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Generation of the Parent Allyl Cation in a Superacid Cryogenic Matrix.

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with strong illtramolecular hvdrogen bonding. but much
smaller upfield shifts of Phh4H and Fhh5H due to' reduced ring
current effects.
[I21 Repeated attempts to confirm helix formation in solution bvaddine chiral shift
reagents were unsuccessful. even at low temperature. presumably due to the
Past exchange between righr- and left-handed helical forms.
1131
. . H. Kessler. Anprw. C/ief?i.1982. 94. 509 - 520: AnFeil. Chrm. I n r . Ed. ENPI.
1982. 21. 512-523.
[14] Further details of the crystal structure investigations are vailable on request
from the Director of the Cambridge Crystallographic Data Centre, 12 Union
Road. GB-Cambridge CB2 1 EZ (UK). on quoting full journal citatlon.
1151 U. Rychleuska. M Gdaniec. Atra Cyrstullogr. Swt. B 1977. 33. 3555-3558;
B. Brrezmski. G Zundel. R . Krdmer. Clirvn. P/?IY.
L ~ r r1986.
.
124. 395-400.
Generation of the Parent Ally1 Cation in
a Superacid Cryogenic Matrix**
Fig. 2. X-ray strnctnre of 9. Left: front view: right. side view.
In summary, we have shown that a very simple series of anthranilic acid based subunits can be induced to take up, in both
the solution and solid state, a helical secondary structure stabilized in part by intramolecular hydrogen bonding. We are currently preparingextended and substituted versions of these scaffolds
to test the generality of the approach.
Received: August 24. 1Y93 [Z 6312 IE]
German version: A n g w . Cheni. 1994. 106. 465
[ l ] C . Brandon, J. Tooze. Inrrodutrion r o Prorcin Srrircrrir~~,
Garland. New York.
1991.
[2] A Family of novel polypeptide-like structures based on vinylogous amino acids
has recently been reported: M. Hagihara. N . J. Anthony. T. J. Stout. J. Clardy.
S. L. Schreiber. J. Am. Chrnr. Soc. 1992. 114. 6568-6570.
[3] Intramolecular hydrosen bonds have recently been used to control the striictnre of oligourea scaffolds. J. S. Nowick. N. A. Powell. E. J. Martinez, E M
Smith. G. Noronha. J. Org. C/imi. 1992, 57. 3763-3765. Bisacylguanidinium
receptors: R. P. Dixon. S. Geib. A. D. Hamilton, J. A m Cheni. Sot. 1992. 114.
365 367.
[4] M. Feigel, G. Lngert. J. Manero, M. Bremer. Z. Notrrrforsrk. B 1989, 44.
1109-1116: ;hid 1990. 45.258-266.
151 For a recent discussion of the role of intramolecular hydrogen bonding in a
family of simple diamides see: G. P. Dado, S. H. Gellman, J . 4 m Chern. Sot.
1993. 11s. 4228-4245.
161 A related approach has been used t o prepare cyclic anthranilainide oligomers:
a) A. Hoorfar. W. D. Ollis. J. F. Stoddart. Trri.ii/?rdronLrir. 1980, 421 1 -4214:
b) M. Feigel. G. Lugerr. Lwhigs Ann. Clieni. 1989. 1089-1092.
[7] Several helical structures stabilized by metal template effects have been reported: E. C. Constable. Aiigeii.. C/wn7. 1991. 103. 1530. Angeic. Clion. I n / . € d
En,?/. 1991. 30. 1490: U. Koert, M. M. Harding. J. M. Lehn. Nutirre 1990,346.
339: C. 0 . Dietich-Buchecker, J. Guilhem, C. Pascard. J.-P. Sauvage. Angew.
Cl~eni.1990, 102, 1202: Angel!.. Chwii. lnr. Ed. Engl. 1990. 2Y. 1154: E. C .
Constable. M. D. Ward. D. A . Tocher.1 Cliem. Sor. Drrlton T r u m 1991. 1675;
D. A. Evans. K. A. Woerpel. M . J. Scott, .4ngeii,. C/im7. 1992, 104. 439: Angriv.
C/KW.h t . ~ dEng/.
. 1992. 31. 430.
181 For examples of helical molecules stabilized by covalent interactions see: K.
Deshayes. R. D. Broene. 1. Chao. C. B. Knohler, F. Diederich. J Org. Cheni.
