Multiply stranded and multiply encircled pseudorotaxanes

Article abstract of DOI:10.1021/ja9714806

The self-assembly of four multicomponent rotaxane-like complexes, in which either (a) three or four dibenzo-[24]crown-8 rings encircle threadlike oligoammonium cations [PhCH₂(NH₂+CH₂C₆H₄CH₂

Full text of DOI:10.1021/ja9714806

12514
J. Am. Chem. Soc. 1997, 119, 12514-12524
Multiply Stranded and Multiply Encircled Pseudorotaxanes†
Peter R. Ashton,‡ Matthew C. T. Fyfe,‡ Peter T. Glink,‡ Stephan Menzer,§
J. Fraser Stoddart,*,‡,| Andrew J. P. White,§ and David J. Williams§
Contribution from The School of Chemistry, The UniVersity of Birmingham,
Edgbaston, Birmingham B15 2TT, UK, and The Chemical Crystallography Laboratory,
Department of Chemistry, Imperial College, South Kensington, London SW7 2AY, UK
ReceiVed May 7, 1997. ReVised Manuscript ReceiVed October 16, 1997X
Abstract: The self-assembly of four multicomponent rotaxane-like complexes, in which either (a) three or four dibenzo-
[24]crown-8 rings encircle threadlike oligoammonium cations [PhCH2(NH2+CH2C6H4CH2)nNH2+CH2Ph] (n ) 2 or
3) to form multiply encircled pseudorotaxanes, or (b) three or four dibenzylammonium ions are threaded simultaneously
through large macrocyclic polyethers, Viz., tris-p-phenylene[51]crown-15 and tetrakis-p-phenylene[68]crown-20, to
give multiply stranded pseudorotaxanes, is described. These supramolecular entities are created on account of
stabilizing [N+sH‚‚‚O] and [CsH‚‚‚O] hydrogen bonds, supplemented occasionally by aromatic face-to-face and
edge-to-face interactions, and [CsH‚‚‚F] intermolecular bonds. Evidence for the existence of these diverse
pseudorotaxane architectures in solution, in the solid state, and in some cases, in the “gas phase”, is provided by 1H
NMR spectroscopy, X-ray crystallography, and mass spectrometry, respectively.
Introduction
Scheme 1. A Generic [2]Pseudorotaxane, Created When a
Macrocyclic Beadlike Component (open square) Encircles a
Threadlike Component (black bar)a
One of the major areas of investigation in modern synthetic
chemistry is the construction1 of thermodynamically stable
supramolecular2 aggregates and arrays in a controlled and
predictable manner utilizing self-assembly processes3 that rely
upon noncovalent bonding interactions.4 One particularly
interesting class of supramolecular aggregates is the so-called
pseudorotaxanes.5 These supramolecular entities are comprised
(Scheme 1) of one (or more) threadlike component(s) which is
(are) encircled by one (or more) beadlike component(s). They
are promising prototypes for a variety of nanoscopic machinelike
systems,6 such as switches7 and shuttles.8 Until recently,
a The prefix of an [n]pseudorotaxane indicates that the complex is
comprised of n components.
pseudorotaxanes have been prepared most conveniently by
utilizing one of the following systems: (a) the van der Waals
interactions9 between cyclodextrin derivatives and hydrophobic
guests, (b) the metal-ligand interactions10 between metal ions,
such as copper(I), and bipyridine-derived beads/threads, and (c)
the attraction between π-electron-rich11 (or π-electron-defi-
cient12) macrocyclic hosts and π-electron-deficient (or π-electron-
rich) threadlike guests. In the past few years, we have
developed13-16 extremely simple self-assembling systems which
produce pseudorotaxane complexes. They are based upon the
association between secondary dialkylammonium ions, such as
the linear threadlike cationic salts, dibenzylammonium
† Molecular Meccano, Part 24. For Part 23, see: Ashton, P. R.; Boyd,
S. E.; Menzer, S.; Pasini, D.; Raymo, F. M.; Spencer, N.; Stoddart, J. F.;
White, A. J. P.; Williams, D. J.; Wyatt, P. G. J. Am. Chem. Soc., in press.
‡ University of Birmingham.
§ Imperial College.
| Address for correspondence: Department of Chemistry and Biochem-
istry, University of California at Los Angeles, 405 Hilgard Avenue, Los
Angeles, CA 90095.
X Abstract published in AdVance ACS Abstracts, December 15, 1997.
(1) Fyfe, M. C. T.; Stoddart, J. F. Acc. Chem. Res. 1997, 30, 393-401.
(2) Lehn, J.-M. Supramolecular Chemistry-Concepts and PerspectiVes;
VCH: Weinheim, 1995.
(3) Philp, D.; Stoddart, J. F. Angew. Chem., Int. Ed. Engl. 1996, 35,
1154-1196.
(4) Some recent examples serve to highlight the kinds of approaches
being taken. See: (a) Fujita, M.; Ogura, D.; Miyazawa, M.; Oka, H.;
Yamaguchi, K.; Ogura, K. Nature (London) 1995, 378, 469-471. (b)
Hartgerink, J. D.; Granja, J. R.; Milligan, R. A.; Ghadiri, M. R. J. Am.
Chem. Soc. 1996, 118, 43-50. (c) Zimmerman, S. C.; Zeng, F.; Reichert,
D. E. C.; Kolotuchin, S. V. Science 1996, 271, 1095-1098. (d) Funeriu,
D. P.; Lehn, J.-M.; Baum, G.; Fenske, D. Chem. Eur. J. 1997, 3, 99-104.
(e) Meissner, R.; Garcias, X.; Mecozzi, S.; Rebek, J., Jr. J. Am. Chem.
Soc. 1997, 119, 77-85. (f) Whang, D.; Kim, K. J. Am. Chem. Soc. 1997,
119, 451-452.
(5) Amabilino, D. B.; Anelli, P.-L.; Ashton, P. R.; Brown, G. R.;
Co´rdova, E.; God´ınez, L. A.; Hayes, W.; Kaifer, A. E.; Philp, D.; Slawin,
A. M. Z.; Spencer, N.; Stoddart, J. F.; Tolley, M. S.; Williams, D. J. J. Am.
Chem. Soc. 1995, 117, 11142-11170.
(9) Wenz, G. Angew. Chem., Int. Ed. Engl. 1994, 33, 803-822.
(10) Baxter, P. N. W.; Sleiman, H.; Lehn, J.-M.; Rissanen, K. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1294-1296.
(11) For instance, see: Ashton, P. R.; Ballardini, R.; Balzani, V.;
Belohradsky, M.; Gandolfi, M. T.; Philp, D.; Prodi, L.; Raymo, F. M.;
Reddington, M. V.; Spencer, N.; Stoddart, J. F.; Venturi, M.; Williams, D.
