3-position, Co(NH3)5(cycl-N4O)3+, which undergoes N2 elimination to yield the Co(NH3)5N2O3+ intermediate. The subsequent substitution of N2O by water follows the Id mechanism with retention of the configuration. No evidence for the existence of the square-pyramidal pentacoordinated intermediate Co(NH3)53+ was found. All of the investigated intermediates, Co(NH3)5N23+, Co(NH3)5[E-N(N2)(NO)]3+, Co(NH3)5(E-ON4)3+, Co(NH3)5ON23+, Co(NH3)5(cycl-N4O)3+, and Co(NH3)5N2O3+, exhibit short lifetimes of less than ∼60 μs and react via the Id mechanism.