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Designing Synthetic Cationic Molecular Receptors for Alcohols.

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CAS Registry numbers:
1, 124869-33-6; 2, 14847-23-5; 3, 139375-80-7; 5, 139244-61-4; H,C=CHPh,
[l] M. Christl, M. Braun, G. Miiller, Angew. Chem. 1992, 104, 471; Angew.
Chem. I n f . Ed. Engl. 1992, 31, 473.
[2] Review article on the experimental and theoretical investigations of strained
cyclic cumulenes: R. P. Johnson, Chem. Rev. 1989,89, 1111-1124.
[3] R. 0. Angus, M. W Schmidt, R. P. Johnson, J. Am. Chem. Sac. 1985,107,
[41 M. J. S. Dewar, E. G. Zoebisch, E. F. Healy, J. J. P. Stewart, J. Am. Chem.
Sac. 1985, 107, 3902.
[5] J. J. P. Stewart, F. J. Seiler Res. Lab. US Air Force Academy, CO 80840,
[6] STARDENT 3040, EDV-Zentrum der Universitat Graz.
[7] R. Janoschek, Chem. Unserer Zeit 1991, 25, 59-66.
[S] M. Balci, W. M. Jones, J. Am. Chem. S o t . 1980,102, 7607.
[9] C. Wentrup, G. Gross, A. Maquestiau, R. Flammang, Angew. Chem. 1983,
95, 551; Angew. Chem. Int. Ed. Engl. 1983,22, 542.
Designing Synthetic Cationic Molecular Receptors
for Alcohols**
By Luis Mkndez, Raymond Singleton,
Alexandra M . Z . Slawin, J ; Fraser Stoddart,*
David J; Williams, and M . Kevin Williams
In the early days of supramolecular chemistry, the complexation['] of cationic guests in apolar solvents was achieved
largely using neutral hosts. In these instances, strong hostguest associations are a consequence of the electrostatic interactions between the charged guest and the dipoles centered on the heteroatoms within the host. The design of hosts
that bind neutral guests successfully has proven to be much
more taxing both intellectually and in practice. The principal
intermolecular interactions that have been exploited in the
complexation['] of neutral guests by neutral hosts have been
hydrogen bonding, 7c--71 stacking interactions, and the hydrophobic effect. In most instances, the host-guest binding has
relied upon the simultaneous and cooperative action of several
such noncovalent bonding interaction^.[^] Guests such as phen o l ~ , [rea
~ ]as,[^] barbiturates,[61and nucleotides['] have been
complexed strongly by sophisticated hosts by means of a combination of hydrogen bonds and/or -71--71 stacking interactions.
Monohydric alcohols of low molecular weight are particularly difficult to bind selectively with synthetic hosts because
a) they possess only a single hydroxyl group, and b) they are
soluble in a wide range of solvents. Although there have been
a number of reportsL8]of selective clathration and inclusion
of short-chain alcohols in the solid state, no strong complexation of these relatively featureless substrates has been
achieved['] in solution. Recently, we described"'] the dis[*I
Prof. J. F. Stoddart
School of Chemistry, University of Birmingham
Edgbaston, Birmingham B15 2TT (UK)
Dr. L. Mendez, Dr. M. K. Williams
Department of Chemistry, The University
Shefield S3 7HF (UK)
A. M. Z. Slawin, Dr. D. J. Williams
Chemical Crystallography Laboratory
Department of Chemistry, Imperial College
London SW7 2AY (UK)
Dr. R. Singleton
Scimat Limited
Techno Trading Estate, Bramble Road
Swindon SN2 6EZ (UK)
[**I This work was supported by the British Science and Engineering Research
Council, Scimat Limited, and the Ministerio de Educacion y Ciencia in
Verlugsgesellschufi mbH. W-6940 Weinheim. 1992
covery of the complexation of MeOH by monoprotonated,
disubstituted 1,7-diaza-12-crown-4 receptor units. Here, we
report a) the preparation of some disubstituted 1,7-diaza4,10-dioxacyclododecanes,b) the quantitative evaluation of
their monoprotonated derivatives as hosts for binding shortchain alcohols in solution, and c) the solid-state structures[' ']
of both the free and complexed hosts.
