Cooperative anion activation at a cobalt center through ion pairing and ligand design.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41654490.
- Also identified by DOI 10.1038/s41467-026-69257-8 and PMC identifier 12992617.
- Licence recorded as CC BY-NC-ND.
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Abstract
Weakly coordinating anions (WCAs) are commonly used to stabilize high-valent, electrophilic transition-metal complexes, owing to their low nucleophilicity and minimal coordinating ability. Here, we present a cobalt platform supported by a tris(2-pyridyl)(N-picolyl)imidazolidine ligand (Py<sub>4</sub>Im) that generates a directional, protic cavity for ion pairing. This environment enables a comparative study of BF<sub>4</sub><sup>-</sup> and PF<sub>6</sub>⁻, showing that PF<sub>6</sub>⁻ undergoes fluoride abstraction under mild conditions, while BF<sub>4</sub><sup>-</sup> remains unreactive unless assisted by a Lewis base. The PF<sub>6</sub>⁻ activation yields a well-defined Co<sup>III</sup>-F complex that acts as an efficient nucleophilic fluoride source. DFT calculations and diffusion NMR experiments highlight the critical role of anion-cation pairing in modulating reactivity, overriding intrinsic thermodynamic preferences. These findings showcase supramolecular control of WCA activation by a late transition metal and provide new design principles for reactivity modulation via counterion selection.