Cyclophanes and [2]catenanes as ligands for transition metal complexes: Synthesis, structure, absorption spectra, and excited state and electrochemical properties

Article abstract of DOI:10.1002/(SICI)1521-3765(19980416)4:4<590::AID-CHEM590>3.0.CO;2-C

Two novel cyclophanes (L₁⁴⁺ and Ln₂⁴⁺), derived from the previously investigated cyclobis(paraquat-p-phenylene) tetracation by the replacement of one and two p-phenylene spacers by 2,2'-bipyridine units suitable

Full text of DOI:10.1002/(SICI)1521-3765(19980416)4:4<590::AID-CHEM590>3.0.CO;2-C

FULL PAPER
Cyclophanes and [2]Catenanes as Ligands for Transition Metal Complexes:
Synthesis, Structure, Absorption Spectra, and Excited State and
Electrochemical Properties**
Peter R. Ashton, Vincenzo Balzani,* Alberto Credi, Oldrich Kocian, Dario Pasini,
Luca Prodi, Neil Spencer, J. Fraser Stoddart,* Malcolm S. Tolley, Margherita Venturi,
Andrew J. P. White, and David J. Williams*
Abstract: Two novel cyclophanes (L14‡
and L42‡), derived from the previously
investigated cyclobis(paraquat-p-phe-
nylene) tetracation by the replacement
of one and two p-phenylene spacers by
2,2'-bipyridine units suitable as binding
sites for the coordination of transition
metals, have been synthesized, as have
the [2]catenanes L43‡ and L44‡ incorpo-
rating L41‡ and the macrocyclic polyethers
bis-p-phenylene-34-crown-10 and 1,5-di-
naphtho-38-crown-10. L41‡, L24‡, L34‡, and
L44‡ were then used to synthesize some
novel mono- and binuclear ruthen-
ium(ii), rhenium(i), silver(i), and copper(i)
complexes, which were characterized by
mass spectrometry, NMR spectroscopy,
and, where possible, X-ray crystallogra-
phy. The absorption spectra, lumines-
cence properties, and electrochemical
behavior of the L41‡, L24‡, and L44‡ ligands
and the complexes [Re(CO)3L1Cl]4‡,
[Re(CO)3L4Cl]4‡, [{Re(CO)3Cl}2L2]4‡,
[Ru(bpy)2L1]6‡, [Ru(bpy)2L4]6‡, and
[{Ru(bpy)2}2L2]8‡ were investigated. Be-
sides the ligand-centered bands, the ReI
and RuII complexes display metal-to-
ligand charge-transfer (MLCT) bands in
the visible region similar to those of
model compounds [Re(CO)3(Cl)(bpy)]
and [Ru(bpy)3]2‡. None of the com-
plexes studied emits at room temper-
ature, because the potentially lumines-
cent MLCT excited state undergoes
electron-transfer quenching by the para-
quat-type units in the ligands. In a rigid
matrix at 77 K, where electron transfer
cannot occur, emission is observed from
the complexes containing the cyclo-
phane ligands L41‡ and L24‡, but not from
those containing the catenane ligand
L44‡, in which quenching can still take
place by energy transfer to a low-energy
CT excited state of the catenane moiety.
In the potential window examined
(
2.2/‡2.1 V), L41‡ and L24‡ can accept
reversibly five and six electrons, respec-
tively, with processes localized on their
paraquat- or bpy-type units. The cate-
nane ligand L44‡, besides the reduction
processes associated with the L41‡ cyclo-
phane, undergoes two oxidation proc-
esses involving the dioxynaphthalene
moieties of the crown ether. The com-
plexes exhibit several redox processes
(up to a total of nine exchanged elec-
trons in the case of [Ru(bpy)2L4]6‡ and
[{Ru(bpy)2}2L2]8‡) that can be assigned
to i) reduction of the paraquat- and bpy-
type moieties of the ligands, ii) reduction
of the bpy ligands (in the Ru com-
plexes), iii) oxidation of the metals, and
iv) oxidation of the dioxynaphthalene
units of the crown ether (in complexes
containing the catenane ligand).
Keywords: catenanes ´ cyclophanes
´ electrochemistry ´ luminescence ´
transition metals
coordination of transition metals to nitrogen-containing
aromatic ligands has been exploited by several research
groups as a viable recognition motif for the construction of
complex and fascinating molecular architectures, such as
double and triple helicates,[2] catenates,[3] molecular knots,[4]
Introduction
Supramolecular chemistry has been considerably enriched by
the introduction of abiotic systems capable of self-assembling
and self-organizing with a high degree of selectivity.[1] The
[*] Prof. J. F. Stoddart,[‡] Dr. O. Kocian, Dr. D. Pasini, Dr. N. Spencer,
P. R. Ashton, M. S. Tolley
Prof. V. Balzani, A.Credi, L. Prodi, M. Venturi
Á
Universita degli Studi di Bologna
School of Chemistry, University of Birmingham
Edgbaston, Birmingham B15 2TT (UK)
Dipartimento di Chimica G. Ciamician
Via Selmi 2, 40126 Bologna (Italy)
Fax : (‡ 39)51-259-456
Prof. D. J. Williams, Dr. A. J. P. White
Chemical Crystallography Laboratory
Department of Chemistry, Imperial College
South Kensington, London SW7 2AY (UK)
Fax : (‡ 44)171-594-5804
‡
[ ] Current address: Department of Chemistry and Biochemistry
University of California at Los Angeles
405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
[**] Molecular Meccano, Part 35. For Part 34, see P. R. Ashton, M. C. T.
Fyfe, S. K. Hickingbottom, S. Menzer, J. F. Stoddart, A. J. P. White,
D. J. Williams, Chem. Eur. J., previous paper in this issue.
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Chem. Eur. J. 1998, 4, No. 4

590±607
and dendritic systems.[5] Metal ± ligand interactions are ex-
tremely appealing because of the strength of the coordinative
bond and the variety of geometries that one can obtain by
changing the central metallic core of transition metal com-
plexes.