Compounds 1 and 2 were prepared by reaction of 1,7-diaza-4,l O-dioxacyclododecane~l'l with benzyl bromide and
2-phenylethyl bromide, respectively, and protonated with
one molar equivalent of NH4PF, in MeOH. The formation
of 1 . HPF, and 2 . HPF, is accompanied by the release of
NH, . These salts are highly soluble in CD,CI,, a property
which we exploited in ' H N M R spectroscopic studies, in
which their complexing ability towards MeOH, EtOH, nPrOH, and n-BuOH, and-in some cases-the fully deuterated derivatives was quantitatively evaluated.
1, R'= PhCHp
l-HPF,, R' = PhCHp
2, R' = PhCHzCHz
2,HPFe. R' = PhCHpCHp
Interestingly, the signals for the OCH, protons in 1 . HPF,
and 2 . HPF, are influenced most['31 on complexation with
alcohols. The chemical shift dependence of the OCH, protons in 1 . HPF, and 2 . HPF, on the addition of these alcohols formed the basis for the titration method employed to
establish 1 :1 stoichiometries for the complexes, and used to
provide data for a quantitative assessment of complexation
strengths (Table 1). The 1:1 stoichiometry of the complex
Table I. The association constants K, and derived free energies of complexation AGO for the neutral receptor 2 and the cationic receptors 1 HPF, and
2 . HPF, with a range of short-chain alcohols [a] in CD,CI, at 20 "C.
1 . HPF,
1 . HPF,
1 HPF,
2 . HPF,
2 . HPF,
2 HPF,
2 HPF,
[kJ mol-
- 5.23
[a] Deuterated alcohols were employed in some titration experiments in order
to avoid masking the NMR resonances of the receptors.
formed between 1 . HPF, and [D,]MeOH was confirmed by
the method of continous variations (Fig.
The determinations of the association constants K, were carried out by
linearization (according to the Higuchi method[14*'1) of the
binding isotherm obtained from the 'H NMR titrations. The
importance of monoprotonation of the receptor is evident
from a comparison of the Ka values for 2 and 2 . HPF, in
Table 1; the K, value of the protonated receptor is 40 times
greater than that of the unprotonated receptor. The strength
of complexation of alcohols is also dependent on the nature
of the substituents (PhCH, in 1 and PhCH,CH, in 2). When
the phenyl groups are more distant from the hydrogen-bond-
oS70~0833/92/0404-0478$3.50+ .25/0
Angew. Chem. Inl. Ed. Engl. 31 (1992) No. 4
gen atoms are on opposite faces of the macrocycle. In
2 . HPF, (Fig. 4), the cation assumes an asymmetric and
folded geometry; the protonated and unprotonated nitrogen
atoms are directed towards each other and form an almost
linear hydrogen bond ([N+-H.. . N] distance 3.01 A). The
Fig. 1. The concentration c of 1 . HPF, . CD,OD relative to CD,OD versus
the mole fraction x of 1 HPF, in CD,CI, at 20 "C.
ing centers in the receptors, the complexes formed with
MeOH, EtOH, and n-PrOH are all stronger.
The disubstituted 1,7-diaza-l2-crown-4 derivatives are
highly suitable receptors1161for RNH: and R,NHl ions,
because they can form two N . . . H - N + hydrogen bonds
with the cationic substrates. When these same receptors are
monoprotonated, it is possible for them to form simultaneously an N . . . H-0 hydrogen bond and an N+-H. . .O
hydrogen bond with a neutral ROH substrate, because the
lone electron-pair on the neutral nitrogen atom acts as a
good hydrogen-bond acceptor and the protonated nitrogen
atom is a strong hydrogen-bond donor. This two-point binding model (Fig. 2) has been confirmed by an organized
sequence of structural investigations which have been carried out in the solid state on neutral and charged-free as
well as complexed-disubstituted 1,7-diaza-12-crown-4 derivatives.
