Recently, we reported the synthesis of a family of unusual 1,2,3-triazoles that are fused with icosahedral carborane anions such as the phenyl substituted compound 1  (figure 1, unlabeled vertices = B-Cl). Interestingly, both the carborane and five-membered-triazole portions of these molecules independently feature aromatic characteristics. The electrochemical properties of 1  have been investigated to ascertain if a radical anion is accessible but due to the electron rich nature of the carborane reduction is not possible. With this fact in in hand it seemed reasonable that if the negative charge of 1  were masked, by the formation of a zwitterion, its electrochemical properties may be altered sufficiently to make one electron reduction feasible. Hence, anion 1  was alkylated with methyl triflate to afford the zwitterionic species 2  in excellent yield. Reduction of this species with cobaltocene led to a radical species that could be detected as one broad signal at g=2.003 by EPR spectroscopy.   To confirm the formation of the radical anion 3  and compare its structural features with those of the unreduced zwitterion 2  , we obtained crystals suitable for single-crystal X-ray diffraction studies of both compounds. Spectroscopic and computational data have been used to assertain that the radical is localized on the triazolium portion. This represents the first isolable and fully characterized 1,2,3-triazolium species.

Synthesis and characterization and isolation of a stable carborane-fused triazole radical anion

247th National Meeting (2014)

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