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Heterotopic Host Molecules for Binding Two Different Guests.

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is nonetheless sufficient to accelerate S,2 reactions: C. L. Liotta, H. P.
Harris, J. Am. Chem. SOC.96 (1974) 2250.
[7] D. N. Reinhoudt, R. T. Gray, Tetrahedron Let/. 197S, 2105.
[8] When the suspension of K F in CH,CI, is allowed to react with 1,3-xylyl[2l]crown-6 1 b for several days under ultrasonication, the ‘H and I3C
NMR spectra of the solution show no evidence of binding of K@ions.
191 Since dative bonds are formed in the ate complexes, the usual values of the
bonding energies, which refer to diatomic molecules, cannot be used (cf. A.
Haaland, Angew. Chem. 101 (1989) 1017; Angew. Chem. In/. Ed. Engl. 28
(1989) 1010). The usual trend toward weaker bonding in the order
B-F > B-CI > B-Br > B-I probably still holds, however.
[lo] a) Tris(dimethy1amino)sulfonium fluoride reacts with 1 ,g-naphthalenediylbis(dimethy1borane) to form an adduct: H. E. Katz, J. Org. Chem. 50
(1985) 5027; b) [18]crown-6 binds the counterion of pentacoordinated i l icon compounds: J. L. Brefort, R. J. P. Corriu, B. J. L. Henner, W. W. C. W.
Chi Man, Organometallics 9 (1990) 2080.
[Ill The mixture containing the catechol ester of phenylboronic acid and 1,3xylyl[2l]crown-6 (1 b) also effects the dissolution of KF. The synergistic
effect, however, is smaller. For example, if adduct 4 a is allowed to react
with a 1:1 mixture containing 1b and the catechol ester of phenylhoronic
acid, an equilibrium is established in favor of 4 a (z70:30).
[I21 H. Noth, B. Wrackmeyer, NMR: Basic Princ. Prog. 14 (1978).
[I31 M. C. Fedarko, J Magn. Reson. 12 (1973) 30; D. Live. S. 1. Chan, J Am.
Chem. Soc. 98 (1976) 3769.
[14] Crystallographic data for 4a: (C,,H,,BFKO,, M,= 516.4): monoclinic,
space group P2,/n, a = 1022.8(2), b = 2075.7(4), c = 1238(2)pm, p =
106.05(3)”, Z = 4,
= 1.357 g ~ r n - ~
= 23.05 cm-’. Measurement carried out on an Enraf-Nonius CAD4 diffractometer (Cu,.
radiation, 1= 1.54184 A, graphite monochromator, room temperature);
2379 measured reflections, 2164 of which were independent (R,,,=
0.0355). 1893 with F > 3u(F) were regarded as observed. Solution by direct
methods and refinement with Semen’s-SHELXTL-PLUS(VMS) program
package, R = 0.0479, R, = 0.0355 (o= 1/u2(F)),all non-hydrogen atoms
anisotropically, H atoms “riding” with groupwise common isotropic temperature factors. Empirical correction of the measurement data with the
program DIFABS (N. Walker, D. Stuart, Acia Crystallogr. Sect. A 39
(1983) 158). Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technischeInformation mbH, W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD320264, the names of the authors, and the journal citation.
No complexation could be observed by NMR spectroscopy. This also
holds for samples heated under ultrasonification.
Why the soft anions do not bind to the hard boron in 3d-e is explained,
among other things, by the weak B-I- and B-S bonds as well as by possible
steric solvent effects.
In the case of KCN, complex 4 1 was formed in about 95% yield; in
addition, 5 % of a further, unidentified ate complex was obtained.
According to the NMR spectra, different adducts are formed during the
first hours of reaction. ‘H, I3C and IIB NMR spectra recorded after 10 d
show only the presence of 4a.
