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FullereneЦAcetylene Hybrids On the Way to Synthetic Molecular Carbon Allotropes.

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Crystal structure analyses: Cryatal data for 1 a (C,,H,,K,O,Fe):
monoclinic, P2,:
ti.
u =11.973(3). h =7.473(1). i =14.604(4) .&. [j = 95.?7(2) . Z = 2. V =
1301.1 A'. measurement temperature 150 ti. Mo,, radiation ( i = 0.71073 A). 28413
independent reflections. 2046 with / > 1.960(/). R = 0.065. w R 2 = 0.1689. structure solution by direct methods. refinement by full matrix least squares method on
F' (SHELXL 93) Crystal data for I b (C,,H,,N,O,PF,Fe):
monoclinic. C2:c.
~ = 1 7 4 3 0 ( 1 3 ) . h=17.746(9). c=10.l64(7),&. / l = l l 0 9 5 ( 5 ) , 2 = 4 . t ' =
2936.02 A'. measurement temperature 290 K. Mo,, radiation ( i = 0.71073 A).
2316 independent reflections. 1419 with I > 1.96n(I). R = 0.0479. i i K 2 = 0.1406,
structure solution by direct methods. refinement by full matrix least squares method
on F 2 (SHELXL 93). Further details of the crystal structure investigation may be
obtained from the Facliinforinations7eiitrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen ( F R G ) on quoting the depository numbers CSD-400554 ( l a ) and CSD400556 ( I b).
Received: January 14. 1994 [Z66181E]
German version: Angrit, Chrm. 1994, 106. 1424
[ I ) Y. Nishida. K. Hayashida. N . Oishi. S. Kida. Inorg. Cliinz. .4"a 1980. 38.
213-219: Y. Nishida. S. Kida, Coord. Chon. Rev. 1979, 27. 275-298.
[2] N. W. Alcock, W.-K. Lin. A . Jircinato. I. D . Mokren, P. W, R. Corfield. G.
Johnson. G Novotnak, C. Cairns, D. H . Busch. Inorg C'hrni. 1987, 26, 440
452; H . Okawa, D. H Busch. /bid. 1979. I#, 1555-1558.
[3] a ) E:G. Jiger, B. Schwseder, S. Radzuweit. Z. Chrm. 1988.28.152-153: E.-G.
Jhger. J. Liehr. E. Morich. A. Dix. Proc. Conf: C o o ~ dCliriii.
.
12th .Yfno/r/iic(~:
Bruti\/uvu. 1989. 123-128, E:G. Jiger. 2.C'h<mi.1985. 25. 446-447: b) E.-G.
Jhger. H Hhhnel. F. Klein, A. Schmidt. J. Prukt. Chr?ii.1991, 333, 423-430:
E -G. Jiger. H. Hdhnel. J /fiorg. B i o < h ~ w1991. 43. 305
[4] An attractive feature of l a . apart from it5 solubility in water and its IOU
tendency for association. is primarily the possibility of studying axial coordination by ligands [3] that usually lead to redox reactions with protein-free iron(111)
porphyrins. e.g.. cyanide or hydroxylamine: cf. D. W. Feng. M. D. Ryan. 1fiorg. Chetir. 1987. 26. 2480- 2483.
[ 5 ] T. Yainanaka in Mrra//u/J,oreifis.fid. 8 (Eds.: S. Otsuka. T. Yamanaka), Elsevier, Amsterdam. 1988. p. 134-139: \?! Cramer. J Whitmarsh. P Horton.
Porp/f.r.riri.s1Y78-1979 1979. 7 , 71-106: F.S. Mathews, E. W. Czerwinrki, P.
Argos. [hid 1979. 7. 107-147.
[6] J. D. Satterlee. M r r . / u ? i ~B d . sl,,\r. 1987. 21. 121 -185
[7] F. A. Walker, B. H. Huynh. W R. Scheidt. S. R. Osvath. J A m . C'heni. S o ( .
