Porphyrin-stoppered [3]- and [5]-rotaxanes

Article abstract of DOI:10.1021/ja9824829

A dicopper(I)-complexed [3]-rotaxane was prepared in 34% yield by a transition-metal-templated strategy involving a bis-chelating molecular thread, macrocycles incorporating the complementary chelating unit, and porphyrin stoppers as key components. A tet

Full text of DOI:10.1021/ja9824829

3684
J. Am. Chem. Soc. 1999, 121, 3684-3692
Porphyrin-Stoppered [3]- and [5]-Rotaxanes
Nathalie Solladie´, Jean-Claude Chambron,* and Jean-Pierre Sauvage*
Contribution from the Laboratoire de Chimie Organo-Mine´rale, associe´ au CNRS (UMR 7513), UniVersite´
Louis Pasteur, Faculte´ de Chimie, Institut Le Bel, 4, rue Blaise Pascal, 67000 Strasbourg, France
ReceiVed July 14, 1998
Abstract: A dicopper(I)-complexed [3]-rotaxane was prepared in 34% yield by a transition-metal-templated
strategy involving a bis-chelating molecular thread, macrocycles incorporating the complementary chelating
unit, and porphyrin stoppers as key components. A tetracopper(I)-complexed [5]-rotaxane was obtained as a
byproduct in 8% yield. Coordination chemistry was performed either at the 2,9-diphenyl-1,10-phenanthroline
(dpp) chelates or at the porphyrin stoppers. The latter were metalated by either Zn(II), Au(III), or Zn(II) and
Au(III). Both Cu(I) template cations could be removed by competitive complexation with CN- when at least
one porphyrin stopper was complexed with Au(III), the other one being metalated with either Au(III) or Zn-
(II). This provided two strictly defined [3]-rotaxanes, in which the macrocycle and the molecular thread are
not held together by metal coordination. Rather, dethreading is prevented by the bulky metalloporphyrin stoppers.
Unexpectedly, when both stoppers were complexed with Zn(II), removal of the metal template in the same
conditions as above yielded, very selectively, a copper(I)-complexed [3]-rotaxane containing only one metal-
free macrocycle. The demetalated bis-dpp site could be remetalated with Ag(I), affording, in good yield, a
dinuclear (Ag(I), Cu(I))-complexed [3]-rotaxane, ended by Zn(II)-porphyrin blocking groups.
Introduction
The transition-metal-templated synthesis of the simplest
rotaxanes, the [2]-rotaxanes, developed in our laboratory, relies
on the copper(I)-directed threading of a 2,9-diphenyl-1,10-
phenanthroline (dpp) ligand (the thread) into a macrocycle
bearing the same chelating unit in endo fashion (the ring).7,8 It
was shown that porphyrins could be used as stoppers, by direct
construction of the tetrapyrrolic macrocycles at the extremities
of the thread, the latter bearing precursor aldehyde functions.8
A step toward the controlled, transition-metal-templated
synthesis of [n]-rotaxanes (n > 2) was the threading of two
macrocycles onto a bis-chelating molecular thread: it was shown
that the equilibrium reaction of Figure 2 was shifted quantita-
tively to the formation of the threaded product.9 In particular,
Cu(I) complexes of the bis-chelating molecular thread, like a
binuclear double helix complex, or a mononuclear complex,
resulting from ligand folding, were not observed. In other words,
the threaded product is formed according to the principle of
maximal chelation of the Cu(I) atoms.9
Threading macrocycles onto molecular threads is a modular,
highly convergent process for assembling molecules. Once
threaded, the macrocyclic rings must be held on the molecular
thread to avoid disassembly of the system. This is performed
by anchoring bulky stoppers at the extremities of the thread.
Figure 1 shows schematically how these different components
assemble to form a molecular system called an [n]-rotaxane,
the number of macrocycles being n - 1.
The idea of making threaded complexes between a chain and
a macrocyclic ring, stoppered by bulky end groups was stated
in 1961 by Frisch and Wasserman.1 Since then, a great variety
of rotaxanes have been synthesized, initially by statistical2 or
directed3 methods and, more recently, by template techniques,
involving either hydrophobic,4 aromatic donor-acceptor5 in-
teractions, hydrogen bonds,6 or transition metals as assembling
species.7,8
This multithreading reaction was subsequently used as a
modular “string-and-ring” approach to build multiporphyrin
assemblies.10
Quite common now are the [2]-rotaxanes. Molecular rotax-
anes containing up to three threaded macrocycles ([4]-rotaxanes)
have been described so far.5k,l,n,o However, of the higher order
molecular rotaxanes, [3]-rotaxanes, i.e. rotaxanes involving two
threaded macrocycles, form the most important class of
molecules.4p,5k,l,n-q,6c [3]-Rotaxanes were prepared by various
methods, including template and directed syntheses, with the
exception of the statistical route, for obvious reasons.
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10.1021/ja9824829 CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/02/1999

Porphyrin-Stoppered [3]- and [5]-Rotaxanes
J. Am. Chem. Soc., Vol. 121, No. 15, 1999 3685
interest as far as the preparation of free rotaxanes, i.e. rotaxanes
lacking the template Cu(I) atoms, is concerned.
Results and Discussion
1. Copper(I)-Templated Synthesis of Copper(I)-Com-
plexed [3]- and [5]-Rotaxanes. Two strategies are possible for
anchoring porphyrins to prerotaxane species: (i) perform a
coupling reaction between the prerotaxane and a preformed
porphyrin, both species being suitably functionalized, or (ii)
build the porphyrin directly at the prerotaxane. We chose the
latter strategy as used earlier for the preparation of [2]-rotaxanes8
and as represented schematically in Figure 3. The chemical
structures of the real precursors are given in Figure 4. The
molecular thread component 1 is a -(CH2)4- bridged bisphen-
anthroline molecule which proved quite efficient for the
threading reaction shown in Figure 2.9
Figure 1. An [n]-rotaxane is made from a dumbbell component and
n - 1 threaded rings.