J. J. Am. Chem. Soc. 1996, 118, 4931-4951.
(12) For leading references, see: Asakawa, M.; Ashton, P. R.; Brown,
G. R.; Hayes, W.; Menzer, S.; Stoddart, J. F.; White, A. J. P.; Williams, D.
J. AdV. Mater. 1996, 8, 37-41.
(13) Ashton, P. R.; Chrystal, E. J. T.; Glink, P. T.; Menzer, S.; Schiavo,
C.; Spencer, N.; Stoddart, J. F.; Tasker, P. A.; White, A. J. P.; Williams,
D. J. Chem. Eur. J. 1996, 2, 709-728.
(6) For leading references, see: Credi, A.; Balzani, V.; Langford, S. J.;
Stoddart, J. F. J. Am. Chem. Soc. 1997, 119, 2679-2681.
(7) Co´rdova, E.; Bissell, R. A.; Kaifer, A. E.; Stoddart, J. F. Nature
(London) 1994, 369, 133-137.
(8) Anelli, P.-L.; Asakawa, M.; Ashton, P. R.; Bissell, R. A.; Clavier,
G.; Go´rski, R.; Kaifer, A. E.; Langford, S. J.; Mattersteig, G.; Menzer, S.;
Philp, D.; Slawin, A. M. Z.; Spencer, N.; Stoddart, J. F.; Tolley, M. S.;
Williams, D. J. Chem. Eur. J. 1997, 3, 1113-1135.
(14) Ashton, P. R.; Glink, P. T.; Stoddart, J. F.; Tasker, P. A.; White,
A. J. P.; Williams, D. J. Chem. Eur. J. 1996, 2, 729-736.
(15) Ashton, P. R.; Collins, A. N.; Fyfe, M. C. T.; Glink, P. T.; Menzer,
S.; Stoddart, J. F.; Williams, D. J. Angew. Chem., Int. Ed. Engl. 1997, 36,
59-62.
(16) Ashton, P. R.; Glink, P. T.; Mart´ınez-D´ıaz, M.-V.; Stoddart, J. F.;
White, A. J. P.; Williams, D. J. Angew. Chem., Int. Ed. Engl. 1996, 35,
1930-1933.
S0002-7863(97)01480-7 CCC: $14.00 © 1997 American Chemical Society

Multiply Stranded and Multiply Encircled Pseudorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12515
Figure 1. Chemical formulas and cartoon representations for the
threadlike oligocations 1+ and 22+ (black bars) and the crown ethers
DB24C8 (open squares) and BPP34C10 (open rectangles).
Scheme 2. Cartoon Representations Illustrating the
Geometries and Stoichiometries of the Complexes between
Linear Secondary Dialkylammonium Mono- and Dications
(black bars) and Macrocyclic Polyethers (open squares and
rectangles) Reported to Date
Figure 2. Chemical formulas and cartoon representations of the
oligocations 33+ and 44+ (black bars) and the macrocyclic polyethers
TPP51C15 (open triangle) and TPP68C20 (open diamond).
of 1:1 (e.g., [DB24C8‚1]+), 1:2 (e.g., [BPP34C10‚(1)2]2+), 2:1
(e.g., [(DB24C8)2‚2]2+), and 2:2 (e.g., [(BPP34C10)2‚(2)2]4+),
respectively. These examples divulge that DB24C8 will ac-
commodate only one secondary dialkylammonium center within
its cavity to generate single-stranded pseudorotaxanes (e.g.,
[DB24C8‚1]+ and [(DB24C8)2‚2]2+), while BPP34C10 can
accommodate two such units to form double-stranded pseu-
dorotaxane complexes (e.g., [BPP34C10‚(1)2]2+ and
+
[(BPP34C10)2‚(2)2]4+), and that separating the NH2 centers
of threadlike units by p-xylyl spacer groups allows each of these
centers to be encircled by an individual crown ether (e.g.,
[(DB24C8)2‚2]2+ and [(BPP34C10)2‚(2)2]4+).13 We were thus
+
intrigued to find out whether we could (a) add more NH2
centers to the threadlike oligocations, in order to encircle more
than two crown ethers around the threads, and (b) further
increase the size of the crown ether macroring to see if more
than two dialkylammonium ions could thread through even
larger macrocyclic cavities. That is, can we extend the cartoon
displayed in Scheme 2, both in a “north-south” and an “east-
west” direction? Here, we report that multiply stranded and
multiply encircled pseudorotaxane complexes are indeed capable
of being formed and characterized, in solution, in the solid state,
and in some instances, in the “gas phase”.
hexafluorophosphate (1‚PF6) and R,R′-bis(benzylammonium)-
p-xylene bis(hexafluorophosphate) (2‚2PF6) (Figure 1), and
macrocyclic polyethers, such as dibenzo[24]crown-8 (DB24C8)
and bis-p-phenylene[34]crown-10 (BPP34C10) (Figure 1), that
have sufficiently large rings to permit the passage of alkyl and
aryl groups through their cavities. These rotaxane-like super-
structures, stabilized primarily by [N+sH‚‚‚O] and [CsH‚‚‚O]
hydrogen bonds, provide a practicable and versatile recognition
motif for supramolecular synthesis, in that the stoichiometries
and geometries of complexation may be altered by changing
either (a) the number of dialkylammonium centers in the cationic
threadlike units, or (b) the size of the macrocyclic polyether’s
cavity.13 By way of illustration, we have reported17 to date,
the characterization13 of four different types of pseudo-
rotaxane complexes (Scheme 2) with stoichiometries (host:guest)
Results and Discussion
Supramolecular Strategy. In the knowledge that 2‚2PF6
forms a 2:1 complex (host:guest) with DB24C8, the obvious
choices for tri- and tetracationic threadlike saltssthat might be
capable of complexing with three and four crown ethers,
(17) For the synthesis of an alternative family of rotaxanes that are
stabilized primarily by hydrogen bonding, see: Vo¨gtle, F.; Du¨nnwald, T.;
Schmidt, T. Acc. Chem. Res. 1996, 29, 451-460 and references cited therein.
+
respectivelysare those in which the NH2 centers are evenly
spaced using p-xylyl groups, i.e., as in the salts 3‚3PF6 and

12516 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Scheme 3. Synthesis of the Tricationic Salt 3‚3PF6
Ashton et al.
the supramolecular system is characterized by equilibria involv-
ing slow kinetic exchange on the H NMR time scale at 300
1
MHz as a result of the large (but surmountable) steric barrier
for the slippage of the rather small DB24C8 ring over the
relatively bulky phenyl and p-xylyl units. Signals associated
with the uncomplexed crown ether and the “free” tricationic
salt, besides those for the 1:1, 2:1, and 3:1 complexes formed
between the two species, are present. The complexity of the
1H NMR spectrum makes signal assignment for the individual
complexes rather difficult. In the case of complexation between
3‚3PF6 and DB24C8 (Scheme 5), there are two possible
“isomeric” 1:1 complexes [DB24C8‚3]3+ (A and B), two
“isomeric” 2:1 complexes [(DB24C8)2‚3]3+ (C and D), and one
3:1 complex [(DB24C8)3‚3]3+. In addition to uncomplexed host
and guest species, this situation means that there are a total of
13 different environments for the protons of the R-, â-, and
γ-OCH2 units of the crown ether in the slowly equilibrating
mixture. Additionally, the necessity of using polar solvents,
such as CD3CN or CD3COCD3, to dissolve the tricationic salt
means that association constants13 for the individual DB24C8‚
R2NH2+ complexes are in the region of 102-103 M-1, an order
of magnitude which corresponds to a significant amount of each
of these species existing in solution at the concentrations usually
employed for recording 1H NMR spectra. We have found that
the complex spectroscopic behavior can be minimized by
1
obtaining the H NMR spectrum of 3‚3PF6 in the presence of
4‚4PF6 (Figure 2). As host molecules, suitable for including
more than two dialkylammonium cations within their cavities,
we chose to study the crown ethers tris-p-phenylene[51]crown-
15 (TPP51C15) and tetrakis-p-phenylene[68]crown-20
(TPP68C20) (Figure 2), i.e., higher homologues of the crown
ether BPP34C10. These two “new” crown ethers, prepared
previously to act as templates for the formation of multiply
interlocked ring systems, i.e., catenanes,18 might be expected
to thread three and four thread-like cations through their
individual cavities, primarily as a result of [N+sH‚‚‚O]
hydrogen-bonding interactions with their respective three and
four tetraethylene glycol-derived polyether loops.
