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Doubly Encircled and Double-Stranded Pseudorotaxanes.

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R = 0 063. R,, = 0.116X f b r 6629 independent observed reflections for
[lF,l > 4n( &)I], ?U t i 1 0 ] X-ray data for [DB24C8.2-H]PF6: monoclinic.
space group Ilr (body-centered cell chosen because C-face-centered cell has
/j = 124 ). LI = 18.597(4). h = 10.362(3). c = 20.265(3) A, [I = 105.48(2)
1 ' = 3763(21A', 2 = 4. p(CuKn)= 1.30 mrn-'.
= 1.28 g ~ m - Siemens
~ .
P4, PC diffractometer. graphite-monochromated Cu,, radiation. The structure
w.'I\ . so
. 1\ed using direct methods, and anisotropic refinement gave R , = 0.063.
<,iR1= 0 1hY for2747 independent observed reflections with [lFol> 40(lF01).
20 < 125 I , Further details of the X-ray crystal structure investigations may be
obtained from the Director of the Cambridge Crystallographic Data Centre, 12
Union Road. GB-Cambridge CB? IEW (UK).
[I71 For :in alternative type of single-point analysis for the determination of K,
\.iilues. \ec J C . Adrian. Jr.. C S Wilcox. J. Am. Clieni. Sor.. 1991. 113. 6786811.
[18] The G u t m m n donor number provides a semiquantitative measurement of the
ability of the solvent to donate its electrons into noncovalent bonds. See a) V.
Gutniann. E . Wychera. h u g . Nucl. Clienz. Lett. 1966, 2. 257-260; b) C. Reichardt. Soilenrs undSulwnr Efferrs in Orgunir. Chemi.r/ry.2nd ed., VCH. Weinheim. 1988.
[19] C. S. Wilcox i n Frontiers o/Suprumokr.ulur Ougonir Cltrmistr~.iindPhoro~henii s m (Eds H.-J. Schneider. H. Durr). VCH, Weinheim. 1991, pp. 123-143
[20] The determination of K, values by either titration or by Job's method of
coiitiiiuou~variation cannot be undertaken in CDCI, because these techniques
both require at some stage that the concentration of the ammonium salt be in
excess rel;ttice to that of the crown ether. This situation cannot be achieved in
practice on account of the low solubility of I-H-PF, in the absence of a molar
equivalent of DB24C8.
I l l ] I n the casc of the dilution experiment, the values of K, and Ahmavwere obtained
after Iineiiruation of the binding data according to Equation (a), where A8,,,
corrcspondh to the value of the complexation-induced chemical shift. Ado is the
obrerved difference in chemical shift between the complex and free species for
a probe proton ofeither host or guest. and cis the concentration of an equimolar solution of host and guest.
A,),, = Ad ,,,,,, ( A ~ , , A ~ , , , . ' c . K , ) ~ * ~
(a)
[22] Thc Eyring equation was employed to calculate AG: values at the coalescence
at which the rate constants k , can be calculated (I. 0 Suthertemperatures
c.
4 , 71 - 2 3 5 ) from the approximate
land. A n n u Rep. N M R S p ~ c ~ u u s 1971,
,
Ail is the chemical shift difference (in
expression. k , = a ( A ~ ) : ( 2 ) ~ " where
Hertz) between the coalescing signals in the absence of exchange.
[23] Note added in proof (August 18. 1995): After this paper had been submitted,
B u s h et :il (A G. Kolchinski. D. H. Busch, N. W. Alcock.1 Ciiem. SOC.Cltrm.
Commun 1995. 1289- 1291) reported the synthesis of a [2]rotaxane composed
of a dumbell. which incorporates a secondary dialkylammonium center, and a
DB24C8 bead. The [2]rotaxane was self-assembled by acylation of a primary
amine--in a molecule also containing a secondary amino center-in the presence of the macrocycle.
~
c.