M. T. Reetz, C. M. Niemeyer, K. Harms, Angew. Chem. 103(1991) 1517;
Angew. Chem. Inr. Ed. Engl. 30 (1991) 1474.
work was motivated by the hope that compounds with one
acceptor site (e.g., a metal centerr3])and several donor sites
(e.g., ether functions) might be potential hosts for alcohols
and amines, because, after proton transfer, the alkoxide anion
and the ammonium cation could bond through reversible dative and hydrogen bonds, respectively (Scheme 1). Such bind-
Scheme 1. Simultaneous molecular recognition of amines and alcohols (M
metal center with empty orbital; D =donor site with occupied orbital).
ing would therefore involve heterotopic host molecules whose
Lewis acid/base property affects the equilibrium of the
Bronsted acid/base pair (alcohol and amine; see Scheme 1).
In an initial experiment the boron-containing crown ether
lr4I was allowed to react with a 1: 1 mixture of methanol and
benzylamine in dichloromethane. A spontaneous reaction
ensued, leading to the formation of 2. The assumption that
methoxide bonds to boron and the ammonium ion to the
crown ether moiety was supported by B, ‘H, and 13CNMR
PhCH&Tl& + C b O H
Heterotopic Host Molecules for Binding
Two Different Guests **
By Manfred T. Reetz,* Christof M . Niemeyer,
and Klaus Harms
An important aspect of host/guest chemistry is the simulation of biological systems.“] It is all the more surprising,
therefore, that practically no host molecules capable of
recognizing and binding two different organic guest molecules have been synthesized.[‘-31 Here we describe a new
concept of molecular recognition in which alcohols and
amines are recognized simultaneously and selectively. This
[*] Prof. Dr. M. T.Reetz [‘I, Dip1.-Chem. C. M. Niemeyer, Dr. K. Harms
Fachbereich Chemie der Universitat
Hans-Meerwein-Strasse, W-3550 Marburg (FRG)
[ ‘1 New address: Max-Planck-Institut fur Kohlenforschung
Kaiser-Wilhelm-Platz, W-4330 Mulheim a. d. Ruhr (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft (Leibniz Program) and the Fonds der Chemischen Industrie.
Verlagsgeselkchafl mbH, W-6940 Weinheim, 1991
The X-ray structure analysisr6]provided final confirmation and also brought to light some structural details. The
ammonium ion is completely embedded in the crown ether
moiety, as a space-filling picture reveals (Fig. 1b[’]). This
structural element is unique, since ammonium ions are usually situated “outside” the crown ether and form hydrogen
bonds to the ether oxygen
In this case, however,
the ammonium ion is drawn deeply into the host owing to
the formation of a hydrogen bond to the methoxide. The N
atom is located exactly in the average plane of the crown
ether atoms, the maximum deviation of the ring atoms being
f 0.8
This type of communication between the two
guests leads to a rotaxane-type structure.
To determine whether host 1 can distinguish
between different alcohols and amines, we first carried out competition
experiments involving benzylamine and, in each case, two
alcohol^.^^^ The results summarized in Table 1 establish that
steric factors are mainly responsible for the molecular recognition.“’] Thus, host can distinguish between
and ethanol (73 YOin favor of the methanol adduct). Control
0 5 7 0 - 0 8 3 3 ~ 9 l / l t l l - l 4 7 48 3.50+ .25/0
Angew. Chem. Ini. Ed. Engl. 30 (1991) No. 11
the IS-membered ring,'"] the amine selectivity turned out to
be significantly lower. In the case of methanol as the alcohol
component, for example, benzylamine is favored over umethylbenzylamine to the extent of only 80%.This has to do
with the fact that the ammonium ions cannot penetrate as
deeply into the smaller crown ether ring,['21as shown by the
result of the X-ray structure analysis of the ethanol/benzylamine adduct 4 (Fig. 2a).[l31Thus difference in steric interactions in the case of different amines is not as great as in the
case of the host 1. In contrast, alcohol selectivity is much
higher. In the case of benzylamine as the amine component
and methanol/ethanol as alcohols, methanol is complexed
exclusively!The smaller ring induces more steric shielding of
the boron (see Fig. 2 b). Further investigations, involving
Fig. 1. a) Asymmetric unit of 2 in the crystal. Boron, dotted; carbon, white;
oxygen, striped; nitrogen, black (H atoms only shown for ammonium ions).
b) Space-filling representation of 2 171. Boron, green: carbon. white; oxygen,
red; nitrogen. dark blue; hydrogen. light blue.
experiments show that the data were obtained under thermodynamic conditions. Although the exchange processes are
reversible, they are slow on the NMR time scale, and two
hostlguest compounds can be detected simultaneously by
NMR spectroscopy.