B ______ N-W
......... 0-H
F'ig. 2. The two-point binding model showing
the hydrogen bonding of an alcohol (ROH)
molecule to a monoprotonated disubstituted
Fig. 4. The structure of 2 . HPF,
in the crystal. The transannular NN and 0-0 distances are 3.01 and
4.17 A, respectively. The H-N(7)
distance is 2.04 8, and the N(1)-HN(7) angle is 169".
solid-state structure of 1 . HPF, . MeOH (Fig. 5) has crystallographic C, symmetry with the mirror plane passing
through the two oxygen atoms in the monoprotonated disubstituted 1,7-diaza-12-crown-4derivative. The MeOH molecule also lies in this mirror plane. The 12-membered ring
HPF,. MeOH in the crystal.
The transannular N-N and
0-0 distances are 4.53 and
3.06 A, respectively. The HO(15) distance is 1.87 A and the
N(l)-H-0(15) angle is 161".
The single-crystal X-ray structures["- 19] of 1, 2 . HPF,,
and 1 . HPF, . MeOH are illustrated in Figures 3, 4, and 5,
respectively. In the solid state, 1 (Fig. 3) possesses crystallographic Ci symmetry, the 12-membered ring adopts a [66]
conformation,120, and the lone electron-pairs of the nitro-
adopts a [48] conformation[201
in which both nitrogen atoms
are oriented over one face of the macrocycle. The position of
the ammonium proton was located from a difference electron-density map, though, of course, because of the crystallographic symmetry constraints, it must alternate between
the two nitrogen sites throughout the crystal lattice. The
position of the OH proton could not be located. But by
inference with the geometry observed['01 in the MeOH complex of the diprotonated analogue 3 .2HPF, we conclude
Fig. 3. The structure of 1 in the crystal. The
transannular N-N and 0-0 distances are 4.37
and 4.35 A, respectively.
that the binding of the MeOH molecule to 1 . HPF, involves
combination of N+-H. . .O and 0-H . . .N hydrogen
bonds.[221The N + . . .O and 0 .. . N distances are by symmetry both 2.81 A.
The two-point binding model for the complexation of alcohols by monoprotonated disubstituted 1,7-diaza-l2-crown-4
derivatives has been firmly established. The opportunity
now exists to develop this type of complexation between
cationic host and neutral guest for the design of receptors
that will exhibit selectivityt231within the homologous series
of simple alcohols (CH,OH, C,H,OH, C,H,OH) and the
Angew. Chem. Int. Ed. Engf. 31 (1992) No. 4
Verlagsgeselischafi mbH. W-6940 Weinheim, 1992
$3.50+ .25/0
constitutionally isomeric alcohols from C,H,OH upwards in
molecular weight.
Experimental Procedure
1 : 1,7-Diaza-4,10-dioxacyclododecane
[12] (200 mg, 1.1 mmol) and Na,CO,
(0.61 g, 5.7 mmol) were suspended in dry MeCN (8 mL). Then, benzyl bromide
(395 mg, 2.3 mmol) was added dropwise to the suspension under reflux. After
10 h the reaction mixture was cooled and filtered. Evaporation of the solvent
from the filtrate under vacuum afforded a residue which was extracted with
CHCI,. Chromatography [SiO,, 3 5 % ] NH,/MeOH/Et,O/CHCI, (0.2/10/30/
80) afforded 1 [386mg, 95%, mp = 89-90"C, m / z (EIMS) = 354 ( M ' ) ;
' H N M R (CDCI,, 250 MHz): 6 = 2.77 (t, 8H, ' J = 4.5 Hz), 3.61 (t. 8H.
' J = 4.5 Hz), 3.70 (s, 4H), 7.20-7.45 (m. ]OH)]. Single crystals suitable for
X-ray crystallography were grown from n-hexane.