Doubly Encircled and Double-Stranded
Pseudorotaxanes" *
Peter R. Ashton, Ewan J. T. Chrystal, Peter T. Glink,
Stephan Menzer, Cesare Schiavo, J. Fraser Stoddart,*
Peter A. Tasker, and David J. Williams
In the preceeding communication,"' we described the formation of pseudorotaxanes from R,NH: ions (R = PhCH, in
l-H.PF,, and R = nBu in t-H.PF,) and dibenzo[24]crown-8
(DB24C8) both in the solution and solid states. Subsequently, in
our evaluation of the propensities of other crown ethers to bind
[*I Prof J. F Stoddart. P. R. Ashton, Dr. P. T. Glink, C. Schiavo
School of Chemistry, University of Birmingham
Edgbaston. Birmingham 815 2TT (UK)
Telelhx: I i i t code + (121)414-3531
Dr E. J. 'T Chrystal
ZENECA Agrochemicdls. Bracknell (UK)
Dr. S. Menzer. Dr. D. J. Williams
Chemical Crystallography Laboratory
imperisl College. London (UK)
Dr. P. A. Tasker
ZENECA Specialities. Manchester (UK)
["I This work was sponsored by the ZENECA Strategic Research Fund and supported additionally by the Engineering and Physical Sciences Research Council.
AiiRrw
Cliim
Itit.
Ed EngI. 1995. 34. N o . 17
;<
with R,NHl ions, we
?,
B Y
discovered that l-H.PF,
c* ,
forms a complex with bisparu - phenylene [ 341 crown 10 (BPP34C10)['] in which
two dibenzylammonium ions
are threaded simultaneously
through the macrocyclic
polyether. Here. we describe
(i) the X-ray crystal structure of this 1 . 2 complex,
BPP34C10
[BPP34C10. (l-H)2][PF,], ,
a "double-standed pseudorotaxane", and also those of
the solid-state superstructures that self-assemble spontaneously from solutions of
r,a'-bis(benzy1ammonium)pavu-xylene bis(hexafluor03-Hz.2PFe
phosphate) (3-H2.2PF,) and
(ii) BPP34C10 and also (iii) DB24C8; these latter structures are
intriguing examples of a double-stranded and a doubly encircled
2:2 complex and a doubly encircled 2: 1 complex, respectively.
Evidence that the 1 :2 and 2: 1 complexes ("a double-stranded
pseudorotaxane" and "a doubly encircled pseudorotaxane", respectively) also exist with the same stoichiometries in solution is
provided by 'H NMR spectroscopy.
The complex formed between BPP34C10 and I-H'PF, crystallized with a I : 2 stoichiometry when an equimolar mixture of
the two components was dissolved in acetone and the solution
layered with n-pentane. The resulting single crystals were analyzedF3]by X-ray crystallography (Fig. l ) . The BPP34ClO component has the expected['] open centrosymmetric structure; its
hydroquinone rings are aligned parallel to each other with a
centroid-centroid separation of 6.99 A. Pairs of 1-H+ ions are
threaded symmetrically through the macrocyclic ring. The conformation of the C-CH,-NHl-CH,-C backbone departs from
the all-onti geometry
adopted by the 1-H+ ion
in [DB24C8.l-H][PF,] in
its solid-state superstructure."] The NH; hydrogen atoms of each
cationic center aredirected toward polyether oxygen atoms at either end
of the macrocycle. However, the 1:2 complex
does not have additional
stabilization through any
significant [C-H . . '01
hydrogen bonds. Secondary stabilization is
achieved by edge-to-face
interactions[41 between
one of the phenyl rings in
each cation and the hydroquinone rings of the
ether, The tenFig. 1. Top. Ball-and-stick representation
troid -centroid distances
for these DairS of svmmetrically related interactions are 5,06 A, and
in each case the approach of one of the
VCH Vrrlu~.r~esell.srhu/t
nihH, D-69451 Weinheim, 1995
of [BPP34C10.(1-H)1]2+in the solid state.
The BPP34C10 component is depicted in
red and the (PhCH,).NH+
CdtiOns in blue
_.