Recently, interest has grown rapidly in the design and
development of photochemical molecular-level devices capa-
ble of performing useful light-induced functions.[6] Transition
metal based systems have the advantage over their organic
counterparts of significant tunability with respect to the
structural and electronic properties of both the inorganic and
organic components.[7] Polypyridine transition metal com-
plexes, particularly of RuII, ReI, and OsII, show great promise
as components of photochemical devices.[7±11]
One approach to the construction of interlocked molecular
compounds and intertwined supramolecular arrays, based on
a self-assembly paradigm, relies upon p-electron-deficient
and p-electron-rich subunits of high mutual complementarity.
Together with the previously reported [2]catenanes 14‡ and
24‡,[12] based on the p-electron-deficient cyclobis(paraquat-p-
phenylene) and the p-electron-rich macrocyclic polyethers
bis-p-phenylene-34-crown-10 (BPP34C10) and 1,5-dinaphtho-
38-crown-10 (1/5DN38C10), we have recently achieved the
self-assembly of the [2]catenanes 34‡ and 44‡ bearing one or
two 3,3'-disubstituted bitolyl spacers inserted into the skel-
eton of the tetracationic cyclophane components.[13]
N
N
N
N
5e
Br
N
Br
N
+
+
+
N
N
N
1)
2)
MeCN / ∆
4 PF6
2 PF6
NH4PF6 / H2O
N
+
+
N
N
+
+
24%
L1·4PF6
6·2PF6
N
N
N
N
5e
Br
Br
+
+
+
N
N
+
N
N
1)
MeCN / ∆
4 PF6
2 PF6
2) NH4PF6 / H2O
N
N
+
25%
N
N
+
+
L2·4PF6
7·2PF6
N
N
N
N
Scheme 1. Synthesis of the tetracationic cyclophanes L1 ´ 4PF6 and L2 ´
4PF6, containing one and two 2,2'-bipyridine moieties, respectively.
N
N
N
N
4 PF6
1) BPP34C10
MeCN / RT
or
5e
O
Br
N
Br
N
O
O
+
+
+
N
N
N+
O
O
O
1/5DN38C10
DMF / 12 Kbar
O
O
O
O
O
+
2 PF6
O
O
O
O
O
+
2)NH4PF6 / H2O
O
N +
N
N +
+
+
+
O
O
N
N
N
N
+
+
O
N
N
N
N
6·2PF6
L3·4PF6
L4·4PF6
(30%)
(41%)
+
+
O
O
O
O
O
O
O
O
O
O
14+
24+
4 PF6
N
N
O
O
O
O
+
+
+
N
N
O
O
O
O
O
O
O
O
O
O
O
O
O
O
1) BPP34C10
MeCN / RT
5e
N
N
2)NH4PF6 / H2O
3%
N
N
+
+
+
+
+
+
N
N
N
N
N
N
O
N
O
Br
N
Br
8·4PF6
+
N
N
N
4 PF6
2 PF6
N
N
+
+
+
N
1) BPP34C10
DMF / 12 Kbar
N
N
+
+
O
O
O
O
O
O
O
O
O
+
+
N
N
O
O
O
O
O
O
O
O
O
O
O
7·2PF6
2)NH4PF6 / H2O
2%
O
O
O
O
O
N
N
O
O
N
O
N
+
+
34+
44+
O
O
N
N
Herein we describe the syntheses and characterizations of
9·4PF6
the novel tetracationic cyclophanes L41‡ and L24‡ (Scheme 1)
and [2]catenanes L34‡ and L44‡ (derived from L41‡ in Scheme 2)
containing 2,2'-bipyridine moieties as binding sites for the
Scheme 2. The self-assembly of the catenanes L3 ´ 4PF6, L4 ´ 4PF6, 8 ´ 4PF6,
and 9 ´ 4PF6; the latter two contain L2 as their tetracationic cyclophane
components.
Chem. Eur. J. 1998, 4, No. 4
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591

V. Balzani, J. F. Stoddart, D. J. Williams et al.
FULL PAPER
coordination of a variety of transition metals. We also report
the syntheses of novel mono- and binuclear ruthenium(ii),
rhenium(i), silver(i), and copper(i) complexes of these ligands,
and an investigation of the absorption spectra, emission
spectra, and electrochemical properties of the L41‡, L24‡ and
L44‡ ligands and the [Re(CO)3L1Cl]4‡, [Re(CO)3L4Cl]4‡, [{Re-
(CO)3Cl}2L2]4‡, [Ru(bpy)2L1]6‡, [Ru(bpy)2L4]6‡, and [{Ru-
(bpy)2}2L2]8‡ complexes.[14]
Attempts to incorporate two bipyridine moieties as ligands
into the tetracationic cyclophane component of a catenated
structure were also made. However, with the crown ether
BPP34C10, the yield from the attempted catenation at room
temperature and ambient pressure was extremely low: the
[2]catenane 8 ´ 4PF6 was isolated in only 3% yield (Scheme 2).