1991. 56.6787. and references therein; R. Fritsch. E. Hartmann. D. Andert. A.
Mannschreck. Chrfn. Ber. 1992. 125, 849; D. Gange, P. Magnus. L. Bass. E. V.
Arnold. J. Clardy. J Am. C h ~ n iS. O L .1980. 102. 2134
[9] The intramolecular hydrogen bonds of the simple 2.6-pyridinedicarboxamide
forming five-membered rings are expected to be weak due to the reduced
basicity of the pyridine [lo]. However. the conformation shown in 5 a is still
expected to be favored, since the alternative (nearly planar) conformations.
involving ~ 1 8 0rotation about one or both pyridine-CO bonds. should be
destabilized by electrostatic repnlsion between the pyridine N and carbonyl 0
atoms.
[lo] G. R. Newkome. F. Fronczek, D. K.Kohli. Acla Cri,ud/ogr. Secr. B 1981, 37.
2114; E. Weber. G. R. Newkome, F. Fronczek, S. Franken. JT Inclusion Phc,nom. 1988. 6, 1.
1111 See, for example: F. Garcia-Tellado, S . Goswami. S K.Chang. S. J. Geib.
A. D. Hamilton, J Am. Cheni. Sor. 1990. 112. 7393: S. Harema. R. J. Gaymans. A(.fu Crysrol/ogr. Swr. B 1977. 33, 3609.
Peter Buzek, Paul von R. Schleyer,* Hrvoj Vantik,
Zlatko Mihalic, and Jurgen Gauss
Although many substituted ally1 cations have been observed
as persistent species in superacid media,"] the parent allyl cation
(1) has remained elusive. The putative ' H N M R spectrum was
reported in the early days of superacid
but this
observation has not been cofirmed. Numerous subsequent atEvidently, the
tempts to obtain 'H and I3C spectra of 1
allyl precursors polymerized instead.
The direct observation of 1 in condensed phases is quite challenging, as this allyl cation is about 6 kcalmol-' less stable
therrnodynami~ally[~~
than the isopropyl cation, 2-C3H;, the
smallest carbocation persistent in superacid media (Scheme 1).
1
Scheme 1
While there were earlier indications of the formation of allyl
cation intermediates in zeolites,[61 the first direct CP-MAS
N M R spectroscopic observation (CP-MAS = cross polarization magic angle spinning) of 1 adsorbed on H-ZSM-5 zeolite
has only just been claimed by Biaglow, Gorte. and White
(BGW) .['I They employed allyl alcohol enriched at the hydroxylated carbon with I3C as the precursor and low surface coverage to minimize polymerization. Upon heating, a 13C N M R
[*I Prof. P. von R. Schleyer. Dr. P. Buzek
Institut fur Organische Chemie I der
Universitit Erlangen-N iirnberg
D-91054 Erlangen (FRG)
Telefax: Int. code (9131)859132
Dr. H. Vancik, Dr. 2 . Mihalic
Laboratory of Organic Chemistry and Biochemistry
University of Zagreb
Strossmayerov trg. 14. 41000 Zagreb (Croatia)
Dr. J. Gauss
lnstitut fur Physikalische Chemie der Universitit Karlsruhe
D-76128 Karlsruhe (FRG)
+
[**I
The work at Erlangen was supported by the Fonds der Chemischen Industrie,
the Stiftung Volkswagenwerk. the Deutsche Forscbungsgemeinschaft. and the
Convex Computer Corporation, at Zagreb by the Research Council of Croatia
(project: 1-07-226). and at Karlsruhe by the Fonds der Chemischen Industrie.
We appreciate the special efforts of Prof. H . 3 . Siehl, Martin Fuss, and Beruhard Miiller to observe the ally1 cation by NMR. Bernd Reindl performed the
geometry optimizations for several of the allyl cations in Table 1. In addition.