1 . HPF,: A solution of 1 (1.0 g, 2.8 mmol) and NH,PF, (0.46 g, 2.8 mmol) in
MeOH (20 mL) was stirred under reflux for 8 h. When the reaction mixture
cooled, colorless crystals formed, which were filtered and dried under vacuum
during 36 h. They were characterized as 1 . HPF, 11.1 g, 78%, mp = 170°C;
'H NMR (CD,CI,, 400 MHz): S = 3.10 (t, 8H, ' J = 4.8 Hz), 3.62 (t. XH,
' J = 4.8 Hz), 4.10 (s, 4H), 5.40 (brs, 1 H), 7.36-7.47 (m. 10H)I. Single crystals
of 1 . HPF, . MeOH suitable for X-ray crystallography were obtained by gradually cooling a saturated solution of 1 . HPF, in MeOH from 60°C to 20°C.
2: 1,7-Diaza-4,10-dioxacyclododecane
[12] (300 mg, 1.7 mmol) and Na,CO,
(1.2 g, 11.3 mmol) were suspended in dry MeCN (40 mL). Then, a solution of
2-phenylethyl bromide (624 mg, 3.5 mmol) in MeCN (5 mL) was added dropwise to the stirred reaction mixture under reflux. After 24 h the reaction mixture
was cooled and filtered. Evaporation of the solvent from the filtrate under
vacuum afforded an oil which was extracted with boiling hexane. The hexane
solution wasconcentrated under vacuum and cooled in an ice-box. Longcolorless needles formed which were identified as 2 [244 mg, 37 %, mp = 58-60 "C,
m / z (EIMS) = 382 ( M ' ) ; 'H NMR (CDCI,, 250 MHz): 6 = 2.70-2.80 (m.
16H), 3.61 (t, XH, ' J = 4.5 Hz), 7.15-7.31 (m, 10H)I.
2 . HPF,: A mixture of 2 (50mg, 0.13 mmol) and NH,PF, (21.3 mg,
0.13 mmol) in MeOH (2.4 mL) was stirred under reflux during 10 h. The solvent was removed under vacuum, affording an oil which crystallized on addition of Et,O. After removal of the solvent, the crystals were dried under vacuum
and characterized as 2 . HPF, [69 mg, loo%, mp = 155-160 "C; ' H NMR
(CD,CI,, 400 MHz): 6 = 2.89 (t. 4 H , ' J = 4.3 Hz), 3.10-3.18 (m, 12H), 3.74
(t, 8H, ' J = 4.8 Hz), 5.38 (brs, 1 H), 7.17-7.34 (m, 10H)I. Single crystals suitable for X-ray crystallography were grown by slow evaporation of a CH,CI,
solution of 2 . HPF,.
Received: November 21, 1991 [Z 5032 IE]
German version: Angew. Chem. 1992, 104, 456
CAS Registry numbers:
1, 139495-32-2: l,HPF,, 139495-34-4; S.HPF,.MeOH, 139495-36-6:
l.HPF;[D,]methanol, 139495-38-8; S.HPF,.ethanol, 139495-39-9; l.HPF,w
propanol, 139495-40-2; 2, 139495-33-3; 2.HPF6, 139495-35-5; tfD,]metbanoi,
139495-37-7; 2.HPF,.[D4]rnethanol, 139495-41-3; 2.HPF6.[D,]ethanol,
139495-42-4; Z.HPF,.n-propanol, 139495-43-5; Z,HPF,.n-butanol, 139495.44294-92-8.
6; 1,7-aza-4,10-dioxacyclododecane,
[l] Y Inoue, G. W Gokel, Cation Binding b y Mucrocycles, Dekker, New York
and Basel 1990.
[2] J. Rebek, Jr., Angew. Chem. 1990, 102, 261-272; Angew. Chem. Int. Ed.
Engl. 1990, 29, 245-255; K. S. Jeong, T. Tjivikua, A. Muehldorf, G.
Deslongchamps, M. Famulok, J. Rebek, Jr., J Am. Chem. Soc. 1991,113,
201 -209.
[3] F. Diederich in Cyclophanes (Ed.: J. F. Stoddart), The Royal Society of
Chemistry, Cambridge, UK, 1991.