Unexpectedly, when the reaction was carried out under
ultrahigh-pressure conditions, no [2]catenane was obtained
and only a trace of the corresponding [3]catenane 9 ´ 4PF6 was
isolated and characterized by mass spectrometry. This result
may be explained by the fact that 4,4'-disubstituted-2,2'-
bipyridine moieties exist in many different conformations as a
consequence of torsion around the aryl ± aryl bond. It is
believed[18] that, when the tricationic complex is formed
(Figure 1), the ring closure to afford the interlocked com-
Results and Discussion
Synthesis of ligands: The ligands L41‡ and L24‡ (Scheme 1) bear
the 2,2'-bipyridine unit as a binding site for metal complex-
ation. This unit was incorporated into L41‡ and L24‡ via 4,4'-
bis(bromomethyl)-2,2'-bipyridine (5e). The synthesis of the
dibromide 5e by radical bromination of 4,4'-dimethyl-2,2'-
bipyridine (5a) has been reported recent-
N
N
N
ly.[15] However, in our hands this reaction
N
N
N
gave a mixture of polybrominated com-
pounds that was difficult to purify. In the
event, we prepared the dibromide 5e in
four steps in 46% yield overall from the
commercially available 5a. We employed
the highly efficient method for oxidation
of 5a to 5b using chromium(vi) oxide in
concentrated H2SO4 (92% yield) as al-
ready reported in the literature.[16] The
diacid 5b was then converted by treatment
with MeOH and H2SO4 into its dimethyl
ester 5c (84% yield), which was subse-
Anti (favored)
R
R
R
O O
O
O
O O
O O
O
O
5a
Me
+
+
+
+
+
5b
5c
5d
5e
CO2H
CO2Me
CH2OH
CH2Br
+
+
••
O
O
O
O O
O
O O O O
Br
Figure 1. Schematic illustration of a possible route for the formation of the
catenanes 8 ´ 4PF6 and 9 ´ 4PF6.
quently reduced (79% yield) to the diol 5d with NaBH4 in
EtOH, once again following a literature procedure.[17] Reflux-
ing the diol 5d with 48% hydrobromic acid produced the
dibromide 5e in 75% yield. The cyclophane L41‡ was
synthesized (Scheme 1) in 24% yield as its hexafluorophos-
phate salt directly under high dilution conditions (MeCN,
reflux) by reaction of the dibromide 5e with the known[18]
bis(hexafluorophosphate) salt 6 ´ 2PF6, followed by flash
column chromatography (SiO2: MeOH/2m aq. NH4Cl/Me-
NO2, 7:2:1) and anion exchange (NH4PF6/H2O). The cyclo-
phane L42‡ was prepared in two steps. Reaction of 4,4'-
bipyridine with the dibromide 5e yielded, after anion
exchange (NH4PF6/H2O), the bis(hexafluorophosphate) salt
7 ´ 2PF6 (90% yield), which was cyclized (again under high
dilution conditions) with the dibromide 5e to give
(Scheme 1), after flash column chromatography and counter-
ion exchange (NH4PF6/H2O), the tetracationic cyclophane
L42‡ as its hexafluorophosphate salt in 25% yield.
The [2]catenane ligands L43‡ and L44‡, containing the
macrocyclic polyethers BPP34C10 and 1/5DN38C10, could
be prepared at room temperature and at either ambient or
ultrahigh pressure using MeCN and DMF as solvents, respec-
tively (Scheme 2). In both cases, one of the precursors of the
interlocked rings, either the macrocyclic polyether BPP34C10
or the bis(hexafluorophosphate) salt 6 ´ 2PF6 and the dibro-
mide 5e, was used in excess. Following chromatography and
counterion exchange, L43‡ and L44‡ were isolated as their
hexafluorophosphate salts in 30 and 41% yields, respectively.
pound is assisted by effective p ± p stacking interactions
throughout the system. The preference of 2,2'-bipyridine to
exist in an anti conformation presumably keeps the bipyr-
idinium and the pyridylpyridinium units of the tricationic
intermediate complex too far away from each other for
efficient ring closure.[19]
Preparation of RuII complexes: The ligands L14‡ ± L44‡ were
introduced into the bis-heteroleptic mononuclear [Ru-
(bpy)2L1](PF6)6, [Ru(bpy)2L3](PF6)6, and [Ru(bpy)2L4](PF6)6,
and dinuclear [{Ru(bpy)2}2L2](PF6)8 complexes in 82 ± 97%
yields (Schemes 3 ± 5) by reactions of excesses of L41‡ ± L44‡
with [Ru(bpy)2Cl2] in EtOH/H2O.
The RuII complexes were separated from excesses of the
starting materials by treatment of the crude products with
H2O and filtration; after counterion exchange (NH4PF6/H2O),
they were purified by slow crystallization/precipitation from
iPr2O/MeCN.
Preparation of ReI complexes: The mononuclear [Re-
(CO)3L1Cl](PF6)4 and [Re(CO)3L4Cl](PF6)4 and the dinuclear
[{Re(CO)3Cl}2L2](PF6)4 rhenium(i) tricarbonyl complexes
(Schemes 3 ± 5) were obtained in each case by refluxing the
ligand (L41‡, L44‡, or L42‡) with an excess of [Re(CO)5Cl] in
anhydrous MeOH. After cooling, the products were collected
by filtration and the excesses of the starting materials were
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Chem. Eur. J. 1998, 4, No. 4

Catenane Ligands
590±607
N
N
+
+
N
N
N
N
AgCF3SO3 / MeCN
or
[Re(CO)5Cl]
MeOH / ∆
4 PF6
Cu(MeCN)4PF6 / MeCN
+
+
+
+
+
+
N
N
N
N
L1·4PF6
RuCl2(bpy)2·H2O
EtOH / H2O / ∆
N
N
N
M +
N
N
N
N
OC CO
OC Re
9 PF6
N
N
Ru2+
Cl
N
N
N
+
+
4 PF6
6 PF6
N
N
N
+
+
+
+
+
+
N
N
N
N
N
N
N
N
N
+
+
+
+
Scheme 3. Preparation of the mononu-
clear AgI, CuI, ReI, and RuII complexes
[Ag(L1)2]·9PF6
[Cu(L1)2]·9PF6
[Re(CO)3ClL1]·4PF6
[Ru(bpy)2L1]·6PF6
containing the cyclophane L14‡
.