J. G. thanks Prof. Ahlrichs for his generosity and encouragement.
'-OH33!94i0404-044X 6 f(J.OO+ .25!0
A n g o r . Cl2ern. I n / . GI. D7gI. 1994. 33. No. 4
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signal at 6 = 218 appeared; this was assigned to C1 and C3 in
1, although other possibilities were discussed. However, this
chemical shift does not agree with 6(13C) = 245.7 predicted by
Schindler from IGLO chemical shift computations (Basis I11
level) for carbocations.[81The chemical shift of 6 = 21 8 is also
lower than a rough estimate (6 = 236) based on an extrapolation of the experimental I3C data for the methylene carbons in
the 1,l-dimethylallyl (6 = 274.3) and I-methylallyl (6 = 255.1)
cations.[']
This paper has several objectives. We first analyze BGW's
data in light of new theoretical results for the 13Cchemical shifts
obtained with the recently developed GIAO-MP2"' method
for calculating chemical shifts as a correlated level. These calculations, which are more accurate and reliable than the previous
SCF based calculations (IGLO['] or GIAO-SCF["]), cast
some doubt on BGW's suggestion that the zeolite species was a
free allyl cation. We then report our own direct observation of
the allyl cation (1) by infrared spectroscopy in a cryogenic
superacid matrix.
Schindler's TGLO I3C shifts for alkyl-substituted allyl
cations['] deviated significantly from the available experimental
values. (The IGLO data in Table 1 have been refined by using
the MP2;6-31
G * geometries, but d o not differ appreciably from
Schindler's.) Similar errors in 13C chemical shifts calculated at
Table 1 Calculated "C N M R chemical shifts of ally1 cations.
Cmpd.
1
C
Atom
c'1
c2
2
('1
C2
C3
3
CI
C2
CI'
C3
4
C.1
c2
5
6
CI'
c3
c4
r l
c2
C3
C1
c2
c3
c4
mean deviation
largest deviation
IGLO [a]
BasII
DZ
232.4
140.2
233.9
149.0
15.3
2576
140.6
216.4
31.8
274.3
137.1
192.X
37.4
29.7
239.0
139.4
28.1
240.8
133.6
36.6
29.6
k6.9
+17.8
241.0
148.2
241.0
162.4
18.4
267.2
146.9
222.0
33.9
285.7
142.3
198.8
39.0
31.7
249.2
144.4
30.6
254.5
135.8
38.9
32.4
k9.l
t23.8
GIAO-MBPT(2) [a]
dzpidz
tzp/dz
SCF
MP2
SCF
MP2
234.1
139.1
234.4
153.3
16.0
258.6
137.8
115.4
29.9
276.4
134.1
193.1
35.4
27.6
241.3
135.8
27.0
245.8
129.4
35.9
29.3
219.5
145.3
218.4
160.9
19.5
245.5
143.7
198.3
36.0
264.1
139.9
174.4
41.0
31.4
226.0
142.5
31.9
228.7
138.7
40.6
33.8
236.5
142.8
236.5
156.7
16.3
261.4
141.3
217.6
31.1
279.9
137.2
195.3
35.9
28.7
244.5
139.5
27.9
249.7
132.1
36.2
29.0
227.4
152.8
226.0
168.3
20.5
257.0
151.0
205.8
38.2
274.9
147.0
isi.1
42.5
33.7
233.9
150.3
33.7
239.0
145.3
42.0
34.5
29.1
+18.1
k4.1
-10.2
k9.2
+20.3
2 2.7
EXP. [bl
218
~
~
~
~
255.1
149.8
201.5
36.3
274.3
146.0
175.0
41.4
33.1
231.3
147.0
29.8
233.7
141.1
~
largest discrepancy is A6 = 24. The GIAO-MP2 performance is
superior. With the larger tzp/dz basis set (tzp = triple zeta
+ polarization, dz = double zeta), the average deviation is reduced to A6 = 2.7, and the largest discrepancy drops to A6 = 6.
3
A
,+.
A
4
3
4
5
6
At the higher tzp/dz level, CIAO-MP2 predicts 6 = 227.4 for
C1 and C3 of the allyl cation. BGW observed a signal at 6 = 21 8
in their solid-state zeolite N M R spectrum.['] While the difference is not large it is outside the error range found for the other
cations in Table 1. The experimental signal may be due to another species, or it may be displaced in the solid state, for example,
by complexation of the allyl cation with the zeolite (cf. ref. [15d]
for a more extreme example of the effects of complexation on
NMR spectra).
The recent development of cryogenic techniques for the determination of the vibrational spectra of carbocations under matrix conditionsl'*] prompted our reexamination of the problem.
