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Tether-Directed Remote Functionalization of Buckminsterfullerene Regiospecific Hexaadduct Formation.

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31G* = - 486.56848 Hartree); the best dipole moment compensation is achieved through the short helical sections with
opposed senses in this isomer ( p = 1.92 Debye). According to
these results the tertiary structure determined by X-ray crystallography is the result of intra- and intermolecular packing
effects in which the bulkiness of the phenyl groups on C1 and C4
plays an important role. In the packing diagrams of 1 (Fig. 1 c)
these phenyl rings are arranged parallel to the y,z plane. Thus a
particularly Favorable packing of the helices (3 ,-helices, Fig.
1 b), which resemble three bladed propellers seen from the top,
can be achieved. The crystal structures and model quantum
mechanical calculations for the shorter homologues (similarly
without taking the phenyl groups into account) agree very
weII.1'. '1
From the diversity of the established structures a high intramolecular flexibility may be deduced. In our earlier studies
we estimated low barriers for rotation around the C - N bonds
(about 4-5 kcal mol-');['ol also ( E ) / ( Z )isomerization of the
C= N bonds seems possible, during which transition states with
a zwitterionic cumulene structure are traversed (about
20 kcal mol I activation energy for 1,3-diazab~tadienes,[~l
and
12 kcal mol- for N-a~ylimines['~l).
This may also explain the
discrepancy between the single set of signals found in the NMR
spectra for a solution and the complex X-ray results.
The X-ray and quantum mechanical results also supply a
convincing explanation for the electronic spectra of 1 ; since
there is clearly no extended Jt-electron system present
(A,,,, < 770 nm) but a sequence of strongly twisted amidine units
and an ainide unit, no long-wavelength n-n* absorption bands
appear; the X - - X * transitions are hidden by arene bands.
hydrogen atoms were geometrically determined and their positional and temperature parameters coupled with the associated carbon atoms. Further details
of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe. D-76344 Eggenstein- Leopoldshafen ( F R G ) on quoting the depository number CSD-58228, the names of the authors, and the
journal citation.
[XI N. N . Greenwood, A. Earnshaw. C'h~w?i.nq~
of /he E / e m v t l ~ Pergamon,
,
Oxford 1985, p. 303 ff.
191 P. Luthardt. M. H. Mdler, U. Rodewald, E:U. Wiirthwein. Chroi. E P ~1989.
.
122. 1705-1710.
[lo] K. B. Wibcrg. P. R. Rablen. M. Marquez,./. ,4111 Clrcni. Soc.. 1992. 114.86548668.
[ l l ] GAUSSIAN 92, Revision B: M. J. Frisch. G . W. Trucks, M. H e x - G o r d o n .
P. M . W. Gill. M. W. Wong. J. B. Foresman. B. G . Johnson. H. B. Schlegel.
M . A. Robb, E. S. Replogle. R. Gomperts, J. L. Andres. K. Raghavachnri. J. S.
Binkley, C. Gonzales, R. L. Martin, D . J, Fox. D. J. DeFreea. J. Baker, J J P.
Stewart. J. A . Pople, Gaussian Inc.. Pittsburgh PA. 1992. M P 3 : C. M d l f r .
M S. Plesset. P/iyr. Rev. 1934, 46. 618: M J. Frisch, R. Krishnan. J. A Pople.
Cliein. Phys. Lett. 1980, 7.5, 66. Details of the calculated structures (GAUSSIAN-92 Archive Entries) can be obtained from E -U. W.
[I21 Finite cluster calculations of polymers with all-rruris configuration. J Chandrasekhar. P. K. Das, J1 Pliys. C'hrni. 1992. Yh. 679 -685.
[I31 R. Allmann, R. Kiipfer, M. Nagel. E.-U. Wurthwein. C'iieni Ber. 1984, 117.
1597- 1605.
114) G. Sheldrick, SHELXTL-PLUS. Programmsystem zur Kristallsirukturheatimmung, Siemens AG. 1989.
