Breaking C-C (sp 3 -sp 3 ) σ Bonds in 1,4-Diazabicyclo[2.2.2]octane (DABCO) by Oxidation with Antimony Pentachloride

Abstract

Evidence of the oxidative cleavage of the C-C (sp 3 -sp 3 ) σ bond of DABCO (1,4-diazobicyclo[2.2.2]octane) is reported. Two crystalline salts have been characterized by XRD analysis, which provides insight about the possible mechanism of bond scission that occurred. EPR and ENDOR spectra of 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 •+ cation radical with two different hyperfine couplings to the two nitrogen atoms. Computations suggest that latter radical is DABCO •+ complexed by SbCl5. DFT and mechanistic analysis provide possible mechanisms for the C-C bond scission, including a new proposed intermediate: methylenevinylpiperazine (MVP) radical cation.