It was synthesized in two steps as follows: at first, 1,10-
phenanthroline was reacted with 4-lithiobenzaldehyde neopen-
tylacetal (prepared by reaction of tert-butyllithium with 4-bro-
mobenzaldehyde neopentylacetal12). After hydrolysis and oxidation
of the addition product with MnO2, monosubstituted phenan-
throline 3 was obtained in 71% yield. It was subsequently
reacted with 1,4-dilithiobutane (obtained by reaction of 1,4-
dichlorobutane with lithium sand13). After hydrolysis and
rearomatization with MnO2, the yield of pure bisphenanthroline
2 was 86%. The target bisphenanthroline 1 was obtained in 79%
yield by hydrolysis of 2 with hydrochloric acid. Threading was
performed as follows: at first, a 1:1 complex between macro-
cycle 47b and Cu(I) was formed, according to the equilibrium
of Figure 2. It was then reacted with 0.5 equiv of bisphenan-
throline thread 1. As represented in Figure 5, the resulting deep
red binuclear complex, prerotaxane 72+, was subsequently
reacted with a mixture of 3,5-di-tert-butylbenzaldehyde14 (5, 8
equiv) and (3,3′-dihexyl-4,4′-dimethyl-2,2′-dipyrryl)methane15
(6, 10 equiv) in the presence of CF3CO2H, used as acid
catalyst.16,8b,c The porphyrinogen species formed were then
oxidized to the corresponding porphyrins with chloranil (31
equiv).
Figure 2. Principle of transition-metal-templated threading of two
macrocyclic rings onto a molecular thread. The black circle is a
transition metal cation, and the thick lines represent coordinating units.
The copper(I)-templated synthesis of dicopper(I)-complexed
[3]-rotaxanes stoppered by porphyrin subunits was presented
in a preliminary communication, together with the unexpected,
but delightful formation of a compartmental tetracopper(I)-
complexed [5]-rotaxane.11 In this full paper, in addition to a
detailed account of the template syntheses, we report on the
coordination chemistry of the [3]-rotaxanes. This is of particular
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3686 J. Am. Chem. Soc., Vol. 121, No. 15, 1999
Solladie´ et al.
square pyramidal, or octahedral, the two latter cases involving
additional, apical ligands in the complexation processes.
3. Coordination Chemistry of the Rotaxanes at the
Porphyrin Stoppers: Preparation of (Cu4)-[5]-Rotaxane 134+
and (Cu2)-[3]-Rotaxanes 122+ and 143+-163+. Reaction of
(Cu2)-[3]-rotaxane 92+ with zinc acetate in a refluxing mixture
of chloroform and methanol afforded, after chromatography,
(Cu2)-[3]-rotaxane 122+ in 83% yield. Porphyrin 8 and (Cu4)-
[5]-rotaxane 104+ were treated similarly, affording, respectively,
Zn(II)-porphyrin 11 and (Cu4)-[5]-rotaxane 134+ (Figure 5) in
79% and 85% isolated yields, respectively.
Since Au(III)-porphyrins belong to stability class I (i.e., not
completely demetalated by 100% sulfuric acid) and Zn(II)-
porphyrins belong to stability class III (demetalated in very mild
conditions, i.e., by a mixture of aqueous HCl and dichlo-
romethane),17 it seemed quite obvious that it was necessary to
start the metalation with Au(III) to avoid transmetalation
problems. At first, reaction of Au(tht)2(PF6) (3 equiv; tht is
tetrahydrothiophene) with 92+ (1 equiv) in refluxing chloroform
in the presence of 2,6-lutidine produced the desired monometa-
lated (Cu2)-[3]-rotaxane 143+ in 38% yield, after repeated
column chromatography.18 The dimetalated (Cu2)-[3]-rotaxane
154+ was isolated in 13% yield as a byproduct, and 28% of
starting material was recovered. Therefore, the distribution of
products is not very far from statistics, given that this method
of metalation generally proceeds in 60-70% yields.18 Inciden-
tally, (Cu2)-[3]-rotaxane 154+ was obtained directly by reaction
of (Cu2)-[3]-rotaxane 92+ with 6 equiv of Au(tht)2(PF6) in the
presence of 2,6-lutidine, in 42% yield after chromatographic
purification. Next, 143+ was reacted with Zn(OAc)2‚2H2O in a
refluxing mixture of chloroform and methanol to afford the
target (Cu2)-[3]-rotaxane 163+ quantitatively.
Figure 3. Principle of copper(I)-templated synthesis of a (Cu2)-[3]-
rotaxane. The black circle is Cu(I), the thick lines represent 2,9-
diphenyl-1,10-phenanthroline coordinating units, and the diamonds are
porphyrin stoppers.
4. Coordination Chemistry of the [3]-Rotaxanes at the Bis-
dpp Subsites. 4.1. Selective Monodemetalation Reaction of
(Cu2)-[3]-Rotaxane 122+ Leading to Cu-[3]-Rotaxane 17+.
The rotaxanes we were dealing with until now are copper(I)-
complexed rotaxanes, and chemical evidence of their very
rotaxane nature has not be given yet, i.e. demetalation should
afford a single molecular species and not a mixture of separated
thread and macrocycles, provided that the relative dimensions
of the macrocycle and the stoppers were well chosen. Demeta-
lation of copper(I)-complexed catenates and rotaxanes is
routinely performed by competitive complexation with cyanide,
using a large excess of KCN (typically 20-25 mol/mol of Cu-
(I)) in CH3CN/CH2Cl2/H2O mixtures.7b,19 This reaction per-
formed in similar conditions starting from 122+ (68 mol of KCN/
mol of 122+, i.e. 34 mol/mol of Cu(I)) afforded cleanly and
almost quantitatively the monodemetalated species (17+), to our
great surprise. Prolongated reaction times or heating to 64 °C
did not improve the extent of demetalation.
