Chemistry Reference
In-Depth Information
Fig. 4.1
Representation of the different [6, 6], [5, 6] and [5, 5] bond types that are more commonly
found in fullerene structures
the free rotation of the metallic cluster only two different regioisomers are possi-
ble after functionalization: the adduct on a corannulenic [5, 6] bond type (type D,
Figs.
4.1
and
4.2
) or the adduct on the type B [6, 6] bond (see Figs.
4.1
and
4.2
).
DFT calculations at BP86/TZP level showed that addition at the corannulene [5,
6] bond (type D) is at least 11 kcal mol
−
1
more stable than the adduct on the [6,
6] bond. (Campanera et al.
2006
; Osuna et al.
2011b
) Moreover, the Prato reac-
tion on M
3
N@
I
h
-C
80
was also achieved. The
N
-ethylazomethine ylide addition on
Sc
3
N@
I
h
-C
80
takes place regioselectively at the corannulene [5, 6] bond, but the [5,
6] and [6, 6] regioisomers are obtained for Y
3
N@
I
h
-C
80
(Cardona et al.
2006
). The
two adducts are also observed in the synthesis of
N
-tritylpyrrolidino derivative of
Sc
3
N@
I
h
-C
80
(Cai et al.
2006a
). Rodríguez-Fortea and coworkers reported that the
[6, 6] and [5, 6] pyrrolidino adducts are almost degenerate in the case of Y
3
N@
I
h
-
C
80
. (Rodríguez-Fortea et al.
2006
) They suggested a pirouette-type mechanism for
the observed [6, 6]-to-[5, 6] isomerization under thermal conditions instead of via
retrocycloaddition (Rodríguez-Fortea et al.
2006
). On the other hand, the Bingel-
Hirsch cyclopropanation on M
3
N@
I
h
-C
80
takes place regioselectively on the [6, 6]
bond for M
Sc, Lu, Y, and Er. However, a higher reactivity for yttrium and erbium-
based EMFs were observed (Lukoyanova et al.
2007
). Finally, Sc
3
N@
I
h
-C
80
were
found to react photochemically with disilirane to afford the corresponding adduct
(Iiduka et al.
2005a
).
=