1986. 108. 5288-5297: W. R. Scheidt. D . M. Chipman, ihrd. 1986. 108. 1163
1167: M. ti Safo. G P. Gupta, C. T. Watson, U . Simonls, F. A. Walker. W. R
Scheidt. ihid 1992, 114. 7066-7075.
[XI W. R. Scheidl. Y. J. Lee. Strucr. BomUnfi f B w / i ? i )1987. 64. 1 -70.
[9] R. Quinn. J. S. Valentine. M . P. Byrn. C. E. Strouse. J. An?. Chem. Soc. 1987.
109, 3301 3308; S M . Soltis. C. E. Strouse, h i d . 1988, 110. 2824-2829.
[lo] F. A. Walker. U . Simonis, J A m Clirni. Soc. 1991. 113. 8652-8657: M. ti
Safo. G. P. Gupta. F. A . Walker, W. R. Scheidt, ihid. 1991. 113. 5497-5510.
[ l l ] M. K . Safo. W. R. Scheidt. G. P. Gupta. /frorg. C'hwi. 1990. 29, 626-633.
[12] F. A. Walker. U. Simonis, H . Zhang. J. M. Walker. T. Ruscitti. C. Kipp. M. A.
Amputch. B. V. Castillo. S. H. Cody, D. L. Wilson. R. E. Graul, G. J. Yong. K.
Tobin. J. T. West, B. A. Barichievich. New J C'lfrti?. 1992, 16. 609-620
113) ti. Hatano. M. K. Safo. F. A. Walker. W. R. Scheidt, Itiwx. C ' h m i . 1991. 30.
1643-1650.
[I41 E.-G. Jlger, B. tiirchhof. E. Schmidt. B. Remde. A. Kipke. R. Muller. Z.
Anorg. Allg. Clicm. 1982, 485. 141- 172
[15] H . GBrls. G . Reck. E:G. Jlger. K. Muller. D. Seidel, C r w . Rrs. k h r i o l . 1990,
25. 1277-1286: G Reck, G. Bannier, B. Heyn. E.-G Jiger. ibid. 1984, 19.
1603-1606: H. Elias. D. Heas, H. Paulus. E.-G. Jlger. F Grlfe. Z . Afiarg. A&.
Chetii. 1990. 58Y. 101-114.
[16] The imidazole ligands could stabilize their orientations in I b by x-donor
bonds. provided that the d,:, orbitals are higher in energy than the d,, orbital
and only sliphtly split in energy. This. however. should be evident in the ESR
spectrum [7] The bond lengths within the imidazole ririgsin 1 bare 1 "A, shorter
than those in 1 a (1.340(6) vs. 1.353(6) A). While this change is not significant
for the individual bonds. it is noteworthy and in agreement with x interactions
in 1 b that this shift occurs in the same direction for all bonds. In the iron(u)
complex 1 a no stabilization by rr-donor bonds is possible, and the sterically
most iivorable orientation. in the direction of the six-membered chelate rings.
is adopted.
[I71 E.-G. Jiger. H. Keutel. M. Rudolph. B. Krebs, F. Wiesemann. Chrni.Err..
submitted
[IS] E.-G. Jlger. E. Stein. F. Grlfe. W. Schade. Z. Afiorg. A& Chrm.1985. 526.
15-2X: E.-G Jiiger, Z.C l i ~ ~1968.
n . 8. 470.
[I91 H.-D. Hardt. W. MBller. 2. Anorg Allg. Chrm. 1961. 313. 57
Fullerene- Acetylene Hybrids: On the Way to
Synthetic Molecular Carbon Allotropes**
Harry L. Anderson, Rudiger Faust, Yves R u b i n ,
and Franqois Diederich*
Our interest in carbon-rich materials"] has prompted us to
explore routes to molecular carbon allotropes based on both
fullerenes and acetylenes. Among the attractive targets are the
cyclic polyynes 1 and 2 in which peripheral C,, spheres stabilize
a central acetylenic core through steric shielding and interact
with this core through the cyclopropane rings. Related macrocyclic polyynes have been reported.['. '] but "end-capping" with
methanofullerenes would avoid the incorporation of heteroatoms and yield new types of carbon allotropes.