N
N
AgCF3SO3 / MeCN
or
O
+
O
O
O
O
+
+
[Re(CO)5Cl]
N
N
N
N
O
O
O
O
Cu(MeCN)4PF6 / MeCN
MeOH / ∆
O
O
N
O
O
+
+
N
N
O
O
O
O
+
O
L3·4PF6
L4·4PF6
N
+
+
O
O
[RuCl2(bpy)2]·H2O
EtOH / H2O / ∆
N
N
N
+
9 PF6
M
N
N
CO
CO
2+
N
N
N
Ru
OC Re Cl
N
N
6 PF6
N
N
4 PF6
O
+
O
O
O
+
+
N
N
N
N
O
O
O
O
O
+
O
O
O
+
O
O
O
N
N
N
+
+
+
O
O
O
N
N
N
N
O
O
O
O
+
O
O
O
N
+
+
O
O
+
O
O
O
[Ag(L3)2]·9PF6
[Ag(L4)2]·9PF6
[Cu(L4)2]·9PF6
Scheme 4. Preparation of the mononu-
clear AgI, CuI, ReI, and RuII complexes
[Ru(bpy)2L3]·6PF6
[Ru(bpy)2L4]·6PF6
[Re(CO)3ClL4]·4PF6
containing the [2]catenanes L43‡ and L44‡
.
removed by washing with THF to give the corresponding
complexes in 66 ± 82% yield.
successive losses of one, two, or three PF6 counterions from
the molecular ion were observed. Additionally, the cleavage
of the crown ethers from the [2]catenanes L3 ´ 4PF6 and L4 ´
4PF6 produces peaks which correspond to the free cyclophane
component L1 ´ 4PF6, once again with the successive loss of
counterions.
Preparation of AgI and CuI complexes: The addition of
Ag(CF3SO3) to MeCN solutions of L41‡, L34‡, and L44‡ in
separate experiments led to the isolation of the silver(i)
complexes [Ag(L1)2](PF6)9, [Ag(L3)2](PF6)9, and [Ag(L4)2]-
(PF6)9 in 82 ± 93% yields. Similarly, when the ligands L41‡ and
L44‡ were treated with [Cu(MeCN)4](PF6), the complexes
[Cu(L1)2](PF6)9 and [Cu(L4)2](PF6)9 were obtained in 83 and
95% yields, respectively (Schemes 3 and 4).
In the case of the [3]catenane 9 ´ 4PF6, peaks corresponding
‡
‡
‡
‡
to [M] , [M PF6] , [M 2PF6] , and [M 3PF6] at m/z ˆ
2330, 2185, 2040, and 1894 were observed. The loss of one
crown ether to produce the corresponding [2]catenane is
responsible for peaks at m/z ˆ 1647, 1502, and 1357, while loss
of the second crown ether produces peaks at m/z ˆ 1111, 966,
and 821, which correspond to the free cyclophane L2 ´ 4PF6
with successive loss of the counterions as usual.
Mass spectrometry of ligands: Liquid secondary ion mass
spectrometry (LSIMS) was employed in the characterization
of the ligands L41‡ ± L44‡ (Table 1). In all cases, peaks for the
Chem. Eur. J. 1998, 4, No. 4
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593

V. Balzani, J. F. Stoddart, D. J. Williams et al.
FULL PAPER
Mass spectrometry of complexes: The results obtained using
LSIMS are summarized in Table 1. A general pattern is
observed where successive losses of counterions from the
molecular ion produce the major significant peaks in the
spectra. In the cases of Ag(L1)2 ´ 9PF6 and Ag(L4)2 ´ 9PF6, it
was necessary to predissolve the complexes in DMSO before
addition to the m-nitrobenzyl alcohol matrix in order to
produce satisfactory spectra: ions corresponding to the loss of
silver from the molecular ion, in addition to the successive
losses of counterions, were detected.
N
N
2+
N
Ru
N
N
N
8 PF6
[RuCl2(bpy)2]·H2O
+
+
+
+
N
N
N
EtOH / H2O / ∆
[{Ru(bpy)2}2L2]·8PF6
N
N
N
4 PF6
N
N
N
1H NMR spectroscopy of ligands: In the 1H NMR spectra, a-
CH, b-CH and a'-CH, b'-CH are used to denote the protons
on the 4,4'-bipyridinium units contained between p-xylyl and
2,2'-bipyridyl spacers. The convention adopted is one in which
a- and b-CH describes the pyridinium ring of the 4,4'-
bipyridinium unit which is adjacent to the p-xylyl spacer. Thus
a'- and b'-CH protons belong to the pyridinium ring which is
adjacent to the 2,2'-bipyridyl spacer. The protons on the 2,2'-
bipyridyl spacers and on the 2,2'-bipyridine ligands coordi-
nated to ruthenium are marked in the Experimental Section
as PyH and bpyH protons, respectively. NOE difference
spectroscopy has been used to obtain full proton assignments.
In the case of L41‡ (CD3CN, 258C), irradiation of the methylene
protons next to p-xylyl spacer at d ˆ 5.77 leads to an NOE
enhancement in the signals for the xylyl protons and a-CH
protons at d ˆ 7.56 and 8.86, respectively. Similarly, irradiation
of the NCH2 protons close to 2,2'-bipyridyl at d ˆ 5.87
produces an increase in the intensity of the signals for the
protons H-5 and H-3 on bipyridyl spacer and the a'-CH
protons on the bipyridinium unit at d ˆ 7.88, 8.13, and 8.92,
respectively. Finally, irradiation of a-CH protons yields an
enhanced intensity of the b-CH proton signals at d ˆ 8.18.
