Stepwise Regioselective Hydrogenation of cis‐2‐C₆₀(CF₂)₂ Homofullerene with [6,6]‐Open/Closed Valence Tautomerism

Abstract

The homofullerene compound cis-2-C (CF ) , which has an unusual kind of open/closed valence tautomerism undergoes consecutive regioselective hydrogenation at bridgehead carbon atoms upon reduction with Zn/Cu couple in H O-toluene mixture. The tautomerism barrier in cis-2-C (CF ) is negligible in the neutral state, whereas negative charging both impedes tautomeric transformation and promotes regioselective addition of electrophilic species at the bridgehead carbon atoms. In light of this observation, two novel homofullerene derivatives, mixed [6,6]-open/closed C (CF ) H and [6,6]-open cis-2-C (CF ) H , were synthesized and their structures were unambiguously determined by means of single crystal X-ray crystallography and NMR spectroscopy.

CF2‐Functionalized Trifluoromethylated Fullerene C70(CF3)8(CF2): Structure, Electronic Properties, and Spontaneous Oxidation at the Bridgehead Carbon Atoms

“…[2,19] As a result, it is reactive toward radical, nucleophilic and electrophilic addition as well as toward cycloaddition of the sterically undemanding addends. Moreover, addition to the said bond affords many derivatives [3] cis-2 C 60 (CF 2 ) 2 closed open 1.726(5) 1.979 (5) 1.65 2.08 [4,7] C 70 (CF 2 )-I closed 1.707(8) 1.72 [5] C 70 (CF 2 )-II open N.A. 2.09 [5] C s -8CF 2 open 2.099(4) 2.28 [2] , t.w.…”

“…In addition, open configuration of the CF 2 -bridge is characterized by enhanced reactivity of the bridgehead atoms that are capable to selectively attach sterically undemanding moieties. [6,7] Such modifications can be used for directed tuning of the physicochemical properties of the fullerene-based functional materials.…”

Difluoromethylenation of fullerene C70 provides isomeric diversity and availability of equatorial [5,6]-homofullerene C70(CF2)

“…Enhanced electrophilicity is typical of the open isomers, both [6,6] and [5,6], which has been previously demonstrated for [6,6]-open C 60 (CF 2 ), [6,6]-open/[6,6]-closed cis -2-C 60 (CF 2 ) 2 , [6,6]-open C 70 (CF 2 ), and [5,6]-open C 70 (CF 3 ) 8 CF 2 . 24,35,43,52…”

“…Enhanced electrophilicity is typical of the open isomers, both [6,6] and [5,6], which has been previously demonstrated for [6,6]-open C 60 (CF 2 ), [6,6]-open/ [6,6]-closed cis-2-C 60 (CF 2 ) 2 , [6,6]-open C 70 (CF 2 ), and [5,6]-open C 70 (CF 3 ) 8 CF 2 . 24,35,43,52 In the open isomers of C 70 (CF 2 ) where no electrons are being withdrawn from the p-system, the LUMO is stabilized by the same 0.10-0.15 eV as in the other known open adducts. Contrariwise, the closed adduct I with its unchanged LUMO energy differs in its behavior from the other closed CR 2 adducts where the LUMO energy is up-shifted by 0.1-0.3 eV, likely due to withdrawal of the bridgehead carbon atoms from the p-system.…”

“…In a further experimental and theoretical study of the same reaction with both C 60 and C 70 , formation of C 60/70 (CCl 3 ) À intermediates has indeed been confirmed through detection of the C 60/70 (CCl 3 )H products. 42 The present reaction with sodium chlorodifluoroacetate has been studied, apart from C 60 33,34,43 and C 70 , 24 also for the C s -C 70 (CF 3 ) 8 , 35,44 Sc 3 N@C 80 , and Sc 3 N@C 78 45,46 compounds. Formation of two isomeric C 70 (CF 3 ) 8 [CF 2 ] adducts was interpreted in terms of concurrence of the nucleophilic and carbene pathways.…”