[4]B. J. Whitlock, H. W Whitlock, Jr., J Am. Chem. Soc. 1990, 112, 39103915; K. M. Neder, H. W. Whitlock, Jr., ibid. 1990, f12, 9412-9414.
[S] T. R. Kelly, M. P. Maguire, J. Am. Chem. Soc. 1987, 109, 6549-6550; T.
Bell, J. Liu, ibid. 1988, 110, 3673-3674; V. Hedge, P. Madhukar, J. D.
Madura, R. P. Thummel, ibid. 1990, ff2,4549-4550; M. Crego, J. J. Raposo, M. J. Sam, V. Alcazar, M. C. Caballero, J. R. Moran, Tetrahedron
Lett. 1991, 32, 4185-4188.
(61 S.-K. Chang, A. D. Hamilton, J Am. Chem. Soc. 1988, 110, 1318-1319.
[7] S . C. Zimmerman, W. Wu, J. Am. Chem. Soc. I989,/11,8054-8055; S . C.
Zimmerman, W. Wu, Z. Zeng, ibid. 1991, 113, 196-201; J. C. Adrian, Jr.,
C. S . Wilcox, ibid. 1989, 111, 8055-8057; T. Tjivlkua, G. Deslongchamps,
J. Rebek, Jr., ibid. 1990, 112, 8408-8414; T. H. Park, J. Schroeder, J.
Rebek, Jr., Tetrahedron 1991, 47, 2507-2518.
[XI E. Weber, H.-P. Jose], H. Puff, S . Franken, J Org. Chem. 1985,50,31253132; W. Moneta, P. Beret, J.-L. Pierre, J Cbem. Soc. Chem. Commun.
1985,899-901; D. Worsch, F. Vogtle, J I n c l . Phenom. 1986,4, 163-167;
K. Kobiro, M. Takahashi, N. Nishikawa, K. Kakiuchi, Y Tobe, Y Odaira,
Tetrahedron Lett. 1987, 28, 3825-3826; B. Dung, F. Vogtle, J Incl. Phenom. 1988, 6 , 429-442; F. Toda, K. Okada, T. C. w. Mak, Chem. Lett.
1988, 1829-1832; .I.
W. Johnson, A. J. Jacobson, W. M. Butler, S. E.
Verlagsgesellschafi mbH. W-6940 Wernheim, 1992
Rosenthal, J. F. Brody, J. T. Lewandoski, J Am. Chem. Soc. 1989, f f f ,
381-383; S. A. Bourne, L. R. Nassimbeni, K. Skobridis, E. Weber, J
Chem. Soc. Chem. Commun. 1991,282-283; M. Czugler, E. Weber, J Incl.
Phenom. 1991, 10, 355-366.
However, weak complexes in solution have been observed with cyclophanes: Y. Kikuchi, Y Kato, Y Tanaka, H. Toi, Y Aoyama, J. Am. Chem.
SOC.1991,113,1349-1354; and withcyclodextrins: Y Matsui, K. Mochida, Bull. Chem. Soc. Jpn. 1979, 52, 2808-2814; A. B. Ari, J. Szejtli, L.
Barcza, J Incl. Phenom. 1983, 1 , 151-157.
8. L. Allwood, L. Mendez, J. F. Stoddart, D. J. Williams, M. K. Williams,
J. Chem. Soc. Chem. Commun., 1992, 331 -333.
Nicolet R3m diffractometer, w scans, Cu,, radiation (graphite monochromator). The structures were solved by direct methods and refined anisotropicically. Further details of the crystal structure investigations are
available on request from the Director of the Cambridge Crystallographic
Data Centre, University Chemical Laboratory, Lensfield Road, GB-Cambridge CB2 1EW (UK), on quoting the full journal citation.
B. Dietrich, J.-M. Lehn, J.-P. Sauvage, J. Blanzat, Tetrahedron 1973, 29,
In the complexation of alcohols by 1 . HPF, and 2 . HPF,, the chemical
shift change of the OCH, signal was larger than that of the NCH, signal
in all cases. In the proposed two-point binding model (Fig. 2), the oxygen
atom of the alcohol is located sufficiently close to the OCH, groups for its
lone pairs of electrons to shield the OCH, protons. Indeed, an upfield shift
(AS = 0.06-0.12) of these protons in 1 ' HPF, and 2 . HPF, is observed
when they complex alcohols.
