Pagodane dication

Pagodane dications 247 Dehydroadamantanediyl dication 249 2,10-para[3,5]octahedranedimethyl dication 250 Bis(Tropylium) dications 251... 

Superelectrophilic onium dications have been the subject of extensive studies and their chemistry is discussed in chapters 4-7. Other multiply charged carbocationic species are shown in Table 2. These include Hogeveen s bridging, nonclassical dication (14)26 the pagodane dication (15)27 Schleyer s l,3-dehydro-5,7-adamantane dication (16)28 the bis(fluroenyl) dication (18)29 dications (17 and 19) 19a trications (20-21)19a,3° and tetracations (22-23).31 Despite the highly electrophilic character of these carbocations, they have been characterized as persistent ions in superacids. 

Prinzbach s 4-center 2-electron bis-homoaromatic pagodane dication... 

Scheme 4.17 presents a couple of other strange-looking cationic species which were discovered in studies in a related field. In connection with the problem of dodecahedrane synthesis via the isomerization of pagodane 34 (cf. data in Schemes 4.10 and 4.11), Olah s and Prinzbach s groups engaged in studies of the behavior of pagodane derivatives under superacid conditions. Their hope was to force the cationic isomerization of 34 to 3. Despite all attempts, this route was unworkable. As a reward for these apparently futile efforts they were able to observe the unexpected formation of a very stable cationic species, the pagodane dication 55 (Scheme 4.17). The pattern of its NMR spectra combined with the nature of its quenching adduct 56, and the theoretical analysis of possible alternatives, enabled the authors to ascribe to this dication the unprecedented four-center/two-electron delocalized bis-homoaromatic structure.

Figure 13.15 Homoaromaticity in the pagodane dication forming an aromatic cyclobutane dication. The deiocaiized system can also be viewed as the frozen transition state of a ther-mochemically allowed [l+l]cycloaddition.

Another 4c/2e dication 51, related to the pagodane dications, was proposed to be formed during electrochemical oxidation of the tetroxide 52. B3LYP/6-31G calculations support the homoaromatic delocalization in 51 and indicate an average homocon-jucative N—N distance of 2.55 A, which is similar to that found in the pagodane dications. 

SO2CIF (eq 28). In these systems, separation of the two cation centers by at least two methylene groups is necessary for the ions to be observable. Aromatic dications are usually prepared by oxidizing the corresponding aromatic compounds with SbFs (eq 29). In the case of pagodane containing a planar cyclobutane ring, oxidation leads to the formation of cyclobutane dication which was characterized as a frozen two-electron Woodward-Hoffmann transition state model (eq 30). ... 

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