~
1
2
A common precursor for compounds 1 and 2 is diethynylmethanofullerene 3[31from which the desired acetylenic carbocycles could be assembled by oxidative coupling. In light of the
radical-trapping properties of C,, ,[41 the viability of such a reaction for coupling
fullerene derivatives was questionable.
Here we describe the first steps towards
H
the construction of 1 and 2, namely two syn\ 1,
thetic entries to symmetrically and unsym3
metrically substituted diethynylmethanofullerenes, as well as the previously unknown hydroethynylation of
C,, leading to 4 (Scheme l).[51
The formation of bis(butadiyny1)methanofullerene 5 (Scheme 3 ) and the dumbbell-shaped
e
1 . Me3Si-C-C-Li,
PhMe, 20°C, 1 h
2.HOAc
)=
a
c60
58%
'SiMe3
4
Scheme 1 . Synthesis of the hydroethynylated fullerene 4
[*] Prof. Dr. F. Diederich. Dr. H . L. Anderson, Dr. R Faust
Laboratorium fur Organische Chemie. ETH Zentrum
Universithtstrasse 16. CH-8092 Ztirich (Switzerland)
Telefax. fnt. code + (1)261-3524
Prof. Dr. Y. Rubin
Department of Chemistry and Biochemistry
University of California at Los Angeles
[**I This work was supported by the Schweizerische Nationalfonds zur Forderung
der wissenschaftlichen Forschung. H. L. A. thanks the Science and Engineering
Research Council ( U K ) for a postdoctoral research fellowship.
0570-0X33/94:1313-1366 B 10.00+ .25V
4ngcu. Cheni. /nr. Ed. Engl. 1994. 33, No. 13
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derivative 6 (Scheme 4) under Hay coupling conditions demonstrates the feasibility of the proposed route to the new allotropes
1 and 2.
Nucleophilic addition to C,, is among the most common
reaction types in fullerene
'I Surprisingly, the use of
acetylide nucleophiles has not previously been reported. Initial
attempts to react C,, with chloromagnesium acetylide failed,
and no reaction was observed in toluene at room temperature,
even with a large excess of the nucleophile. Lithium trimethylsilylacetylide, on the other hand, reacted with the fullerene under these conditions to produce 4 upon quenching with acetic
acid (Scheme 1). This reaction proceeded much slower than the
addition of aromatic or aliphatic organolithium and Grignard
reagents."] The structure of 4 is evident from its spectral data
(Table 1 ) ; the characteristic ' H NMR resonance at 6 = 6.92 corresponds to the fullerene proton. The addition proceeds in a 1,2
fashion across the junction of two six-membered rings, as
judged by the 32 distinct fullerene resonances in the 13C N M R
spectrum of 4. The signals of the newly formed sp3 carbon
centers appear at 6 = 61.8 (C,,,-H) and 6 = 55.1 (Csp3-Csp).
Evidently, the successful synthesis of 4 suggests a new entry into
mixed fullerene-acetylene molecular scaffolding.[' b. 'I
Rubin et al.I3]recently prepared symmetrically protected bis(trimethylsilylethynyl)methanofullerene[60] by reacting C,,
with carbenes derived from the tosylhydrazone of 1,5-bis(trimethylsily1)-I.4-pentadiyn-3-one.['l We applied this methodology
to obtain the unsymmetrically protected species 7 in 28 % yield
(Scheme 2). We also explored an ionic route to diethynylmeth-
anofullerenes inspired by Bingel's recent report1g1that fullerenes
can be cyclopropanated by x-halocarbonyl compounds in the
presence of base. We found that bromopentadiyne 8[lo1reacts
with C,, to form bis(trimethylsi1ylethynyl)methanofullerene 9
in 55 % yield (Scheme 2) in the presence of 1.8-diazabicyclo[5.4.0]undec-7-ene (DBU). Since the pK, of 8 is probably less
than 21 (in EtOH),["] it should be acidic enough to be deprotonated by DBU (pK, = 24.3 in MeCN) .I1*]Alternatively DBU
could react as a nucleophile and displace bromide from 8 to give
a more acidic salt,1131which would be deprotonated to form an
ylid, which could attack C,,.