Synthesis. The tricationic salt 3‚3PF6 was obtained in an
overall yield of 39% (Scheme 3) via a six-step process from
the known14 diol 5. The tetracationic salt 4‚4PF6 was prepared
(Scheme 4) in 40% overall yield from benzylamine and methyl
4-formylbenzoate using a similar protocol. The macrocyclic
polyethers TPP51C15 and TPP68C20 were synthesized accord-
ing to established procedures.18
Complexation: Tricationic Salt 3‚3PF6 and DB24C8.
Although the tricationic salt 3‚3PF6 is soluble in polar solvents,
such as Me2CO and MeCN, that are capable of hydrogen
bonding with the NH2+ centers, not surprisingly, it is insoluble19
in halogenated solvents such as CH2Cl2 and CHCl3. A solution
of the salt in either MeCN or Me2CO in the presence of >3
mol equiv of DB24C8 may be diluted with CH2Cl2 or CHCl3
such that no precipitate is formed from what is essentially a
solution of 3‚3PF6 and DB24C8 in the halogenated solvent. This
behavior, comparable with solubility characteristics we have
observed13 for the dicationic salt 2‚2PF6 previously, points to
the formation of a multiply encircled complex that is soluble
in chlorinated solvents.
an excess (∼10 mol equiv) of DB24C8 in a CDCl3/CD3CN
solvent mixture. The presence of the halogenated solvent
increases the association constants for the complexation proc-
esses, while the excess of the crown ether ensures that the
equilibria between the uncomplexed and rotaxane-like systems
are driven toward the 3:1 complex. In this case, a spectrum
was obtained20 in which two major species, Viz., the excess of
uncomplexed DB24C8 and the [4]pseudorotaxane,
[(DB24C8)3‚3]3+, were found to be present in solution. The
stoichiometry of the complex was ascertained to be 3:1 from
an examination of the relative intensities of the signals associated
with the complexed host and guest for the (a) aromatic protons
and (b) methylene protons.
Crystals were obtained when i-Pr2O vapor was allowed to
diffuse into an Me2CO solution containing a 3:1 molar mixture
of DB24C8 and 3‚3PF6. Analysis of one such crystal by liquid
secondary ion mass spectrometry (LSIMS) revealed20 an intense
peak at m/z 2077, corresponding to the 3:1 complex with the
loss of only one of its counterions, i.e., [(DB24C8)3‚3‚2PF6]+.
The fact that the integrity of the 3:1 complex is maintained in
the “gas phase”, with an intensity ca. 3% of that of the base
peak (in this case, the 1:1 complex [DB24C8‚3 - 2H+] which
is observed at m/z 884), is a testament to the stability, and
presumably the slow rates of dissociation (cf., the solution state),
of the four-component pseudorotaxane superstructure.
A single crystal of the complex was analyzed by X-ray
crystallography. The solid-state structure of the 3:1 complex
[(DB24C8)3‚3][PF6]3 shows (Figure 3) the trication to be
threaded through the centers of three DB24C8 macrocycles, one
of which (A) has a folded geometry, while the others (B and
C) have extended Ci-like conformations. Host-guest stabiliza-
tion is achieved by a combination of [N+sH‚‚‚O] and [CsH‚‚‚O]
hydrogen bonding, supplemented by face-to-face π-π stacking
between the p-xylyl rings of the trication and one of the catechol
rings of each of the DB24C8 hosts (Figure 4). Inspection of
the packing of the [4]pseudorotaxanes reveals (Figure 5) that
centrosymmetrically related pairs are oriented such that one of
the terminal phenyl rings of one trication (that proximal to
Analysis of an CD3CN solution containing a 3:1 molar ratio
of DB24C8 and 3‚3PF6 revealed a complicated scenario, since
(18) Amabilino, D. B.; Ashton, P. R.; Brown, C. L.; Co´rdova, E.;
Go´dinez, L. A.; Goodnow, T. T.; Kaifer, A. E.; Newton, S. P.; Pietraszk-
iewicz, M.; Philp, D.; Raymo, F. M.; Reder, A. S.; Rutland, M. T.; Slawin,
A. M. Z.; Spencer, N.; Stoddart, J. F.; Vicent, C.; Williams, D. J. J. Am.
Chem. Soc. 1995, 117, 1271-1293.
(19) We have noted previously13 that the hexafluorophosphate salts of
1
+ and of 22+ are practically insoluble in CHCl3 and CH2Cl2 in the absence
of a suitably sized crown ether for complexation.
(20) See the Supporting Information for details.

Multiply Stranded and Multiply Encircled Pseudorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12517
Scheme 4. Synthesis of the Tetracationic salt 4‚4PF6
macrocycle C) is parallel to, and overlapping with, that of
another, in a geometry which is consistent with a strong π-π
stacking interaction. This interaction results in the formation
of a π-π-linked [7]pseudorotaxane, the distance between the
centroids of the terminal phenyl rings being 45.1 Å (cf., 21.6 Å
within the covalent framework of the 33+ trication).21 Adjacent
[7]pseudorotaxanes are oriented such that the catechol rings of
one interleave with those of the next. Although these rings are
aligned essentially parallel to each other, the interplanar
distances and centroid-centroid separations are too large to
represent any significant π-π interactions.
Complexation: Tetracationic Salt 4‚4PF6 and DB24C8.