The [N-H . . 01 hydrogen bonds have the
following distances and angles [ N . . . O ]
2.83, 2 . 8 2 A ; [ H - . . O ] 2.10, 2.06;
[ N - H . . . O ] 137, 141 . Bottom: Space-filling representation of the complex.
~
0570-/iX33:95~3417-/X69
3 10.00 + .25:f)
1869
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ortho hydrogen atoms of the hydroquinone ring to the phenyl
ring center is almost linear (171"; H . ' 'ring centroid distance,
2.73 A). The distance between the two NH; centers in the complex is 8.4 A. The BPP34C10 rings are arranged to form channels (Fig. 2) that extend in the crystallographic c direction, again
conjuring up the prospect of the formation of polyrotaxane~.[~I
The distance between the closer NH; centers within the stack is
6.9 A.
Fig. 2. Space-filling representation showing the pseudopolyrotaxane stacking motif in the crystals of [BPP34C10.(l-H),]2'.
Single crystals suitable for X-ray analysis were also obtained
when an equimolar mixture of BPP34C10 and 3-H,.2PF6 was
dissolved in acetone and the solution layered with n-pentane.
The X-ray crystal structure showed the complex to have 2:2
stoichiometry (Fig. 3) .[31 In this superstructure, both dications
a+
+
0
1: 1:
-
+
-
Fig. 4. Schematic representation of the formation of the 2 . 2 complex between two
BPP34C10 macrocycles (red) and two [3-H2]'+ ions (blue).
formations of the two BPP34C10 macrocycles are similar, with
centroid-centroid distances between the hydroquinone rings in
the upper and lower macrocycles of 7.18 and 7.00 A, respectively. However, unlike the parallel alignments of these matching
rings in [BPP34ClO.(l-H),] [PFJ,, here they are inclined by 30"
and 26", respectively. In common with the 1 :2 complex, the 2:2
complex packs with pairs of tori oriented in tubelike arrays; the
enthreaded dications in each complex are aligned with respect to
each other along the crystallographic b direction. When the
crown ether is changed from BPP34CIO to DB24C8, a 2:1
~ o m p l e x [ ~results
. ~ l in which the [3-H2]'+ dication is threaded
through the centers of two DB24C8 macrocycles (Fig. 5 ) . The
Fig. 5. Top: Ball-and-stick representation of [(DB24C8),.3-HJZt in the
solid state. The DB24CS macrocycles are depicted in red and the
[(PhCH,NH:CH,),C,H,]
dication in blue. The [N-H . . O]hydrogen bonds have
1 3.10,3.05,3.00A; [H '''02.25,
1 2.39,
the following distances and angles [N . . . 0
2.33A;[ N - H . . . O ] 155. 133, 131". The [ C - H . . - O ] hydrogen bonds have the
following distancesand angles [ C . . . O ] 3.24A;[ H . . - O ]2.30A;[C-H...O] 163..
Bottom: Space-filling representation of the complex.
'
Fig. 3. Top: Ball-and-stick representation of [(BPP34C10),.(3-H,),]4i in the
solid state. The BPP34C10 components are depicted in red and the
[(PhCH,NH:CH,),C,H,]
dications in blue. The [N-H . ''01 hydrogen bonds
, [H...0]2.02-2.27
A,
have thefollowingdistancesandangles[N~~~0]2.85-3.10
and [ N - H . . . O ] 127-168". The [C-H...O] hydrogen bonds have the following
distances and angles [ C . . . O ] 3.25-3.43,[ H . . . O ] 2.32-2.48A,and [C-H-"O]
158- 167'.Bottom: Space-filling representation of the complex.
are threaded through two BPP34C10 macrocycles positioned
immediately adjacent to each other, producing an extended
torus (Fig. 4). This double-stranded, doubly encircled superstructure is stabilized by a series of nine [N-H . . '01 and three
[C-H . '01 hydrogen bonds between the NH: centers and
benzylic CH, groups of the dicationic threads and oxygen atoms
of the encircled macrocyclic polyethers, respectively. The con1870
8 VCH
VerlaR.~~esrllschafr
mbH. 0-69451 Weinheim.1995
complex is centrosymmetric with respect to the central para-xylyl unit of the dication. Once again, the complex is stabilized by
a combination of [N-H . . '01 and [C-H . '01 hydrogen
bonds. In addition, there are n--71 stacking interactions between
the almost parallel, aligned catechol and para-xylyl units within
the superstructure (these rings are inclined by ca. 5" and have
centroid-centroid separations of 3.65 A). In this complex, there
is an absence of any pronounced channel formation within the
crystals.
