Dications of Fluorenylidenes. The Effect of Substituent Electronegativity and Position on the Antiaromaticity of Substituted Tetrabenzo[5.5]fulvalene Dications

Abstract

Oxidation of 3,6-disubstituted tetrabenzo[5.5]fulvalenes by SbF(5) results in the formation of dications that behave like two antiaromatic fluorenyl cations connected by a single bond. Both fluorenyl systems exhibit the paratropic shifts and nucleus independent chemical shifts (NICS) characteristic of antiaromatic species. Comparison with analogous 2,7-disubstituted tetrabenzo[5.5]fulvalenes reveals that the antiaromaticity of the substituted ring system can be altered substantially by changes in the placement of the substituents, possibly due to changes in the delocalization of charge in the system. Substituents in the 3,6-position decrease the antiaromaticity because of the increase in the benzylic resonance compared to 2,7-substituents.

Superelectrophiles: Recent Advances

“…For example, the hydroxyketone 62 reacts in triflic acid to provide the substituted fluorene 63 in 70% yield ( Scheme 16 ) [ 55 ]. Other reports describe similar conversions to the functionalized fluorenes [ 56 , 57 , 58 , 59 , 60 ]. The 4π electrocyclization step was studied by computational methods and it was estimated that formation of the dication superelectrophile ( 64 ) lowers the transition state activation energy by about 16 kcal·mol −1 , compared to the monocationic species ( 65 ).…”

Towards Norcorrin: Hydrogenation Chemistry and the Heterodimerization of Nickel(II) Norcorrole

“…The combination of direct pyrroleÀpyrrole bonding with an onorthogonal arrangemento fn orcorrole subunitsf urnishes ad imer with as trong electronic interaction between the subunits that has not been observed in previously reported dimerics peciesc ontaining two antiaromaticr ings. [31][32][33][34] The dimericc omplex 4 possesses four distinct and easily accessible oxidation states that may be exploited for the preparationo fs table bis(radical) systemsh aving either dianionic or dicationic character.T he magnetic and opticalp roperties of these and relateds ystems as well as their reactivity will be furthers tudied in our laboratories.…”

Intramolecular Aromatic Carbenoid Insertion of Biaryldiazoacetates for the Regioselective Synthesis of Fluorenes

“…Fluorene derivatives obtained by the present study can have various synthetic utilities. [29] Indeed, a highly interesting example is demonstrated in Scheme 5. Diazoacetate 1 e bearing a chloro substituent was readily prepared in two steps starting from 9 by Suzuki-Miyaura coupling to form a biaryl linkage of 10 followed by a diazo-transfer reaction in 91 % overall yield.…”