It was shown earlier that the CN--triggered dissociation of a
copper(I)-complexed threaded species such as 72+ took place
in two consecutive bimolecular steps.9b The first step cor-
responded to the dethreading of one macrocycle, leaving an
intermediate containing a single threaded macrocycle. It took
place at a rate of 1120 M-1 s-1. The second Cu(I) atom
dissociated from the threaded complex at a rate of 354 M-1
s-1. The ratio of these rate constants is 3, which is of the same
order of magnitude as the statistical value (2). This indicates
After purification by repeated chromatography, three por-
phyrin-containing compounds could be isolated from the reaction
mixture (Figure 5): 5,15-bis(3,5-di-tert-butylphenyl)-2,8,12,-
18-tetrahexyl-3,7,13,17-tetramethylporphyrin (8) in 32% yield
from 5, (Cu2)-[3]-rotaxane 92+ in 34% yield, and (Cu4)-[5]-
rotaxane 104+ in 8% yield, the copper complexes being isolated
as PF6- salts. Noteworthy is the high yield of (Cu2)-[3]-rotaxane
9
2+. Since two porphyrins are created simultaneously, the yield
of individual porphyrin formation is ca. 60%. (Cu4)-[5]-rotaxane
104+ deserves some comment. First of all, it is a molecule with
four threaded macrocycles, that is, it has a [5]-rotaxane structure;
second, it results from the simultaneous formation of three
porphyrins, the central one resulting from the condensation of
two prerotaxane-like units. The yield of individual porphyrin
formation is ca. 45% in this case. This copper(I)-complexed
[5]-rotaxane may be considered as what we could call a
compartmental [5]-rotaxane, since two groups of two macro-
cycles each are separated by an inner porphyrin blocking group.
The compounds of Figure 5 (prerotaxane and rotaxanes), as well
as all the other [3]-rotaxanes of this study, were characterized
by fast atom bombardment (FAB) or electrospray (ES) mass
1
spectrometry and H NMR spectroscopy.
2. Coordination Chemistry of the Copper(I)-Complexed
[3]-Rotaxanes. The various coordination chemistry studies
performed starting from the free-base dicopper(I)-complexed
[3]-rotaxane 92+ are summarized schematically in Figure 6. The
[3]-rotaxane framework of this study contains two quite different
coordinating sites: (i) the combination of two dpp chelates, one
from the dumbbell and the other from a threaded macrocycle,
which enforce a tetrahedral geometry around the complexed
metal cation, and (ii) the porphyrinic stoppers, which bind
cations with square planar, and derived geometries such as
(17) Buchler, J. W. In Porphyrins and Metalloporphyrins; Smith, K. M.,
Ed.; Elsevier: New York, 1975; pp 196-198.
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237.
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Soc. 1984, 106, 3043.

Porphyrin-Stoppered [3]- and [5]-Rotaxanes
J. Am. Chem. Soc., Vol. 121, No. 15, 1999 3687
Figure 4. Chemical structures of the precursors to the [3]- and [5]-rotaxanes described in this study, with atom numbering.
that the probability that CN- effectively finds Cu(I) is twice in
the case of the binuclear complex than in the case of the
mononuclear complex. Therefore, in the case of the prerotaxane,
there is no particular hamper to demetalation. The outcome of
the demetalation reaction of (Cu2)-[3]-rotaxane 122+ is linked
to its rotaxane nature. This phenomenon can be related to
allosteric effects,20 in the sense that the reactivity of a given
site of the molecule is governed by another fragment, both units
being apparently relatively remote from one another. The
simplest explanation is that, after removal of the first copper-
(I), which proceeds with a normal rate (i.e., similar to other
analogous complexes), the molecule undergoes some profound
rearrangement. The new conformation obtained is such that the
second coordination site has now become fully protected from
attack by CN- and is thus totally inert toward decomplexation.
4.2. Metalation of (Cu)-[3]-Rotaxane 17+ with Silver(I),
Affording (Ag,Cu)-[3]-Rotaxane 182+. The 2,9-diphenyl-1,-
10-phenanthroline chelates embedded respectively in the mac-
rocyclic and the dumbbell-shaped components of Cu-[3]-
rotaxane 17+ are in fact imprints of the metal template which
has been partially removed. The tetradentate cavity initially
formed around Cu(I) could be restored, by reacting (Cu)-[3]-
rotaxane 17+ with AgBF4 in a CH2Cl2/CH3CN mixture. (Ag,-
Cu)-[3]-rotaxane 182+ was isolated in 51% yield after chro-
matographic purification.
rotaxane 122+, which contained Zn(II)-porphyrin stoppers,
complete removal of the Cu(I) atoms took place, affording the
first free [3]-rotaxane of this series, 192+, in 62% yield after
chromatography. The demetalation reaction is depicted in
Figure 7.
As seen above, template removal was complete when both
porphyrinic stoppers were metalated with Au(III). When the
stoppers were metalated with Zn(II), only one Cu(I) atom of
two could be extracted using CN- as a competitive ligand. The
last issue to remain was the case of the (Cu2)-[3]-rotaxane
bearing a Zn(II)- and a Au(III)-porphyrin as stoppers. There-
fore, (Cu2)-[3]-rotaxane 163+ was reacted with a slight excess
of KCN in a CH2Cl2/H2O mixture. Unexpectedly, total removal
of the Cu(I) template atoms took place, leaving the free
[3]-rotaxane 20+ as product. It was isolated in 59% yield after
chromatography.
6. Mass Spectrometry Study of the Copper(I)-Complexed
and Free [3]-Rotaxanes. With the exception of (Cu2)-[3]-
rotaxane 163+, which was characterized by electrospray ioniza-
tion mass spectrometry, all the other [3]-rotaxanes were
examined by FAB mass spectrometry. The data are collected
in Table 1.