NNLiTs
I
K2C03
c60
8
7 (R = SiMes, 28%)
10 (R = H, 64%)
9 (R = SiMe3, 55%)
K2C03
Scheme 2 Syntheses of diethynylmethanofullerenes. Ts
Table I. Selected physical data of 4-7 and 10 [a]
c
L
3(R=H,89%)
= p-tosbl.
4: FT-IR: i. = 2951 (w). 2155 (w). 839 (s). 526 (s) cm-'. ' H N M R (CS,): 6 = 6.92
( s , 1 H ) . 0.37( 5 . 9 H). "CNMR(CS,): 6 =150.98, 150.77,147.22,146.96,346.30.
The silyl groups in 7 and 9 greatly enhance the solubility of
these fullerene derivatives in common organic solvents (THF,
hexane, aromatic hydrocarbons), which facilitates their spectroscopic characterization (Table 1). Both cyclopropanations occur at the 6,6 ring junction leading to structures with closed
C,,H,,,Si.
transannular bonds.['41 In the 13C NMR spectra all 16 C,,,
5 : FT-IR. i = 2953 (m). 2894 ( w ) . 2222 (w). 2105 (m),1248 (s), 844 (s), 526 (s)
fullerene resonances expected for 9 (C2,,symmetry) are well
em-' ' H NMR (CS2): 6 = 0.24(s). I3C N M R (CS,): 6 = 145.10,
145.08,145.03.
resolved between 6 = 147 and 6 = 139, while only 28 out of the
144.84.144.74,144.70.144.40,143.82. 143.70,142.71.142.68.142.53,142.04,
74.41,70.88.68.62.
27.23.-0.65. UViVIS:i,,,
141.76.140.89. 138.84.89.32.87.57,
31 C,p3resonances are clearly discernible for 7 with C, symmetry.
[nm] = 256 ( I : 127000).329 (40700).435 (2190).487 (1580), 687 (170).FAB-MS:
Diagnostic for both compounds are the resonances of the methI J I , ~ : 976 I (M ' ) 720.0
~
(C6J. Satisf'nctory C,H analysis for C,,H,,Si,.
ano bridge C atoms at 6 = 32.24 (7) and 6 = 27.91 (9), along
6 : FT-IR. i= 2933 (s). 2856 (s), 2167 (w). 1456 (m),1422 (m), 878 (m).678 (m).
with their respective bridgehead carbon signals at 6 = 75.98 (7)
522 ( s J cin-'. ' H N M R (CS,/C,D,): 6 =1.14 (s). "C N M R (CS2;C,D,):
and 6 = 76.04 (9).
6 =14S.Y2.145.76,145.73.145.71,145.70( 2 x ) . 145.68,145.67,145.39,145.30,
145.24.145.01.144.97.144.95.144.90,144.30.144.28,143.32.143.31.143.28,
Protodesilylation of 7 and 9 is rapidly effected by K,CO, in
143.27.143.19.13.3.08, 142.76.142.39.142.34.141.53.141.39,139.55.139.35,97.20,
MeOH/THF to generate regioselectively deprotected 10 and the
8X.YO.75.31.73.9S.69.72.28.61,19.18.11.9X.UV~VIS:i.,,,[nm]=256(c310000),
parent hydrocarbon 3.I3I The NMR signals of the acetylenic
330 (37200).434 (2300),483 (1600).687(200).MALDI-TOF-MS (2.5-dihydroxyprotons appear at 6 = 2.87 (3) and 6 = 2.88 (10, Table 1).
benroic :icid m a t r i x ) : m'; 1877.6( M - ) , 722.03(Ce0).
