Syntheses and structures of phenyl-C81butyric acid methyl esters/ (PCBMs) from M3N@C80

Article abstract of DOI:10.1021/ol9002527

Two new 6,6-open phenyl-C_81-butyric acid methyl ester metallofulleroids, M₃N@C₈₀PCBM (M = Sc, Y), were synthesized by diazoalkane addition reactions and fully characterized. The results demonstrate that the reactive sites

Full text of DOI:10.1021/ol9002527

ORGANIC
LETTERS
2
009
Vol. 11, No. 8
753-1756
Syntheses and Structures of
Phenyl-C -Butyric Acid Methyl Esters
1
81
(PCBMs) from M N@C80
3
†
Chunying Shu, Wei Xu, Carla Slebodnick, Hunter Champion, Wujun Fu,
‡
†
†
†
†
Jonathan E. Reid, Hugo Azurmendi, Chunru Wang,* Kim Harich,
†
,‡
†
,†
,†
Harry C. Dorn,* and Harry W. Gibson*
Chemistry Department, Virginia Polytechnic Institute and State UniVersity, Blacksburg,
Virginia 24061, and Institute of Chemistry, Chinese Academy of Sciences,
Beijing, China 100080
crwang@iccas.ac.cn; hdorn@Vt.edu; hwgibson@Vt.edu
Received February 7, 2009
ABSTRACT
Two new 6,6-open phenyl-C81-butyric acid methyl ester metallofulleroids, M
reactions and fully characterized. The results demonstrate that the reactive sites are the same for M
different from that of C60
3
N@C80PCBM (M ) Sc, Y), were synthesized by diazoalkane addition
3
N@C80 (M ) Sc, Y) but dramatically
.
4
Modified fullerenes and metallofullerenes with good solubil-
ity and processability are of great importance for expanding
their potential applications in material science. For example,
templated (TNT) endohedral metallofullerenes, especially
3
Sc N@C80, as the most abundant species in the endohedral
1
metallofullerene family, are expected to exhibit novel proper-
ties relative to empty cage fullerenes and their derivatives
due to the electron-transfer from the endohedral cluster to
the carbon cage. However, TNT metallofullerenes are less
reactive than empty fullerenes and classical EMFs due to
the formal transfer of six electrons from the metal atoms to
the fullerene cage, which leads to a closed shell electronic
structure and an increase of the HOMO-LUMO gap with a
the methanofullerene phenyl-C61-butyric acid methyl ester
2
(C
60PCBM) has been widely utilized as an electron-acceptor
3
in bulk heterojunction (BHJ) solar cells. Trimetallic nitride
†
Virginia Polytechnic Institute and State University.
Chinese Academy of Sciences.
‡
(
1) (a) Guldi, D. M.; Martin, N. Fullerenes: From Synthesis to
Optoelectronic Properties; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 2002. (b) Akasaka, T.; Nagase, T. Endofullerenes: A New
Family of Carbon Clusters; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 2002. (c) Mateo-Alonso, A.; Guldi, D. M.; Paolucci, F.; Prato,
M. Angew. Chem., Int. Ed. 2007, 46, 8120–8126.
5
corresponding reduction in reactivity. Herein, we report
(4) Stevenson, S.; Rice, G.; Glass, T.; Harich, K.; Cromer, F.; Jordan,
M. R.; Craft, J.; Hadju, E.; Bible, R.; Olmstead, M. M.; Maitra, K.; Fisher,
A. J.; Balch, A. L.; Dorn, H. C. Nature 1999, 401, 55–57.
(5) Osuna, S.; Swart, M.; Campanera, J. M.; Poblet, J. M.; Sola, M.
J. Am. Chem. Soc. 2008, 130, 6206–6214.
(
2) Hummelen, J. C.; Knight, B. W.; Lepeq, F.; Wudl, F.; Yao, J.;
Wilkins, C. L. J. Org. Chem. 1995, 60, 532–538.
3) Thompson, B. C.; Frechet, J. M. J. Angew. Chem., Int. Ed. 2008,
7, 58–77.