Peaks due to fragments of various charge, corresponding to
(i) intact [3]-rotaxane structures, (ii) [2]-rotaxane structures
resulting from the [3]-rotaxanes by dethreading of one macro-
cycle, and (iii) bisporphyrin dumbbells, resulting from the
[3]-rotaxanes by the loss of both macrocycles, are observed in
the FAB mass spectra of all copper(I)-complexed and free
[3]-rotaxanes studied. What is essentially differing from one
molecule to the other is the ionization process, that is how the
molecular fragments have “managed” to acquire or keep their
positive charges. The charges are provided either by the metal
cations complexed by the dpp sites (Cu+ or Ag+) or by the
metal complexed by the porphyrinic stoppers (Au3+). It can also
be provided by protonation. This is observed for the cases of
the free [3]-rotaxanes 17+, 192+, and 20+, where free bis-dpp
sites are available. This is consistent with the fact that these
5. Preparation of Free [3]-Rotaxanes 192+ and 20+. To
test the influence of the metal cation incorporated in the
porphyrinic stoppers on the outcome of the demetalation
reaction, (Cu2)-[3]-rotaxane 154+, containing Au(III)-porphy-
rins as stoppers, was treated similarly with potassium cyanide
in a CH2Cl2/H2O heterogeneous mixture. Unlike (Cu2)-[3]-
(20) (a) Rebek, J., Jr.; Marshall, L. J. Am. Chem. Soc. 1983, 105, 6668.
(b) Rebek, J., Jr.; Costello, T.; Marshall, L.; Wattley, R.; Gadwood, R. C.;
Onan, K. J. Am. Chem. Soc. 1985, 107, 7481. (c) Gavin˜a, F.; Luis, S. V.;
Costero, A. M.; Burguete, M. I.; Rebek, J., Jr. J. Am. Chem. Soc. 1988,
110, 7140. (d) Gagnaire, G.; Gellon, G.; Pierre, J.-L. Tetrahedron Lett. 1988,
29, 933. (e) Schneider, H.-J.; Ruf, D. Angew. Chem., Int. Ed. Engl. 1990,
29, 1159.

Figure 5. One-pot preparation of copper(I)-complexed [3]- and [5]-rotaxanes: (i) 5 (8 equiv), 6 (10 equiv) cat. CF3CO2H, CH2Cl2, room temperature, then chloranil (35 equiv), CH2Cl2, reflux.

Porphyrin-Stoppered [3]- and [5]-Rotaxanes
J. Am. Chem. Soc., Vol. 121, No. 15, 1999 3689
to the singly charged species, doubly charged species such as
[M4+ + 2PF6- 2+/2 and a triply charged species ([M4+
] +
PF6 ]
- 3+/3) are observed. The same observations hold true for
[2]-rotaxane-like fragments. In addition, a feature particular to
these fragments is that macrocycle dethreading is not necessarily
accompanied by the loss of the complexed Cu+ cation, when
the molecule under investigation is a (Cu2)-[3]-rotaxane. The
dumbbell fragments, except for those stoppered by Au(III)-
porphyrins, are not naturally charged. Therefore, the positive
charge is provided by coordination of metal cations such as Cu+
or Ag+, or protons (in the case of 17+ and 20+).
7. Proton NMR Spectroscopy Study of the Complexed and
Free [3]-Rotaxanes. 7.1. Effect of the Metal Complexing the
Porphyrin Stoppers or the dpp Sites. Whereas incorporation
of Zn(II) has little effect on the chemical shifts by comparison
with the free-base porphyrin, this is not the case of Au(III).
The electron-withdrawing effect of cationic Au(III) is expressed
into deshielding effects only for protons either directly connected
or one C-C bond away from the porphyrin macrocycle. For
example, the meso protons of (Cu2)-[3]-rotaxane 122+ (Zn(II)-
porphyrin stoppers) show up at 10.12 ppm, whereas the same
protons of 154+ (Au(III)-porphyrin stoppers) show up at 10.56
ppm (∆δ ) +0.44 ppm). Similar observations can be made by
examining the spectrum of 163+, a (Cu2)-[3]-rotaxane containing
both Zn(II)- and Au(III)-porphyrins as stoppers: it is a
superimposition of the spectra of 122+ and 154+
.
(Cu,Ag)-[3]-rotaxane 182+ allows the study of the effect of
complexation of one bis-dpp site of (Cu2)-[3]-rotaxane 122+ with
Ag(I), which has roughly the same stereoelectronic requirements
as Cu(I). The spectra of 182+ and 122+ look similar, except that
most of the peaks of the former are split, in agreement with the
nonsymmetrical nature of the molecule.
Figure 6. Coordination chemistry of (Cu2)-[3]-rotaxane 92+. The
diamonds are the porphyrin stoppers: empty ) free-base, hatched )
Zn(II)-complexed, black ) Au(III)-complexed. The black circles are
Cu(I), and the white circle is Ag(I).
7.2. Removal of the Metal Template. Removal of the Cu-
(I) metal template of (Cu2)-[3]-rotaxanes 122+, 154+, and 163+
to afford (Cu)-[3]-rotaxane 17+ and [3]-rotaxanes 192+ and 20+
1
respectively, has dramatic effects on the H NMR spectra of
the molecules, suggesting that some rearrangement is taking
place. Since these molecules share several common features,
only a detailed comparison between the spectra of 154+ and
192+, the simplest ones, because of their symmetry properties,
will be provided here. Figure 8 compares the aromatic regions
of the spectra of these molecules. See also Figure 7 for
highlighting of selected protons. The most prominent feature is
the strong upfield shift of the singlet of the (5′,6′) protons of
the phenanthroline moiety incorporated in the macrocycles: ∆δ
) -2.00 ppm. The other phenanthroline protons show a similar
trend: for (4′,7′), ∆δ ) -1.68 ppm, and for (3′,8′), ∆δ ) -0.84
ppm. Therefore, the closer the protons from the symmetry plane
of the [3]-rotaxane molecule, containing the bisphenanthroline
thread, the stronger their shielding. Protons o′ and m′ of the
macrocycles experience the opposite effect upon demetalation,
since resonance signals move downfield: ∆δ ) +0.90 ppm for
both of them. The same is true for protons R and â of the alkyl
bridge linking the rotaxane subunits.