Ally1 cation formation, rather than polymerization, might be
favored under the codeposition conditions, which ensure lower
concentrations, and the controlled gradual increase in temperature.
Moreover, computed a b initio IR spectra['31 (see, for example, Table 2 and the simulation in Figure 1 for I at CISD/631G**) provide a reliable basis for interpreting experimental
results. Such theoretical spectra predict that allyl cations have a
Table 2. Experimental and calculated (CISD/6-31G**) vibrational frequencies
[cm '1 of the ally1 cation 1
~
Experiment
Freq. [cm-'I
Int. [a]
Calculation
Freq. [cm-'1 [b] Int. [kmmol-'I
3117
3121. 3120
3083
3017, 3016
1558
1505
W
3033
1578
W
s
~
1418
1267
1249
vs
vs
S
~
SCF levels (e.g.. IGLO or GIAO) for unsaturated organic compounds are corrected at GIAO- MP2,[" which includes electron
correlation in a practical method for the computation of magnetic properties for the first time. Our recent application to the
benzenonium and the phenonium ions demonstrates the decisive improvements that are possible in unsaturated carbocations.l''] The agreement with the experimental data for the set
of four methyl-substituted allyl cations included in Table 1 is
improved similarly. The 13C chemical shifts at the IGLO-SCF
and GIAO- SCF levels differ by an average of A6 = 9.2, and the
\
Scheme 2. Structures of the allyl cations in Table 1, showing the numbering of the
C atoms.
~
[a] All ally1 cations were optimized at MP2(FULL)/6-31G*: 4. 5. 6 by Bernd
Reindl; for numbering of C atoms, see Scheme 2. [b] 1 : [7],3: [I g]; 4: [I f l , 5 : [I c];
6 : [I b]. [c] Averaged values for C l and C1' ( C , symmetry).
3
4
4
~
f6.1
2
1
1195
1074
1061
I043
957
928
845
814
m
m
m
m
m
m
m
m
1391
1265
1240
1120
19.4. 9.2
5.5
4.8, 1.6
280.2
10.8
153.1
4.2
72.5
0.0
Ass. [c]
Al. 8 2
A1
B2, A 1
B2
A1
82
Al
82
A2
~
1112
24.2
B1
1013
986
91 5
1.6
40.2
1.7
A1
B1
82
0.0
0.3
16.5
A2
A1
B1
-
613
425
298
[a] Intensities: vs (very strong), s (strong), m (medium), w (weak). [b] Calculated
frequencies scaled by 0.92. [c] Assignment of the vibrations (C2"symmetry).
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characteristic feature: an intense IR absorption near 1580 cm-'
attributable to the asymmetric allyl C-C-C stretching vibration.
We have reported an intense peak at 1581 cm-' for the trans-Imethylallyl cation generated from crotyl chloride under cryogenic
The MP2/6-31G* computed frequenwhen scaled by 0.94, was 1604 cm- Since the harmonic
approximation is employed,[131a b initio frequencies are systematically too high and are scaled to correspond with the anharmonic experimental values (see Table 2). The asymmetric
C-C-C stretching vibration of 1 is predicted to be 1592 cm-'
(MP2/6-31G*, scaled by 0.94) and 1558 cni-' (CISD/6-31G**,
scaled by 0.92).
'.
warming, and at 230 K both the 1547 cm-' and the 1577 cm-'
peaks are prominent (Fig. 2 b). This suggests that the allyl
cation formed first (1577cm-' peak) but then converted to
undefined products (1 547 cm- ;perhaps polymer) at the higher
temperatures. However, since the observed spectra (Fig. 2) have
many more peaks than are computed for the allyl cation
(Fig. l ) , oligomerization or other side reactions must have occurred even at the low temperatures.
Ally1 bromide gave analogous results in Zagreb. There was
also some evidence for the formation of the allyl cation indirectly
from trimethylsilyl propyne codeposited with a HBr/SbF, protonation medium. The initial IR spectrum at 77 K (displaying
the C = C stretching frequency of the precursor at 2184 cm-I),
underwent a number of changes on warming (details will be reported elsewhere). A transient signal at 201 7 cm- was assigned
to the Si-C hyperconjugatively ~tabilized"~]vinyl cation,
(CH,),SiCH=C+CH,. Above 180 K this peak disappeared, but
the spectrum, while still indicating some starting material, resembled Figure 2 b rather closely. Evidently, /I-elimination of
the SiMe, group (presumably as FSiMe,) from the starting material gave propyne, which, at least in part, was protonated
immediately in situ. and rearranged to the allyl cation 1. Nevertheless. attempts to prepare I directly by protonating propyne
failed to give any promising IR spectra.
