[(μ-H)3Re3 (CO) 9 (ν2, ν2,ν2-Sc2C2@C 3v(8)-C82)]: Face-capping cluster complex of an endohedral fullerene

Article abstract of DOI:10.1002/anie.201207261

Fullerenes with atoms, ions, or clusters in their inner space are referred to as endohedral fullerenes. These spherical molecules have unique properties that can be very different from those of the empty fullerenes.[1, 2] Among these hybrid molecules, end

Full text of DOI:10.1002/anie.201207261

.
Angewandte
Communications
DOI: 10.1002/anie.201207261
Fullerene Complexes
2
2
2
[
(m-H) Re (CO) (h ,h ,h -Sc C @C (8)-C )]: Face-Capping Cluster
3
3
9
2
2
3v
82
Complex of an Endohedral Fullerene**
Chia-Hsiang Chen, Wen-Yann Yeh,* Yi-Hung Liu, and Gene-Hsiang Lee
Fullerenes with atoms, ions, or clusters in their inner space are
referred to as endohedral fullerenes. These spherical mole-
cules have unique properties that can be very different from
After purification of the reaction products by HPLC (with
a Buckyprep-M column and toluene as the eluent) and
recrystallization from CS /n-hexane, [(m-H) Re (CO) -
2
3
3
9
[
1,2]
2
2
2
those of the empty fullerenes.
Among these hybrid
(h ,h ,h -Sc C @C (8)-C )] (2; 57%) was obtained as an
2 2 3v 82
molecules, endohedral metallofullerenes (EMFs) have
attracted great attention because substantial charge transfer
from encaged metal atoms or clusters to the fullerene cage
occurs, and this property may find application in catalysis,
air-stable, greenish-brown crystalline solid. The molecular-ion
peaks around m/z 1914 in the MALDI mass spectrum of 2
(Figure 1) match the isotope distribution calculated for 2. The
1
H NMR spectrum displayed only one singlet signal at d =
[3]
photovoltaic components, electronics, and biomedicines.
Not only conventional metal atoms (usually one or two),
ꢀ16.00 ppm, which indicated the presence of bridging hydride
[4]
ligands.
but a wide variety of metallic species have been encapsulated
in fullerenes. Fullerenes encapsulating a metal nitride
[
5]
[6]
(
a
(
M N),
a
metal-carbide cluster (M C /M C /M C ),
2 2 3 2 4 2
3
[
7]
metal oxide (M O/M O /M O ),
M NC), and even a metal sulfide (M S) were all success-
3 2
a metal cyanide
2
4
2
4
3
[
8]
[9]
fully obtained and structurally characterized. The functional-
ization of EMFs with organic adducts has also attracted much
interest, because the resulting EMFs could have more useful
properties, including perhaps higher solubility and stability,
[10]
than those of pristine EMFs. However, to our knowledge,
the coordination chemistry of EMFs has not been described.
Several interesting questions await an answer in this unex-
plored field: 1) Will the metals add regiospecifically to the
EMF surface? 2) How will the geometry and properties of the
EMF be affected by the bonded metals? 3) Will the encapsu-
lated species interact with the coordinated metals? Our
Figure 1. HPLC chromatogram for the final stage of the separation of 2
and MALDI mass spectrum of 2.
[11]
continuing interest in fullerene chemistry led us to prepare
the scandium carbide endofullerene Sc C @C (8)-C (1) and
2
2
3v
82
investigate its complexation with a Re cluster.
Crystals of 2 suitable for an X-ray diffraction study were
grown from CH Cl /CS /n-hexane in a capillary tube at
ambient temperature over several weeks. The identification
3
Compound 1 was synthesized by modifying a previously
2
2
2
[
12]
described method. Graphite rods filled with Sc O were
2
3
annealed at 10008C for 12 h and then evaporated by arc
of three Sc pairs in different positions indicated rotation of
the Sc atoms inside the C82 cage. The ORTEP drawing of 2
2
[
13]
discharge under a flow of He/N . The soot was subjected to
2
Soxhlet extraction with CS and then purified by a multiple-
displays the Sc C moiety with 50% occupancy (Figure 2).