Tether-Directed Remote Functionalization of
Buckminsterfullerene: Regiospecific
Hexaadduct Formation**
Lyle Isaacs, Richard F. H a l d i m a n n , and Franqois
Diederich*
I . ri-Butyllithiiiiii solution ( 1 . 6 ~2.7
, mL, 4.4 mmol) was slowly added to a solution
of ,V,A'-(l.3.3-triinethqIbicyclo[2.2.1]hept-2-ylidenebenzamidine [5] (2-H. 1.11 g,
4.4 mmol) i n T H F (15 mL) at -78 C. After 5 min a suspension of 2,4.6-triphenyl1.3..i-oxadi;iriniuin pentachlorostannate (3. 2 65 g. 4.4 mmol) in T H F (5OmL) &as
added drop\\ise. and the reaction mixture was stirred at -78 C . The reaction
mixture w i i z .illowed to \+aimto i-oom temperature over approximately 12 h. After
27 h themixlure\\ascooled t o 0 C. and thecloudy.yellowso1utionwasshaken with
40 mL of ice cold 1 u sodium hydroxide solution. The aqueous solution was extracted twice \ b i t 1 1 dichloromethane (20 mL). The combined organic phases were dried
over mngnevum wlf'ite. and the solvetit removed under vacuum. The residue was
takcn up in ii Iictlc dichloi-omethane. filtered. and worked up by flash chromatography (petroleum ether'diethyl ether 2 1 . 1 : R,,,,, = 0 24). The yello\v residue thus
obtained wa\ recr>stallized from diethyl ether. Yield 0.84 g ( 3 4 % ) I. pale yellow
crystels. i1i.p. 155 C
R e c e i ~ e d June
:
8. 1994 [Z7014IE]
German Version. Angzw. Chem. 1994, 106,2386
[ l ] D. Whhrle. Mukroiiiol.
10.35
C'/ieni.
1974. f75. 1751- 1760. A d r . Po/yr?ier S(t. 1972,
107
[2] M. Buhmann. M. H. Moller. E.-U. Wurthwein. Cheni. E w . 1993. 126. 957967.
131 3) M . Bii1itn;inn. M. H. Moller. U. Rodewald, E:U. Wurthwein, C h n E w .
1993. 1 3 . 2467-2476: b) M . Buhmann. Dissertation, Universttit Miinster.
1993, c j H. Naxi-mann, E.-U. Wurthwein. M. Buhmann, DE-A 4223264.1992
[ C ' / i c w i A / J \ / ~ .1994. 120. 269854x1.
[4] W. Funke. ti. Hornig. M. H. Miiller. E.-U. Wurthwein. Chcni. Bw. 1993, 126.
2069 '077
[5] F. Bondaialii. 0. Bruno. P. Schenoiie. W. Filipelli. S. Russo. E. Marmo.
Funiimo 1987. 42. 335 340.
[6] R . R . Schmidt. C/iwii. E r r . 1965. YH. 334-345: see also R . Fuks. M. Strebelle.
A. Wenders, S)/i//!c.\i.!1977, 788 789
(71 Crystallographic data for I (C,,H,,N,O. Mr = 564.7: triclinic, space group
P1.u = 1093.4(2)./~= 1 1 9 5 . 7 ( 2 ) , ~= 1300.7(3) pm. I = 68.36(3).[i = X6.36(3).
;' = 80.4_5(3), Z = 2.
= 1.201 gcm-'.
) I = 0.7 cm-'.
Measured at
293(2) K Hith 'in Enraf-Nonius CAD4 diffractometer. Mo,, radiation.
graphite monochromator. 18826 measured reflections, of which 18541 are
independent(R,,,,= 0.0326). Solution by direct methods. SHELXTL-PLUS
program [IJ]. R = 0.0648. wRZ = 0.1745. Confirmation of the structure solu[ioii h y incans o l a smaller set data Il-om a low temperature measurement (77 K )
on the wine crystal. All positions of the noii-hydrogen atoms antsotropic; all
Following the development of a great variety of methods for
monofunctionalization.[" the regiospecific formation of covalent polyadducts has become the frontier in the chemistry of
buckminsterfullerene C,, .121 Reversible reactions with transition metal complexes'3i or halogens[41yield the thermodynamically most stable isomer o r an isomer that selectively crystallizes
out of the reaction mixture. Alternatively, mixtures of many
possible multiple adducts are produced by successive. irreversible reactions at the C,, sphere. Purification is then achieved
by tedious, scale-limiting HPLC separation of the isomeric mixtures or by recrystallization, when possible.[21In an attempt to
develop a more rational approach to the production of one
desired regioisomer in multiple functionalization reactions. we
turned to the tether-directed remote functionalization of C,,, , B
concept that was introduced by Breslow for the regioselective
functionalization of steroids and long-chain alkanes.['] Here, we
describe the application of remote functionalization to the regiospecific formation of bis- and trisadducts of C,,,. With a
trisadduct as the starting material, formation of a hexaadduct
with the six functional groups aligned in pseudooctahedral positions on the C,, surface (positions a-,f in Fig. 1 ) is readily
achieved. This unique functionalization pattern has previously
only been described for transition metal complexes.[3,('I All
compounds are isolated in pure form without the application of
HPLC methods.