The 1H NMR spectra of the [2]catenanes L34‡ and L44‡ both
showed temperature-dependent behavior. Two dynamic proc-
esses (Scheme 6) occurring within these [2]catenanes could be
+
+
+
2+
N
N
N
N
N
N
Ru
N
+
CO
CO
OC Re Cl
N N
N
N
4 PF6
L2·4PF6
+
+
+
+
N
N
N
N
[{Re(CO)3Cl}2L2]·4PF6
[Re(CO)5Cl]
MeOH / ∆
N
N
OC
Cl
CO
Re
CO
Scheme 5. Preparation of the binuclear ReI and RuII complexes containing
the cyclophane L24‡
.
Table 1. LSIMS data[a] for the bis(hexafluorophosphate) salt 7 ´ 2PF6, the
[2]catenane 8 ´ 4PF6, the [3]catenane 9 ´ 4PF6, the ligands L1 ´ 4PF6, L2 ´
4PF6, and their corresponding RuII, ReI, AgI, and CuI complexes.
M[b]
M
PF6
M
2PF6
M
3PF6
7 ´ 2PF6
8 ´ 4PF6
9 ´ 4PF6
L1 ´ 4PF6
L2 ´ 4PF6
L3 ´ 4PF6
L4 ´ 4PF6
[Ru(bpy)2L1](PF6)4
[{Ru(bpy)2}2L2](PF6)4
[Ru(bpy)2L3](PF6)4
[Ru(bpy)2L4](PF6)4
[Re(CO)3ClL1](PF6)4
[Re(CO)3ClL1](Cl4)
[{Re(CO)3Cl}2L2](PF6)4
[Re(CO)3ClL4](PF6)4
[Ag(L1)2](PF6)9
[Ag(L3)2](PF6)9
[Ag(L4)2](PF6)9
[Cu(L1)2](PF6)9
[Cu(L4)2](PF6)9
(784)[c]
(1792)
2330
(1178)
(1256)
(1715)
1814
(1882)
(2664)
(2318)
(2518)
(1484)
(1046)
(1868)
2120
(2610)
(3828)
(3883)
(2566)
(3839)
639
493
1647
2185
1033
1111
1570
1669
1737
2519
2273
2373
1339
1011
1723
1975
2465
1502
2040
888
1357
1894
743
966
821
2
1422
1524
1592
2375
2128
2229
1194
974
1578
1830
2320
3538
1379
1447
2229
1983
2084
1049
939
1433
1685
2176
3393
A
A
B
B
A
B
B
A
1
1
[d, e]
(3683)
(3738)
2420
[d, f]
(3593)
2274
3549
(3448)
2130
3403
3693
[a] LSIMS mass spectra were obtained with
a VG ZabSpec mass
B
A
A
B
B
B
A
A
spectrometer equipped with a Cs ion source. [b] M ˆ molecular weight.
[c] The numbers in parentheses refer to peaks that were not observed.
[d] The spectra were run in a mixture of m-nitrobenzylalcohol and DMSO.
‡
2
[e] The fragmentation pattern corresponding to [M Ag 2PF6] ,
‡
‡
[M Ag 3PF6] , [M Ag 4PF6] was also observed. [f] The fragmen-
‡
‡
Scheme 6. The dynamic processes occurring in the [2]catenanes L43‡ and
L44‡ on the H NMR time scale.
tation pattern corresponding to [M Ag 2PF6] , [M Ag 3PF6] ,
‡
‡
1
[M Ag 4PF6] , [M Ag 5PF6] was observed.
594
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Chem. Eur. J. 1998, 4, No. 4

Catenane Ligands
590±607
identified and characterized. 1H NMR spectra (Figure 2)
recorded for the [2]catenane L44‡ in CD3CN at 354 K indicate
fast circumrotation of the crown ether ring through the
tetracationic cyclophane. As a result of this process, two
signals each for chemically nonequivalent a-bipyridinium
protons, b-bipyridinium protons, and NCH2 protons are
revealed. On cooling a CD3COCD3 solution to 243 K, two
sets of four signals corresponding to a-bipyridinium protons
and b-bipyridinium protons are observed. This temperature-
dependent behavior indicates that the circumrotation of the
macrocyclic polyether is slow on the 1H NMR time scale and
that C2 symmetry is imposed on the tetracationic cyclophane
by the 1,5-dioxynaphthalene residue. When a CD3COCD3
solution of the [2]catenane L44‡ is cooled to 178 K, the
circumrotation of the tetracationic cyclophane through the
1
crown ether is slow on the H NMR time scale and the two
bipyridinium units become anisochronous, since one bipyr-
idinium unit lies inside and the other alongside the cavity of
the crown ether. This temperature-dependent behavior is
reflected in two sets of eight signals for the a- and the b-
protons of the bipyridinium unit. The a/b pairs were assigned
following DQF COSY experiments.
The kinetic and thermodynamic parameters[21] (Table 2) for
the circumrotation of the macrocyclic polyether component
through the cavity of the tetracationic cyclophane component
(process 1 in Scheme 6) show that the activation barrier for
this process is decreased upon introduction of one bipyridine
spacer into the skeleton of the tetracationic cyclophane
component. The activation barriers obtained for the [2]cate-
nanes L43‡ and L44‡ are in agreement with the values reported
for the [2]catenane 34‡ (Table 2), but show a marked decrease
when compared with the data obtained for their parent
[2]catenanes, 14‡ and 24‡, with p-xylyl spacers present in the
tetracationic cyclophane component. This decrease in the
activation barrier presumably reflects the reduced stability of
the p-acceptor/p-donor/p-acceptor recognition motif in the
catenane, as the bipyridinium acceptor units are held further
apart, enlarging the cavity of the cyclophane component. The
values for the activation energy barriers obtained for proc-
ess 2 (Scheme 6) in the case of the [2]catenanes L43‡ and L44‡
,
which involves the circumrotation of the tetracationic cyclo-
phane components around the neutral macrocyclic compo-
nent, do not show any dramatic variation when compared with
the [2]catenanes mentioned above (Table 2).