Figure 7. Removal of the metal template of (Cu2)-[3]-rotaxane 154+
,
affording [3]-rotaxane 192+. The porphyrin substituents have been
omitted for clarity.
sites are expected to be more basic than isolated dpp.21 Singly
charged species are usually formed by loss of one PF6- anion.
However, if more PF6- anions are lost, charge compensation is
provided by electronic reduction.
Multiply charged species also contribute significantly to the
mass spectra. Of course the more charged the molecule, the
more multiply charged species are observed. For example, in
the case of (Cu2)-[3]-rotaxane 154+, which bears the highest
charge and whose tetrapositive charge is due to the two Cu(I)
cations and the two Au(III)-porphyrinic stoppers, in addition
These results are consistent with the following picture of free
rotaxane 192+ (Figure 7): the metal-free macrocycles have
slipped toward the closest porphyrin stopper so that the
phenanthroline moiety they incorporate is embedded in the
strong shielding field of the porphyrins. Simultaneously, the o′
and m′ protons of the phenyl substituents of the macrocycles
are no longer in the shielding field of the phenanthroline
fragments of the molecular thread, hence the downfield shift
of their signals upon demetalation. The deshielding of protons
R and â is certainly due to similar reasons: in the complex these
(21) Cesario, M.; Dietrich-Buchecker, C. O.; Edel, A.; Guilhem, J.;
Kintzinger, J.-P.; Pascard, C.; Sauvage, J.-P. J. Am. Chem. Soc. 1986, 108,
6250.

3690 J. Am. Chem. Soc., Vol. 121, No. 15, 1999
Solladie´ et al.
Table 1. FAB-MS Data for Selected Metal-Complexed and Free [3]-Rotaxanes in This Studya
a The diamonds are the porphyrin stoppers: empty ) free-base, hatched ) Zn(II)-complexed, black ) Au(III)-complexed. The black circles are
Cu(I), and the white circle is Ag(I).
porphyrin. Mass spectral data were obtained on either Thomson THN
208 (chemical ionization), ZAB-HF (FAB), or VG BIOQ triple
quadrupole (ES-MS). Melting points were determined in open capillary
tubes on a Bu¨chi SMP-20 apparatus and were uncorrected. Elemental
analyses were performed by the Service de Microanalyse de l’Institut
de Chimie de Strasbourg. IR spectra were recorded with a Perkin-Elmer
580 spectrophotometer.
protons are shielded by the ring currents of the phenanthroline
incorporated in the macrocycle, which are switched off once
the metal is removed.
Conclusion
The preparation and characterization of various porphyrin-
stoppered [3]-rotaxanes have been described in this study.
Among all of the compounds prepared, of paramount importance
is the [3]-rotaxane 20+ containing both a Zn(II)-porphyrin and
a Au(III)-porphyrin as stoppers, with respect to electron transfer
studies. This molecule is the [3]-rotaxane homologue of the
[2]-rotaxane that was described a few years ago8a,b and showed
an intramolecular photoinduced electron transfer between a Zn-
(II)-porphyrin stopper in its excited state and a Au(III)-
porphyrin stopper in its ground state.22 Photophysical studies
on [3]-rotaxane 20+ and analogues are underway and will be
reported in due course.
All of the reactions were performed under an atmosphere of argon,
using Schlenk techniques unless otherwise noted. p-Bromobenzaldehyde
neopentylacetal,12 Cu(CH3CN)4PF6,23 3,5-di-tert-butylbenzaldehyde
(5),14 and (3,3′-dihexyl-4,4′-dimethyl-2,2′-dipyrryl)methane (6)15 were
prepared according to literature procedures. MnO2 was purchased from
Merck (ref 805958). Note that only the preparation and characterization
of precursors 1-3, and prerotaxane [72+](PF6-)2 are provided here, in
-
addition to (Cu2)-[3]-rotaxane [92+](PF6
) and (Cu4)-[5]-rotaxane
2
[104+](PF6-)4, as examples. The other rotaxanes are described in the
Supporting Information.
2-(p-Benzaldehyde neopentylacetal)-1,10-phenanthroline 3. 89 mL
of a 1.30 M solution of tert-butyllithium in pentane (116 mmol) were
added at -78 °C to a solution of 15.0 g (55 mmol) of p-bromobenz-
aldehyde neopentylacetal in THF (110 mL). The solution was then
stirred at -78 °C for 2 h, before allowing the temperature to rise to
-5 °C three times. The end of the reaction was detected by the Gilman
color test.24 The resulting organolithium solution was added to a solution
of 1,10-phenanthroline (8.97 g, 50 mmol) in dry THF (500 mL)
maintained at 0 °C. The dark red solution obtained was stirred at 0 °C
for 1 h and 30 min and at 5 °C for 1 h, and was thereafter hydrolyzed
by 150 mL of water. The THF was evaporated and the resulting aqueous
Experimental Section
1H NMR spectra were obtained on either a Brucker WP 200 SY
(200 MHz), AM 400 (400 MHz), or ARX 500 (500 MHz) spectrometer.
Chemical shifts are referenced downfield from tetramethylsilane (“h”
means hidden peaks). Labels of the protons of the [3]-rotaxanes are
provided in Chart 1. They hold true for the [5]-rotaxane, which uses in
addition, subscript c for protons of the central porphyrin, and superscript
* for protons of the copper(I) complex fragments proximal to the central
(22) (a) Chambron, J.-C.; Harriman, A.; Heitz, V.; Sauvage, J.-P. J. Am.