Both 1-H.PF6 and 3-H,.2PF6 have very low s~lubilities['~
in CD,Cl,. On the addition of BPP34C10, the solubility of
1 - H . PF, increases significantly (ca. tenfold). The 'H NMR
spectrum of a saturated solution of I-H'PF, in CD,C1, in the
presence of BPP34C10 exhibits signals['] that integrate for the
0S7O-Os33ls5!3417-lX70 $ 10.00 t .2S!O
Angew. Cliem. Inr. Ed. Engl. 1995. 34, N o . I7
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expected stoichiometry associated with the 1 : 2 complex
[BPP34C10.(l-H),][PF6],.
By contrast, in the case of
3-H2.2PF,.when BPP34C10 is added to a saturated solution of
the salt in CD,Cl2:CD,CN (4:l, v/v), an approximately 1 : l
ratio''] of salt to crown ether is observed by integration. It was
also noted that 3-H;2PF6 does not dissolve in CDCI,. even in
the presence of a large excess of DB24C8. However. when the
spectrum of a 10:l mixture of DB24C8 and 3-H;2PF6 in CDCI,;CD,CN (1 : I , viv) was recorded, only signals for the expected 2 : 1 complex['ol and the excess of DB24C8 were observed
under conditions of slow exchange on the 'H NMR time scale.
The stoichiometry of the complex was established by direct integration of the signals associated with its DB24C8 and [3-H,]'+
components.
When positive-ion FAB mass spectrometry" 'I was used to
characterize these complexes, peaks for [ M - PFJ+ ions were
observed at HI:'= 1077 and 1360 for [BPP34Cl0.(I-H),][PFJ2
and [(DB24C8);3-H,][PF6],, confirming the respective 1 : 2
and 2 : 1 stoichiometries of these species. The 2 : 2 complex
formed between 3-H,.2PF6 and BPP34ClO in the solid state
(Fig. 3) was not observed by positive-ion FABMS. However. a
peak with )pi/: 999, corresponding to a species with 1 : 1 stoichioinetry that has lost one counterion, is observed.
The ease with which both the monocationic (I-Hi) and dicationic ([3-H,]' +) species containing NHT recognition sites selfassemble with crown ether receptors such as DB24C8 and
BPP34ClO to give highly ordered superstructures in solution, as
well as in the solid state. could herald some new and fascinating
developments in macromolecular science as a result of a productive marriage["] between macrocyclic and supramolecular
chemistry.
E.xperinienttrl Procedure
3-H2.?PF,,: A solution of benzylamine (5.14 g. 0.048 mol) and terephthaldehyde
(3.26 g. 0.024 mol) was heated under reflux with stirringina Dean-Stark apparatus
for 10 h. After the reaction mixture was cooled down to room temperature.
the solvent was evaporated off under vacuum to give the 1.4-bis(benzylimiiiornet1i~l)benzeneasabrownsolid['H NMR(CDC1,): 6 = 4.84(s.4H). 7.18--7.47
(m. 1 0 H ) . 7 . Q (s. 4H). 8.41 (s, ZH)] which was dissolved in MeOH ( 5 0 m L ) .