Like its tricationic congener 3‚3PF6, the tetracationic salt 4‚4PF6
dissolves readily in MeCN and Me2CO, but is insoluble in
chlorinated solvents. However, in the presence of >4 mol equiv
of DB24C8, a solution of 4‚4PF6 in Me2CO or MeCN may be
diluted with either CHCl3 or CH2Cl2 without precipitation of
the salt or its complexes, again suggesting the presence of
pseudorotaxane complexes in solution. Analysis of an CD3CN
solution, containing a 4:1 molar mixture of DB24C8 and 4‚4PF6,
1
by H NMR spectroscopy points again to the existence of a
complicated mixture of uncomplexed host-guest species and
a number of different complexes formed between them. For
4‚4PF6 and DB24C8, there exists (Scheme 6) the possibility of
two “isomeric” 1:1 complexes [DB24C8‚4]4+ (E and F), four
“isomeric” 2:1 complexes [(DB24C8)2‚4]4+ (G, H, I, and J),
two “isomeric” 3:1 complexes [(DB24C8)3‚4]4+ (K and L), and
one 4:1 complex [(DB24C8)4‚4]4+. Presumably, since a situ-
ation of slow kinetic exchange operates, different amounts of
each of these complexes, as well as of uncomplexed 4‚4PF6
and DB24C8, are present in solution. Not surprisingly, the
spectrum is exceedingly complicated; in this case, there are 33
possible different chemical environments for the protons of each
of the crown ether’s R-, â-, and γ-OCH2 groups. Nonetheless,
the situation can be made less complicated by recording the
spectrum of 4‚4PF6 in the presence of an excess (∼10 mol
equiv) of DB24C8 in a CDCl3/CD3CN solvent mixture. The
(21) Further extension of this [7]pseudorotaxane does not occur: the
non-π-π-stacked terminal phenyl rings are offset substantially with respect
to their symmetry-related counterparts and the shortest centroid-centroid
distance is 5.1 Å.

12518 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Ashton et al.
Scheme 5. Cartoon Representations Illustrating the Seven Discrete SpeciessComplexed and UncomplexedsExpected for a
Solution of 3‚3PF6 and DB24C8a
a Atoms labeled H1 to H13 represent the hydrogen atoms of the polyether loops’ OCH2 groups.
the [5]pseudorotaxane [(DB24C8)4‚4]4+. Comparison of the
relative intensities of the proton resonances on both the
complexed tetracationic thread and complexed DB24C8 macro-
cycle indicate that the stoichiometry of the major complex is
4:1 (host:guest) in solution.
Repeated attempts at growing a single crystal of the 4:1
complex, suitable for X-ray crystallographic structure determi-
nation, proved fruitless. In all cases, amorphous powders were
obtained from solutions of DB24C8 and 4‚4PF6, even after
applying various techniques and solvent systems. Analysis of
the powder, obtained as a result of slow evaporation of an
Me2CO solution containing a 4:1 molar ratio of DB24C8 and
4‚4PF6, by LSIMS revealed20 an intense peak, corresponding
to the [5]pseudorotaxane [(DB24C8)4‚4‚3PF6]+, at m/z 2786.
Additionally, we detected peaks representing ions created as a
result of the extrusion of one, two, and three DB24C8
macrorings (with concomitant loss of HPF6 units) from the
complex. Moreover, the peak corresponding to the fully
complexed thread, in this case, [(DB24C8)4‚4‚3PF6]+, exists as
the peak of highest mass, with an intensity roughly 5% of that
of the base peak (which in this case, is the species [DB24C8‚4
- 3H]+). The observation of such an intense peak for a complex
comprised of five components suggests that mass spectrometric
soft ionization techniques are particularly valuable tools for the
Figure 3. The 3:1 complex formed between DB24C8 and 33+ in the
solid state. The three independently threaded DB24C8 macrocycles are
labeled A, B, and C.
1H NMR spectrum20 obtained under these conditions is remark-
ably simple and indicates the presence of two major species in
solution, specifically, the excess of uncomplexed DB24C8 and

Multiply Stranded and Multiply Encircled Pseudorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12519
Figure 4. The host-guest hydrogen bonding and π-π stacking interactions in the [(DB24C8)3‚3]3+ superstructure. Interactions involving macrocycle
A [N+sH‚‚‚O] hydrogen bonds [[N+‚‚‚O], [H‚‚‚O] distances (Å) and [N+sH‚‚‚O] angles (deg)] (a) 2.97, 2.18, 140; (b) 3.11, 2.28, 144; (c) 3.04,
2.15, 152; [CsH‚‚‚O] distances and angle (d) 3.26, 2.35, 158; π-π stacking (e) interplanar separation 3.47 Å and centroid-centroid separation
3.71 Å. Interactions involving macrocycle B: [N+sH‚‚‚O] hydrogen bonds [[N+‚‚‚O], [H‚‚‚O] distances (Å) and [N+sH‚‚‚O] angles (deg)] (f)
2.92, 1.98, 166; (g) 3.19, 2.25, 165; [CsH‚‚‚O] distances and angle (h) 3.28, 2.49, 140; π-π stacking (i) interplanar separation 3.47 Å and
centroid-centroid separation 3.71 Å. Interactions involving macrocycle C: [N+sH‚‚‚O] hydrogen bonds [[N+‚‚‚O], [H‚‚‚O] distances (Å) and
[N+sH‚‚‚O] angles (deg)] (j) 3.17, 2.25, 161 (k) 3.05, 2.12, 164; π-π stacking (l) interplanar separation 3.44 Å and centroid-centroid separation
3.67 Å.
Figure 5. The packing of the [4]pseudorotaxane showing the formation of a [7]pseudorotaxane via π-π linking. The interplanar separation and
centroid-centroid distance between the π-stacked trications are 3.62 and 3.66 Å, respectively.
characterization of higher order [n]pseudorotaxanes of this type
in the “gas phase”.
not unexpected, since the LSI mass spectrum of a mixture of
BPP34C10 and 1‚PF6 exhibited13 only an extremely weak peak
(<1% of the base peak’s height) for a 1:2 complex. It is not
unreasonable to conclude that the very large cavity of the
TPP51C15 macrocycle is not suited for simultaneous accom-
modation of three 1+ guest ions without a significant degree of
decomplexation of at least one of them occurring in the “gas
phase”.
Complexation: TPP51C15 and Monocationic Salt 1‚PF6.
To explore the potential of the macrocyclic polyether TPP51C15
as a suitable host molecule for guest 1+ ions, >3 mol equiv of
1‚PF6 were suspended in a CDCl3 solution of the crown ether.
After filtration, the 1H NMR spectrum obtained from the solution
suggested, on the basis of the integrals associated with the
signals for host and guest probe protons, that <1 equiv of the
salt had been extracted into the solution. On the other hand,
using CD2Cl2 as the extraction solvent resulted in the dissolution
of what approximates very closely to 3 mol equiv of 1‚PF6.22
Since the solubility of 1‚PF6 in CD2Cl2 is extremely low in the
absence of TPP51C15, we believe that all of the salt must be
complexed by the crown ether in solution. Significant chemical
shift changes were detected23 for the proton resonances of both
the macrocyclic polyether and 1+, thus indicating strong
complexation between the two species in solution.
The X-ray analysis24 of one of the aforementioned crystals
reveals (Figure 6) a supramolecular architecture in which three
1+ cations are threaded through the center of the TPP51C15
macrocycle, which adopts a saddlelike conformation with
approximate Cs symmetry. Complex stabilization is achieved
via a combination of [N+sH‚‚‚O] and [CsH‚‚‚O] hydrogen
bonding. Despite the large number of aromatic rings in the
1:3 complex, there is a marked absence of any intra- or
intercomplex face-to-face or edge-to-face interactions. The
packing interactions appear to be only of a van der Waals nature.
However, inspection of the relationship between the cations and
Crystals of the complex were obtained by layering a 1:3
mixture of TPP51C15 and 1‚PF6 in CH2Cl2 with n-C6H14.
