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 K2 L2 Cr2 (CO3 ) linked by KCl into a product of formula [K2 L2 Cr2 (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 13 CO2 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 CrII . Guiding principles for selectivity in CO2 reduction are deduced from the diverse successful molecular constructs to date.