Chem. Soc. 1993, 115, 6109. (b) Chambron, J.-C.; Harriman, A.; Heitz,
V.; Sauvage, J.-P. J. Am. Chem. Soc. 1993, 115, 7419.
(23) Kubas, G. J.; Monzyk, B.; Crumbliss, A. L. Inorg. Synth. 1990, 28,
68.
(24) Gilman, H.; Haubein, A. H. J. Am. Chem. Soc. 1944, 66, 1515.

Porphyrin-Stoppered [3]- and [5]-Rotaxanes
J. Am. Chem. Soc., Vol. 121, No. 15, 1999 3691
Chart 1
solvent and recrystallization in benzene, 13.1 g (35.4 mmol, 71% yield)
of 2-(p-benzaldehyde neopentylacetal)-1,10-phenanthroline (3) was
obtained. White solid (mp ) 216 °C). 1H NMR (200 MHz, CDCl3): δ
9.25 (dd, 1H, H9, 3J′ ) 4.4 Hz, 4J ) 1.7 Hz), 8.38 (d, 2H, Ho, 3J ) 8.4
3
3
4
Hz), 8.33 (d, 1H, H4, J ) 8.5 Hz), 8.28 (dd, 1H, H7, J ) 8.1 Hz, J
) 1.8 Hz), 8.12 (d, 1H, H3, 3J ) 8.4 Hz), 7.81 (AB, 2H, H5,6, 3J ) 8.8
Hz), 7.70 (d, 2H, Hm, 3J ) 8.3 Hz), 7.66 (dd, 1H, H8, 3J ) 8.1 Hz, 3J′
) 4.3 Hz), 5.51 (s, 1H, CH), 3.77 (AB, 4H, CH2, 2J ) 10.9 Hz), 1.34
(s, 3H, CH3), 0.84 (s, 3H, CH3). Anal. Calcd for C24H22N2O2: C, 77.8;
H, 6.0; N, 7.6. Found: C, 77.6; H, 6.3; N, 7.6.
Bisphenanthroline 2. 1,4-Dilithiobutane was prepared by the direct
interaction of 1,2-dichlorobutane with lithium sand13 and titrated. A
21 mL portion of the 1.23 M solution of 1,4-dilithiobutane obtained
(12.9 mmol) was added to a suspension of 2-(p-benzaldehyde neopen-
tylacetal)-1,10-phenanthroline (12 g, 32.4 mmol) in dry ether (250 mL)
maintained at 0 °C. The resulting dark red solution was stirred for 24
h at 0 °C and hydrolyzed with 70 mL of water. A bright orange organic
phase was obtained. Ether was evaporated off and the aqueous phase
extracted three times with CH2Cl2. The combined organic layers were
washed three times with water, treated with 45 g of MnO2, and dried
over 45 g of MgSO4. The MnO2/MgSO4 aggregates were filtered on a
sintered glass funnel and thoroughly washed with CH2Cl2. After
evaporation of the solvent, 16.9 g of crude beige product was obtained.
After chromatography on alumina (L ) 5 cm, h ) 34 cm, eluent: CH2-
Cl2/MeOH 99.6/0.4) and two recrystallizations in a mixture of CH2-
Cl2/hexane, 1:2, the desired bis(1,10-phenanthroline) (2) was isolated
pure in 86% yield (8.8 g, 11.1 mmol). White solid (mp ) 219 °C). 1H
3
NMR (200 MHz, CDCl3): δ 8.42 (d, 4H, Ho, J ) 8.3 Hz), 8.29 (d,
2H, H4 or 7, 3J ) 8.4 Hz), 8.12 (d, 4H, H8 and H4 or 7, 3J ) 7.9 Hz), 7.73
(s, 4H, H5,6), 7.70 (d, 4H, Hm, 3J ) 8.4 Hz), 7.61 (d, 2H, H3, 3J ) 8.2
Hz), 5.49 (s, 2H, CH), 3.76 (AB, 8H, CH2 , 2J ) 10.8 Hz), 3.39 (t, 4H,
HR), 2.24 (t, 4H, Hâ), 1.34 (s, 6H, CH3), 0.83 (s, 6H, CH3). Anal. Calcd
for C52H50N4O4‚0.25C6H14: C, 78.7; H, 6.6; N, 6.9. Found: C, 78.8; H,
7.0; N, 7.2.
Figure 8. Comparison of the 1H NMR spectra (400 MHz) of (a) (Cu2)-
[3]-rotaxane 154+ and (b) [3]-rotaxane 192+. The black diamonds are
the Au(III)-complexed porphyrinic stoppers, and the black circles are
Cu(I) atoms. See Figure 7 for selected atom labels and Chart 1 for
complete proton labeling.
Bisphenanthroline 1. A 5% solution of hydrochloric acid (15 mL,
24.3 mmol) was added to a suspension of 1.0 g of bisphenanthroline
(2) (1.26 mmol) in THF (80 mL). The resulting solution was stirred
for 3 days at room temperature and neutralized with 50 mL of a 10%
aqueous solution of sodium hydrogen carbonate. The solvent was
evaporated off and the resulting aqueous phase extracted three times
phase extracted three times with CH2Cl2. The combined organic layers
were treated by 70 g of MnO2 and dried over the same weight of
MgSO4. The MnO2/MgSO4 aggregates were filtered on a sintered glass
filter and thoroughly washed with CH2Cl2. After evaporation of the

3692 J. Am. Chem. Soc., Vol. 121, No. 15, 1999
Solladie´ et al.