[*I
[**I
Prof. F. Diederich. L. Isaacs, R. F. Haldimann
Lahoratorium fur Organische Chemie
ETH Zentrum. Universititstrasse 16
CH-8092 Zurich (Switzerland)
Telefax: Int. code + (1)632-1109
This work was supported by the Schweizerlscher Nationalfonds i u r i-iirderung
der wissenschaftlicheii Forschung.
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f
Fig. 1. Schematic depiction of the tether-directed remote functionaliration of C,,". The bonds
a-/(in red) represent the six pseudooctahedrally
disposed double bonds on the C,, sphere; bonds
fi and / I (in green) do not react with the reactive
group for steric reasons. A =anchor. T =
tether. RG = rsactive group
First, we targeted the regiospecific production of an equatori2b
2a
al bisadduct of C,, (Fig. 1) using a reactive group anchored by
a tether to the fullerene. As the anchor, we chose the carboxylate
+6.5 kcal mol-'
A h (rel.) 0 kcal mot-'
of the methanofullerene carboxylic acid 7"' (Scheme 2) and as
Fig. 2. PM3-calculated structures and heats of formation for the t u o possible rereactive group, a 2-substituted 1,3-butadiene known to undergo
gioisomeric bisadducts 2 a and 2 b.
irreversible Diels-Alder reactions with C,, at 6-6 bonds (bonds
between two fused six-membered rings) .['?The choice
of the tether between anchor and reactive group was
critical for the regioselective attack. Its size and shape
were chosen to favor attack at the equatorial bond h
(Fig. 1 ) over attack at the other possible reactive 6-6
bonds g and fz located in the same hemisphere in
somewhat closer proximity to the anchor bond a
(Fig. 1). PM3 computational studies[g]show that the
chosen 4-substituted benzyl alcohol tether in I
(Scheme 1 ) would lead to a preference for the targeted
bisadduct 2 a over regioisomer 2 b. The heat of formation of 2 a is calculated to be 6.5 kcalmol-' lower
than that of the lowest energy conformer of 2b
(Fig. 2). A close examination of the calculated geometry of 2 b shows that the tether is too short in the
conformer shown and too long in the higher energy
conformer in which the double bond of the cyclohexene boat is oriented towards the anchor. This mismatch of the tether length leads to distortions in the
bridging benzene ring and also to skewing of the ester
10
group, which both increase the heat of formation. The
1 3 R== Hzc*
Bu
different symmetries of 2 a (C,) and 2 b (C,) should
Scheme 2. Synthesis of the bis- and trisadducts 2 a and 10. DCC = dicyc1ohex)lcarbodiimide.
make it easy to identify by I3C N M R spectroscopy
HOBT = 1 -hydroxybeo~otriazole.DMAP = 4-dirnethylaminopyridrlle
the bisadduct formed.
The synthesis of 1, which contains both tether and
reactive group, is shown in Scheme 1. Reaction of 1 with 7
toluene/hexane 2/l) and identified in solution by the two diag(Scheme 2) under dicyclohexylcarbodiimide (DCC) coupling
nostic UV/VIS absorption bands of a monoadduct at
conditions[71 afforded the intermediate wine-red methano1,,, = 429 and 692 nm. Further characterization was not atfullerene 8, which was purified by flash chromatography (SiO,,
tempted owing to the rapid polymerization of 8 upon evaporation to dryness. However, heating of a solution of
8 (ca. 0.1 mM) in toluene to 80°C led to a color
a) Zn, THF, 5
change from wine-red to yellow-orange. Flash
b) CuCN, LiCI. THF, -75 'C [lo]
KOAc, 18-C-6,
c
chromatography (SiO,, toluene/hexane, 2/1) folBr*jr
CH&N,47%
* AcOB
-r
c) Br'F-, [ll], -75 'C-20 ~ C ,
61%
/ \
lowed by recrystallization (CSJhexane) afforded
3
the isomerically pure bisadduct 2 a in 23 YOyield,
which was fully characterized spectroscopically
(Table 1). The presence of 32 signals for the
+o,
CICOCH2COCI,
CHzCIz, C&N. 0 ~ C 3
fullerene C atoms in the I3C N M R spectrum
80%
demonstrates conclusively that the Diels-Alder reaction occurred at the equatorial double bond h
5
1:
J Kzc03,
MeOH, 96%
(Fig. I ) with formation of the C,-symmetrical
isomer. The bisadduct, like the other highly functionalized fullerenes described below, is air- and
DBU, PhCH3,Br2.
