Two Spin-State Reactivity in the Activation and Cleavage of CO2 by [ReO2]-

The rhenium dioxide anion [ReO₂]^– reacts with carbon dioxide in a linear ion trap mass spectrometer to produce [ReO₃]^– corresponding to activation and cleavage of a C–O bond. Isotope labeling experiments using [Re¹⁸O₂]^– reveal that ¹⁸O/¹⁶O scrambling does not occur prior to cleavage of the C–O bond. Density functional theory calculations were performed to examine the mechanism for this oxygen atom abstraction reaction. Because the spins of the ground states are different for the reactant and product ions (³[ReO₂]⁻ versus ¹[ReO₃]⁻), both reaction surfaces were examined in detail and multiple [O₂Re-CO₂]⁻ intermediates and transition structures were located and minimum energy crossing points were calculated. The computational results show that the intermediate [O₂Re(η²–C,O–CO₂)]^– species most likely initiates C–O bond activation and cleavage. The stronger binding affinity of CO₂ within this species and the greater instabilities of other [O₂Re–CO₂)]^– intermediates are significant enough that oxygen atom exchange is avoided.