3
3
with CH2Cl2. The combined organic layers were washed three times
with water and dried over MgSO4. After filtration and evaporation of
the solvent, 860 mg of crude beige product was obtained. Purification
by recrystallization in CHCl3/hexane and chromatography on silica gel
(L ) 2 cm, h ) 24 cm, eluent: CH2Cl2/MeOH, 99/1) afforded the
desired bisphenanthroline 1 in 79% yield (622 mg, 1.0 mmol). White
CH3), 2.22 (quint, 8H, Hâ′′, J ) 6.7 Hz), 1.78 (q, 8H, Hγ′′, J ) 7.6
Hz), 1.51 (s, 36H, HBu), 1.51 (m, 16H, Hδ′′,ꢀ′′), 0.92 (t, 12H, Hú′′), 3J )
t
7.0 Hz), -2.50 (br s, 2H, NH). [92+](PF6-)2: Dark red solid. 1H NMR
(400 MHz, CD2Cl2): δ 10.16 (s, 4H, Hmeso), 9.08 (d, 2H, H7, 3J ) 8.3
Hz), 8.67 (d, 2H, H4, 3J ) 8.3 Hz), 8.49 (d, 2H, H6, 3J ) 9.0 Hz), 8.46
(d, 4H, H4′,7′, 3J ) 8.3 Hz), 8.23 (d, 2H, H5, 3J ) 9.0 Hz), 8.22 (d, 2H,
1
3
3
solid (mp ) 123 °C). H NMR (200 MHz, CDCl3): δ 10.08 (s, 2H,
H8, J ) 8.2 Hz), 8.00 (s, 4H, H5′,6′), 7.96 (d, 4H, H3′,8′, J ) 8.2 Hz),
4 3
3
3
CHO), 8.54 (d, 4H, Ho, J ) 8.3 Hz), 8.34 (d, 2H, H7, J ) 8.5 Hz),
7.89 (d, 4H, Ho′′, J ) 1.7 Hz), 7.86 (s, 2H, Hp′′), 7.71 (d, 4H, Ho, J
3 3
3
3
8.16 (d, 2H, H8, J ) 8.5 Hz), 8.15 (d, 2H, H4, J ) 8.2 Hz), 8.01 (d,
4H, Hm, 3J ) 8.3 Hz), 7.77 (s, 4H, H5,6), 7.62 (d, 2H, H3, 3J ) 8.2 Hz),
3.40 (t, 4H, HR), 2.27 (t, 4H, Hâ). MS (EI): 622.2 (M, calcd 622.2). IR
(neat): ν (cm-1) ) 2821, 2738, 1695.
) 7.9 Hz), 7.56 (d, 4H, Hm, J ) 8.0 Hz), 7.26 (d, 8H, Ho′, J ) 8.6
3 3
Hz), 7.25 (d, 2H, H3, J ) 8.1 Hz), 6.11 (d, 8H, Hm′, J ) 8.6 Hz),
3
3.97 (t, 8H, HR′′d, J ) 7.7 Hz), 3.87 (s, 8H, Hꢀ′), 3.78 (t, 8H, HR′′p),
3
3.72 (m, 8H, Hδ′), 3.72 (m, 8H, HR′), 3.54 (t, 8H, Hγ′, J ) 5.4 Hz),
Prerotaxane 72+(PF6-)2. By the double-ended needle technique,
[Cu(CH3CN)4+]PF6- (0.164 g, 0.44 mmol) in acetonitrile (10 mL) was
added to a solution of 4 (0.250 g, 0.44 mmol) in methylene chloride
(25 mL). The mixture turned orange instantaneously, indicating the
formation of [Cu4(CH3CN)2]+PF6-. After 20 min at room temperature,
a solution of bisphenanthroline 1 (0.137 g, 0.22 mmol) in methylene
chloride (15 mL) was added to the orange complex. The solution turned
3.51 (br s, 8H, Hâ′), 2.46 (s, 12H, CH3d), 2.19 (quint., 8H, Hâ′′d, J )
3
3
7.8 Hz), 2.04 (quint., 8H, Hâ′′p, J ) 7.8 Hz), 1.78 (s, 4H, HR), 1.75
3
3
(m, 8H, Hγ′′d, J ) 7.4 Hz), 1.73 (m, 8H, Hγ′′p, J ) 7.4 Hz), 1.71 (s,
t
12H, CH3p), 1.51 (s, 36H, HBu), 1.51 (h, 16H, Hδ′′(p,d)), 1.40 (m, 16H,
3
3
H
ꢀ′′(p,d)), 0.95 (t, 12H, Hú′′d, J ) 7.3 Hz), 0.92 (t, 12H, Hú′′p, J ) 7.3
Hz), 0.36 (br s, 4H, Hâ), -2.61 (br s, 2H, NH), -2.70 (br s, 2H, NH).