[14] K. A. Connors, Binding Constants. The Measurement of Molecular Coinplex Stability, Wiley, New York, 1987.
[I51 M. Nakano, N. I. Nakano, T. Higuchi, J Phys. Chem. 1967, 71, 39543959.
(161 J. C. Metcalfe, J. F. Stoddart, G. Jones, J. Am. Chem. SOC.1977,99, 83178319; J. C. Metcalfe, J. F. Stoddart, G. Jones,W E. Hull, A. Atkinson, I. S .
Kerr, D. J. Williams, J Chem. SOC.Chem. Commun. 1980, 540-543.
[17] Crystaldata for 1: monoclinic, a = 9.735(1), b =7.339(1), c = 14.591(2) A,
p = 106.92(2)", V = 997 A,, space group P2,/n, Z = 2 (the molecule is
disposed about a center of symmetry), p =1.18 gcn-', ~(CU,.) =
6cm-', 1148 independent observed reflections with IFol > 3u1F01, 20 5
116", refined to R = 0.038, R, = 0.040.
[18] Crystal data for 2 ' HPF,: monoclinic, a =11.218(11), b =19.882(14),
c = 11.480(6) A, p = 94.98(6)", V = 2551 A', space group P2,/n, Z = 4,
p = 1.38gcm-', &(Cu,.) = 16 cm-', 2670 independent observed reflections with IFoI > 3alF01, 2 0 1116",refined to R = 0.094, R, = 0.102.
[19] Crystal data for 1 . HPF, . MeOH: monoclinic, a = 14.263(8), b =
13.088(7), c = 14.916(7) 8,/3 = 97.23(4)", V = 2762 A', space group I2jm
(body-centered cell chosen because C-face-centered cell had p % 133"),
Z = 4 (the molecule has crystallographic C. symmetry), p = 1.28 gem-',
~(CU,,)=15 cm-', 1629 independent observed reflections with IFo] >
3alFoI, 2 0 1116", refined to R = 0.098, R, = 0.112.
[20] J. Dale, Top. Stereochem. 1976, 9, 199-270.
[21] P. Groth, Acta Chem. Scand. 1978, 32A, 279-280.
[22] The distance between O(15) and the ether oxygen O(7) is 3.01 A. A hydrogen bond between these twoatomsis not likely, since thisdistance is almost
the same as the transannular 0 . .' 0 distance in 1 . HPF, . MeOH and in
its diprotonated analogue 3 . ZHPF,. The O(15). ' O(4) distance is somewhat shorter (2.89 A) and may be a possible alternative MeO-H...O
hydrogen bond.
[23] After this communication was submitted for publication, novel boroncontaining crown ethers were reported to bind alcohols, such as MeOH,
EtOH, iPrOH, and PhCH,OH, with good selectivities in the presence of
amines like PhCH,NH, or PhCHMeNH,: M. T. Reetz, C. M. Niemeyer,
K. Harms, Angew. Chem. 1991, 103, 1515-1517, 1517-1519; Angew.
Chem. Inl. Ed. Engl. 1991.30. 1472-1474, 1474-1476.
An Opinion on the Heterogeneous Photoreactions
of N, with H,O **
By Jimmie G . Edwards,* Julian A . Davies, David L. Boucher,
and Abdelkader Mennad
Artificial photosynthesis of ammonia is an important research goal. In the course of other work,"' we have reviewed
[*I Prof. J. G. Edwards, Prof. J. A. Davies, Mr. D. L. Boucher,
Dr. A. Mennad
Department of Chemistry, University of Toledo
Toledo, OH 43606 (USA)
[**I This work was supported by Dr. H. L. McMaster, CEO, Glasstech, Inc.
Angew. Chem. Int. Ed. Engl. 31 (1992) No. 4
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