(
4
10.1021/ol9002527 CCC: $40.75
Published on Web 03/23/2009
 2009 American Chemical Society

3
Scheme 1. Synthesis of M N@C80PCBMs
TNT analogues of C60PCBM, which are significantly dif-
ferent from C60PCBM. The demonstration that diazoalkanes
are effective reagents for functionalization of TNT EMFs
abromobenzyloxypropyl silica] columns consist of single
symmetric peaks centered at retention times of 25.2 min
(Figure 1a) and 14.0 min (Figure 1b), respectively, revealing
6
7
1
13
provides an alternative to Diels-Alder, Bingel-Hirsch,
pure isomers as confirmed by H and C NMR spectroscopy.
The MALDI-TOF mass spectrum exhibits a strong molecular
8
9
Prato and free radical reactions for synthesis of derivatives
of these novel species for various applications.
+
ion peak from 2a at m/z 1300 (Figure 1c). The peak at m/z
M
3
N@C80PCBMs were prepared from M
3
N@C80 and
1109 is attributed to Sc
3
N@C80 formed by loss of the
methyl 4-benzoylbutyrate p-tosylhydrazone (1) (Scheme 1).
exohedral functional groups as usually observed under laser
9
desorption conditions. In similar fashion, Y
2b) was synthesized and purified in 34% yield.
In the UV-vis absorption spectrum of 2a (Figure 2), the
lowest energy transition occurs at 736 nm, similar to that of
3
N@C80PCBM
(
1
0
pristine Sc
3
N@C80
,
revealing that the C80 chromophore is
Figure 1
.
HPLC profiles of Sc
3
N@C80PCBM (2a) on (a) PYE and
(
b) PBB columns. (c) Positive mode MALDI-TOF MS of 2a.
Figure 2
(
(
.
(left) UV-vis spectra (in toluene) of Sc
2a, red line) and Sc N@C80-I (black line); (right) Y
2b, red line) and Y N@C80-I (black line).
3
N@C80PCBM
3
h
3
N@C80PCBM
3
h
Sc
3
N@C80PCBM (2a) was isolated in 30% yield based on
N@C80 after silica gel column chromatography
consumed Sc
3
and subsequently purified by high performance liquid chro-
matography (HPLC) using a PYE [2-(1′-pyrenyl)ethyl silica]
column. The HPLC traces of 2a on PYE and PBB [pent-
minimally perturbed by the functional group and suggesting
7a,9a
an open π-homoaromatic structure.
spectrum of the yttrium analog 2b resembles that of its
precursor, Y N@C80 (Figure 2), with a maximum at 693 nm,
Similarly, the UV-vis
(
6) (a) Iezzi, E. B.; Duchamp, J. C.; Harich, K.; Glass, T. E.; Lee, H. M.;
Olmstead, M. M.; Balch, A. L.; Dorn, H. C. J. Am. Chem. Soc. 2002, 124,
24–525. (b) Angeli, C. D.; Cai, T.; Duchamp, J. C.; Reid, J. E.; Singer,
E. S.; Gibson, H. W.; Dorn, H. C. Chem. Mater. 2008, 20, 4993–4997.
7) (a) Lukoyanova, O.; Cardona, C. M.; Rivera, J.; Lugo-Morales, L. Z.;
3
7a
again consistent with a fulleroid structure.
5
Addition at the 5,6-ring junction of the C80 cage results
in two sets of nonequivalent hydrogens from the functional
groups, since the pentagons and hexagons on the carbon cage
(
Chancellor, C. J.; Olmstead, M. M.; Rodriguez-Fortea, A.; Poblet, J. M.;
Balch, A. L.; Echegoyen, L. J. Am. Chem. Soc. 2007, 129, 10423–10430.
