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Host-Guest Complexes with Closed Half-open and Stretched Receptors Hydrophobic Cavity Effects and Induced Pole-Dipole Interactions.

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Host-Guest Complexes with Closed, Half-open,
and Stretched Receptors: Hydrophobic Cavity
Effects and Induced Pole-Dipole Interactions**
Table 1. FreecomplexationenthalpiesAG"[kJmol-']at 25"Cforcomplexesof
1-3 with 4-9. Standard deviation f0.2 kJmol-'.
By Hans-Jorg Schneider,* Thomas Blatter,
and Patrick Zimmermann
Lipophilic receptor cavities are an essential element for
molecular recognition and the binding of unpolar substrates
in aqueous solution."] We report here on the experimental
differentiation of the underlying hydrophobic effects and
van-der-Waals interactions by binding studies with closed,
half-open, and stretched host compounds (Scheme 1). These
studies also emphasize the exceptional properties of water,
Scheme 1. Schematic diagram of closed (A), half-open(B), and stretched host
compounds (C).
which can scarcely give rise to entropically determined interactions in complexes with the open structures 2 ( & B) and 3
(P C)."'
The marked complexation of aromatic hydrocarbons
compared to aliphatic substrates by azoniacyclophanes of
type 1 12. and the pronounced decrease in binding upon re-
moval of positively charged nitrogen atoms from the cavityt3b1 can be explained both by electrostatic interactions between the N@ units and the quadrupoles of aromatic substrates as well as by the induction of a dipole in the
complexed arene
The observation that di-
Prof. Dr. H.-I. Schneider, Dip].-Chem. T. Blatter, P. Zimmermann
Fachrichtung Organische Chemie der Universitat
D-6600 Saarbriicken 11 (FRG)
Host-Guest Chemistry, Part 25.This work was supported by the Deutsche
Forschungsgemeinschaftand the Fonds der Chemischen 1ndustrie.-Part
24:H.-J. Schneider,D. Ruf, Angew. Chem. 102 (1990) 1192;Angew. Chem.
Int. Ed. Engl. 29(1990) 1159.
Angew. Chem. Znt. Ed. Engl. 29 (1990) No. 10
0 VCH &rlagsgesellschaft
[a] In CD,OD/D,O (S/95,vol/vol). [b] In CD,OD:D,O (10190, vol/voi). [c] In
CD,OD/D,O (20/80, vol/vol).
iodomethane 8, in contrast to dichloromethane 9, forms a
complex with 1 (Table 1) now reveals the dominance of the
second effect, for iodine has an especially easily polarizable
electron cloud. The dependence of the complexation constants of 1 and lipophilic substrates on the water content of
the solution gave values which approach those observed in
corresponding studies with cyclodextrins:[3 the hydrophobic effect in the case of the dominating Ne-arene interactions discussed here is thus due to the fact that the polarizability of water is much lower than that of substrates such as
With the host compound 2, a complexation with a halfopen receptor is observed-to our knowledge for the first
time-which is analogous to that of a macrocyclic host
(Table I). Molecular mechanics simulations demonstrate
that the polarizable substrate moieties can, especially in the
complexes with 6,7 and 8, assume an almost ideal position
with respect to the inducing Ne-pole (Fig. 1a, b). From the
Fig. 1. Space-filling models (from CHARMM/QUANTA simulations) of the
complexes 2 ' 6 (a), 2 ' 8 (b) and 3 ' 5 (c). The optimum position of the polarized
phenyl ring (a) and iodine atoms (b) with respect to the inducing N" of the
receptor 2 is clearly recognizable.
measured complexation enthalpies an average value of
AG,,,x x 3 kJmol-' can be calculated for the interaction
between a phenyl ring and an Ne-charge. This value is in
satisfactory agreement with previously assumed
similar order of magnitude is found for the complexation
enthalpy even with the stretched receptor 3 (Table 1). The
somewhat lower values can be explained in terms of a rather
poor fit (cf. Fig. 1c) (charge transfer contributions to these
complexes are relatively small, as shown by a comparison of
structurally similar ion-pair complexes[@).
The enthalpies of free binding the substrates 4 and 6-8 in
the macrocyclic host 1 are in each case about 7 kJmol-'
higher than in the half-open analogue 2 (Table 1). The reason
for this surprisingly constant difference can be entropic effects, or the unfavorable enthalpy of water molecules, which
can form fewer hydrogen bridges inside than outside of the
receptor cavity.['] Molecular mechanics simulations of 1 in a
water box using the CHARMM programfS1show that the
azoniacyclophane 1 in fact contains about five water
molecules in or near the cavity, which altogether participate
in only about five hydrogen bridges (Fig. 2); water molecules
mbH, 0-6940 Weinheim, 1990
of novel organic materials with specific properties by incorporating classical structural building blocks into macrocyclic
systems, and we now report on the configurationally and
conformationally stiffened cyclopolyenes 1 and 2.
Fig. 2. Molecular structure obtained from CHARMMiQUANTA simulations
for the azoniacyclophane 1 with five water molecules in the cavity; hydrogen
bridges in the cavity are indicated by dotted lines.
a: R =H ; b:R=CH,
outside of the cavity, on the other hand, are stabilized by an
average of four bridges per molecule.
Received: June 25, 1990 [Z 4035 IE]
German version: Angew. Chem. 102 (1990) 1194
111 See, e.g., W. P. Jencks: Catalysts in Chemistry and Enzymology, McGraw-
Hill, New York 1969.