light-sensitive and must be stored under argon in
O V O
-20 'C, 31%
the dark. One other fullerene product (ca. 5 %
4
B
r
yield) was also present in the reaction mixture, but
6
matrix-assisted laser desorption -ionization timeScheme 1. Synthesis of the "tether-reactive group" fragments 1 and 6. 18-C-6 = [1X]crown-6.
of-flight mass spectrometry (MALDT-TOF MS)
DBU = 1,8-diazabicyclo[5.4.O]undec-7-ene.
.XX0
-4
%
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-
ing to the methine resonance in the methano bridge is absent.
The I3C N M R spectrum shows the expected 17 resonances for
2 a : Black solid. R, = 0.51 (SiO?. to1uene:hexane. 2: 1 ) . M.p. > 270 C . ' H NMR
the fullerene C atoms in a C,,.-symmetrical molecule.
(CS,(C'D,)1COii~capillary.300MHz):d = 7 . 0 6 ( s . 4 H ) . 6 4 7 ( t . J = 5.4.1 H).5.09
( ~ . 2 H ) . 4 4 7 ( s .I HJ.366(d.J=5.4.2H).3.33(~.2H).3.06(s.4H):'.'CNMR The fact that we had access to relatively large quantities (ca.
(CS2:(CD,J,C0 i n capillary. 125.8 MHz): 6 = 163.46. 160.19. 156.41. 149.16.
100 mg batches) of trisadduct 10, prompted us to test the re148 35. 147.90. 147.42. 146.81, 146.53. 146.32, 146.29. 146.26. 145.99. 145.86.
gioselectivity of further reactions on the fullerene sphere. The
145.33. 145.20. 145.09. 144.99, 144.69. 14423, 144.11. 144.01. 143.20. 143.14.
regioselectivity observed by Hirsch et al.[2b1in the formation of
142.59. 142.4'). 142.22. 140.32. 139.09.138.97. 138.58. 136.59.132.72.130.79.128.51
a trisadduct (a,b.c-functionalized, Fig. 1) from an equatorial
(hr). 125.9X. 69.60. 68 00. 05.78. 64.99. 43.77. 41.71. 40.14. 35.67. 34.75: UV:VIS
I.,,,.,. [nm]= 508 s h I C = 2180). 449 (3050).427 (4030). 399 sh (4000). 397
bisadduct (ah-functionalized) made us optimistic that further
34U \I) 115340). 309 sh (32040). 279 sh (51370). 248 (77100): MALDIfunctionalization of 10 would lead to regioisomerically pure
TOF MS. i i i :Y4X (100%. ,M')
tetra- through hexaadducts. When a 1 mM solution of 10 in
10: Black aolid. R, = 0.60 (SiO?. toluene). M.p >270 C ' H N M R (CI,DCCDCI,.
chlorobenzene was reacted with five equivalents of diethyl a300 M H z J : d =7.13 (bra. 8 H). 6 . 5 2 1 ~
J = 5.3. 2 H ) . 5 18(s. 4 H ) . 3.80 (d. J = 5.3.
bromomalonate and DBU at room temperature (Scheme 3), the
4 H ) . 3 . 3 2 ( \ . 4 H ) . . ~ . 0 6 ( s . X H ) 'JCNMR(C1,DCCDCI,, 125.8 MHz):d =162.88.
Tiihle 1. Selected physical dxta ofcompounds 2a. 10. 11. and 12 [ah].
146.97. 146.50, 146.24. 145.70. 145.51. 145.19. 144.60. 143.09.
158.36. I M X .
142.81. 142 27 ( b r J . 140.17. 139.90. 139.72, 139.57. 132.02. 130.61, 128.62 (br).