In contrast to all these experiments, clean spectra were obtained in Erlangen by using cyclopropyl bromide as a precursor
for 1. Schleyer et al. had shown in 1969 that 1,3-dimethylallyl
cations could be generated stereospecifically from the 2,3dirnethylcyclopropyl chloride
Codeposition with
SbF, at 110 K results in an IR spectrum (Fig. 321) completely
different from the starting material. The prominant signal at
1578 cm-' already had been observed (at 1577 cm-', Fig. 2)
from the reaction of allyl chloride (and allyl bromide) with
SbF,. The intensity ofthe signals at 1578, 1418, and 1267 cm-'
increased when warmed to 140 K (cf. Fig. 3b), but additional
peaks at 966 and 901 cm-', due to some side product also arise.
At 250 K, the peak attributable to the asymmetric C-C-C
stretching vibration of 1 (1578 cm-') is almost completely replaced by a peak at 1535 cm-'.
'
'
I
0
4000
3500
-
3000
2500
2000
V
[ cm-'1
1500
1000
Fig 1 Simuldled IR spectrum of the ally1 cation (CISD 6-31G** level)
Different procedures and precursors were employed in attempts to prepare the parent allyl cation (1). The most obvious
way is to ionize allyl halides directly. In Erlangen. allyl chloride
was codeposited with SbF, in vacuo on a sodium chloride window at 130 K . Even at that temperature, new signals accompanied the allyl chloride spectrum, which was characterized by the
C = C stretching vibration at 1641 cm-'. Further changes occurred on warming to 170 K (Fig. 2 a). In particular, two signals
at 1577 (the more intense signal) and 1547 cm-' became
stronger as the 1641 cm-' peak first diminished and then disappeared. Other changes in the spectrum occurred on further
I00
t
15
T 1%)
49
24
4000
0
4000
3500
3000
2500
-
2000
1500
1000
4000
V
[cm
'1
Fig. 2. a) Experimental I R spectrum from ally1 chloride in an SbF, matrix at 170 K.
Note the peak for the allyl cation (1) at 1577 cm- '. Some "polymer" is present (e.g.
band at 1547 c m - ' ) b) Final spectrum a t 230 K. attributed t o "polymer".
450
(
-
3000
3500
VCH l+i.rlufi~yrwll\ihu// mhH 0-69451 W ~ I N I I C IIYY4
III
3500
-
3000
I 1
2500
V
2500
V
2000
[cm
1500
1000
1500
1000
'1
2000
[cm-'1
Fig. 3. a) Experimental IR spectrum of the ally1 cation (1) generated from cyclopropyl bromide in SbF, matrix at 110 K h) The spectrum at 140 K ; the new signals
at 966 and YO1 c m - ' are due to side products.
0570-0833 94/0404-0450 $ I U U O + 25 0
A n g m C h m Inr Ed Engl 1994, 33, hi0 4
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Angew. Chrm. I n / . Ed. Engl. 1990, 29, 183; c) P. Buzek, P. von R . Schleyer. S
Sieber. W. Koch, J. W de M. Carneiro, H. Vani-ik, D. E. Sunko. J. Chrm. S o ( .
Cheni. Comniun. 1991, 671; d ) P. Buzek. P von R. Schleyer, H. VanEik. D. E .
Sunko, rhid. 1991, 1538.
a) W. Hehre, L. Radom, P. von R. Schleyer, J. A. Pople. A h Inrrro M o k u l u r
Orbitui 717eori. Wiley. New York, 1986; b) B. A. Hess, Jr., L. J. Schaad. P
Carsky. R. Zahradnik. Chem. R e v 1986, 86. 709.
a) H. VanEik, V. Gabelica, D. E. Sunko. P. Burek. P. von R. Schleyer, J. Ph,w
Org. Chem. 1993. 6,421: b) W. Koch. B. Liu. D. J De Frees, J Am. ('hein. So<.
1988, i i o . 7325.
a) H:U. Siehl. F. P. Kaufmann, Y. Apeloig. V. Braude. D. Danovich. A .
