Regioselective Synthesis of [6,6]‐Open and [5,6]‐Closed C₇₀(CF₃)₈[CH₂] Methanofullerenes with Rapid [6,6]‐to‐[5,6] Phototransformation

Abstract

Fullerene derivatives with >CH2 addends in [6,6]‐open or [5,6]‐closed configuration are uncommon of fullerene derivatives, but they are readily accessible via treatment of Cs‐C70(CF3)8 with diazomethane followed by thermolysis or photolysis. Both thermodynamic and kinetic factors favor regioselective addition of diazomethane at the near‐equatorial [5,6]‐double bond of Cs‐C70(CF3)8 to give a thermally labile pyrazoline intermediate. Thermal extrusion of N2 from the latter is a kinetically controlled process with orbital symmetry controlled Woodward–Hoffmann‐allowed mechanism. It quantitatively yields the less thermodynamically favorable [6,6]‐open isomer of C70(CF3)8[CH2] homofullerene, but the latter turns out to be capable of unexpectedly rapid quantitative phototransformation into the thermodynamically preferable [5,6]‐closed methanofullerene isomer. The transformation involves the manifold of the triplet states that facilitate the required cleavage of the Ccage–CH2 bonds.

Structures of Gd3N@C80 Prato Bis-Adducts: Crystal Structure, Thermal Isomerization, and Computational Study

“…The similar isomerization of bis-adducts via a “walking on the sphere” rearrangement was observed for six bis-malonate adducts of C 60 , but being induced electrochemically . So far, only [6,6]-to-[5,6] or [5,6]-to-[6,6] isomerizations were reported in endohedral ,,,,, and empty fullerenes. − Most likely in previous work it was impossible to detect the [6,6]-to-[6,6] isomerization in monoadduct of I h -C 60 or C 80 fullerenes, since the starting materials and products are identical. In any case, although the isomerization in this study was observed as a [6,6]-to-[6,6] process, it is expected to proceed in a similar manner to the reported studies on fulleropyrrolidine derivatives of M 3 N@C 80 , (M = Sc, Lu, Y, Gd, Er) via the sigmatropic rearrangement. ,, …”

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

“…Thus, the electronic spectrum of [C s -8CF 2 ](OH)H is close to that of the isostructural [5,6]-closed C s -C 70 (CF 3 ) 8 [CH 2 ]. [22] The absorption threshold in [C s -8CF 2 ](OH)H is blueshifted by 0.4-0.6 eV with respect to the C s -C 70 (CF 3 ) 8 and its difluoromethylenated derivatives ( Table 3).…”

“…[c] According to XRD data for starting C s -C 70 (CF 3 ) 8 . [8] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 like C 70 (CF 3 ) 8 X 2 (X=H, Cl, CN), [19][20][21] C 70 (CF 3 ) 8 CR 2 (R=H, F, Ar), [2,22] and even the {C 70 (CF 3 ) 8 } 2 dimer [12] with high regioselectivity.…”

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

“…Contrariwise, the closed adduct I with its unchanged LUMO energy differs in its behavior from the other closed C R 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 π-system. 23,24,56,57 Perhaps, the difference results from the fact that the configuration of the electron-withdrawing CF 2 group in the isomer I is actually rather soft, and the bond between the bridgehead atoms is almost broken. The 2nd and 3rd formal reduction potential in all isomers of C 70 (CF 2 ) and the 4th potential in isomers I and II are all positively shifted with respect to those in C 70 by 0.02–0.17 V (see Table 3).…”