(
b) Fatouros, P. P.; Corwin, F. D.; Chen, Z. J.; Broaddus, W. C.; Tatum,
provide different chemical environments, but addition at the
J. L.; Kettenmann, B.; Ge, Z.; Gibson, H. W.; Russ, J. L.; Leonard, A. P.;
Duchamp, J. C.; Dorn, H. C. Radiology 2006, 240, 756–764. (c) Chaur,
M. N.; Melin, F.; Athans, A. J.; Elliott, B.; Walker, K.; Holloway, B. C.;
Echegoyen, L. Chem. Commun. 2008, 2665–2667.
8a,9a
6,6-ring junction produces only one set of proton signals.
(9) (a) Shu, C. Y.; Cai, T.; Xu, L. S.; Zuo, T. M.; Reid, J.; Harich, K.;
(8) (a) Cardona, C. M.; Kitaygorodskiy, A.; Echegoyen, L. J. Am. Chem.
Dorn, H. C.; Gibson, H. W. J. Am. Chem. Soc. 2007, 129, 15710–15717.
(b) Shu, C. Y.; Slebodnick, C.; Xu, L. S.; Champion, H.; Fuhrer, T.; Cai,
T.; Reid, J. E.; Fu, W. J.; Harich, K.; Dorn, H. C.; Gibson, H. W. J. Am.
Chem. Soc. 2008, 130, 17755–17760.
Soc. 2005, 127, 10448–10453. (b) Cai, T.; Slebodnick, C.; Xu, L.; Harich,
K.; Glass, T. E.; Chancellor, C.; Fettinger, J. C.; Olmstead, M. M.; Balch,
A. L.; Gibson, H. W.; Dorn, H. C. J. Am. Chem. Soc. 2006, 128, 6486–
6
492.
(10) Krause, M.; Dunsch, L. ChemPhysChem 2004, 5, 1445–1449.
1754
Org. Lett., Vol. 11, No. 8, 2009

1
In the H NMR spectra of 2a and 2b, only one set of signals
was observed: for 2a 1.98 (2H, m, J ) 7.5 Hz), 2.41 (2H, t,
J ) 7.5 Hz), 2.73 (2H, m, J ) 5.5 Hz), 3.65 (3H, s), 7.49
(
1H, m), 7.55 (2H, m) and 7.94 (2H, d, J ) 7.0 Hz) ppm;
for 2b 2.06 (2H, m, J ) 7.0 Hz), 2.45 (2H, t, J ) 7.0 Hz),
.81 (2H, m, J ) 5.5 Hz), 3.68 (3H, s), 7.50 (1H, m), 7.56
2H, m) and 8.08 (2H, m, J ) 8.0 Hz) ppm, revealing that
addition of the functional group took place at a 6,6-junction.
2
(
Figure 4
showing the two positions of two of the Sc atoms of the disordered
Sc N cluster. The solvate molecules are omitted for clarity.
3
. Two views of one enantiomer of Sc N@C80PCBM (2a)
3
Black crystals of 2a·(CS
diffraction were obtained by liquid diffusion of hexane into
solutions of 2a and 2b in CS at 4 °C. The two enantiomers
2
)
3
2
and 2b·CS suitable for X-ray
Figure 3
v/v, doped with chromium acetylacetonate) of Sc
2a), and expanded parts from (b) 122 ppm to 154 ppm and (c) 15
ppm to 98 ppm.
.
(a) 13C NMR spectrum (150 MHz, CD
2
Cl
3
2
/CS
N@C80PCBM
2
) 20/80
2
(
of 2a/2b present in the crystals lead to apparent disorder in
the positions of the cage atoms. And as observed in similar
7a
3 3
compounds, the Sc N and Y N clusters are truly disordered.
The 13C NMR spectrum of 2a (Figure 3) contains
resonances at 172.13 (CO CH ), 129.27, 128.91, 128.87 (2C),
28.61 (2C), 51.51 (CO CH ), 49.16 (PhCCH ), 38.46
PhCCH ), 33.77 (CH CO ) and 20.31 (CH CH CO ) ppm
The Sc2 and Sc3 atoms can be modeled with 2-position
disorder with relative occupancies of 0.737(5) and 0.263(5),
respectively, but attempts to model Y2 and Y3 of 2b failed.