NaBH, (3.80 g. 0.10 mol) was added in small portions to the reaction mixture which
was heated under reflux with stirring for 8 h. It was then allowed to cool down to
room temperature and concentrated HCI was added (pH < 2). After evaporation of
the sohent. the residue was suspended in H,O (30 mL) and extracted with CH,Cl,
(4 x 30 m L ) . The combined extracts were washed with 5 % aqueous NaHCO,
(2 x 60 mL). H,O (50 mL), and then dried (MgSO,). Removal of the solvent under
vacuum .ifforded 1.4-bis(benzylaminomethyl)benzene(4.00 gj as a colorless solid
['H NMR (CDCI,): 6 = 3.80 (s. 4 H ) . 3.51 (s, 4 H ) . 7.15-7.45 (m. 14H)] of w,hich
2.00 g (0.006 mol) was dissolved in MeOH (30 mL). Concentrated HCI was added
(pH < 2) and the ireaction mixture was stirred fora further hour. Evaporation of the
solrent afforded ii colorless solid which was suspended in acetone (30 mL)
An aqueous solution of NH,PF, was added until dissolution occurred. Evaporation
of acetone affordcd colorless crystals of 3-H, .2 PF,. which were isolated. washed
with H,O, and air-dried (3.50 g, 90%. m.p. 238 ' C with decomp.). Positive-ion
F A B M S : ~ Z ~~ ~PF,]';
[ M 'HNMR(CD,CN):d'= 4 . 2 4 ( ~ . 4 H j . 4 . 2 5 ( ~ , 4 H ) ,
7.45-7.51 (m.10H). 7.52 (s, 4 H ) ; "C NMR (CD,CN): 6 = 51.6, 52.4, 129.9.
130.6, 131.0. 131.2. 131.6, 132.9.
Received May 15, 1995 [Z7990IE]
German version: Angew. Chem. 1995, 107. 2001 -2004
Keywords: crown ethers . molecular recognition
self-assem bl y
rotaxanes .
[I] P. R. Ashton, P. J. Campbell, E. J. T. Chrystal. P. T. Glink, S. Menzer. D.
Philp. N . Spencer, J. F. Stoddart, P. A. Tasker. D. J. Williams. Angew. Chem.
1995. 107. 1997-2001; Angew. CIiem. Int. Ed. Engl. 1995,34. 1869-1871.
[2] P L. Anelli. P. R. Ashton, R. Ballardini, V. Balzani. M. Delgado, M. T. Gandolfi, T. T. Goodnow, A. E. Kaifer, D. Philp, M. Pietraszkiewicr. L. Prodi.
M. V. Reddington. A. M . Z. Slawin. N. Spencer, J. F. Stoddart. C. Vicent, D. J.
Williams. .I. An?. Chmi. So,. 1992. 114. 193 -218 and references therein.
[3] Crystal data for [BPP34ClO.(I-H),][PF,1,:
monoclinic. space group P2,/a.
II = 12 13?(9). b = 18.378(7), 1' = 13.824(5) A. / j = 105,l)317) . V = 2977(2) A'.
Z = 2(tliecomplexhasC,symmetry)./),,,, =1.36gcin-'.p(Cuk,) = 1 5 c m - ' .
Siemens P4:PC diffractometer. graphite-monochromated Cu,, radiation. The
structure was solved by direct methods and the anisoti-opic refinement gave
R = 0.084, Rw = 0.093 for 3237 independent obserred reflections with
[I<,l > 4u(\F01),20 1 1 2 5 1. Crystal data for [(BPP34C10),-(3-H,),][PF6],:
monoclinic. space group PZ,:n, (1 = 18.101(4).h = 28.2i?(h). c = 27.525(6) A,
/i= 99.71(3)'. !'-=l3865(5) A'.
z=4. {JLdrc =1.1: gem-'. fL(cUK,) =
12 cm- I. Siemens P4:RA diffractometer. graphite-monochromated Cu,, radiation. The structure was solved by direct methods and ,inisotropic refinement
gave R , = 0.154. irRi = 0.398 for 6773 independent ohvxved reflections with
[lF,l > 4u(lF01),20 <110 ].CrystaIdatafor[(DB24C8),.3-H,](PF,j2:
monoclinic, space group PZ,;C. u =11.538(3), h = 29.291(7). c =10.820(3) A.