[2] Cf. K. Odashima, K. Koga in P. M. Kuhn, S. M. Rosenfeld (Eds.): Cyclophanes. Vol. 2, Academic Press, New York 1983, pp. 629-677.
[3] a) H.-J. Schneider, R. Kramer, S. Simova, U. Schneider, J. Am. Chem. Sot.
I10 (1988) 6442; b) H.-J. Schneider, T. Blatter Angew. Chem. 100 (1988)
1211; Angew. Chem. Int. Ed. Engl. 27 (1988) 1163; c) H.-J. Schneider, T.
Blatter, S. Simova, I. Theis J. Chem. Soc. Chem. Commun. 1989, 580.
[4] Cf. a) S. K. Burley, G. A. Petsko, Adv. Protein Chem. 39 (1988) 125; b) J.
Sunner, K. Nishizawa, P. Kebarle, J. Phys. Chem. 85 (1981) 1814; c) C. A.
Deakyne, M. Meot-Ner, J. Am. Chem. SOC.107 (1985) 474; d) M. A. Petti,
T. J. Shepodd, R. E. Barrans, Jr., D. A. Dougherty, zbid. 110 (1988) 6825;
e ) D. A. Stauffer, D. A. Dougherty, Tetrahedron Lett. 29 (1988) 6039, and
references cited therein.
cm']: H,O 1.45 (D,O 1.26).
[51 Examples of average polarizabilities
CHCI, 9.5, benzene 10.5 (Handbook of Chemistry and Physics, E66-E75,
67th edit., CRC Press, Boca Raton, FL, USA 1986/1987).
[6] a)Cf. H.-J. Schneider, I. Theis, Angew. Chem. 101 (1989) 757; Angew.
Chem. Int. Ed. Engl. 28 (1989) 753; and references cited therein; b) H.-J.
Schneider, T. Schiestei, P. Zimmermann, unpublished results.
[7] Such an effect had already been postulated for cyclodextrin complexes:
a) D. W. Griffith, M. L. Bender, Adv. Catal. 23 (1973) 209; b) W. Saenger,
Angew. Chem. 92 (1980) 343; Angew. Chem. I n t . Ed. Engl. 19 (1980) 344.
c) Diederich et al. have on many occasions emphasized the role of cohesive
forces in the formation of apoiar complexes: D. B. Smithrud, F. Diederich,
J. Am. Chem. Soc. 112 (1990) 339, and references cited therein.
[8] See, for example C. L. Brooks, M. Karplus, Methods, Enrymot. 127 (1986)
Although the McMurry reaction has found wide application,12] so far it has rarely been employed for the directed
cyclodimerization of dicarbonyl compounds in one ~tep.1~1
The one-pot synthesis of the hydrocarbons 1 and 2, which
proceeds in comparatively good yields (1 a: 36 YOafter optimized coupling of5a14])makes this method attractive for the
synthesis of macrocycles.
In order to work out optimal reaction conditions, but also
for comparative purposes, we first prepared the "open
chain" triene 4 a from 3a.
The cyclization to 1 or 2 was best achieved under moderate
dilution conditions; we assume that the principle of rigid
groups plays a role thereby. The synthetic concept is widely
applicable. Thus, in addition to 1 a and 4a, the macrocycles
1 b (20%), 2a (20%), and 2 b (4% yield), as well as the triene
4b could be prepared.
," -11.4-dioxane
Macrocyclically Fixed Diarylhexatrienes**
By Fritz Vogtle* and Carlo Thilgen
Open-chain and cyclic polyenes have been the subject of
intensive research in organic chemistry for many years.'']
(DPH), for example, is a commonly used fluorescence indicator in investigations concerning the arrangement of molecules in vesicle and cell membranes, in liquid crystal phases, and in polymer films. Our
studies in this context are currently directed to the synthesis
Prof. Dr. F. Vogtle, Dip].-Chem. C. Thilgen
Institut fur Organische Chemie und Biochemie der Universitat
Gerhard-Domagk-Strasse 1, D-5300 Bonn 1 (FRG)
This work was supported by the Volkswagen-Stiftung. We thank Prof. Dr.
E. Steckhan, Universitat Bonn, for measuring and evaluating the cyclovoltammograms, and Dipl. Chem. P . M . Windscheif, Universitat Bonn,
for carrying out calculations.
Verlagsgesellschafr mbH, 0-6940 Weinheim, 1990
The yellowish, sparingly soluble microcrystals of the cycloalkene 1, which precipitated in analytically pure form on
recrystallization from pyridine, melt in an evacuated tube
at 385-388°C (decomp). Besides the peaks for M a
[m/z = 468.2817(calcd); 468.2814(obs), base peak] and M z a
[m/z = 2341, the mass spectrum of 1a also exhibits peaks of
graduated intensity for all the dehydrogenation products
down to mlz = 456, which corresponds to the especially
stable hexa-m-phenylene[6a1 (same carbon framework). The
'H-NMR spectrum (200 MHz, CDBr,) shows the following
signals: 6 = 1.93 (m, 8H; CH,), 2.51 (m, 8 H ; CH,), 2.60 (m,
8 H ; CH,), 7.20-7.38 (m, 6H; Ar-CH), 7.57 (s, 4 H ; vinylCH), 8.08 (s, 2H; Ar-CH). A striking feature is the down-
0570-0833~90/1010-1162$3.50+ .2S/O
Angew. Chem. Int. Ed. Engl. 29 (1990) No. 10
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interactions, induced, cavity, complexes, stretches, guest, effect, open, closer, receptors, pole, half, hydrophobic, host, dipole
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