The Journal of
Physical Chemistry VOLUME 97, NUMBER 26, JULY 1,1993
Q Copyright 1993 by the American Chemical Society
LETTERS Reactions of Cm and C70 with Cyclopentadiene Louis S. I(. Pang' and Michael A. Wilson' CSIRO Division of Coal and Energy Technology, PO Box 136, North Ryde NS W 21 13, Australia Received: February 1 1 , 1993; In Final Form: April 8, 1993
The kinetics of addition of cyclopentadiene to fullerene Cm and fullereneC70have been studied in the temperature range 291-354 K by high-pressure liquid chromatography. The rate of addition of cyclopentadiene to fullerene CWis about 7 times as fast as the rate of addition to fullerene c 7 0 a t 293 K. The activation energies for the two reactions are 29 and 67 kJ mol-', respectively, and reflect the increased electron density in bonds adjoined to two hexagonal rings ( C 6 4 6 bonds) in CWrelative to c70. The log A frequency factor for the reaction of c70with cyclopentadiene is over twice that for Cm because of the presence of a greater proportion of C 6 4 6 bonds.
It has been known for a long time that cyclopentadiene (1) undergoes reversible dimerization to dicyclopentadiene (2) and unless freshly distilled exists mainly in the form of the dimer (2).
1
2
The reaction has been studied by Wassermann and co-workers in thegas phaseand in various solvents.1-3 The activation energies for dimerization and dissociation are about 69 and 144 kl, respectively, and are independent of solvent. This is consistent with an electrocyclic reaction in which no charge is developed in the transition state. Cyclopentadiene (CpH) or dicyclopentadiene ((CpH)2) would thus be expected to undergo electrocyclic reactions with fullerenes.6'1 Indeed Wudl et al.9 have reported that it reacts as a solvent, but no details are given. Initially, we determined that dicyclopentadiene is unreactive to fullerenes over the temperature range 293-353 K. However, freshly distilled cyclopentadiene or refluxed and undiluted commercial samples of dicyclopentadiene(Aldrich)rapidly undergo reaction with both fullerene Cm and fullerene C70. The product on evaporation appeared to be thermally stable (100 "C), and a dark brown solid is produced on removal of excess cyclopentadiene. Diluted 0022-3654/93/2097-6761$04.00/0
dicyclopentadiene at about 1 mM in toluene does not react with C, even up to 354 K. The functionalization of C a through addition reactions can yield a large number of compounds including mono-, di-, and polyfunctionalized products. If random, bifunctionalization should produce 54 isomers.12 Studiesof osmy1,1~16platinM,17-19 and iridium complexes*%dicate that addition first occursacross a 6-6 ring junction rather than a 6-5 ring junction since these bonds are shorter and more reactive.22-26 If a second addition occurs across a 6-6 ring junction at least eight regioisomers should be produced, and for CpH addition there is also the possibility of isomers arising from the orientation of the cyclopentadiene with respect to the first addition. For C~[Os04(py)2]2,py = pyridine, derivatives, separation can be achieved by high-pressure Iiquid chromatography (HPLC).In this work three adducts of different retention time were observed for both C ~ (Figure O 1) and c 7 0 reactions. The adduct of longest retention time (A, Figure l), asoutlinedbelow,is themonoadduct. Figure 2 shows data obtained on a solution with [C,] = 0.98 X lW3 M and [ C P H I ~=I [CpH] 2[(CpH)t] = 4.21 X 10-3 M. There is an initial buildup of adduct of longest retention time followed by a gradual decrease. The adduct of next longest retention time increases in concentration and reaches a constant value at about 40 min, whereas the adduct of shortest retention time is still increasing in concentrationat 130min. The decrease
+
0 1993 American Chemical Society
Letters
6762 The Journal of Physical Chemistry, Vol. 97, No. 26, 1993
m
TABLE I: Observed Rate ConscIllta for the Reaction of Fullerwith Cyclopencrdiew fullerene [CpHIO [CpHIS temp kz fullerene concn(mM) (mM) (mM) (K) (Lmols-*) c70 c70 c 7 0 c70 c 7 0 c 7 0
0.720 0.655 0.655 0.655 0.600 0.655
0.520 2.872 0.234 0.144 0.379 0.305
1.OOO 2.872 0.574 0.514 0.574 0.374
292 291 292 316 328 347
0.088 0.069 0.088 0.90 1.4 2.15
CSO
1.359 1.359 1.359 1.163 1.204 1.204
0.359 0.368 1.700 0.837 1.113 0.822
0.925 0.891 1.780 1.124 1.177 1.177
293 293 323 354 312 302
0.64 0.60 1.08 3.63 0.86 0.51
CSO CSO
CSO CSO CSO
a [CpH] estimated from fullerenes reacted. This value is less than the [Cp] added because somecyclopentadiene has dimerized. * [CpH] added to the solution, consists of monomer and dimer [ c p H ] ~= [CpH] + 2 [(CpH)21.
