The methyl substituents of diquaternized 4,4'-dimethyl-2,2'-bipyridine are sufficiently acidic to be used as the source of a bridgehead carbon in the formation of cage amine derivatives from [Co(sen)](3+) [sen = 4,4',4"-ethylidynetris(3-azabutan-1-amine)]. The resulting octapositive bis(cage)-bipyridinium species can be obtained in both meso and optically active forms, the latter showing readily detectable potential shifts in the presence of enantiomeric anions.
Donnelly, P. S., Harrowfield, J. M., Skelton, B., & White, A. (2001). An Octapositive Cation Incorporating Multiple Redox Centres: Cage Amine Complexes of Cobalt(III) Linked by a 2,2'-Bis(pyridinium) Unit. Australian Journal of Chemistry, 54, 15-17. https://doi.org/10.1071/CH01026