125.93. 69.34. 69.13. 62.90. 62.85. 54.45, 43.53. 39.93. 35.49. 34.49: UV:VIS
(CH,CI,). i,,,,,,
[nm] = 498 ( I : = 3120). 468 (2660). 368 sh (6320). 337 sh (13830).
i o x \i1 (20970). 264 141350):MALDI-TOF MS: i17:: 1162 (100%. M + ) .
11: Ormpe \olid. R , =0.13 (SiO?. tolucne). M.p.>270 C. ' H N M R (CDCI,.
300 MH7): 0 =7.20(hr s . 4 H ) . 7.12ihr 7, 4 H ) . 6.41 (t, J = 5.3. 2 H). 5.19 (s. 4 H).
4 40 4.20 (m. 4 H ) . 3.60 (dd. J = 5.3, 14.1. 2 H ) . 3.56 (dd. J = 5.3. 14.1. 2 H). 3.2s
( d . J = 14.3. 3 H I . 3.18 1d.J =14.3. ? H I . 3.06(brs. 8 H). 1 . 3 2 ( t , J = 7 . 1 , 3 H ) 1.30
~
HI. " C N M R ICDCI,. 75 MHz): 6 =163.42. 163.11. 162.42. 158.10,
26. 151.16. 150.21, 148.14. 14723, 147.14, 146.19. 146.11. 145.82,
31. 145.08. 145 00. 144.45 (2 x), 142.65. 142.44 (2 x ) . 141.95, 141.93.
1.11 8%. I ~ I . I ( ~ 140.7~.
.
1 . 3 ~ 3 I. F ~ S I . 139.47, 131.85. 130.37, 130.28. 128.25.
125 39. 71.82. 6X.61. 67.49. 67.28. 62.74. 62.63, 62.47. 62.25. 53.60. 52.72. 41.82,
34.23. 14.13 ( 2 x), U V ' V l S (CH,CI,). i,,, Inm] = 578 ( f : =1040). 556
3 a h (2370). 492 ( 3 5 5 0 ) . 459 (3880). 414 sh (5670). 386 (8740). 278
(71650). M A L D I - T O F MS: 171:: 1320 (loooh. M + ) .
PhCI, DBU (5 equiv).
Et02CCHBrC02E1 (5 equiv),
11
72%
PhCI, DBU (loequiv),
EtO?CCHBrCOpEl (10 equiv),
12
73%
11 X = Et02CCCOZEt Y = 12 X = Y = EIOZCCCOEEt
Scheme 3. Synthesis of the tetra- and hexaadducts 11 and 12
0.41 ( S O ? . CH,CI,). M.p.>270 C . ' H N M R (CDCI,,
300~Hr).~~=7.15~7.05(brm.8H).6.16(t,J=5.5,2H),5.22(~.4H),4.34(q,
J =7.1. 4 111. 1.28 (q, J = 7 . 1 , 4 H). 4.24 (q, J =7.1, 4 H ) . 3.21 (d, J = 5.5. 4 H ) ,
C,-symmetrical bright red tetraadduct 11 functionalized at the
3.05 2XS(m. 12 H ) . 1.35(t. J = 7 . 1 . 6 H ) . 1.29 ( t , J = 7 . 1 . 6 H ) . 1 . 2 6 ( t . J = 7 . 3 . 6
a,b,c,d bonds was selectively obtained in 72% yield. The
H J : "C N 4 I R (CDC-I,. 125.8 MHz): 6 =164.14. 163.85. 163.67. 162.99. 155 27.
155.07. 145.77. 145.41. 145.29. 144.85. 143.65. 143.36. 143.14, 142.51. 139.98,
' H N M R spectrum of 11 shows two sets of ethyl ester reso139.73. 130.34. 1 3 y . o ~131 75. 13024, 128.26. 125.12. 70.66. 68.56. 65.88. 62.62.
nances, and the presence of 32 fullerene-core resonances in the
62.53. 62.42. 61.70. 61.60. 45.84. 45.52. 44.54. 42.29, 39.61. 34.84. 34.23. 14.14,
" C N M R spectrum supports the assigned molecular symmetry
14.03. 14.00. U V VIS (CH,CI,): i,,, [nm] = 353 sh ( c = 21790). 332 sh (35000).