Figure 2. The partial temperature-dependent 1H NMR spectra (400 MHz)
of the [2]catenane L4 ´ 4PF6 recorded a) in CD3CN at 354 K, b) in
CD3COCD3 at 243 K and c) in CD3COCD3 at 178 K.
Table 2. Kinetic and thermodynamic parameters[a] for processes 1 and 2 (Scheme 6) obtained from the temperature-dependent 400 MHz 1H NMR spectra of
the [2]catenanes L3 ´ 4PF6, L4 ´ 4PF6, 1 ´ 4PF6, 2 ´ 4PF6, and 3 ´ 4PF6.
kc[a] (s
(kex)[b]
)
Tc[a] (K)
(Tex)[b]
DGˆc [a] (kcalmol
)
Process
1
1
[2]catenane
Probe
protons
DnÄ[a] (Hz)
(DnÄ)[b]
ˆ
[b]
(DGex
)
[c]
1 ´ 4PF6
OC6H4O
(19)
74
(108)
24
(24)
65
714
115
220
50
(60)
165
(240)
75
(75)
144
1586
255
(313)
250
(361)
257
(257)
239
299
229
263
189
(15.7)
12.0
(17.2)
12.7
(12.8)
11.5
13.1
10.8
12.1
9.1
1[d]
2
a-CH ± bpy
OC10H6O
a-CH ± bpy
OC6H4O
a-CH ± bpy
OC6H4O
a-CH ± bpy
b-CH ± bpy
b-CH ± bpy
[e]
2 ´ 4PF6
1[f]
2
[g]
3 ´ 4PF6
1[f]
2
L3 ´ 4PF6
L4 ´ 4PF6
1[d]
2
489
111
1[d]
2
[a] Data not in parentheses relate to the coalescence method (see ref. [20]). [b] Data in parentheses relate to the exchange method (see ref. [20]). [c] P. R.
Ashton, T. T. Godnow, A. E. Kaifer, M. V. Reddington, A. M. Z. Slawin, N. Spencer, J. F. Stoddart, C. Vicent, D. J. Williams, Angew. Chem. 1989, 101, 1404 ±
1408; Angew. Chem. Int. Ed. Engl. 1989, 28, 1396 ± 1399. [d] In CD3COCD3. [e] P. R. Ashton, C. L. Brown, E. J. T. Chrystal, T. T. Godnow, A. E. Kaifer, K. P.
Parry, D. Philp, A. M. Z. Slawin, N. Spencer, J. F. Stoddart, D. J. Williams, J. Chem. Soc. Chem. Commun. 1991, 634 ± 639. [f] In CD3CN. [g] See ref. [13].
Chem. Eur. J. 1998, 4, No. 4
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595

V. Balzani, J. F. Stoddart, D. J. Williams et al.
FULL PAPER
1H NMR spectroscopy of complexes: Selected 1H NMR
portion acts as a bidentate ligand to the Re center, which has
distorted octahedral coordination geometry (the angles at Re
are in the range 74.4(3) ± 99.8(4)8 and 172.2(4) ± 175.4(3)8, the
most acute angle being due to the bite of the 2,2'-bipyridyl
ligand). The two Re ± N bonds are of the same length
(2.167(7), N(1) and 2.165(7), N(8) Š) as are the two trans
Re ± C distances (1.90(1) and 1.91(1) Š). The Re ± C bond
trans to Cl is slightly longer at 1.93(1) Š, reflecting the trans
effect of the Cl atom; the Re ± Cl distance is 2.468(3) Š. There
are no significant intercomplex p ± p interactions, though the
included benzene solvent molecules enter into both intra- and
intercomplex p ± p stacking interactions. One of these inter-
actions involves a benzene molecule inserted into the cyclo-
phaneꢁs cavity and sandwiched between the two bipyridinium
units (mean interplanar separations of 3.50 and 3.55 Š), an
interaction which is supplemented by a C ± H ´´´ p interaction
between one of the hydrogen atoms of the benzene molecule
and the p-xylyl spacer of the cyclophane (the H ´´´ p distance is
2.88 Š and the associated C ± H ´´´ p angle 1788). The other
included benzene molecule is p-stacked between the N(1)-
containing pyridyl ring of one complex and its Ci related
counterpart of another. The associated ring centroid/ring
centroid and interplanar separations are 3.36 and 3.46 Š,
respectively.
chemical shift data for the cyclophane ligands L41‡ and L24‡
,
and for the corresponding metal complexes, are listed in
Table 3. In the case of the [Re(CO)3L1Cl]4‡ and [{Re-
(CO)3Cl}2L2]4‡ complexes, considerable shifts to the higher
frequencies could be observed upon attachment of the
electron-withdrawing Re(CO)3Cl group compared with the
same protons in the free ligands L41‡ and L24‡. On the other
hand, a remarkable shift to lower frequencies has been
observed for the H-6 proton resonances of the 2,2'-bipyridyl
spacer in all investigated RuII complexes. The 1H NMR
spectra of the CuI and AgI complexes show no marked
differences in chemical shifts upon metal complexation.
In the case of the dinuclear [{Ru(bpy)2}2L2]8‡ complex, one
might expect a mixture of meso (LD) and rac (LL/DD)
diastereoisomeric forms. Unfortunately, we have not been
successful in separation of the diastereoisomeric pairs using
base-deactivated reversed phase HPLC with 0.1% TFA in a
H2O/MeCN solvent gradient.
