Observation of inserted oxocarbonyl species in the tantalum cation-mediated activation of carbon dioxide dictated by two-state reactivity.

Reductive activation of carbon dioxide (CO) has drawn increasing attention as an effective and convenient method to unlock this stable molecule, especially transition metal-catalyzed reactions. Taking the [TaCO] ion-molecule complex formed in the laser ablation source as a representative, the reactivity of the tantalum metal cation towards CO molecules is explored using infrared photodissociation spectroscopy combined with quantum chemical calculations. The strong absorption in the carbonyl stretching region provides solid evidence for the insertion reactions into CO bonds by the tantalum cation. Two inserted oxocarbonyl products are identified based on the great agreement between the experimental results and simulated infrared spectra of energetically low-lying structures in the singlet and triplet states. The pivotal role of two-state reactivity in driving CO activation among three different spin states is rationalized by potential energy surface analysis. Our conclusion provides valuable insight into the intrinsic mechanisms of CO activation by the tantalum metal cation, highlighting the affinity of tantalum for CO bond insertion in addition to typical "end-on" binding configurations.