Hogeveen dication

Trihydroxycyclopropenium ion and homologous ions Hogeveen dication [C6(CH3)6] 256 11 Oxygen-stabilized carbodications 257 References 258... 

Clear, unequivocal experimental evidence has by now been obtained for nonclassical ions such as the norbomyl cation.38 10 The bonding concept required to define nonclassical ions is simply to consider them as penta(or higher)-coordinated carbonium ions involving at least one two-electron three-center (or multicenter) bond, of which CH5+ (themethoniumion-carbonium ion) is the parent, asCH3+ (the methenium ion, methyl cation, carbenium ion) is the parent for trivalent carbenium ions. An example of a hexacoordinate carbonium ion is the pyramidal dication of Hogeveen.41... 

The dication (CgMefi)21 (437) and the CLi62+ dication (438) are two additional six-coordinate carbon-containing species. Ion 437 was observed by Hogeveen and... 

CH)62+-Type Dications. The first known representative of the (CH)62+-type hexacoordinate pyramidal dications is Hogeveen s hexamethyl cation 437.41 789 1108 This dication 437 can be prepared from a variety of precursors in superacidic media (HSO3F, HS03F-SbF5) at low temperature (Scheme 3.28). 

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. 

There are several other carbodications that may be represented as 1,3-dicationic systems (or nonclassical, highly delocalized systems), including Schleyer s l,3-dehydro-5,7-adamantanediyl dication (28),11 Hogeveen s pyramidal dication (29),12 diallyl dications (i.e., 30),13 dicationic ethers (i.e., 31),14 diprotonated pyrones (32),15 as well as various aromatic dications. 

Perturbation results by Hogeveen and van Kruchten (1981) conhrm their proposed symmetrical structure for the pyramidal dication [36]. 

Precedents of this type of bonding pattern are the assumed bicyclo[2.2.2] octane-1,4-diyl dication 195 which was found to be in a subsequent rcinvcstigation of the monocation monodonor-acceptor complex, and the octamethylnorbornadienediyl dication 196 prepared and characterized by Hogeveen et al ... 

The first known representative of the (f d 1)6 pyramidal-type dications was the hexamethyl derivative 23. " " This unique dication was prepared by Hogeveen and Kwant from a variety of precursors in superacid media at low temperatures (Scheme 5.13). 

Hogeveen, Heldeweg, and coworkers also prepared the ethyl and isopropyl derivatives of these pyramidal dications (235a-235d) and their bridged structures have been conhrmed by II and NMR spectra and quenching studies ... 

Hogeveen and Kwant have also converted 5-substituted bicyclo[2,l,l]hexenyl cations, as well as some products of their quenching , in a superadd medium into the unusually stable dication. 673-675) jjjg latter is formally regarded... 

Ab initio calculations for a model dication (CH)g also support the nonclassical pyramidal structure Of late Hogeveen has corroborated the nonclassical structure of dication 506 with both Saunders isotopic perturbation method and the comparison — after Schleyer et al. — of the sum of all chemical carbon shifts in the NMR spectrum of the ion with that for the neutral hydrocarbons 507 and 508 the calculated differences were 54.6 and 195.7 ppm per charge unit, respectively, typical for nonclassical ions. 

Hogeveen et al. have generated stable pyramidal dications of the general formula (CCH3)jCR and (CCHj)4(CR)2 (R is ethyl, isopropyl), e.g. ... 

The H and C nmr spectra of the pyramidal dication of Hogeveen shows a five-fold symmetry with no significant line-broadening at temperatures as low as — I50°C. The alternative structures could be either a hypercoordinated five-fold symmetrical pyramidal dication [120] or a set of rapidly equilibrating carbodications [121] with the same time-averaged symmetry, as indicated in (88). 

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