(Table 1). When an 18 mM solution of 10 was reacted with a
?OX sh (64390). 2x8 (73260); MALDI-TOF MS: n:: 1637 (100%. M ' ) . 1593 (41,
[,ZI-EtO]' J. 1481 (48. [M-EtO,CCCOiEt]+).
tenfold excess of the reagents, flash chromatography (SO,,
12: Y e l l o ~ .r o l ~ d R,
=
[ a ] All new compounds in Scheme 1 Nere fully characterized by ' H and 13C NMR.
FT-IR. and ElLMS data. as well 3 s by elemental analysis o r high-resolution MS.
[h] MALDI-TOF MS spectra were measured w,ith 2.5-dihydroxybenzoic acid or
2-(4-hydrox! phcny1aro)henzoic acid as the matrix.
showed it to be a by-product due to oxidation[2d1of 2 a rather
than a regioisomeric bisadduct. The rather low isolated yield of
2 a is a reflection of the difficulties encountered with its chromatographic separation from its oxidation product.
For the regiospecific formation of a trisadduct resulting from
double Did-Alder addition to the two equatorial double bonds
h and d (Fig. 1). the doubly tethered system 6 was prepared
(Scheme 1 ) and anchored to C,, by the versatile x-bromomalonate alkylation method introduced by Bingel.[121Addition of
6 to C,,, (2 equiv) in toluene with DBU as base gave
methanofullerene 9. Following flash chromatography (SiO, ,
tolueneihexane, 1/1 then 211) to recover the excess C,,, the
identity of 9 was established by ' H N M R and UV/VIS spectroscopy. The ' H N M R spectrum showed all expected resonances for tether and reactive groups, and the electronic absorption spectrum contained the two diagnostic monoadduct bands
at i,,
=
,429 and 690 nm. Heating of a solution of 9 in toluene
(ca. 0.07 InM) at 80 "C for 83 h resulted in a color change from
wine-red to yellow-orange. Flash chromatography (SiO, ,
toluene) afforded a single trisadduct (48% yield based on 6).
which was assigned the C2,.-symmetrical structure 10 on the
basis of its spectroscopic data (Table 1 ) . The ' H N M R spectrum
of 10 is similar to that of 2a, except that the signal correspond-
CH,CI,) allowed the isolation of the bright yellow hexaadduct
12 in 73 % yield. The overall yield of 12 was a remarkable 35 %
based on C60.
In the MALDI-TOF mass spectrum of 12, the expected
molecular ion appears as the base peak at mi; = 1637, in addition to weaker peaks resulting from the fragmentation of the
ethyl malonates. In accord with the proposed C,,-symmetrical
structure, the 'H N M R spectrum contains three nonequivalent
ethoxy groups, and the I3C N M R spectrum shows 17 resonances for the fullerene core C atoms. Hexaadduct 12 is highly
soluble and dissolves readily in chlorinated and aromatic solvents; more than 40 mg can be dissolved in 1 mL of CHCI,.
The change in the extent of conjugation in the fullerene chromophore when passing from a mono- to a hexaadduct is readily
apparent from the visual color changes. Accordingly. the electronic absorption spectra change dramatically (Fig. 3). Compared to C,,, compound 13 (Scheme 2), which is typical of
methanofullerene monoadducts, shows much less fine structure
for
in the 400 to 700 nm range, and a hypsochromic shift of imax
the broad, long-wavelength band to about 500 nm is observed.
Two additional diagnostic bands appear at about i,,, = 430
and 700 nm. The characteristic peak at I.,
=700 nm in the
spectrum of 13 is no longer observed for the bisadduct 2 a, and
the broad band in the visible region is further hypsochromically
shifted to i.,,, = 449 nm. Trisadduct 10 exhibits little fine structure in its electronic absorption spectrum, and the characteristic
band at J~,, at about 430 nm, present in the mono- and bisadducts, is not observed. However, a new strong band appears at
the surprisingly long wavelength of 3.,,, = 498 nm. The spec-
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120001
-1000
!
375
80000 I
475
575
L[nrn]
-
Fig. -7. Elect~onic absorption spectra of C,,, (---),
I 1 ( - - - - -..I.
12
). and 13 ( - . . j in CH,CI,.
675
2 a (-).
775
LO
(-----).
trum of the tetraadduct 11 is much more intense and structured
than that of 10; no absorption is observed beyond 600 nm in the
spectrum of 1 1 . Hexaadduct 12 has a x system composed of
eight benzene-type rings placed in the corners of a cube; each
ring is connected to three neighboring rings by biphenyl-type
nieiu bonds. Absorption above 475 nm is no longer observed;
this is consistent with a drastic reduction in 71 conjugation as
compared to the precursor molecules.