In order to probe the potential of diethynylmethanofullerenes
7 : FT-IR. i = 2929 (s). 2856 (s). 2167 (w). 1461 (m),1422 (m), 1248 (m). X43 (m).
525 (s) cin-'. ' H N M R (CDCI,): 6=1.19 (s, 21 H), 0.33(s, 9 H). I3C NMR
as building blocks for molecular carbon allotropes, LO and 3 were
(CDC'I,):0 =146.41.146.24.145.74.
145.67.145.38,145.37.145.36,145.05,
144.85.
subjected to Hay coupling conditions (Schemes 3 and 4). Initial
144.81.144.75. 144.70.144.02,144.01,142.99,142.96.142.95,142.93,142.88.
attempts at homocoupling of 3 did not yield tractable products,
142.86.141.36.142.23.142.10.142.09.141.05.141.02,139.24.139.00.98.1X,97.25,
which prompted us to try heterocoupling to trimethylsilylacet90.69.87.32.75.58.32.24,18.60.11.34,
0.00. UViVIS:i,,, [nm] = 258 ( E 107000).
329 ( 3 5 5 0 0 ) . 436 (2200). 488 (1500).687(100).FAB-MS: m;; 1011.0(Mi).
720.0
ylene under conditions previously developed for the preparation
146.06.146.04. 145.88.145.87.145.43,145.36.145.31.145.17.145.08.145.01,
144.34.144.17,142.81.142.29.142.25.141.75.141.72.141.70.141.51. 141.36,
141.31.140 04,140.02.
135.73.134.74,107.33.88.15.61.82.55.10,-0.04.UV;VIS:
[nm] = 256 (i:l04000).306 (31 200), 327 (32500).404(4270).431 (3240).701
(260) I-AB-MS: I W ; 818.9 ( M i ) . 719.8 (C6"). Satisfactory C.H analysis for
(C,,,,).
LO: FT-IR: i,= 32239(m),2922(s). 2856(s). 2167 (w). 2119 (w). 1456(m),1422(m),
672 ( m l . 522 ( s ) cm-'. ' H N M R (CDCI,): 6 = 2.88 (s. 1 H). 1.20(s. 21 H). " C
NMR (CS,:C,D,): 6 =146.21.146.12.145.78.145.65(several overlapping peaks).
145.30.145.19.145.15.144.97.144.89.144.28.144.26.143.28(severat overlapping
peaks). 143.18.142.61.142.41,142.36.142.34.141.3X.141.36,139.42.9821.87.61.
76.47,74.94.73.35.29.51.1X.95.11.66.UV/VIS:
[nm] = 258 (c 148000). 328
145700).406(4700).434(3200).493 (2200).688 (890).FAB-MS: rn;;939.0(M ').
719.8(Ch,,).
[a] 'H and I3C NMR spectra were measured at 500 MHz and 125.8 MHz, respectively: IR and UV:VIS spectra were recorded in KBr and CH,CI,. respectively.
Aiycii
CIi(wi. I f i f Ed. Digl. 1994, 33. No. 13
Me3Si-CS-H.
CuCI, TMEDA. PhCl
-
H
3
02,20"C, 1 h
29%
5
Scheme 3. Synthesis of dibutadiynylmethanofullerene5. TMEDA
tetramet hylethylenediamine.