FAB-MS: m/z ) 3750.2 ([M2+ + PF6-]+, calcd 3750.9, 75%). [104+]-
dark red immediately. After the mixture was stirred overnight at room
(PF6-)4: Dark red solid. 1H NMR (500 MHz, CD2Cl2): δ 10.16 (s, 4H,
temperature, the solvents were evaporated to afford crude 72+(PF6
)
2
H
meso), 10.06 (s, 2H, Hmeso-c), 9.08 and 9.07 (2d, 4H, H7,7*, J ) 8.2
Hz), 8.68 and 8.67 (2d, 4H, H4,4*, J ) 8.0 Hz), 8.49 (d, 4H, H6,6*, J
-
3
1
3
3
in quantitative yield. Dark red solid. H NMR (200 MHz, CD2Cl2): δ
3
3
3
9.50 (s, 2H, CHO), 8.66 (d, 2H, H7, J ) 8.4 Hz), 8.46 (d, 2H, H4, J
∼ 10.2 Hz), 8.47 (d, 8H, H4′,7′, J ∼ 8.6 Hz), 8.24 and 8.23 (2d, 4H,
3
3
) 8.4 Hz), 8.30 (d, 2H, H5 or 6, J ) 8.9 Hz), 8.23 (d, 4H, H4′,7′, J )
8.3 Hz), 7.96 (d, 2H, H5 or 6, 3J ) 8.9 Hz), 7.72 (s, 4H, H5′,6′), 7.72 (d,
2H, H8, 3J ) 8.3 Hz), 7.66 (d, 4H, H3′,8′, 3J ) 8.3 Hz), 7.44 (d, 2H, H3,
3J ) 8.4 Hz), 7.10 (d, 4H, Ho, 3J ) 7.5 Hz), 7.06 (d, 8H, Ho′, 3J ) 8.4
H
5,5*, 3J ∼ 9.3 Hz), 8.22 and 8.21 (2d, 4H, H8,8*, 3J ∼ 8.7 Hz), 8.01 (s,
8H, H5′,6′), 7.97 and 7.96 (2d, 8H, H3′,8′, 3J ) 8.2 Hz), 7.89 (d, 4H, Ho",
4J ) 1.8 Hz), 7.85 (t, 2H, Hp′′, J ) 1.7 Hz), 7.70 (d, 8H, Ho,o*, J ∼
8.0 Hz), 7.56 (d, 4H, Hm, 3J ) 7.8 Hz), 7.51 (d, 4H, Hm*, 3J ) 7.8 Hz),
7.25 and 7.24 (2d, 16H, Ho′, 3J ) 8.5 Hz), ca. 7.24 (h, 4H, H3,3*), 6.11
and 6.10 (2d, 16H, Hm′, 3J ) 8.5 Hz), 3.97 (t, 8H, HR′′d, 3J ) 7.8 Hz),
3.87 (s, 16H, Hꢀ′), ca. 3.71 (m, 48H, Hγ′,δ′ and HR′′(p,c)), ca. 3.54 (m,
32H, HR′,â′), 2.46 (s, 12H, CH3d)), 2.19 (quint, 8H, Hâ′′d, 3J ) 7.6 Hz),
2.02 (m, 16H, Hâ′′(p,c)), ca. 1.74 (m, 32H, Hγ′′(p,c,d) and HR,R*), 1.71 (s,
12H, CH3p), 1.68 (s, 12H, CH3c), ca. 1.54 (m, 24H, Hδ′′(p,c,d)), 1.50 (s,
4
3
3
3
Hz), 6.73 (d, 4H, Hm, J ) 8.1 Hz), 5.78 (d, 8H, Hm′, J ) 8.6 Hz),
3.78 (s, 8H, Hꢀ′), 3.68-3.46 (m, 32H, HR′,â′,γ′,δ′), 2.27 (t, 4H, HR), 1.13
(t, 4H, Hâ). FAB-MS: m/z ) 2028.6 ([M - PF6-]+, calcd 2028.1, 5%),
-
941.3 ([M - 2PF6
]
2+, calcd 941.6, 84%).
(5,15-Di-tert-butylphenyl)-2,8,12,18-tetrahexyl-3,7,13,17-tetra-
methylporphyrin (8), (Cu2)-[3]-Rotaxane [92+](PF6-)2, and (Cu4)-
[5]-Rotaxane [104+](PF6-)4. [72+](PF6-)2 (0.398 g, 0.18 mmol), di-
tert-butyl-3,5-benzaldehyde (5) (0.32 g, 1.47 mmol), and (dihexyl-3,3′-
dimethyl-4,4′-dipyrryl-2,2′)methane (6) (0.627 g, 1.83 mmol) were
dissolved in methylene chloride (180 mL). Trifluoroacetic acid (4 drops)
was then added, and the reaction mixture was stirred overnight at room
temperature. Chloranil (1.39 g, 5.65 mmol) was added and the reaction
mixture refluxed for 1.5 h. After cooling, the crude reaction mixture
was neutralized with 10% aqueous sodium carbonate (80 mL). The
resulting organic phase (200 mL) was washed three times with water,
stirred overnight with 6.5% aqueous KPF6 (200 mL), washed again
twice with water, and evaporated to dryness. The residue (1.1 g) was
subjected to several column chromatographies. Elution with 2%
methanol in methylene chloride on silica afforded 8 (0.255 g, 32%
from 5). Elution with 0.5% methanol in methylene chloride on alumina
afforded pure [3]-rotaxane [92+](PF6-)2 (240 mg, 34%). Elution with
1.5% methanol in methylene chloride on alumina afforded pure
t
36H, HBu), ca. 1.41 (m, 24H, Hꢀ′′(p,c,d)), ca. 0.92 (m, 36H, Hú′′), 0.32 (t,
8H, Hâ,â*), -2.62, -2.72 and -2.84 (3 br s, 6H, NH). ES-MS: m/z )
-
1532.51 ([M - 4PF6
]
4+, calcd 1532.99, 100%).
Acknowledgment. We warmly thank Dr. C. O. Dietrich-
Buchecker for fruitful discussions, Dr. R. Graff and Mr. J.-D.
Sauer for the NMR spectra, Dr. A. van Dorsselaer, Dr. E. Leize,
Mr. R. Hueber, and Mr. G. Teller for the mass spectrometry
measurements. N.S. thanks the Ministe`re de l’Enseignement
Supe´rieur et de la Recherche for a fellowship. We also thank
one of the reviewers for very helpful comments.
Supporting Information Available: Preparation and char-
acterization of compounds 11-20+ and a chart describing proton
labeling (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
1
[5]-rotaxane [104+](PF6-)4 (50 mg, 8%). 8: Dark red solid. H NMR
(200 MHz, CD2Cl2): δ 10.26 (s, 2H, Hmeso), 7.93 (d, 4H, Ho′′, 4J ) 1.7
3
Hz), 7.85 (s, 2H, Hp′′), 4.01 (t, 8H, HR′′, J ) 7.6 Hz), 2.49 (s, 12H,
JA9824829