Chemistry Reference
In-Depth Information
tetrazine (Kurihara et al.
2012
)toSc
3
C
2
@
I
h
-C
80
took place at a 1,4 position of a
six-membered ring.
From the experimental examples seen above, it becomes apparent that endohedral
clusters play a major role in directing the addition sites of the exohedral reactivity of
the fullerene cage. This fact has been computationally reinforced by a series of ther-
modynamic and kinetic studies performed by some of us and reported in this chapter
on the DA reaction between
s
-
cis
-1,3-butadiene and several EMFs: Sc
3
N@
D
3h
-C
78
,
(Osuna et al.
2008
)Y
3
N@
D
3h
-C
78
,
(Osuna et al.
2009a
)Y
3
N@C
2
-C
78
, (Osuna et al.
2009a
)Ti
2
C
2
@
D
3h
-C
78
, (Garcia-Borràs et al.
2012a
)X@
I
h
-C
80
(X
Ø, Sc
3
N,
Lu
3
N, Y
3
N, La
2
,Y
3
,Sc
3
C
2
,Sc
4
C
2
,Sc
3
CH, Sc
4
O
2
, and Sc
4
O
3
) (Garcia-Borràs et al.
2013c
) and X
3
N@
D
5h
-C
80
(X
=
Sc, Lu, Gd) (Osuna et al.
2012b
).
In the next sections, we summarize the results obtained in all these previous
studies. First, in order to analyze the changes on the regiochemistry due to: (i) the
size and orientation of the metallic clusters; (ii) the deformation and strain induced
on the carbon structure by the encapsulated moiety; and (iii) the different amounts of
charge transferred from the metallic cluster to the fullerene cage, we studied the DA
cycloaddition involving X@
D
3h
-C
78
(M
=
Ø, Sc
3
N,Y
3
N and Ti
2
C
2
) species. (Osuna
et al.
2008
,
2009a
; Garcia-Borràs et al.
2012a
) The different nature, size and shape of
Sc
3
N, Y
3
N and Ti
2
C
2
metallic clusters, which remain immobile inside the
D
3h
-C
78
cage, make them as perfect candidates to achieve our goals. Then, we compared
the TNT based EMFs reactivity between
I
h
-C
80
and
D
5h
-C
80
hosting cages (Osuna
et al.
2012b
). The
I
h
-C
80
cage encapsulating different metal clusters is one of the
EMF cages for which more experimental work has been reported. For this reason,
in a subsequent study we selected a number of
I
h
-C
80
-based EMFs to perform an
exhaustive analysis of the influence of the metal cluster in their chemical reactivity
using our recently proposed FCM approach for exploring all the possible cluster
orientations inside the
I
h
-C
80
cage (Garcia-Borràs et al.
2012b
,
2013c
).
Next, we discussed the importance of including van der Waals dispersion correc-
tions in DFT calculations involving fullerenes in order to obtain reaction barriers
and energies much closer to the experimental ones (Osuna et al.
2011b
). Finally,
we show that different experimentally observed product stabilities for La@
C
2v
-
C
82
Cp (Cp
=
1,2,3,4,5-pentamethyl-
cyclopentadiene) adducts can only be explained when the dispersion interaction
energies are considered (Garcia-Borràs et al.
2013a
).
=
cyclopentadiene) and La@
C
2v
-C
82
Cp* (Cp*
=
4.2
Metal Effects on Diels-Alder Cycloaddition Regioselectivity
4.2.1
The Diels-Alder Reaction on D
3h
-C
78
and Sc
3
N, Y
3
N, Ti
2
C
2
Related EMFs: The Role of Fullerene Strain Energy
In some experimental studies, it was observed that exohedral reactivity of EMFs is
highly affected by the nature of the encapsulated cluster (Cardona et al.
2005a
). In
order to evaluate the effect of the metal cluster on the exohedral reactivity of the