TABLE Ik Arrbeniaa Data for the Reaction of Fpllcrenecr
with CyclopentaUiene fullcrenc AE (W/mol) ~
~~
2
0
4
Retention Time Figure 1. Typical HPLC trace of the three products from reaction of Cm with cyclopentadiene. Assignments of the adducts are shown. Time is in minutes.
16
-. 0
20 40
1
-.c,
80 100 120 140 Time ( m i d
60
Figure 2. Plot showing the buildup of products during reaction of CSO with cyclopentadiene at 350 K with [C,] 0.979 X 10-3 mol/L and [CpH]w = [CpH] + 2[(CpH)z] = 4.21 X lo-’ mol/L.
in concentration of the first adduct strongly suggests that consecutive reactions are involved in which first one CpH unit adds to C ~ and O then a further CpH unit add to the monoadduct. c60
C,CpH
+ CpH
-
+ CpH
C,oCpH
-
C,(CpH),
This is confirmed by experiments in which the concentration of Cm or C70 is made in excess with respect to CpH. Only the product of longest retention time is produced. Moreover, when [CpH] and [C,] are equal, formation of C&pH or C70CpH is fmt order in Cp as is consumption of C a or c70. Typical rate constants obtained at various concentrations and temperatures are shown in Table I. At 293 K,k2 for C ~ isO0.61 f 0.02 L mol s-1. Data for Arrhenius plots are shown in Table 11. AE for c 7 0 is greater than that for c60. The ground-state energy of Cm is believed to be higher than that of C ~ OHence, . ~ ~ the higher
cso
29.0
log A 4.8
fullerene AE (kJ/mol) log A c 7 Q
67.0
10.9
activation energy of c70 probably reflects the stability of the (26x6 bond in C70. Table I also shows that the frequency factor for c 7 0 is greater than that for CM. This may reflect, in part, that there is a greater ratio of C64S bonds to other bonds than in CWso that those collisions with appropriate translational and vibration energies which lead to product are more frequent. Because the adduct of shortest retention time builds up in concentration at longest reaction time, and because it is also the major product of reaction when CpH is used in excess as solvent, it is probable that this represents a cyclopentadiene tri-adduct Cm(CpH)3 and C70(CpH)s, and the product of intermediate retention time is the di-adduct. The possibility that both these products represent regioisomersof the dimer cannot be discounted but would only be possible if the two regioisomers were in equilibrium at longer reaction times, e.g., at 140 min (Figure 2). The main point reported here is that C ~ is O more reactive to cyclopentadiene than c70.
Experimental Section Fullerene Caa was prepared from coal as outlined el sew her^.^^.^^ Fullerene c 7 0 was purchased from Polygon Enterprises, Waco, TX. The purity of both fullerenes was checked by HPLC on a Waters Instrument equipped with a 486 tunable UV detector operating at 590 nm, a 590 programmable pump, and a Waters C- 18 (8 mm X 100 mm) reverse phase column. Toluene (40% v/v) to 2-propanol (60%v/v) mixtures were used as mobile phase. A flow rate of 2 mL/min was used. Cyclopcntadienewas prepared by distilling the dimer. The distillate was stored for not more than 2 days at -10 OC before use. In kinetic experiments a solution of cyclopentadiene in toluene (A.R. grade) was added rapidly to a solution of fullerene also in toluene. The samples (volume about 15 mL) were kept at the required temperature in a water bath, and aliquots (usually 5 pL) were removed for HPLC analysis as described above. Up to three products were observed with retention times shorter than those of the pure fullerenes. Kinetic analysis was carried out using the signal intensities observed by HPLC. The absorbance of C ~or Oc 7 0 was monitored together with the absorbance of the three products. When the concentration of the fullerene was similar or greater than that of cyclopentadiene, rate constants were calculated from the
Letters second-order rate equation
where a = b = 1. The cyclopentadiene concentration was calculated indirectly from the fullerene concentration at t = infinity, since even in freshly distilled cyclopentadienesome material is still dimerized. Note Added in Proof. The monoadduct has been characterized (Rotello, V. M.; Howard, J. B.; Yadav, T.; Conn, M. M.; Viani, E.; Griovane, L. M.;Lafleur, A. L. Tetrahedron Lett. 1993,34, 1561).