VCH Verlu~.s~e.\cll.scliu/f
m h H . 0-69451 U'rmhr,irn, 1994
0570-0833i9411313-1367 $ 10.00f.25'0
=
hi,N,N.N'-
1367
COMMUNICATIONS
of butadiynyl porphyrins.["I In situ preparation of the Hay
catalyst [CuCl.TMEDA, O,] in chlorobenzene in the presence
of 3 and a large excess of trimethylsilylacetylene indeed furnished bis(butadiyny1)methanofullerene 5, which was readily
isolated by column chromatography (SiO,, cyclohexane). The
butadiynyl substructure of 5 is easily identified in its 13CN M R
spectrum by the four resonances observed in the typical range
for acetylenic carbon atoms (6 = 89.32. 87.57. 70.88. and 68.62:
Table I ) . A total of 17 distinct fullerene carbon signals (1 6 between 6 = 146 and 138. one at 6 =74.41) indicates no change of
symmetry on passing from 3 to 5. which demonstrates that the
methanofullerene moiety remains intact in the course of the
coupling reaction.
Similarly, monoprotected diethynylmethanofullerene 10 could
be homocoupled to the butadiynyl-linked "dimeric" methanofullerene 6 in 37% yield (Scheme 4). In contrast to previously
10
two fullerene units. The electrochemistry of this material is currently under investigation, and we are working on transforming
5 and 6 into new molecular carbon allotropes.
Exprriiwntnl Procedure
4 : A solution of C,,, (500 mg. 0.695 mniol) in toluene (600 m L ) was treated with
lithium ti-imeth~lsilylacetylide(10 mL of 0 . 2 solution
~
in THF. 2.0 mmol) under
N 2 The purple solution slowly discolored. and a black precipitate formcd. After 1 11
thin-layer chromatography (TLC) shobed that most of the C,, had been consumed.
so the ieaction was quenched with acetic acid (0.5 mL). The product \bas isolated
by column chromatograph) (S
Et,O yielded 374 mg (58%) of
e ) . and recrystallization from CS,
9: DBU (300 pL, 2.01 mmoli was added under N 1 to a solution of C,,, (500 mg.
0 694 mmol) and 8 (400 mg. 1.39 mmol) in toluene (550 mL). After 4 h the product
was icolated by coluinii chromatography (Si02:cyclohexane). The product was
recrystalllccd from cyclohexane to yield 305 mg (47% o r 55% based on recovered
skirting material) o f large black cubic crysrals
10: To a solution of 7 (176ing. 0 125 mmol) in T H F (50inL) was added MeOH
(25 mL) and K,CO, (50 mg,0.362 mmol). After 20 min a t room temperature the
reaction was complete by TLC. The suspension was partitioned between toluene
(100mL) and H,O (100mL). and the organic phase was washed with H,O
(3 x 20 mL) and dried over MgSO,. Filtration and removal of solvent left a red solid
that was loaded o n a short column o f silica and eluted with hexane. Evaporation of
solvent furnished a black material that was recrystallized from CS2:Et,0 to yield
75 ing (64O,'0) of bronLe flakes.
6: A suspeiision of 10 (70 mg. 0.075 minol) and CuCl (600 mg, 6.0 mmol) in
chlorobenzene (I00inL) was srirrrd vigorously with TMEDA (0.85 mL. 5.5 mmol)
under dry air for 8 h. The product was isolated by column chromatography (SiO,:
cyclohexane). and recrystallization from CS,'Et,O furnished 26 mg (37 X ) of black.
shiny plates.