/i=91.39(2) ; V = 3656(2)A3.Z= ? . { J ~=~1, .~3 7 g c r n ~ ' . y c ( C ~ , , ) = l 4 c m ~ ~ ,
Siemens P4;PC diffractometer. graphite-monochromated Cu,, radiation. The
structure was solved by direct methods and refined anisotropically (based on
F') to give R , = 0 087. wR, = 0.202 for 2516 independent observed reflections
with [If;J < 4u(lFO1).2H<114-]. FurtherdetailsoftheL.rystalstructureinvestigations may he obtained from the Director of the Cambridge Crystallographic Data Centre. 12 Union Road. GB-Cambridge CB2 IEW ( U K ) .
141 a ) W. L. Jorgensen, D. L. Severance. J A m Chern. SO( 1990. 112.4768~4774;
h) M. C. Grossel. A. K . Cheetham. D. A. Hope. S. C. Weston. J. Org. C'hrm.
1993. 58. 6651 -6661 ; c) S. Paliwal. G Geib. C. S. Wilcoh. J. . h i . ('hem. SOC.
1994. 116. 4497-4498.
IS] a ) D. B. Amabilino. I. W. Parsons. J. F. Stoddart. T r c n d A 111 P o h Sci. /Camhridjie. U K ) 1994. 2. 146 152; b) H . W Gibson, M . C ' Bheda. P. T. Engen
Prog. Polvni. S u 1994.19.843-945: c) H. W Gibson. S Lui. P. Lecavalier. C.
Wu. Y.X , Shen. J. 4 m . Cheni. SOC.1995. 117. 852-874
The 2 : 1 complex was crystallized by vapor diffusion of diisopropyl ether into
an acetonitrile solution of the bisammonium salt 3-H, ' 2 PF,, and DB24C8 (1 : 2
stoichiometry).
The solubility of I-H.PF, is roughly Xmg in 1 0 m L of CD,CI,, while
3-H,-2PF6 is virtually insoluble in this solvent.
The 4A valuer (with reference to the uncomplexed crown ether) for the C,H,,
r-CH,, [ K H , , y C H , . and A-CH, protons in BPP34CIO deduced from the
'H NMR spectrum of [BPP34CI0.(I-H),][PFJ2 recorded in CD2CI,
are t 0 . 1 8 . -0.03. -0.12. -0.31. and -0.43. respectively.
For an equimolar mixture of BPP34CIO and 3-Hz.2PF, in CD,CI,!CD,CN
( 3 : l , b , v ) . A6 values (with reference to the free salt) of -0.34 and -0.11,
respectively. are observed in the ' H NMR spectrum for the aromatic and benrylic methylene protons associated with the bridging /JU~O-XYIYI group in the
[3-HJ2 dication.
The 46 values (with reference to the uncomplexed crown ether and the free salt)
for different protons obtained from the ' H NMR spectrum of this sample
recorded in CDCI,/CD,CN ( l : l , v:v) range a) from -0.05 to -0.19
for protons i n DB24C8 and b) from -0.67 to + 0.35 for protons in
3-H, ,?. PF,.
FABMS were recorded on a Kratos MS80RF mass spectrometer (accelerating
voltage 3 kV, resolution 1000) coupled to a DS data \)stem and off-line Sun
Workstation for processing the raw data. The atom gun was an adapted saddle
field source (lon Tech Limited) that operated at ca. 8 keV and with a tube
current ofca. 2 mA. Krypton was used to provide a primdry beam ofatoms and
the samples were dissolved in a small volume of 3-nitrohenryl alcohol which
had previously been coated on to a stainless steel probe tip. Spectra were
recorded in the positive-ion mode at a scan speed of 311 s per decade.
The double-stranded inclusion complexes that are formed %hen7-cyclodextrin
threads simultaneously on to two poly(ethy1ene glycol) chains is one of the very
few examples in the literature of this particular form of supermolecule involving a macrocycle. See A Harada, J. Li. M. Kamachi. Nuturc. 1994. 370,
126-128. The formation of molecular nanotube aggregates of B- and ;'-cyclodextrins has been reported. See G . Li. L. B. McGown. S(.ienw 1994. 264.
249-251.
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