The structures shown in Figures 4 and 5 represent one
2
3
1
(
2
3
2
2
2
2
2
2
2
for the functional group and another 80 resonances in the
range of 95-155 ppm for the carbon cage, consistent with
C symmetry. Notably, the bridged fullerene C-atoms (C1
1
on a 6-membered ring and C41 on a 5-membered ring in
Figure 4 below) are assigned at δ 95.55 and 96.49 ppm in
agreement with an “open” methano-bridged transannular
5
bond due to π-homoaromaticity. The structure of this final
2
product is dramatically different from the analogous and
1
1
similar diazo derivatives of C60 (6,6-closed and 5,6-open
isomers) formed under the same conditions. Likewise, the
1
3
C NMR spectrum of 2b is similar to that of 2a, having
resonances at 172.44 (CO
2
CH
3
), 51.09 (CO
CO
2
CH
3
), 52.04
(
PhCCH
CH CH
2
), 38.39 (PhCCH
CO
2
), 33.43 (CH
2
2
) and 19.47
(
2
2
2
) ppm for the functional group and another 84
3
Figure 5. Two views of one enantiomer of Y N@C80PCBM (2b)
resonances in the range of 95-150 ppm for the carbon cage
and phenyl group, also in agreement with C symmetry.
Notably, the C NMR signals of sp hybridized carbons of
the C80 cage for Y N@C80PCBM exhibit a larger chemical
shift range relative to those of Sc N@C80PCBM, indicating
showing one position of the Y atoms of the disordered Y
The solvate molecules are omitted for clarity.
3
N cluster.
1
1
3
2
3
3
enantiomer of 2a and 2b, respectively. Both of them prove
unambiguously that addition occurred at a 6,6-ring junction.
The distance between the bridgehead carbon atoms (C1 and
that the different clusters inside the cage do influence the
properties of the molecule.
3
C41) of the cage is 2.116(4) Å for Sc N@C80PCBM and
(
11) Isaacs, L.; Wehrsig, A.; Diederich, F. HeIV. Chim. Acta 1993, 76,
1
231–1250.
2.218 Å for Y
3
N@C80PCBM, much longer than that of
Org. Lett., Vol. 11, No. 8, 2009
1755

12
Sc
3 h
N@C80-I [1.421(2) Å]. These results are consistent with
an open structure and comparable to other metallofulleroids:
7
a
Y
3
N@C80C(CO
the cage and 2.28(4) Å in the other] and La@C82(Ad)
2.097 Å). The Sc N and Y N clusters are planar; the sums
of the angles are 359.95° (0.74)/359.39° (0.26) for the former
and 360.0° for the latter. The planar structure of the Y
cluster in Y N@C80PCBM is consistent with another 6,6-
open case derived from a Bingel reaction, Y N@C80C-
2
CH
2
Ph)
2
[2.30(3) Å for one orientation of
1
3
(
3
3
3
N
3
3
7
a
(
CO
2
CH
2
Ph)
2
;
in contrast the cluster geometry is different
N@C80 in which
from that of the pyrrolidino adduct of Y
3
14
the cluster is slightly pyramidal. The Sc1/Y1···C1 distances
are 2.447(3)/2.524(6) Å and the Sc1/Y1···C41 distances are
2
.456(3)/2.544(6) Å, respectively, much longer than in
4
3 h
Sc N@C80-I [2.188(9) and 2.170(1) Å], indicating that the
functional group leads to distortion of the carbon cage.
Notably, under the same conditions, the addition of unsym-
metrically substituted diazoalkanes on C60 produces two
isomers, a 6,6-closed structure (methanofullerene) and a 5,6-
2
,15
open structure (fulleroid);
the Prato addition on
produces 5,6- and 6,6-
1
6
8a,17
3 3
Sc N@C80 and Y N@C80
pyrrolidino adducts, respectively; the Bingel reaction works
8a
well on Y
3
N@C80 but fails on Sc
3
N@C80
. However, in this
diazoalkane addition reaction, both Sc
3
N@C80 and Y N@C80
3
produce single stable PCBM isomers with 6,6-open struc-
tures.
