Phosphazene Base Mediated (sp3)CH Functionalization with CO2 and CS2

H Functionalization with CO2 and CS2"/>

Selective deprotonation of HCF₃, HC₂F₅, and CH₃CN by the phosphazene base EtP₄ in the presence of CO₂ or CS₂ affords the phosphazenium carboxylates [EtP₄H]⁺[F₃CCO₂]⁻ and [EtP₄H]⁺[F₅C₂CO₂]⁻, as well as the corresponding dithiocarboxylates [EtP₄H]⁺[F₃CCS₂]⁻ and [EtP₄H]⁺[F₅C₂CS₂]⁻. In the presence of H₃CCN and CS₂, the novel heterocyclic salts [EtP₄H]⁺[NC₄S₄]⁻ and [EtP₄H]⁺[NC₅S₅]⁻ are formed via distinct pathways that share a common intermediate.

The activation of weakly acidic (sp³)CH bonds in substrates such as fluoroform (HCF₃), perfluoroethane (HC₂F₅), and acetonitrile (H₃CCN) remains a fundamental challenge in synthetic chemistry. We report that the phosphazene base {(Et₂N)₃P=N}₃P=N ^t Bu (EtP₄) enables the selective deprotonation of these molecules when combined with electrophilic small molecules such as CO₂ or CS₂. This cooperative approach affords a variety of structurally diverse anions, including CF₃-substituted dithiocarboxylates and novel five- and six-membered cyano-thiolato-dithioheterocycles resulting from activation of H₃CCN. The ring compounds are stable in air and are characterized by single-crystal X-ray diffraction, infrared spectroscopy, and mass spectrometry. These findings expand the scope of metal-free base/electrophile systems for (sp³)CH functionalization and provide synthetic access to isolable carbanions derived from otherwise inert substrates.

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