Berndt, N. Stamatis, Angen.. Chem. 1991. 103, 1546. A n p . . Chem. In(. El/.
EngI. 1991, 30, 1479; b)G. A. MeGihbon, M. A. Brook, J. K . Terlouw. J.
Chem. Soc. Chrru Commun. 1992. 360; c) Y Apeloig in Th1, Chemrstri. of
Orgunic Sdrron Compounds (Eds.: S. Patai. 2.Rappaport); Wiley, Chichester.
1989; d) P. von R. Schleyer. P. Burek, T. Miiller, Y. Apeloig. H.-U. Siehl.
Angcw. Chrm. 1993, lf)S, 1558; A n p i . Chrm. I n / . Ed. Engl. 1993. 32, 1471
P. von R. Schleyer. T. M. Su, M. Saunders, J. C. Rosenfeld. J A m . Chern. So1
1969, 91. 5174.
It has not been possible t o observe the allyl cation by NMR starting with
cyclopropyl bromide. New experiments carried out at Tiibingen hy Prof H -U.
Siehl, Martin Fuss, and Bernhard Miiller using the matrix cocondensation
technique (ref. [I g] p. 31) only gave the broad, featureless spectra characteristlc
of polymers. The 'H N M R spectra were not clean enough to allow identification of signals expected for the allyl cation. N o peak near 6 = 227 in the j 3 ( 1
N M R spectrum. as predicted from CIAO-MP2 calculations tor I . could he
detected.
Very good agreement is found between the calculated and
experimental frequencies for 1 (Table 2). The graphical comparison (Fig. 4) demonstrates that the experimental frequencies
correspond excellently to the calculated values.
2500
t
s (exp)
[ cm
-' j
-
'OoO-
1500 1000
1000
I500
2000
S (calcd) [ cm -'I
2500
3000
+
Fig. 4. Correlation of the experimental and calculated (CISD,631G**) IR frequencies of the ally1 cation I . cc = correlation coefficient. rn = slope.
The allyl cation 1 is now the smallest long-lived carbocation
observable in a solid SbF, matrix. Our findings provide solid
evidence that the allyl cation was formed under cryogenic conditions by ionizing cyclopropyl bromide. Unlike the unsaturated
precursors of 1, cyclopropyl bromide evidently does not react
with 1 during generation. The IR asymmetic stretching vibration at about 1575 cm-' characterizes 1 as well as allyl cations
in general. Although accompanied by side reactions, 1 apparently also formed from allyl chloride and bromide, and possibly
BGW's NMR evidence
from trimethylsilylpropyne as
for 1 is equivocal. In light of the difference of A8 = 10 in the 13C
chemical shifts of the zeolite and the GIAO-MP2 I3C chemical
shifts, confirmation is desirable.
Received: April 14, 1992
Revised: August 31, 1993 [Z 5303 IE]
German version: Angen. Chem. 1994, 106, 470
[I] a) N. C. Deno in Curhonium Ions, Yo/. 2 (Ed.: G . A. Olah, P. von R. Schleyer),
Wiley-lnterscience, New York, 1970, Chapter 2; b) G. A. Olah. P. R. Clifford,
Y. Halpern, R. G. Johanson, J. Am. Chem. Soc. 1971, 93,4219; c) G. A. Olah,
R. J. Spear, ihid. 1975, 97, 1539. 1845; d) G . A. Olah, J. S. Staral, R. J. Spear,
97, 5489; e ) G . A. Olah, H . Mayr, ihid. 1976. 98, 7333;
f ) H. Mayr, G. A. Oiah. ;hid. 1977.99. 510; g) Mefhoden
Or-g. ('hem. (Houhen-Wed) 41h ed. 1952-, Bd. E19c, 1990.
[2] G. A. Olah, M. B. Comisarow, J. A m . Chem. Soc. 1964. 86. 5682.
[3] a) H.-U. Siehl, C. S. Yannoni. G. A. Olah, personal communication; b) P.
Vogel. Curhocurron Chemistrj,, Elsevier, Amsterdam, 1985, p. 173.
[4] a ) G . A. Olah, E. B. Baker. J. C. Evans, W. S. Tolgyesi, J. S. McIntyre, I. J.
Bastien, J. Am. Chem. Sot. 1964.86, 1360; b) W. Koch, P. von R. Schleyer. P.