Table 1. Molecular recognition of alcohols by host 1 in the presence of benzylamine at room temperature [9].
Ratio of complex
93: 7
>97: < 3
Fig. 2. a) Asymmetric unit o f 4 (R = PhCH,, R = Et) in the crystal. b) Spacefilling representation of 4 [7]. Same notation as in Fig. 1 .
variation of the guests,['41the ligands on boron, the topology
of the cavity, and the metal, are in progress.
Received: July 26, 1991 [Z 4825 LEI
German version: Angew. Chem. 103 (1991) 1517
On the basis of the X-ray structure analysis of adduct 2
(Fig. l), we expected a high degree of molecular recognition
of amines. Indeed, competition experiments with the amine
pair benzylamine/a-methylbenzylamine and one alcohol
(methanol, ethanol, or isopropyl alcohol) show that, in each
case, only one host/guest1/guest2 combination is realized,
namely, l/benzylamine/alcohol.
When similar competition experiments were performed
with a smaller analogous host containing five oxygen atoms in
Angew. Chem. Inr. Ed. Engl. 30 (1991) No. 11
CAS Registry numbers:
1, 136426-45-4; 2, 136426-48-7; 2 . toluene, 136426-53-4; 3, 136426-46-5; 4,
[I] See, for example: F. Vogtle: Supramolekulare Chemie, Teubner, Stuttgart
1989; Supramolecular Chemistry, Wiley, Chichester. England 1991 ; D. J.
Cram, Angew. Chem. 100 (1988) 1041; Angew. Chem. Int. Ed. Engl. 27
(1988) 1009; J.-M. Lehn, ibid. 100 (1988) 91 and 27 (1988) 90; ibid. 102
(1990) 1347 and 29 (1990) 1304; F. Vogtle, E. Weber (Eds.): Hosl Guest
Complex Chemistry-Macrocycles, Springer, Berlin 1985; J. Rebek, Jr.,
Top. Curr. Chem. 149 (1988) 189; Angew. Chem. 102 (1990) 261; Angew.
Chem. Int. Ed. Engl. 29(1990) 245; E. Weber, J. Mol. Graphics 7(1989) 32;
R. M. Kellog, Angew. Chem. 96 (1984) 769; Angew. Chem. Int. Ed. Engl.
23 (1984) 782.
[2] Systems obtained by molecular biological techniques are not considered
here. Several host compounds that bind organic molecules and metal cations simultaneously are known: F. Diederich, M. R. Hester, M. A. Uyeki,
Angew. Chem. 100 (1988) 1775; Angew. Chem. In!. Ed. Engl. 27 (1988)
1705, and references cited therein; crystalline clathrate compounds with
several guests, such as alcohols: E. Weber, M. Hecker, 1. Csoregh, M.
Czugler, Mol. Cryst. Liq. Cryst. 187 (1990) 165; see also J. L. Atwood,
J. E. D. Davies, D. D. MacNicol (Eds.): Inclusion Compounds. Vol. 1-3,
Academic Press, London 1984.
[3] Host molecules with metal centers have been reported in recent years.
Examples include the following: a) compounds with two zinc-containing
porphyrin rings, which complex dipyridines and diamines: S. Kugimiya. J.