The described tether-directed remote functionalization
methodology should provide a versatile entry into the unexplored area of multiply and differentially functionalized
buckminsterfullerenes. which may prove to be useful in chemical, materials, and biomedical applications
Esperinientai Procrd~wc
Trisadduct 10: To a solution of C,, (264mg, 0.367 mmol) and 6 (96mg.
0.183 mmol) in toluene (155 mL) was added DBU (29 mg, 0.187 mmol) in toluene
( 5 mLj over 5 min. After 2.75 h. the reaction mixture was concentrated to 100 mL,
diluted with hexane (100 mL). and chromatographed (SiO,). Unreacted C,,,was
recovcred with a 1 :1 mixture of to1uene:hexane as eluent; the monoaddiict 9 was
eluted with a 2 : l mixture. The resulting solution was concentrated on a rotary
e\'apoi-ator to remove the hexane and then diluted to I 5 L with toluene. The solution was thoroughly deoxygenated by bubbling Ar through the solution for 1.5 h
and then heated at 80 C for 83 h. The reaction mixture was concentrated and
loaded onto acolumti (SO,). which waseluted with toluene. Recrystallization from
CHCI,;MeOH followed by drying at 25 C:IO-' Torr gave 10 (102 mg. 48% yield)
as a black solid.
Hexaadduct 12: A solullon of diethyl a-hromomalonate (42.1 mg. 0.176 mmol) in
anhydrous chlorohenzene (0.45 mLj was added under argon to trisadduct 10
(20 5 mg. 0,0176 mmol). and DBU (26.8 mg. 0.176 mmol) in anhydrous chlorohenzene (0.55 m L ) was subsequently added to the suspension. After 5 min. a bright red.
homogeneous reaction mixture was obtained. After 2 h, the mixture was loaded
onto a SiO, column and eluted with CH,CI,. The bright yellow product was collected and concentrated to dryness. Recrysta~lizationfrom CH2C1,:pentane gave. after
drying at 25 C:10-' Torr, 12 (21.1 mg. 73% yield) as a yellow solid.
Received: July 21, 1994 [Z7150IE]
German version: Angcw. Chrw. 1994, 1U6. 2434
[I] a ) R . Taylor. D. R. M. Walton. Nufurr 1993. 363, 685-693: b) A. Hirsch.
Arigiw. Chrr?~.
1993. 105. 1189-1192; Angcw. Chon. /n1. Ed. Engl. 1993. 32.
1138-1141 : c) F. Diederich. L. Isaacs. D. Philp, Cliein. So<. Rev. 1994. 23.
243-255.
(21 a) J. M. Hawkins, A. Meyer, T. A. Lewis. U . Bunz, R. Nunlist. G. E.Ball, T.
W. Ebbesen, K . Tanigaki, J. An?. Cheni. Soc. 1992, 114, 7954-7955: h) A.
Hirsch. I. Lamparth. H. R. Karfunkel, Angew. Cliem. 1994, 106. 453-455;
Arig.ru.. Chon. /!I/.Ed. Engl. 1994, 33. 437-438: c) C. C. Henderson, C. M.
Rohlfing, R. A. Assink, P. A. Cahill. ibid. 1994. 106. 803--805 and 1994. 33.
786-788: d ) M. Tsuda. T. Ishida. T. Nogami. S. Kurono, M. Ohashi, J. Chern.
Sor. Cliem. Coiiimuri 1993. 1296 1298.
2342
('
VCH C'o.l~ig.rjie,srllsc/?~i~/
mbH. D-69451 Webihrirn, 1994
[3j a ) P J. Fagan. .I.C . Calahrese. B. Malone. J. h i ? . Ciwm Soc. 1991. 113.
9408-9409: b) F N. Tehbe. R. L. Harlow. D. B. Chase. D. L. Thorn. G. C.
Campbell. Jr.. J. C. Calahrese. N. Herron. R. J. Young. J r . E. Wasserman,
Sricrrrr 1992, 256. 822-825. c ) P. J. Fagan. J. C. Calahrese. B. Malone, Acr
Chrni. RE.\. 1992. 25. 134-142; d ) A. L. Balch. D . A. Costa. J. W. Lee. B. C.