Buzek. B. Liu, Croal. Chem. Actu 1992, 65. 655.
[5] S. G. Lias. J. E. Bartmess, J. F. Liebman, J. L. Holmes, R. D. Levin, G . Hallard,
J Phw. Chein. Ref. Dutu Suppl. 1988, 17, 1
[6] a) G . I. Hutchings, D. F. Lee, C. D. Williams, .lChrm. Soc. Chem. Cummun.
1990. 1475; b) E. J. Munson, T. Xu. J. F. Haw, ibid. 1973, 75.
[7] A. I . Biaglow. R. J. Corte, D. White, J. Chem. SOC.Chrrn. Commun. 1993, 1164.
[8] M Schindler, J. A m . Chem. Sot. 1987. 109. 1020. IGLO = Individual Gauges
for Localized Orbitals.
[9] a) J. Gauss. J. F. Stanton, R. J. Bartlett. Chem. P h w . Let/. 1992. 191, 614; J
Chcw. Plzw. 1993. 99. 3629. The (GIAO)-Gauge-Including Atomic Orbital
MP2-Programm has been implemented into the ACES I1 program system (J. F.
Stanton. J. Gauss, J. D. Watts, W. J. Lauderdale, R. J. Bartlett, Quantum Theory Project. University of Florida, Gainsville. 1992). h) Basis sets are given in:
A. Schifer. H Horn, R. Ahlrichs, J. Cheni. Phys. 1992, 97, 2571.
[lo] a) R. Ditchfield. Mol. Phvs. 1974, 27, 789; b) K. Wolinksi. J. E Hinton, P.
Pulay. J. Am. Chern. Sor. 1990, 112, 8251 ; c) M. HBser. R . Ahlrichs, H. P.
Baron, P. Weis. H. Horn, Theor. Chim. ACIU 1992, 83. 455.
[ l l ] S. Sieher. P. von R. Schleyer, J. Gauss, J. Am. Chem. Soc. 1993, 115, 6987.
[12] a) H. VanEik. D. E. Sunko. J. Am. Chem. Soc. 1989, 111. 3742; b) W. Koch, B.
Liu, D. J. DeFrees, D. E. Sunko. H. VanEik, Angew. Chem. 1990. 102, 198;
A i r g i , ~. ~Chmri. I n r . Ed. Enk.1. 1994, 33. N o . 4
Novel Conjunction of Hetero(macro)cycles
and a Pentamolybdodiphosphonate Cage**
Mark P. Lowe, Joyce C. Lockhart,* William Clegg,
and Kelly A. Fraser
Macrocycles having separate additional functionality are much
sought after for the development of supramolecular chemistry.[']
Polyoxometalates with separate, additional functionality are also
in demand in materials sciences for the development of difunctional catalystsr2]and a whole gamut of other applications.[31
The conjunction of these two major areas of current research has
been achieved with the synthesis of the first examples of polyoxomolybdate cages derivatized with hetero(macro)cycles. The
potential of these novel conjugates for a variety of applications
from catalysis to nuclear medicine is under investigation.
Incorporation of the heterocycles as their methylphosphonates was achieved by mixing phosphonate (1 or 2) and molybdate according to Equation (a) at pH 2-5. The mixture was
2 [C(NH,),]+
+ 2 ZP0,H + 5 MOO:- + 8 H' e
(a)
z+=1,2
heated to nearly boiling and allowed to cool slowly to give
colorless crystals suitable for X-ray ~rystallography.[~]
Since heterocycle Z has a protonated nitrogen atom, ZPO,H
is a zwitterion. The structure of [C(NH,),], [3] 3 H,O consists
["I
[**I
Dr. J. C. Lockhart, M. P. Lowe, Prof. W. Clegg, K . A. Fraser
Department of Chemistry, University of Newcastle
Newcastle-upon-Tyne, NE1 7RU ( U K )
Telefax: Int. code + (91)261-1182
This work was supported by the Science and Engineering Research Council
and Courtaulds Coatings PLC. We thank C. J. Matthews for preliminary
"P NMR measurements and a particularly careful referee for his helpful
comments.
VCH Vrr/u~sk.e.rr/l.rchrrft
mbH, D-69451 Weinhc~irn,1994
0S70-0833/94~0404-0481
8 10.00+ .28!0
45 1
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