2
2
2
stage HPLC separation process. The pure compound 1
There is a crystallographic symmetry imposed on the
complex (Figure 3). The hexagon perpendicular to the
(>99%; 0.7 mg obtained from the evaporation of 16 compo-
site graphite rods) was treated with [(m-H) Re (CO) -
symmetry plane is coordinated to the Re cluster in an
h ,h ,h bonding fashion. The three hydride ligands were not
3
3
11
3
2
2
2
(
NCMe)] (2 equiv) in chlorobenzene at reflux for 3.5 h.
located directly, but are believed to lie on the Re plane in
3
such an arrangement that each H atom spans one Re–Re
[
*] Dr. C.-H. Chen, Dr. W.-Y. Yeh
Department of Chemistry, National Sun Yat-Sen University
Kaohsiung 804 (Taiwan)
edge, as determined for [(m-H) Re (CO) (CNCH Ph)-
3
3
8
2
2
2
2
[14]
(
h ,h ,h -C )].
The trimetallic moiety is based on an
6
0
isosceles triangle, in which the Re1–Re2 distance
E-mail: wenyann@mail.nsysu.edu.tw
(
(
3.176(2) ꢀ) is slightly shorter than the Re1–Re1A distance
3.201(2) ꢀ). Each Re atom is associated with three terminal
Y.-H. Liu, Dr. G.-H. Lee
Instrumentation Center, National Taiwan University
Taipei 106 (Taiwan)
carbonyl groups. The ReꢀCO distances range from 1.91(4) to
.01(3) ꢀ, CꢀO bond lengths range from 1.06(4) to 1.17(5) ꢀ,
and Re-C-O angles are in the range 163(3)–177(3)8. The Re
2
[
**] We are grateful for support of this research by the National Science
Council of Taiwan.
3
triangle is positioned over the three 6:6 junctions of the
hexagon; the two planes are essentially parallel (0.5(8)8). The
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201207261.
1
3046
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Figure 3. Highlighted configuraton of 2. A plane of symmetry passes
through the Re2, Sc2, C40, and Sc1 atoms. The Sc1 and Sc2 atoms
Figure 2. Molecular structure of 2. Thermal elliposids are shown at
0% probability. The Re atoms and the Sc C moiety are disordered at
show interactions with the fullerene core. The CꢀC bonds within the
3
coordinated hexagon are localized, with the distances [ꢀ]: C6–C6A
1.48(4), C6–C11 1.43(3), C11–C12 1.52(4), and C12–C12A 1.32(5).
2
2
their sites; the ORTEP diagram displays the Re atoms with 95% and
the C Sc moiety with 50% occupancy. Selected bond distances [ꢀ]:
2
2
Re1–Re2 3.176(2), Re1–Re1A 3.201(2), Re1–C1 2.01(3), Re1–C2
1.98(4), Re1–C3 1.95(4), Re1–C6 2.33(2), Re1–C11 2.31(2), Re2–C4
1.96(3), Re2–C5 1.91(4), Re2–C12 2.33(2), Sc1–C50 2.2(1), Sc2–C50
2.6(1), C50–C50A 1.20(2). Selected bond angles [8]: Re1-Re2-Re1A
60.52(5), Re2-Re1-Re1A 59.74(3), Sc1-C50-Sc2 109(5), Sc1-C50-C50A
74.3(10), Sc2-C50-C50A 76.8(6), C50-Sc1-C50A 31(2), C50-Sc2-C50A
26(1).
in the Sc C skeleton is caused by elongation of the C core
and charge-density redistribution upon complexation to the
2
2
82
Re cluster.