Noll. M. M. OhIlStedd, /fiorg. Cheni. 1994, 33, 2071 -2072.
[4] a ) P R. Birkett. P. B. Hitchcock. H W Kroto. R. Taqlor. D. R. M. Walton,
f ~ i i 1992.
i ~ 357. 179 481: b) P. R. Birkett. A. G Avent. A. D. Darwish. H.
W. Kroto. R . Taqlor, D. R. M . Walton. J, C h i ? Soc. Cliiwr C o m i i i i i i i . 1993.
1230-1232: c ) A G. Avent. P. R. Birkett. J. D. Crane. A. D. Darwish. G . J.
Langley, H. W. Kroto. R. Taylor. D. R M. Walton. ihid. 1994. 1463-1464.
[5] R. Breslow, .4cr. C/icn7. R r . 1980. 13. 170-177
[6] A hexaxiduct of C,,,, uith di(ethoxycnrhonyl)methS.lene has been reported by
A. Hirsch and I . Lamparth at the International Winterschool "Electronic
Properties of Novel Materials": Progress in Fullerene Research i n Kirchberg.
Austria, March 5 12. 1994. Book of Abstracts.
[7] L . Isaacs. F. Diederich. H d . . Chirii. . A r / o 1993. 76. 2354-2464.
[8] B. Kriutler. M. Puchberger. H c h . Chiin Actri 1993. 76, 1626-1631.
[9] a) J. J. P. Stewart. J. Coriipur. Clirn?. 1989. 10. 209-220: 221 264: bj F.
Diederich. L. I~aacs.D. Philp. J. C%cnr.Soc. Po.kiw Duns 2 1994. 391 394.
[lo] S. C . Berk. P. Knochel, M . C.P. Yeh, J Org. Clwm. 1988,53, 5791-5793.
[ I l l a) E. J. Corey. N. H. Anderaen. R . M . C;lrlson. J. Paust, E. \iedejs, I. Vlattas.
R. E. K . Winter. J Aiii. Clierii. .Tor.. 1968. YO. 3245-3241, b) R . C Krug. T. F
Yen, J. Or,q. C/imi. 1956.21.1082 1OX6:c) R. L. Frank. R. P. Seven. Org. S v i
Cdl. I+/. 3. 1955, 499-500.
[12] C.Bingel. Chwi. Bcr 1993. 126. 1957-1959.
Polar Superstructures Stabilized by Polymeric
Oxometal Units: Columnar Liquid Crystals
Based on Tapered Dioxomolybdenum
Complexes**
Andri: G. Serrette and Timothy M. Swager*
The design of molecule-based materials requires the controlled assembly of specific superstructures that effectively
transform discrete molecular properties into collective material
properties. Liquid crystalline (mesomorphic) materials are the
best examples of designed supermolecular materials, and the
cooperative physical properties of these materials have led to
numerous technological applications. The continued development of liquid crystal based technologies requires new types of
mesomorphic materials that integrate novel structural elements
and physical properties. To this end, liquid crystals and transition metals have been combined to give metallomesogens. materials with new properties.['] In this report we describe columnar
mesomorphism in a new class of rnetallomesogen based upon
dioxomolybdenum complexes with tapered structures. The
polymeric ( . - M o = O . . . Mo=O..),, units in these materials
provide a strong organization force that directs the assembly
process and stabilizes the mesophase.
Thermotropic columnar liquid crystalline phases of discshaped molecules have been extensively studied. However, in
recent years the structural diversity of materials displaying a
columnar mesophase has grown to include hemi-disc,[*]
pha~midic,'~
b ]~ w l i c , [ octahedral.[5]
~]
and tapered mesogens.[61
Of these columnar materials, the stabilization of mesophases
based upon tapered materials is most demanding, requiring the
simultaneous assembly of four molecular units to produce the
[*I
[**I
Prof. T. M. Swager. A. G . Serrette
Department of Chemistry,
University of Pennsylvania
Philadelphia, PA 191044323 (USA)
Telefax: Int. code + (215)573-2112
This work was supported by the Office of Naval Research and the National
Science Foundation.
0570-0833/94'2222-2342 $ 1U.OU + ,2510
Angew. Clierii. In/.Ed. Engl. 1994, 33, No. 21
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remote, tethers, buckminsterfullerene, hexaadduct, functionalization, formation, regiospecific, directed
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