Analysis of one such crystal by LSIMS failed to indicate
complexation beyond a 1:2 stoichiometry. This observation was
-
anions reveals that one of the PF6 anions is located almost
centrally within the cleft formed by the folded saddlelike
co-conformation25 of the 1:3 complex (Figure 6). The planes
of the three hydroquinone rings, together with one of the phenyl
(22) We have used this technique previously13 in order to determine the
complexation stoichiometry for the association between BPP34C10 and
1‚PF6 in CD2Cl2.
(23) ∆δ values were obtained for the proton resonances of the polyether’s
R-, â-, γ-, and δ-OCH2 and hydroquinone CH groups. For a solution of
TPP51C15 (∼5 × 10-3 M) and 1‚PF6 (∼1.5 × 10-2 M) in CD2Cl2 at 20
°C these were 0.00, -0.17, -0.29, -0.36, and +0.13 ppm, respectively.
(24) Fyfe, M. C. T.; Glink, P. T.; Menzer, S.; Stoddart, J. F.; White, A.
J. P.; Williams, D. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 2068-2070.
(25) Strictly speaking, the term “conformation” refers only to discrete
molecular species. Consequently, we have used24 “co-conformation” to
designate the three-dimensional spatial arrangement of the atoms in
supramolecular systems.

12520 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Ashton et al.
Scheme 6. Cartoon Representations of the 11 Discrete SpeciessComplexed and UncomplexedsExpected for a Solution
Containing a Mixture of 4‚4PF6 and DB24C8a
a Atoms labeled H1 to H33 represent the hydrogen atoms of the polyether loops’ OCH2 groups.
rings of one of the 1+ cations, are all inclined toward, and
intersect at, the phosphorus atom. An analysis of [CsH‚‚‚F]
contacts reveals the presence of several stabilizing hydrogen
bonding interactions with [H‚‚‚F] distances in the range 2.43-
2.67 Å (associated [C‚‚‚F] distances range from 3.20-3.51 Å).
It is interesting to note that hydrogen atoms of both hydro-
quinone rings and benzylic methylene groups are involved in
these interactions.
for the proton resonances on both the host and guest species,
suggesting strong intercomponent association in CD2Cl2.
Analysis of a 1:4 mixture of TPP68C20 and 1‚PF6 by LSIMS
did not reveal any host-guest association beyond a 1:2
stoichiometry. This result is entirely in line with that observed
for the “gas phase” association of the [TPP51C15‚(1)3][3PF6]
system. It suggests that, for the most part, it is not possible to
obtain meaningful information (i.e., observing peaks corre-
sponding to “fully” complexed supramolecular entities) on the
“gas phase” association between secondary dialkylammonium
ions and these very large ring crown ethers using this particular
soft ionization technique.
A suitable single crystal for X-ray crystallography was grown
by liquid diffusion of n-C6H14 into a CH2Cl2 solution containing
a 1:4 molar mixture of TPP68C20 and 1‚PF6. The X-ray
analysis of one of these crystals reveals24 the creation of a
crystalline aggregate containing two independent 1:4 complexes
Complexation: TPP68C20 and Monocationic Salt 1‚PF6.
Deployment of the macrocyclic polyether TPP68C20, which
possesses four polyether loops each capable, in principle, of
binding secondary dialkylammonium ions, provided some
notable findings in its complexation behavior with 1‚PF6. In
order to obtain information on the complex’s approximate
stoichiometry, we used the established technique (Vide supra)
of extracting this insoluble salt into a TPP68C20-containing
1
CD2Cl2 solution. Using this technique, we observed, by H
NMR spectroscopy,20 the dissolution of an amount of salt that
approximates to the extraction of 4 mol equiv of 1‚PF6 from a
CD2Cl2 suspension containing about a 10-fold excess of the salt.
Once again, significant chemical shift changes were observed26
(26) ∆δ values were obtained for the proton resonances of the polyether’s
R-, â-, γ-, and δ-OCH2 and hydroquinone CH groups. For a solution of
TPP68C20 (∼5 × 10-3 M) and 1‚PF6 (∼2.0 × 10-2 M) in CD2Cl2 at 20
°C these were -0.03, -0.15, -0.23, -0.38, and +0.16 ppm, respectively.

Multiply Stranded and Multiply Encircled Pseudorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12521
Figure 6. Ball-and-stick representation of the 1:3 complex [TPP51C15‚
(1)3]3+ in the solid state, showing the [N+sH‚‚‚O] and [CsH‚‚‚O]
-
hydrogen-bonding interactions and the PF6 anion that interacts with
the supermolecule. [N+sH‚‚‚O] hydrogen bonds [[N+‚‚‚O], [H‚‚‚O]
distances (Å), [N+sH‚‚‚O] angles (deg)]: (a) 2.89, 1.94, 168; (b) 3.02,
2.07, 176; (c) 2.88, 2.09, 138; (d) 2.91, 2.02, 153; (e) 2.98, 2.16, 142;
(f) 2.86, 2.09, 137; (g) 2.85, 1.95, 155; [CsH‚‚‚O] distances and angles
(h) 3.36, 2.47, 155; (i) 3.38, 2.45, 163.
(Figure 7), together with an additional pair of nonrelated Cs
symmetric 1+ cations, all with their associated PF6- counterions,
in the asymmetric unit. The two 1:4 complexes have essentially
identical geometries with each TPP68C20 macrocycle adopting
a tennis ball seam-like conformation with S4 symmetry.
Complex stabilization is achieved via a combination of
[N+sH‚‚‚O] and [CsH‚‚‚O] hydrogen-bonding interactions
between the hydrogen atoms of the ammonium centers, and their
adjacent CH2 groups, with oxygen atoms from the macrocyclic
polyether. The nonthreaded cations, which lie on the crystal-
lographic Cs plane, are not involved in any hydrogen-bonding
interactions. The only notable intercomplex interaction is an
aromatic-aromatic edge-to-face association between one of the
phenyl rings of a 1+ ion in one complex and one of the
macrocyclic polyether’s hydroquinone rings in the other (the
[H‚‚‚π] distance is 2.75 Å and the associated [CsH‚‚‚π] angle
is 138°). The most striking feature of the 1:4 complexes is the
siting (Figure 7) of a single PF6- anion within their cores in an
ordered arrangement. The anion is totally encapsulated by both
the four hydroquinone rings, which are oriented with their planes
intersecting on the phosphorus center, and the four tetrahedrally
disposed, positively charged CH2-NH2+-CH2 units of the four
1+ cations (Figure 8). The phosphorus atoms lie only ∼0.3 Å
from the complexes’ centroids. As in the 1:3 complex (Vide
supra), the anion is held in place by [CsH‚‚‚F] hydrogen bonds
involving a combination of hydroquinone methine and benzylic
methylene hydrogen atoms. The [H‚‚‚F] distances range
between 2.41-2.73 Å, with associated [C‚‚‚F] contacts of
between 3.16-3.52 Å.
Figure 7. (a) Ball-and-stick representation of the solid-state super-
structure of one of the 1:4 complexes [TPP68C20‚(1)4]4+, illustrating
the gross binding mode of the threadlike cations by the macrocyclic
polyether that permits the complete encapsulation of a PF6- anion. (b)
Detailed analysis of the [N+sH‚‚‚O] and [CsH‚‚‚O] hydrogen-bonding
interactions for the four independent complexation sites (A-D).