Interestingly, similar cyclic voltammetric (CV) profiles
were observed for 2a and Sc
reduction of 2a is chemically reversible but electrochemically
irreversible, reminiscent of the starting material, Sc
3
N@C80 (Figure 6). The first
Figure 6
3
. Cyclic voltammograms of (a) Sc N@C80 and (b)
Sc N@C80PCBM (2a). Scan rate, 250 mV/s. Solvent: 1,2-dichlo-
3
3
N@C80
-
robenzene. Values are relative to the ferrocene/ferrocenium couple.
red1
ox1
I
h
, whose
E
p
and
reports. The red1E
of 2b (see Supporting Information) is
cathodically shifted 40 mV relative to Y , whereas
p
E are consistent with previous
1
0
p
effective reagents for functionalization of these compounds
provides an alternative to Diels-Alder, Bingel-Hirsch, Prato
and free radical types of reactions for synthesis of derivatives
of these novel species for various applications.
N@C80-I
3 h
that of Sc analog is cathodically shifted 100 mV relative its
precursor. These results demonstrate the large electronic
effects of encapsulated metal clusters in the TNT endohedrals
vs empty cage systems such as C60
.
Acknowledgment. We are grateful for support of this
work by the National Science Foundation [DMR-0507083],
the National Institutes of Health [1R01-CA119371], and the
National Natural Science Foundation of China [20702053].
In conclusion, two new TNT metallofullerene derivatives
were synthesized by diazoalkane addition and characterized
in detail. The successful demonstration that diazoalkanes are
(
12) Lee, H. M.; Olmstead, M. M.; Iezzi, E.; Duchamp, J. C.; Dorn,
H. C.; Balch, A. L. J. Am. Chem. Soc. 2002, 124, 3494–3495.
13) Maeda, Y.; Matsunaga, Y.; Wakahara, T.; Takahashi, S.; Tsuchiya,
Supporting Information Available: Details of synthesis
1
1
1
of 2; HLPC profiles and MS spectra of 2b; H, H- H
(
1
3
T.; Ishitsuka, M. O.; Hasegawa, T.; Akasaka, T.; Liu, M. T. H.; Kokura,
K.; Horn, E.; Yoza, K.; Kato, T.; Okubo, S.; Kobayashi, K.; Nagase, S.;
Yamamoto, K. J. Am. Chem. Soc. 2004, 126, 6858–6859.
COSY, HMQC NMR spectra of 2; C NMR spectrum of
b and FTIR spectrum of 2a; cyclic voltammograms of
N@C80 and Y N@C80PCBM (2b), electrochemical meth-
ods; thermal ellipsoid drawings, crystal data, structure
refinement of 2a/2b and crystallographic files for 2a·(CS
and 2b·CS in CIF format; scheme showing formation of
2
Y
(14) Echegoyen, L.; Chancellor, C. J.; Cardona, C. M.; Elliott, B.; Rivera,
3
3
J.; Olmstead, M. M.; Balch, A. L. Chem. Commun. 2006, 2653–2655.
15) Rispens, M. T.; Meetsma, A.; Rittberger, R.; Brabec, C. J.; Sariciftci,
N. S.; Hummelen, J. C. Chem. Commun. 2003, 2116–2118
16) (a) Cai, T.; Ge, Z.; Iezzi, E. B.; Glass, T. E.; Harich, K.; Gibson,
(
2 3
)
.
(
2
H. W.; Dorn, H. C. Chem. Commun. 2005, 3594–3596. (b) Cardona, C. M.;
Kitaygorodskiy, A.; Ortiz, A.; Herranz, M. A.; Echegoyen, L. J. Org. Chem.
racemic 2a/2b. This material is available free of charge via
2
005, 70, 5092–5097.
17) Cardona, C. M.; Elliott, B.; Echegoyen, L. J. Am. Chem. Soc. 2006,
28, 6480–6485.
the Internet at http://pubs.acs.org.
(
1
OL9002527
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Org. Lett., Vol. 11, No. 8, 2009