A bis-Pyrazolate Pincer on Reduced Cr Deoxygenates CO2: Selective Capture of the Derived Oxide by CrII

Reduction of the bis-(pyrazolyl)pyridine complex [LCr]₂ with stoichiometric KC₈ in THF produces a species that is reactive with CO₂ to produce an aggregate composed of paramagnetic K₂L₂Cr₂(CO₃) linked by KCl into a product of formula [K₂L₂Cr₂(CO₃)]₄⋅2KCl. X-ray diffraction reveals a pincer hydrocarbon exterior and an inorganic interior composed of K⁺, Cl⁻ and carbonate oxygens. Every Cr is five coordinate and square pyramidal, with the axial N donor weakly bonded to Cr due to the Jahn–Teller effect of a high spin d⁴ configuration. Reaction with ¹³CO₂ confirms that carbonate here is derived from CO₂, that oxide is derived from CO₂, and that CO is indeed released, since it is not a competent ligand to Cr^II. Guiding principles for selectivity in CO₂ reduction are deduced from the diverse successful molecular constructs to date.