X-ray crystallography: The X-ray analysis (Figure 3) of
[Re(CO)3ClL1](PF6)4 shows the tetracationic cyclophane
component to have a toboggan-like conformation with the
The X-ray structure (Figure 4) of [Ag(L1)2](PF6)9 shows the
2:1 complex to have crystallographic C2 symmetry, the
geometry at Ag being severely distorted tetrahedral with
angles at Ag in the range 71.6(2) ± 135.4(2)8. The size of the
smaller of these angles is again due to the bite of the 2,2'-
bipyridyl ligand, and the other distortion from tetrahedral is
due to a twisting of the two Ag ± N2 coordination planes about
the vector bisecting the N-Ag-N angle by 118 from an
Figure 3. X-ray crystal structure of the complex [Re(CO)3L1(Cl)](PF6)4.
p-xylyl and 2,2'-bipyridyl spacers inclined by 92 and 1228,
respectively, to the mean plane of the cyclophane (as defined
by the four methylene carbon atoms). The 2,2'-bipyridyl
Figure 4. X-ray crystal structure of the complex [Ag(L1)2](PF6)9.
Table 3. 1H NMR chemical shift data [d values] for ligands and complexes in CD3CN at ambient temperature.
Bipyridinium
a'-CH a-CH b'-CH b-CH
Py
H-3
p-Xylyl
CH2N C6H4 CH2N
‡
‡
H-6
H-5
L1 ´ 4PF6
8.92
9.07
8.88
9.00
9.51
8.95
9.02
8.96
8.86
8.89
8.84
8.88
9.44
±
8.21
8.21
8.16
8.21
8.59
8.17
8.29
8.28
8.18
8.18
8.12
8.19
8.59
±
8.83
9.17
7.90
8.76
8.77
8.77
9.15
7.89
8.13
8.51
8.33
8.11
8.24
8.27
8.30
8.30
7.88
7.95
7.66
7.73
7.90
7.72
7.93
7.64
5.87
5.96
5.81
5.83
5.91
5.84
5.97
5.89
7.56
7.64
7.63
7.55
7.67
±
5.77
5.79
5.79
5.75
5.83
±
[Re(CO)3ClL1](PF6)4
[Ru(bpy)2L1](PF6)4
[Ag(L1)2](PF6)8
[Cu(L1)2](PF6)4
L2 ´ 4PF6
[a]
[{Re(CO)3Cl}2L2](PF6)4
[{Ru(bpy)2}2L2](PF6)8
±
±
±
±
±
±
±
±
[a] In CD3SOCD3. The d values for L1 ´ 4PF6 in CD3SOCD3 are 9.54, 9.44, 8.60, 8.77, 8.24, 7.90, 5.95, 7.68, and 5.83 for the a'-CH, a-CH, b'-CH, b-CH, H-6, H-
3, H-5, bpy NCH2, C6H4, and xylyl NCH2, respectively.
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Catenane Ligands
590±607
orthogonal relationship between them. The two independent
Ag ± N distances are essentially the same at 2.297(5), N(1) and
2.315(5), N(8). The cyclophane has a conformation that is
similar to that in the Re complex, although in [Ag(L1)2](PF6)9
the p-xylyl and 2,2'-bipyridyl rings are inclined by 84 and 1078
to the mean plane of the cyclophane. In common with the Re
complex, here again we see the trapping of a benzene solvent
molecule within the cyclophane by a combination of a C ± H ´´
´ p interaction to the p-xylyl spacer (H ´´´ p, 2.65 Š; C ± H ´´´ p,
1608) and p ± p stacking with one of the bipyridinium units
(interplanar separation ca. 3.55 Š). The presence of only this
single p ± p interaction is due to a substantial twist, (ca. 408)
between the two pyridinium rings of one of the bipyridinium
units causing an offset of the included benzene ring within the
cavity. Inspection of the packing of the 2:1 complex (Figure 5)
Figure 6. X-ray crystal structure of the complex [{Ru(bpy)2}2L2](PF6)8.
is disordered, there being a superimposition of D and L
configurations.[23] The crystallographic evidence suggests an
inability to produce a resolved (i.e. chiral) complex. What we
cannot be certain about is whether we have a structure that is
disordered with an equal mixture of DD and LL forms or of
DL (and LD) formsÐor, indeed, a mixture of all three
diastereoisomers. The shortest intermolecular Ru ´´´ Ru sep-
arations (9.05 Š) are significantly shorter than the intra-
molecular separation (17.43 Š) of these atoms.
Figure 5. Packing of the molecules of the complex [Ag(L1)2](PF6)9.
The X-ray structure (Figure 7) of the [2]catenane L4 ´ 4PF6
shows the 2,2'-bipyridyl spacer in the tetracationic cyclophane
to have a twisted anti conformation (mean twist between the
two pyridyl rings of 1398), a geometry distinctly different from
that observed in the metal complexes (vide supra). Despite
this geometry the four corner methylene carbon atoms are
coplanar to within 0.09 Š. The 1/5DN38C10 ring component
is threaded in a conventional manner through the center of
the tetracationic cyclophane, the inside and alongside
OC10H6O vectors being inclined by 49 and 108, respectively,
to the mean plane of the tetracation. The catenane is
stabilized by i) p ± p stacking interactions between the inside
reveals an extensive array of both face-to-face and T-type
edge-to-face aryl/aryl interactions involving the 2,2'-bipyridyl,
a pyridinium, the p-xylyl, and the other included benzene
solvate molecule (the other benzene molecule is held within
the cyclophane; see above). This included benzene molecule
is involved in a pair of C ± H ´´´ p interactions: one of these is
to one of the pyridinium rings of the cyclophane (H ´´´ p,
2.73 Š; C ± H ´´´ p, 1568), whereas the other is to the opposite
face of the ring from one of the p-xylyl hydrogen atoms (H ´´´
p, 2.86 Š; C ± H ´´´ p, 1408). The intercomplex interactions are
a parallel p ± p stacking between pairs of 2,2'-bipyridyl rings
(interplanar separation, 3.41 Š) and a weaker face-to-face
interaction (3.77 Š) between the p-xylyl ring of one molecule
and the pyridinium ring of another, that involved also in a C ±
H ´´´ p interaction with the included benzene molecule.