6
Scheme 4. Synthesis of the dumbbell-shaped fullerene derivative 6
Received: March 7. 1994 [Z6735IE]
German version: Angcir. C/irm. 1994. 106. 1427
reported dumbbell-shaped molecules containing two fullerene
moieties,["] the black shiny crystals of 6 are reasonably soluble
in cyclohexane. toluene. and CS, . and complete spectroscopic
characterization was possible (Table 1, Fig. 1 ) . Matrix-assisted
I
140
120
100
80
-6
60
40
20
Fig. 1 . "CCNMR spectrum o f 6 in CS,:C,D,. The inset shows an expansion ofthe
aromatic rcsion of the fullerene sigii;ils.
laser-desorption time-of-flight (MALDI-TOF) mass spectrometry in the negative-ion mode with 2.5-dihydroxybenzoic acid as
the matrix confirmed the "dimeric" nature of 6 with a signal at
1877.6 (C,,,H,ZSi,; calculated 1876.1 gmol-'). In the 13C
NMR spectrum (Fig. 1) 31 fullerene resonances are distinguishable (30 in the aromatic region, one at 6 = 73.95). The signals of
the four acetylenic carbon atoms appear at 6 = 97.20, 88.90,
75.31, and 69.72, while the methano bridge C atoms resonate at
6 = 28.61. The electronic absorption spectrum is remarkably
similar in shape and intensity to those of other methanofullere n e ~ , [which
' ~ ~ indicates little electronic interaction between the
0
a ) F. Diederich. Y. Rubin. A I T ~ P I C
I . h. i n . 1992, 104. 1123-1 146. Anyrii..
Chem
Ed. EtigI. 1992. 31. 1101 1123: b) F. Diederich. Nurure /London),
1994. 36Y. 199-207.
A. de Meijere. S. Kozkushkov. C. Puls. T. Haumann. R. Boese. M. J. Cooney.
L. Scott. A n p x . Cheni 1994. 106.934-936: A n g w . Chem. Int. Ed. Engl. 1994,
33. 869-871.
Y:Z. An, Y. Rubin. C. Schaller, S. W. McElvany, J. Org. Chem., 1994, 59,
2927 -2429.
P. 1. Krusic, E. Wasserman, P N Keizer. J. R. Morton. K. F. Preston. Science
i Wu.shinyronJ 1991.254. 1183- 1 1 85: P. J. Krusic. E. Wasserman, B. A. Parkinson. B. Malone, P. N . Keizer. J. R. Morton, K . F. Preston. J. h i . Clzem. Soc.
1991, 113, 6214-6275: C. McEwen. R. McKay. B. Larsen. ;hid. 1992. 114.
4412 4414: J. R. Morton, K . F. Preston. P. J. Krusic. S. A. Hill, E. Wasserman. ihrrl. 1992, 114. 5454-5455. M. A. Cremonini. L. Lunazzi. G. Placucci.
J. Org. Cheni. 1993. 58. 4735-4138.
A. Hirsch. A. Sol. H. R. Karfunkel. Angeii,.C h m . 1992. 104. 808-810: Angew
Cl~eni.Inr. Ed. Enyl. 1992. 31, 766-768.
R. Taylor, D. R. M . Walton, Norrrre (London) 1993, 363. 685-693; A. Hirsch,
.4ng~'.C/imi. 1993. 105. 1189- 1192: A n g e ~C/iwi. Inr. Ed. Engl. 1993. 32,
1138-1141: K.-D. Kampe.N. Egger,M.Vogel,ihid.1993,105.1203- 1205and
1993. 32. 1174-1176: A. Hirsch. C/im?. (/n.seriw Zeit 1994. 28. 79-87.
R. H. Baughman. D. S. Galvtio. C. Cui, Y. Wang. D. Tomanek, Ciwrii P I i w
Lt>fr 1993. 204. X 14.
H. H'iuptmann. fi,tru/idrori 1976. 32. 1293 1297.
C. Bingel. Chrn?. Bpi. 1993. 126. 1957-1959.
H. Hauptinann. I i ~ r r u h r r l r o nLfrr. 1974. 3587-3588.
The pKa for the methylene protons of nonhalogenated 1.4-pentadiynes has
been estimated to he less than 21 (in EtOH), I. M. Mathai, H. Taniguchi, S. 1.
Miller. 1 Am. C I I E ISOC.
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synthetic, allotropic, fullereneцacetylene, hybrid, molecular, way, carbon
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