Breaking C–C (sp3–sp3) σ bonds in 1,4-diazabicyclo[2.2.2]octane (DABCO) by oxidation with antimony pentachloride

Abstract

Evidence for the oxidative cleavage of the C–C (sp³–sp³) σ bond of DABCO (1,4-diazabicyclo[2.2.2]octane) is reported. Two crystalline salts have been characterized by XRD analysis, which provides insight into the possible mechanism of bond scission that occurred. EPR and ENDOR spectra of the reaction solutions show the existence of two radical species: the delocalized DABCO˙⁺ cation, where the electron is delocalized between the two nitrogen nuclei, and a localized DABCO˙⁺ radical cation with two different hyperfine couplings to the two nitrogen atoms. Computations suggest that the latter radical is DABCO˙⁺ complexed with SbCl₅. DFT and mechanistic analysis provides possible mechanisms for the C–C bond scission, including a newly proposed intermediate: the methylenevinylpiperazine (MVP) radical cation.