Vol. 35, No. 32. pp. 5189-5792. 1994 Etsevta Science Ltd Printed in Great Britain oo404039/94 57.awo.00
Synthesis of Hydrogenated
Fullerenes by Zinc/Acid Reduction1
Mark S. Meier,* Perry S. Corbin,t Virginia K. Vance, Mark Clayton, and Michael Mollman, Department
Magdalena Poplawska Faculty of Chemistry, Warsaw Technical University (Politechnika), 00-664 Warszawa, Noakowskiego 3, Poland
Abstract: Reduction of Cm with zinc and acid resulu in the formation of [email protected]
and more highly
The chemical modification simplest
types of chemical of Q&l36
the literature. the formation
by the Birch reduction*
to be a high-energy may contribute
(2) has been proposed.
species due to the interactions to the Bitch reduction
of so many eclipsed at the c&36
Cm in particular,
is an aggressive reducing agent with a Li+/Li potential of
with suitable reduction
The protonated products, C&I2 to the eventual
metal reduction potentials,
at a potential
and at the Q-J-‘/-~ potentials
of the reduced
h,ydrogen atoms,6 and these
has been extensively
-3.0 V versus Fc+/Fc. very close to the would be easily reduced
of Qr~H36. We are interested
in the products
of Qo using less highly Educing
and we chose to investigate
metals. There are a number of tin (t? (Sn2+/8n) = -0.75 V vs Fc+/Fc),
= -1.37 V vs Fc+/Fc).
where CM is not electrochemically
(-0.98 V and -1.37 V vs F&PC. C&L2,
being the simplest,
iron (Eo (Pe2+/Pe) = -1.05 V vs Fc+/Pc), and zinc (Ep (Zn2*/Zn) conveniently
might result from dissolving
as being the result of the deconjugation
double bonds. of a fullerene The formation
under these conditions,”
One of the
as a proton source leads to
ranging from Cfjt-$Ltg to C!&LX.~
species has been rationalized
and using t-butanol
1 The reductive
was among the first chemical
of a series of polyhydrofulletenes
double bonds, and one such structure interactions
a highly active area of research.2*3
of Q-J (1) with lithium in ammonia
rather than more highly reduced predicted
C&H6 and others by dissolving
and acid. 5789
These three reagents as well as near the Herein we report the
metal reduction using zinc
Results Heating a heterogeneous
toluene. tin dust, and aqueous HCl for periods of up to six
hours under a nitrogen or argon atmosphere leads to very little reaction as indicated by gel permeation chromatography
The same was found using iron dust instead of tin, suggesting that if any C& radical
anion is produced under these conditions it is fairly unreactive toward acid. However,
treatment of t&o with
sn excess of zinc dust and acid in refluxing toluene under argon or nitrogen results in a change in color from the magenta color of C&o to a dark brown. GPC analysis of the reaction mixture shows three new, evenly spaced bands that elute after C&. Different acids (6 M HCl. 12 M HCI, glacial HOAc, and concentrated (35 psi Hz, 10% Pd/C, 24 hours) lead to the formation
H2SO4) as well as catalytic hydrogenation three new bands.
of reaction over the six hour reaction period.
Control experiments with each acid alone and with zinc alone
. do not, under these conditions, show the formation mixture
of the same
of the new species differ somewhat,
with DDQ results in smooth conversion
of any new compounds.
of the mixture back to %,
of the Z&I-I+ reaction with the assignment
these new bands as reduced fullerenesS4
Fig. 1. Gel Permeation
We have separated
See text for specific
the new bands by preparative GPC16*18 using a bank of four 19 mm diameter
columns operating at ambient temperature with toluene as the mobile phase. rechromatographed solutions
The known lability of C&2, to dryness,
Each band was isolated
in solution and not evaporated
necessary. Mass spectrometric
back to the parent fullerene.17
parent ion, along with the expected under these conditions,
m/e 720, again accompanied the 720 line expected fragment
of these compounds
a strong tendency
by the expected
to t& occurs, and the spectrum isotope lines.