References and Notes (1) Khambata, B. S.; Wassermann, A. Nature 1936, 137, 496. (2) Khambata, B. S.; Wassermann, A. Nature 1936, 138, 368. (3) Wassermann, A. J. Chem. Soc. 1936, 1028. (4) Wilson, M. A.; Pang, L. S.K.; Willett, G. D.; Fisher, K. J.; Dance, I. G. Carbon 1992,30,675. (5) Kroto, H. W.; Allaf, A. W.; Balm, S.P. Chem. Reu. 1991,91, 1213. (6) McLafferty, F. W., Ed. Acc. Chem. Res. 1992,25,98 (special issue). (7) Hammond, G. S., Kuck, V. J., Eds. Fullerenes, synthesis, properties and chemistry of large carbon clusters. ACS Symp. Ser. 1992, 481. (8) Kroto, H. W., Guest Ed. Special Issue on Fullerenes; Pergamon Press: New York; Carbon 1992, 30, 1139. (9) Wudl, F.; Hirsch, A.; Khemani, K. C.; Suzuki, T.; Allemand, P.-M.; Koch, A.; Edcert, H.; Srdanov, G.; Webb, H. M. Survey of Chemical Reactivity of Cm, electrophile and dieno-polarophile par excellence. In Hammond, G. S., Kuck, V. J., Eds. ACS Symp. Ser. 1992,481, 161-176. (10) Benford, G. A.; Khambata, B. S.; Wassermann, A. Nature 1937, 139, 669.
(1 1) Wassermann, A. Trans. Faraday SOC.1938,34, 128.
The Journal of Physical Chemistry, Vol. 97, No. 26, 1993 6763 (12) Hawkins, J. M.; Meyer, A.; Lewis, T. A.; Bunz, U.; Nunlist, R.; Ball, G. E.; Ebbesen, T. W.; Tanigaki, K. J . Am. Chem. Soc. 1992. 114, 7954. (13) Hawkins, J. M.; Meier, A.; Lewis, T. A.; Loren, S. D.; Hollander, F. J. Science 1992, 252, 312. (14) Hawkins, J. M.; Lewis, T. A,;Loren, S. D.; Meyer, A,; Heath, J. R.; Shibato, Y.; Saykally, R. J. J. Org. Chem. 1990, 55, 6250. (15) Hawkins, J. M. Acc. Chem. Res. 1992, 25, 150. (16) Hawkins, J. M.;Meyer, A.; Lewis, T. A,; Loren, S. Crystal Structure of Osmylated Cm. Confirmationof thesoccer-ballframework. In Hammond, G. S., Kuck, V. J., Eds. ACS Symp. Ser. 1992,481,91-103. (17) Fagan, P. J.; Calabrese, J. C.; Malone, B. Science 1991,252, 1160. (18) Fagan, P. J.; Calabrese, J. C.; Malone, B. The Chemical Nature of Cm as revealed by the synthesis of metal complexes. In Hammond, G.S., Kuck, V. J., Eds. ACS Symp. Ser. 1992, 481, 177-186. (19) Fagan, P. J.; Calabrese, J. C.; Malone, B. J. Am. Chem. Soc. 1991, 113,9408. (20) Balch, A. L.; Catalano, V. J.; Lee,J. W. Inorg. Chem. 1991,30,3980. (21) Koefcd, R. S.; Hudgens, M. F.; Shapley, J. R. J . Am. Chem. Soc. 1991, 113, 8957. (22) Haser, M.; Almlof, J.; Scuseria, G. E. Chem. Phys. Lett. 1991,187, 497. (23) Yannonni, C. S.; Bemier, P. P.; Bethune, D. S.;Meijer, G.; Salem, J. R. J. Am. Chem.Soc. 1991,113,3190. (24) David, W. I. F.;Ibberson, R. M.; Matthewmann, J. C.;Prassides, K.;
Dems, T. J. S.;Hare, J. P.; Kroto, H. W.; Taylor, R.; Walton, D. R. M. Nature 1991, 353, 147. (25) Liu, S.;Lu, Y.; Kappas, M. M.; Iben, J. A. Science 1991,254,408. (26) Hedberg, K.; Hedberg, L.; Bethune, D. S.;Brown, C. A,; Dom, H. C.; Johnson, R. D.; de Vries, M. Science 1991, 254,410. (27) Scuseri, G. E. Chem. Phys. Lett. 1991, 180,451. (28) Dunlop, B. I.; Brenner, D. W.; Mintmise, J. W.; Mowrey, R. C.; White, C. T. J. Phys. Chem. 1991, 95, 8737. (29) Bakowies, D.; Thiel, W. J. Am. Chem. Soc. 1991, 113,3704. (30) Fowler, P. W. Chem. Phys. Lett. 1986, 131,444. (31) Fuson, R. C. Reactions of Organic Compounds;J. Wiley and SOM: New York, 1962; pp 687699. (32) Pang, L. S.K.; Vassallo, A. M.; Wilson, M. A. Nature 1991, 353, 480. (33) Pang, L. S.K.; Vassallo, A. M.; Wilson, M. A. Energy Fuels 1992, 6, 176.