[XsH‚‚‚O] Hydrogen bonds [[X‚‚‚O], [H‚‚‚O] distances (Å), [XsH‚‚‚O]
angles (deg)]: (a) 3.00, 2.04, 170; (b) 3.01, 2.05, 174; (c) 3.24, 2.35,
154; (d) 3.29, 2.40, 155; (e) 2.87, 1.92, 171; (f) 2.86, 2.25, 120; (g)
3.07, 2.15, 160; (h) 2.78, 1.88, 155; (i) 2.98, 2.25, 132; (j) 3.20, 2.33,
151; (k) 2.91, 1.96, 170; (l) 2.82, 1.89, 162. The other 1:4 complex
exhibits a virtually identical hydrogen-bonding array. [XsH‚‚‚O]
hydrogen bonds [[X‚‚‚O], [H‚‚‚O] distances (Å), [XsH‚‚‚O] angles
(deg)]: (a) 2.98, 2.03, 168; (b) 2.95, 2.00, 170; (c) 3.26, 2.45, 141; (d)
3.33, 2.41, 161; (e) 2.88, 1.92, 172; (f) 2.87, 2.28, 119; (g) 3.10, 2.17,
162; (h) 2.89, 2.08, 141; (i) 2.85, 2.00, 148; (j) 3.19, 2.46, 133; (k)
2.93, 1.97, 177; (l) 2.83, 1.88, 169.
in some cases, the “gas phase”), is retained, although with
occasional surprises. Nonetheless, these self-assembling sys-
tems are characterized by their simplicity on the one hand (i.e.,
constitutionally), and their complexity and intricacy (i.e.,
superstructurally) on the other.
Conclusions
The research documented in this Article represents a signifi-
cant extension (Figure 9) to the knowledge that we have already
obtained from studying relatively simple host-guest systems
based upon interactions between macrocyclic polyether hosts
and secondary dialkylammonium ion guests. By either extend-
ing the number of recognition sites in the threadlike oligocations,
or by increasing the size of the crown ether macrorings, we
have demonstrated that the control and predictability of the
binding modes, in addition to the complexation stoichiometries
of the resulting solution- and solid-state superstructures (and
Experimental Section
General. Anhydrous THF and MeCN were distilled from sodium
benzophenone ketyl and CaH2, respectively. Column chromatography
was carried out using silica gel 60F (Merck 9385, 230-400 mesh).
Melting points were determined on an Electrothermal 9200 apparatus
and are uncorrected. 1H NMR spectra were recorded on either a Bruker
AC300 (300.1 MHz) spectrometer or a Bruker AMX400 (400.1 MHz)
spectrometer at 20 °C using either the solvent reference or TMS as the

12522 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Ashton et al.
was dissolved in PhMe (50 mL), and the solvent was evaporated again.
This procedure was repeated twice to yield a thick oil [1H NMR (CDCl3)
δ 1.52 (9H, br), 4.39 and 4.50 (both 2H, two br), 4.85 (4H, s), 7.10-
7.40 (14H, m), 7.76 (4H, d, J ) 8 Hz), 8.42 (2H, s)] which was
dissolved in MeOH (50 mL). NaBH4 (1.0 g, excess) was added with
stirring portionwise to the solution over a period of 60 min, and then
the reaction mixture was quenched by the addition of 2 N HCl to adjust
the pH to less than 2. The solvents were evaporated in Vacuo, and the
residue was partitioned between CHCl3 (50 mL) and a 10% NaOH
solution (50 mL). The aqueous phase was further extracted with CHCl3
(3 × 50 mL). The combined organic phases were dried (MgSO4), and
the solvent was evaporated to yield a thick oil [1H NMR (CDCl3) δ
1.48 (9H, s), 1.70 (2H, br), 3.80 (4H, s), 3.83 (4H, s), 4.33 and 4.40
(both 2H, two br), 7.18 (4H, br), 7.23-7.40 (14H, m)] which was
dissolved in CH2Cl2 (50 mL). TFA (1 mL, excess) was added, and
the solution was stirred for 12 h. The solution was washed with a
10% NaOH solution (50 mL) and dried (MgSO4), and the solvent was
evaporated to yield a thick oil. HCl (2 N, 50 mL) was added, and the
mixture was sonicated to break up the resulting solid. The HCl solution
was evaporated under reduced pressure, and the residue was suspended
in Me2CO (10 mL). A solution of NH4PF6 (1.0 g, excess) in H2O (2
mL) was added. After more H2O had been added to the suspension to
effect dissolution, the mixture was filtered to remove insoluble materials.
Ultimately, a copious amount of H2O was added to the filtrate, causing
a precipitate to form, which was collected, washed with cold H2O (3
× 5 mL), and dried to yield the tetracationic salt 3‚3PF6 (187 mg, 39%)
as an off-white solid: 1H NMR (CD3CN) δ 4.25-4.35 (12H, m), 7.20
(6H, br), 7.48 (10H, s), 7.56 (8H, s); 13C NMR (CDCl3) δ 51.7, 51.9,
52.5, 130.0, 130.7, 131.1, 131.2, 131.7, 132.1, 132.6, 132.8; LSIMS
m/z (%) 582 (12) [M - PF6 - HPF6]+, 436 (100) [M - PF6 - 2HPF6]+.
Anal. Calcd for C30H36N3P3F18: C, 41.25; H, 4.15; N, 4.81. Found:
C, 41.25; H, 4.16; N, 4.96.
Figure 8. Cartoon representation depicting the binding of one of the
-
PF6 anions within the cavity formed by one of the 1:4 complexes
[TPP68C20‚(1)4]4+
.
N-(tert-Butoxycarbonyl)-N-benzyl-4-carbomethoxybenzylamine
(7). Benzylamine (1.38 g, 12.9 mmol) and methyl 4-formylbenzoate
(2.11 g, 12.9 mmol) were condensed in PhMe (200 mL), using a similar
procedure to that described above (Vide preparation of 3‚3PF6), to
furnish a thick oil [1H NMR (CDCl3) δ 3.95 (3H, s), 4.87 (2H, s),
7.24-7.45 (5H, m), 7.85 (2H, d, J ) 8 Hz), 8.09 (2H, d, J ) 8 Hz),
8.45 (1H, s)], which was reduced with NaBH4 (Vide preparation of
3‚3PF6). The oily product was dissolved in CH2Cl2 (100 mL). Boc2O
(2.82 g, 12.9 mmol) and DMAP (20 mg, 0.16 mmol) were added, and
the resulting solution was stirred at ambient temperature for 12 h. The
solvent was evaporated to yield a colorless oil (4.45 g, 97%), a small
portion of which was purified by column chromatography (EtOAc/n-
C6H14, 1:4) for analytical purposes which was characterized as the title
compound 7: 1H NMR (CDCl3) δ 1.47 (9H, br), 3.92 (3H, s), 4.36
and 4.48 (both 2H, two br), 7.10-7.36 (7H, m), 8.00 (2H, d, J ) 8
Hz); 13C NMR (CDCl3) δ 28.3, 48.9/49.3/49.6 (three br), 52.0, 80.3,
127.0/127.3 (two br), 127.7/127.9 (two br), 128.5, 129.0, 129.8, 137.6,
139.9, 143.4, 155.9, 166.8; LSIMS m/z (%) 356 (8) [M + H]+, 300
(100) [M + H - C4H8]+. Anal. Calcd for C21H25NO4: C, 70.96; H,
7.09; N, 3.94. Found: C, 71.09; H, 6.99; N, 4.07.