3
The electronic structure of 1 has been described as
4
+
4ꢀ
(
Sc C ) C
as a result of four-electron transfer from
2
2
82
[
16]
Sc C to C . Therefore, 1 should act as a more efficient
2
2
82
electron donor than neutral fullerenes, such as C . This
6
0
Re atoms are bonded to the ring carbon atoms about equally
2.31(2)–2.33(2) ꢀ), and the average ReꢀC
distance of
hypothesis is supported by the carbonyl region of the IR
(
2
spectrum of 2, the absorption pattern of which is identical to
ring
2
2
2
[14]
.32 ꢀ is comparable to that measured for [(m-H) Re (CO) -
that of [(m-H) Re (CO) (h ,h ,h -C )], except that the CO
3
3
8
3 3 9 60
2
2
2
[14]
ꢀ1
(
CNCH Ph)(h ,h ,h -C )] (average: 2.31 ꢀ).
The CꢀC
stretches for 2 are all red-shifted by 2 cm in agreement with
2
60
bonds within the coordinated hexagon are localized and
range from 1.32(5) to 1.52(4) ꢀ in length. Shorter and longer
the increase in p back-donation from the more electron rich
1
Re center of 2. The H NMR spectrum is also consistent with
3
bonds appear to alternate around the ring. The C ring is
an electron-rich fullerene: the bridging hydride resonance of
6
pulled out of the fullerene sphere. This distortion of the
regular fullerene structure is consistent with the change in
2 at d = ꢀ16.00 ppm is shielded by 0.68 ppm with respect to
2
2
2
that of [(m-H) Re (CO) (h ,h ,h -C )] (ꢀ15.32 ppm).
3
3
9
60
3
[15]
hybridization of these C ring atoms to sp
and is reflected
The visible/near-infrared (Vis/NIR) absorption spectra of
compounds 1 and 2 in CS2 are shown in Figure 4 for
comparison. It is well-established that the electronic absorp-
tions of fullerenes are predominantly due to p!p* carbon-
cage transitions and depend on the structure and charge state
6
by lengthening of the distances from the tip C40 atom to the
ring C6, C11, and C12 atoms (8.61–8.63 ꢀ; average: 8.62 ꢀ).
These distances are approximately 0.15 ꢀ longer than those
[
13]
measured for pristine 1 (8.43–8.50 ꢀ; average: 8.47 ꢀ).
The endohedral Sc C cluster assumes a butterfly shape,
[1]
of the carbon cage. The onsets in the spectrum of 2 are blue-
shifted relative to those in the spectrum of 1, which suggests
that the HOMO–LUMO gaps for 2 are larger than for 1.
2
2
which is positioned in such a way that neither of the two Sc
atoms is close to the exo Re cluster. The shortest cage–Sc
3
contacts (2.08 ꢀ to Sc1 and 2.25 ꢀ to Sc2) are not much
These shifts can be ascribed to the difference in the amount of
[
13]
[17]
changed from those in 1 (1.99–2.22 ꢀ). The hinge C50ꢀ negative charge on the C82 core. Theoretical calculations
C50A distance (1.20(2) ꢀ), typical of a CꢁC triple bond, and
the Sc···Sc separation (3.95 ꢀ) are comparable with those in 1,
whereas the mean Sc–Ccarbide distance in 2 (2.40 ꢀ) is 0.19 ꢀ
longer than that in 1 (2.21 ꢀ). This difference gives rise to
showed that the HOMO of Sc C @C (8)-C was delocalized
2 2 3v 82
[
18,19]
not only over the Sc C cluster but also over the C cage.
2
2
82
Presumably, the donation of six electrons from the C82 core to
the Re cluster leads to stablization of the HOMO levels.
3
a smaller dihedral angle between the two ScC planes in 2
The C (8)-C core consists of 31 hexagons and 12
2
3v
20]
82
[
(
114.38) in comparison with 1 (1308). Apparently, the change
pentagons.
Only one C6 ring is surrounded by three
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Communications
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3
to one hexagon of the Sc C @C (8)-C core. The geometry
2
2
3v
82
and electronic properties of Sc C @C (8)-C were altered by
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Keywords: cluster compounds · fullerenes · rhenium ·
.
scandium · structure elucidation
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