0 VCH VerlagsgesellschafimbH, W-6940 Weinheim, 1991
0570-0833i91j1111-1475 $3.50+ .25/0
Chem. Soc. Chem. Comniun. 1990, 432; H. L. Anderson, C. A. Hunter,
M. N. Meak, J. K. M. Sanders, J. Am. Chem. Soc. 112 (1990) 5780; b) metallomacrocycles, such as uranium-containing chelates, which form complexes with pyridines: A. R. van Doorn, M. Bos, S. Harkema, J. van
Eerden, W. Verboom, D. N. Reinhoudt, J. Org. Chem. 56 (1991) 2371;
c) numerous multidentate Lewis acids that bind two molecules of the same
kind. see, e.g.: B. Bachand, J. D. Wuest. Organometallics 10 (1991) 2015.
and references cited therein; d) Note added by the editorial staff See also
the communication by E Hawthorne et al. in this issue, in which a host
compound analogous to a [12]crown-4 with four Hg atoms is reported: X.
Yang, C. B. Knobler, M. F. Hawthorne, Angew. Chem. 103 (1991) 1519;
Angew. Chem. Inr. Ed. Engl. 30 (1991) 1507.
[4] In the preceding communication we describe the synthesis of the host
compound 1 as well as its ability to bind potassium salts, KX (X = F. CI,
Br, 1, SCN. CN, OCH,) selectively: M. T. Reetz, C. M. Niemeyer. K .
Harms, Angew. Chem. 103 (1991) 1515; Angew. Chem. Int. Ed. Engl. 30
(1991) 1472.
[S] The "B NMR spectrum (CD,CI,, BF,-ether as external standard) of 2
shows one signal at 6 = 9.0, a reliable indication of the presence of a
compound with tetracoordinated boron (41. The 'Hand I3C NMR spectra
exhibit chemical shifts characteristic of cation inclusion [4].
16) Crystallographic data for 2 toluene (C,,H,,BNO,, M, = 689.6): triclinic, space group P1,a = 1093.8(1), b = 1392.3(1), c = 1447.7(2) pm, c( =
101.16(1), /l = 109.52(1), 7 = 104.29(1)". Z = 2 , Q . . , . ~ = 1.193 gcrn--',
~(CU,,)= 6.42 cm-'. Measurement carried out on an Enraf-Nonius
= 1.54184 A, graphite monoCAD4 diffractometer (Cn,, radiation, i.
chromator, T = 190 K); 4666 measured reflections, 4404 of which are
independent (R,,, = 0.0185), 4081 with F > 4a(F) were regarded as observed. Solution by direct methods and refinement with the Siemens
SHELXTL-PLUS(VMS) program package, R = 0.0641, R, = 0.0797
(w = l/u'(F)); all non-hydrogen atoms refined anisotropically; N- and
0-bonded H atoms localized; the others "riding" with groupwise common
isotropic temperature factors. Further details of the crystal structure investigation are available on request from the Fachinformationszentrum
Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH,
W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository
number CSD-320298, the names of the authors. and the journal citation.
171 In order to generate the space-filling representation, the X-ray data were
processed on a Silicon graphics computer using the Sybyl program.
[8] See, e.g.: D. J. Cram, K. N. Trueblood. Top. Curr. Chern. 98 (1981) 43; I.
Goldberg in S. Patai, Z. Rappoport (Eds.): Crown Ethers and Analogs,
Wiley, Chichester, England 1989, p. 359.
[9] In a typical experiment, 0.1 mmol of host 1 and 0.1 mmol of an amine were
placed in 1 mL of dry CD,CI, at room temperature and treated with
0.2 mmol of each alcohol. The analysis was carried out by I3C NMR
spectroscopy at room temperature. When 1.3, or 5 mmol of the methanol/
ethanol pair was used, no change in the selectivity was observed. The
selectivities thereby obtained (Table 1) provide no information concerning
the absolute magnitudes of the binding constants, which are the subject of
a more detailed investigation.
1101 The equilibrium constants for the reaction of boranes and amines to form
borane/amine adducts were measured by Brown et al. and interpreted on
the basis of front strain: H. C. Brown, R. B. Johannesen, J. Am. Chem.
SOC.75 (1953) 16; H. C. Brown, Rec. Chem. Prog. 14 (1953) 83; Related
studies have recently been reported by Yamamoto et al. on this kind of
molecular recognition in the complexation of ethers and carbonyl compounds by bulky aluminum compounds: K. Marnoka, S. Nahahara, H.
