Chemistry Reference
In-Depth Information
R
O
O
R
H
N
N
R'
R'
R
N
R'
Pd(II)
C
60
O
H
13
Pd (II)
Pd (0)
14
oxidant
Scheme 5 Fulleroindolines prepared by Pd(II) catalysis
The use of [Rh(cod)
2
]BF
4
gave rise to an optimal combination of good yield
(61%) and excellent selectivity (
95%) showing an important effect of the
counteranion of the rhodium complexes in sharp contrast with the reported example
of conventional olefins. The authors claimed a catalytic cycle reaction where
cationic Rh complex and water produce Rh-OH species. After transmetalation of
the thus-formed Rh-OH with RB(OH)
2
, the Rh-R species undergoes addition on
the C
60
double bond. Finally, protonolysis of the formed fullerenyl Rh species
affords the product R-C
60
-H (11, 12) with regeneration of the cationic Rh species.
Shortly after, the same authors also developed a palladium(II) catalyst Pd(2-
PyCH
>
NPh)(OCOC
6
F
5
)
2
for the hydroarylation of fullerene with boronic acids
that, along with good catalytic activity (reaction generally occurs at room tempera-
ture), presents a bench stability in the solid state and efficiency under air conditions.
Single crystal X-ray diffraction analysis confirmed unequivocally the addition of
the aryl moiety and hydrogen in a 1,2-fashion at the
═
bond of C
70
with the phenyl
group attached at the position close to the pole of the C
70
unit [
36
].
Analogously, Co-catalyzed hydroalkylation of C
60
with reactive alkyl bromides
in the presence of Mn reductant and H
2
O at ambient temperature gave the
monoalkylated C
60
in good to high yields. The reaction probably occurs through
a reduced Co(0 or I) complex that promotes generation of a radical (R
) and the
addition to C
60
[
37
].
An intriguing copper-catalyzed radical reaction that involves a formal C-H bond
activation has been reported by Nakamura. The reaction efficiently couples an
arylacetylene or enyne to a penta(aryl)[60]fullerene bromide in a formal [4+2]
fashion to form a dihydronaphthalene ring fused to a fullerene sphere [
38
].
Palladium acetate catalyzes cycloaddition onto C
60
of a variety of anilides
through a C-H bond activation, affording fulleroindolines (14) in a highly
regioselective manner (Scheme
5
)[
39
].
α
2.2 Asymmetric Catalysis on Fullerenes
Chirality is an important but undeveloped topic in fullerene science [
40
,
41
]. Along
with inherently chiral pristine fullerenes, optically active derivatives have been