Figure 9. Cartoons representing the pseudorotaxane superstructures
which have been described in this Article: (a) a triply encircled
[4]pseudorotaxane; (b) a quadruply encircled [5]pseudorotaxane; (c) a
triply stranded [4]pseudorotaxane which partially envelops an anion;
and (d) a quadruply stranded [5]pseudorotaxane which totally encap-
sulates an anion.
internal standard. 13C NMR spectra were recorded on a Bruker AC300
(75.5 MHz) spectrometer or a Bruker AMX400 (100.6 MHz) spec-
trometer at 20 °C. Liquid secondary ion mass spectra (LSIMS) were
obtained from a VG Zabspec mass spectrometer, using either a
m-nitrobenzyl alcohol or a thioglycerol matrix, operating in the positive
ion mode at a scan speed of 5 s per decade. Microanalyses were
performed by the Microanalysis Department at the University of North
London.
N-(tert-Butoxycarbonyl)-N-benzyl-4-(hydroxymethyl)benzyl-
amine (8). A solution of the ester 7 (4.40 g, 12.4 mmol) in THF (250
mL) was heated under reflux and then cooled. LiAlH4 (2.0 g, 52.7
mmol) was added portionwise to the warm solution over 30 min. The
reaction mixture was then heated under reflux for 12 h, before being
cooled down to ambient temperature. H2O was added until the
remaining aluminum hydrides had been quenched and then 2 N HCl
was added until the pH was less than 2. The solvents were evaporated,
and the residue was partitioned between H2O (100 mL) and CH2Cl2
(100 mL), with the aqueous phase being extracted further with CH2Cl2
(3 × 100 mL). The combined extracts were dried (MgSO4). The
solvent was then evaporated off to yield a clear oil (3.52 g, 87%), a
small portion of which was purified by column chromatography
(EtOAc/n-C6H14, 2:3) to afford the title compound 8: 1H NMR (CDCl3)
δ 1.49 (9H, s), 1.90 (1H, br), 4.33 and 4.40 (both 2H, two br), 4.67
(2H, s), 7.14-7.23 (4H, br), 7.23-7.40 (5H, m); 13C NMR (CDCl3) δ
28.4, 48.9, 65.1, 80.1, 127.2, 127.9, 128.2, 128.5, 129.1, 137.4, 137.9,
139.9, 156.0, 191.7; LSIMS m/z (%) 328 (18) [M + H]+, 272 (100)
[M + H - C4H8]+. Anal. Calcd for C20H25NO3: C, 73.37; H, 7.70;
N, 4.28. Found: C, 73.54; H, 7.82; N, 3.98.
N-(tert-Butoxycarbonyl)bis(4-formylbenzyl)amine (6). PCC (420
mg, 1.95 mmol) was added to a solution of N-(tert-butoxycarbonyl)-
bis[4-(hydroxymethyl)benzyl]amine14 (5) (348 mg, 0.97 mmol) in
CH2Cl2 (25 mL), and the resulting solution was stirred under a N2
atmosphere for 2 h. The mixture was then washed with H2O (50 mL),
and the aqueous phase was extracted with CH2Cl2 (3 × 50 mL). The
combined organic phases were then dried (MgSO4), the solvent was
evaporated under reduced pressure, and the residue subjected to column
chromatography (EtOAc/n-C6H14, 1:2) to yield the bisaldehyde 6 as a
colorless, viscous oil (311 mg, 91%): 1H NMR (CDCl3) δ 1.48 (9H,
s), 4.45 and 4.53 (both 2H, two br), 7.36 (4H, br s), 7.86 (4H, d, J )
8 Hz), 10.02 (2H, s); 13C NMR (CDCl3) δ 28.3, 49.9 (br), 80.9, 127.6
and 128.2 (both br), 130.1, 135.7, 144.8, 155.7, 191.7; LSIMS m/z
(%) 354 (32) [M + H]+, 298 (100) [M + H - C4H8]+. Anal. Calcd
for C21H23NO4: C, 71.37; H, 6.56; N, 3.96. Found: C, 71.31; H, 6.41;
N, 3.99.
Tricationic Salt 3‚3PF6. The bisaldehyde 6 (186 mg, 0.55 mmol)
and benzylamine (148 mg, 1.38 mmol) were dissolved in PhMe (50
mL), and the solvent was evaporated in Vacuo at ∼60 °C. The residue

Multiply Stranded and Multiply Encircled Pseudorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12523
Table 1. Crystal Data, Data Collection, and Refinement Parametersa
[(DB24C8)3‚3][PF6]3
[TPP51C15‚(1)3][PF6]3
[TPP68C20‚(1)4][PF6]4
formula
C102H132N3O24‚3PF6
C84H108N3O15‚3PF6
C112H144N4O20‚4PF6‚
[0.5(C6H5CH2)2NH2‚0.5PF6]
1.75CH2Cl2
solvent
formula weight
Me2CO‚0.25H2O
2281.6
2CH2Cl2
2004.5
2766.4
color, habit
crystal size, mm
lattice type
space group
red plates
0.60 × 0.23 × 0.13
triclinic
P1h
218
colorless blocks
0.67 × 0.43 × 0.20
orthorhombic
Pca21
colorless blocks
0.77 × 0.66 × 0.60
monoclinic
P21/m
173
T, K
293
cell dimensions
a, Å
b, Å
c, Å
11.909(5)
14.926(5)
36.100(5)
87.87(1)
83.45(1)
68.28(1)
5922(3)
2
1.279
2397
1.294
1.2-50.0
12155
6760
1211
19.592(1)
25.240(1)
20.117(3)
19.179(3)
70.669(7)
19.993(2)
R, deg
â, deg
90.55(1)
γ, deg
V, Å3
9948(2)
4
1.338
4176
2.350
1.8-60.0
6518
3846
670
0.103
0.269
0.175, 18.974
27096(6)
8b
1.356
11532
2.083
1.3-55.0
34335
20274
3282
Z
Dc, g cm-3
F(000)
µ, mm-1
θ range, deg
no. of unique reflections: measured
observed, |F0| > 4σ(|F0|)
no. of variables
c
R1
0.134
0.359
0.274, 6.568
0.100
0.269
0.199, 41.458
d
wR2
weighting factors
a, be
largest difference peak, hole, eÅ-3
1.11, -0.66
0.39, -0.33
1.42, -0.82
a Details in common: graphite monochromated Cu KR radiation, ω scans, Siemens P4 rotating anode diffractometer, refinement based on F2.
2
b There are two crystallographically independent molecules in the asymmetric unit. c R1 ) ∑||Fo| - |Fc||/∑|Fo|. d wR2 ) x{∑[w(Fo - Fc2)2]/
2
2
∑[w(Fo )2]}. e w-1 ) σ2(Fo ) + (aP)2 + bP.