Yamamoto. J. Am. Chem. Sor. 112(1990) 6115; K. Maruokoa, S. Nagahara. H. Yamamoto, Terruhedron Let[. 31 (1990) 5475.
[ll] The host was prepared in the same way as 2 [4].
1121 An indication of the weaker complexation is the fact that rapid exchange
processes are detectable by NMR spectroscopy for the ammonium components at room temperature. In this case the competition experiments were
therefore carried out at - 40°C.
[13] Crystallographicdata forl(C,,H,,BNO,, M, = 567S):monoclinic, space
group P2/n, a = 1535.9(3). b = 994.4(2). c = 2067.8(4) pm, /l = 105.55(3)",
Z = 4,
= 1.239 gcm-3. ~(CU,,)= 6.82 cm-'. Measurement carried
out on an Enraf-Nonius CAD4 diffractometer (Cu,, radiation, 2. =
1.54184 A, graphite monochromator, T = 190 K); 4290 measured reflections, 3830 of which were independent (& = 0.0660); 2605 with F >
4a(F) were regarded as observed. Solution by direct methods and refinement in Siemens SHELXTL-PLUS(VMS) program system, R = 0.0686,
R, = 0.0613 (w = l/u2(F)),all non-hydrogen atoms relined anisotropically; N-bonded H atoms localized; the others were refined using the riding
model with gronpwise common isotropic temperature factors. Further
details of the crystal structure determination are available on request from
the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, W-7514 Eggenstein-Leopoldshafen 2,
on quoting the depository number CSD-320335, the names of the authors,
and the journal citation.
[14] For example, host 1 can bind water and benzylamine in the same way as
2. Furthermore, preliminary experiments show that hosts form 1 : 1 inclusion complexes with amines and even ammonia.
VCH ~ ~ e r l u g s ~ e . ~mbH,
~ l l sW-6940
~ h ~ ~ Weinheim,
Naphtho[2,3-4 [1,2,3]oxadiazole**
By Achim Blocher and Klaus-Peter Zeller *
Dedicated to Professor Michael Hanack
on the occasion of his 60th birthday
The early history of "diazoanhydrides", obtained on diazotization of a-amino /?-keto esters and of o-aminophenols,
is marked by controversy over the constitution of these compounds.['] Much evidence initially favored the presence of
1,2,3-oxadiazoles of type 1 and 2, respectively. In the end,
however, the application of spectroscopic methods settled
this structural discussion in favor of the isomeric ct-diazo
carbonyl compounds 3 and the o-quionone diazides 4, respectiveIy.[21
R a ; 2
Only recently were Schulz and Schweigf3.41 able to detect
the formation of an equilibrium[5]between the parent compound, the o-quinone diazide 5, and its valence isomer, the
benzo[l,2,3]oxadiazole 6, in the gas phase and in nonpolar
solvents and thus provide the first experimental evidence for
the existence of this five-membered heterocycle.
- a"pr
The o-quinone diazide 8, expected on deprotonation of the
diazonium tetrafluoroborate 7,contains the o-quinone bismethide substructure A together with the o-quinonoid structural element B. On going to naphtho[2,3-d][1,2,3]oxadiazole
(9), both of these energetically unfavorable structures should
give way to the more stable naphthalene system. Thus, the
cyclization to 9 should be particularly favored.
We have carried out the deprotonation of 7[61on basic
alumina and sublimed the product (which is slightly colored
owing to impurities) at about 10°C under vacuum. The white
to pale lemon yellow solid thereby obtained is stable for
several days in the dark at - 20°C. Its spectroscopic data
[*I Prof. Dr. K.-P. Zeller, Dipl.-Chem. A. Blocher
lnstitut fur Organische Chemie der Universitat
Auf der Morgenstelle, W-7400 Tubingen (FRG)
[**I This work was supported by the Fonds der Cbemischen Industrie
0570-0N33/91/l/fl-1476S 3.50+.25/0
Angew. Chem. Ini. Ed. Engl. 30 ( 1 9 9 1 ) No. 11
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