or the adduct of a hydrogen
of t3C. indicates
of Band I exhibited
lines (67% M+l, 24% M+2), corresponding
due to the natural abundance
ion FABS MS analysis
m/e 722 as the
shows a prominent
at m/e 721, beyond
a small quantity
Even line at
the 67% of
of C&H, either a
ion t8 from the FABS matrix to the t&o formed
Analysis of the C&-I2 band by high-resolutionCl8 HPLC (70% CH$&30% aCetonitrilC) indicated thatthis band contains a single component, suggestingthata single isomer is fotmed. Calculationsby Cahill suggest thatof the 23 all-exe isomers of -2,
t6 one isomer (1.9) is 3.8 kcal/mole more stable than any
other isomer. This isomer, resulting from the placementof hydrogensacross a 6,6 ring fusion, has been preparedby tmatmentof f&u with BH3-THF followed by protonolysis.19and by hydrogenationover rhodium.” When we prepare a sample of C&II2 using BH$I’I-IP. we find that it is chromatographicallyand spectroscopically(UV/Vis, III NMR) identicalto the compound we prepateby zinc/acid reduction. indicating thatthe same isomer is produced.
3 Reversed-phaseHPLC indicated thatbands II and III each contain a numberof components. Analysis of Band II by negative-ion FABS mass spectromeny shows thatit is primarilyQuI&
Analysis of this band
with a “‘Buckyclutcher”HPLC column showed that threecompounds, presumablydifferent isomers, are present. This is consistentwith resultsreportedby Cahill, althoughthe relativeamountsof the isomers producedby this method are quite different from the relativeamountsproducedby BH3*THF. Buckyclutcheranalyses made before GPC separationconfirm that this ratio is not an artifactof prior GPC treatment.
C6&4 bmm z
Fig. 2. HPLC (19 mm preparativeBuckyclutcher)Chromatogramof Band II (C&-J-k+ Toluene/hexane (70/30,5
mIJmin) mobile phase, UV/Vis detection at 330 nm.
Band III, containingthe most highly reduced materialproducedunder these conditions, exhibits mass lines from ml+?720 (C&) to 730 (M+2 line from Q&Is). fragmentationfrom C&I,5 or -8.
Again, the lower mass lines are most likely due to
Reversed phase HPLC analysis clearly shows that this band is
composed of a mixture of a large number of compounds. Given the difficulty in obtainingfragmentation-free mass spectrawe can not be certain if QoHe is the parentand thatother lines result from fragmentation.
Clearly,8 zmmbcxof hydrogenated fullerenes C&-I6 to c6oHzz are produced, and these compounds are not
separated by GPC. To a suspension of 20 mg (0.0278 mmoIos) Cm in 5 mL toluene was added 360 mg (5.54 mmoles) in powder aud 0.5 mL 6 M HCI, The suspension was heated at reflux under Ar for a period of 6 hours. The resulting brown suspension was diluted with toluene and filtered to remove the metal salts. The resulting solution was washod with water, then dried (NazSO4) and concentrated to 2 mL before being miorofiltered and purified by GPC!. Preparative GPC of hydrogenated fullerencs was performed using a bank of four 19 mm x 300 mm GPC columns (#l - Jordigel E-277 (SKIA).#2 and #3 - Waters Ultrastyragei (NOA), #4 Waters Ultrastyragel (loOA)) using toluene as the mobile phase at a flow rate of 5 &mm. Injections of up to 5 mL of saturated solutions of the fullerones in tolucne were made. Evaporation to dryness was avoided due to difEculty in redissolving
the solid products. Typical mass balances were 70%. In oases where the
samples were evaporated to dryness, the yields obtained were QH2 tQ&6+,
(7%), C&I-I4 (3%) and band III
AcknowIedgmenb: We gratefully acknowledge support for P. L. C., provided by National Science
Fouudaticm REU grant CHE-9000653.
The authors thank the University of Kentucky Major Fquipment fund
and the Vice Charm&or for Research and Graduate Studies for their support of this research. We also thank Dr. Paul A. Cahill of Sandia National Laboratory for making his results available to us prior to publication. REFERENCES AND NOTES t Participant in the NSF-E’tEWprogram in summer, 1992. 1.
2. 3. 4. 5.
: : lb. :;: :: :z 17: :;* 20:
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(Received in USA 17 May 1994; accepted
16 .&me N!W)