N-(tert-Butoxycarbonyl)-N-benzyl-4-formylbenzylamine (9). A
solution of the alcohol 8 (1.0 g, 3.05 mmol) in CH2Cl2 (10 mL) was
added portionwise to a suspension of PCC (0.66 g, 3.05 mmol) in
CH2Cl2 (70 mL), and the reaction mixture stirred vigorously at ambient
temperature. Further quantities of PCC (a total of 0.50 g, 2.32 mmol)
were added portionwise over the next 45 min. The solution was then
washed with 1 N NaOH (4 × 100 mL) until no color remained in the
organic phase, which was then dried (MgSO4). The solvent was
evaporated to yield a white solid (0.80 g, 81%), a portion of which
was subjected to column chromatography (EtOAc/n-C6H14, 1:4) to
obtain a significantly purer sample of the title compound 9: 1H NMR
(CDCl3) δ 1.50 (9H, s), 4.40 and 4.48 (both 2H, two br), 7.12-7.48
(7H, m), 7.85 (2H, d, J ) 8 Hz), 9.98 (1H, s); 13C NMR (CDCl3) δ
28.4, 44.9 and 49.9 (both br), 80.5, 127.4, 128.0 (br), 128.6, 130.0,
131.2, 135.5, 137.5, 150.0 (br), 155.9, 191.8; LSIMS m/z (%) 326 (15)
[M + H]+, 270 (100) [M + H - C4H8]+. Anal. Calcd for C20H23-
NO3: C, 73.82; H, 7.12; N, 4.30. Found: C, 73.71; H, 7.15; N, 4.43.
Tetracationic Salt 4‚4PF6. The aldehyde 9 (0.80 g, 2.46 mmol)
and p-xylylenediamine (0.187g, 1.37 mmol) were condensed in PhMe
(200 mL), using a procedure similar to one described above (Vide
preparation of 3‚3PF6), to provide a thick, pale yellow oil [1H NMR
(CDCl3) δ 1.52 (18H, br s), 4.38 and 4.46 (8H, br m), 4.83 (4H, s),
7.15-7.42 (18H, m), 7.75 (4H, d, J ) 8 Hz), 8.38 (2H, br s)] which
was reduced with NaBH4 (Vide preparation of 3‚3PF6) to yield a thick
oil [1H NMR (CDCl3) δ 1.52 (18H, br s), 3.82 (8H, br s), 4.34 and
4.43 (both 4H, two br), 7.10-7.24 (8H, br), 7.24-7.40 (14H, m)] that
was converted into the tetracationic salt 4‚4PF6 (0.81 g, 58%), using a
similar procedure to that delineated for 3‚3PF6, which was isolated as
a white, amorphous solid: 1H NMR (CD3CN) δ 4.27 (4H, s), 4.29
(4H, s), 4.31 (8H, s), 7.00 (8H, br), 7.48 (10H, s), 7.56 (8H, s), 7.57
(4H, s); 13C NMR (CDCl3) δ 51.7, 52.0, 52.6, 130.0, 130.8, 131.1,
131.7 (m), 132.8 (m); LSIMS m/z (%) 701 (8) [M - PF6 - HPF6]+,
555 (100) [M - PF6 - 2HPF6]+. Anal. Calcd for C38H46N4P4F24: C,
40.08; H, 4.07; N, 4.92. Found: C, 40.18; H, 4.13; N, 5.02.
All the structures were solved by direct methods and were refined by
full-matrix least squares based on F2 (blocked in the case of
[TPP68C20‚(1)4][PF6]4). In structure [(DB24C8)3‚3][PF6]3, part of one
of the crown ethers was found to be disordered. This disorder was
resolved into two alternate, 50% occupancy orientations which were
refined isotropically. The rest of the complex in this structure, and
the whole of the complexes in the other two structures, were ordered
and of full occupancy. In [(DB24C8)3‚3][PF6]3 and [TPP68C20‚(1)4]-
[PF6]4, all of these atoms were refined anisotropically, but in [TPP51C15‚
(1)3][PF6]3, only the oxygen and nitrogen atoms of the complex were
refined anisotropically, the carbon atoms being treated isotropically.
-
Each of the structures contain PF6 anions; in [(DB24C8)3‚3][PF6]3
and [TPP51C15‚(1)3][PF6]3 these anions were ordered and refined
anisotropically, but in [TPP68C20‚(1)4][PF6]4 there were a mixture of
ordered and disordered PF6- anions, the latter distributed over multiple
partial occupancy sites. Only the major occupancy atoms were refined
anisotropically. The nonthreading 1+ ions in [TPP68C20‚(1)4][PF6]4
were found to have crystallographic Cs symmetry and were refined
anisotropically. All three structures included solvent molecules; in
[TPP68C20‚(1)4][PF6]4 the CH2Cl2 molecules were ordered, of full and
partial occupancy, and were refined anisotropically. The full occupancy
Me2CO molecule in [(DB24C8)3‚3][PF6]3 was refined anisotropically,
but the 25% occupancy H2O molecule was refined isotropically. In
[TPP51C15‚(1)3][PF6]3, only the chlorine atoms of the disordered, partial
occupancy CH2Cl2 molecules were refined anisotropically. All of the
C-H hydrogen atoms in each of the three structures were placed in
calculated positions, were assigned isotropic thermal parameters, U(H)
) 1.2Ueq(C) [U(H) ) 1.5Ueq(C-Me)], and were allowed to ride on
their parent atoms. In all three structures, the N-H hydrogen atoms
were located from ∆F maps and were subsequently optimized, were
assigned isotropic thermal parameters, U(H) ) 1.2Ueq(N), and were
allowed to ride on their parent atoms. The hydrogen atoms of the partial
occupancy H2O molecule in [(DB24C8)3‚3][PF6]3 were not located.
Complex [TPP51C15‚(1)3][PF6]3 crystallized in a polar space group
(Pca21); the polarity of the structure was determined using the Flack
X-ray Crystallography. Table 1 provides a summary of the crystal
data, data collection and refinement parameters for the [(DB24C8)3‚3]-
[PF6]3, [TPP51C15‚(1)3][PF6]3, and [TPP68C20‚(1)4][PF6]4 complexes.

12524 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Ashton et al.
parameter [x+ ) 0.20(15), x- ) 0.80(15)]. Computations were carried
(ZENECA Agrochemicals) and Drs. Peter Tasker and Andrew
Collins (ZENECA Specialities) for fruitful discussions.
out using the SHELXTL PC program system.27
Acknowledgment. This research, which was funded in the
UK by the ZENECA Strategic Research Fund, was also
supported additionally by the Biotechnology and Biological
Sciences Research Council and the Engineering and Physical
Sciences Research Council. We thank Dr. Ewan Chrystal
Supporting Information Available: Crystallographic data
for [(DB24C8)3‚3][PF6]3 in addition to LSI mass and 1H NMR
spectra (19 pages). See any current masthead page for ordering
and Internet access instructions.
(27) SHELXTL PC version 5.03, Siemens Analytical X-Ray Instruments,
Inc., Madison, WI, 1994.
JA9714806