The X-ray analysis (Figure 6) shows the diruthenium
complex [{Ru(bpy)2}2L2](PF6)8 to have an averaged Ci sym-
metric geometry.[22] The tetracationic cyclophane, which
functions as a bis-bidentate ligand, adopts a chairlike con-
formation. The two 2,2'-bipyridyl spacers are inclined by 648
to the mean plane of the cyclophane, while the two
independent pyridinium rings are tilted steeply inwards, being
inclined by 17 and 278 to this plane. The latter two ring-tilts
are in opposite senses, thereby producing a 448 twist between
them. As a result of these tilts, the macroring is essentially
self-filling. The geometry observed at each ruthenium center
Figure 7. X-ray crystal structure of the [2]catenane L4 ´ 4PF6.
Chem. Eur. J. 1998, 4, No. 4
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597

V. Balzani, J. F. Stoddart, D. J. Williams et al.
FULL PAPER
1,5-dioxynaphthalene ring system and the inside and along-
side bipyridinium units (interplanar separations of 3.45 and
3.59 Š, respectively) and between the alongside 1,5-dioxy-
naphthalene ring system and the inside bipyridinium unit
(interplanar separations of 3.46 Š), and ii) a C ± H ´´´ p
interaction involving one of the peri hydrogen atoms on the
inside 1,5-dioxynaphthalene ring system and p-xylyl ring of
the cyclophane (H ´´´ p, 2.81 Š; C ± H ´´´ p, 1498). There are no
C ± H ´´´ O hydrogen bonds. Futhermore, somewhat unusually,
there are no extended intermolecular p ± p stacking inter-
actions between molecules in the crystal.
the electron-accepting paraquat-type units and the electron-
donating dioxynaphthalene units.
Absorption spectra of complexes: The results obtained are
summarized in Table 4, where the previously available data
for the [Re(CO)3(Cl)(bpy)] and [Ru(bpy)3]2‡ model com-
pounds are also included for comparison purposes. The
absorption spectra of the [Re(CO)3L1Cl]4‡, [Re(CO)3L4Cl]4‡,
and [{Re(CO)3Cl}2L2]4‡ complexes are shown in Figure 9 and
those of the [Ru(bpy)2L1]6‡, [Ru(bpy)2L4]6‡, and [{Ru-
(bpy)2}2L2]8‡ complexes in Figure 10. The discussion that
follows is based on the usual assumption that the ground and
excited states of ReI and RuII polypyridine complexes can be
described by localized molecular orbital configurations.[7±11]
The ReI complexes containing a bpy-type ligand are
characterized by a metal-to-ligand charge-transfer (MLCT)
band at the border between the UV and Vis spectral region
resulting from an electron transition from an orbital mainly
localized on Re to a p* orbital mainly localized on the bpy-
type ligand.[11] In the spectrum of [Re(CO)3L1Cl]4‡, one can
see a strong absorption band below 300 nm, which is due to
Absorption spectra of ligands: The absorption spectra of the
ligands L41‡, L24‡, and L44‡ are shown in Figure 8; the wave-
lengths of the absorption maxima and the molar absorption
coefficients are listed in Table 4. The ligands L41‡ and L24‡
display strong absorptions in the UV region, consistent with
the absorption bands shown by the 2,2'-bipyridyl-[21] and
paraquat-type[18] subunits. The catenane ligand L44‡, besides an
intense UV absorption, shows the expected[24] charge-transfer
band in the visible region owing to the interaction between
the paraquat-type and bpy-type chromophoric groups of L14‡
.
Figure 9. Absorption (MeCN, 298 K) and luminescence (inset: butyroni-
trile, 77 K) spectra of the complexes [Re(CO)3L1Cl]4‡ (full line), [{Re-
(CO)3Cl}2L2]4‡ (dotted line), and [Re(CO)3L4Cl]4‡ (dashed line).
Figure 8. Absorption spectra (MeCN, 298 K) of the ligands L41‡ (full line),
L42‡ (dotted line), and L44‡ (dashed line).
Table 4. Absorption and emission properties of ligands and complexes.
Absorption 298 K[a]
lmax (nm)
Emission 298 K[a]
Emission 77 K[b]
lmax (nm) t (ms)
1
e (m 1 cm
)
lmax (nm)
t (ns)
L41‡
L42‡
L44‡
266
273
271
512
370[c]
255
396
394
512
250
394
450[f]
255
285
450
285
470
285
448
48000
60000
55000
1100
±
±
±
±
±
±
±
±
±
±
±
±
[Re(CO)3(Cl)(bpy)]
[Re(CO)3L1Cl]4‡
3400[c]
54000
3900
622[c]
±
25[c]
±
530[d, e]
561
3.8[d, e]
3.1
[Re(CO)3L4Cl]4‡
4800
1600
71000
7800
14300[f]
64000
80000
11500
80000
9000
±
±
±
±
±
±
[{Re(CO)3Cl}2L2]4‡
579
1.7
[Ru(bpy)3]2‡
[Ru(bpy)2L1]6‡
630[f]
±
1150[f]
±
582[f, g]
597
5.1[f, g]
6.0
[Ru(bpy)2L4]6‡
±
±
±
±
±
±
[{Ru(bpy)2}L2]8‡
132000
23500
603
5.2
[a] Acetonitrile solution. [b] Butyronitrile rigid matrix. [c] See ref. [11]. [d] EPA matrix. [e] See ref. [25]. [f] See ref. [7]. [g] In MeOH/EtOH rigid matrix.
598
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Catenane Ligands
590±607
units of the crown ether are potentially luminescent. In the
catenane ligand L44‡, however, the luminescent excited state of
the dioxynaphthalene units is quenched because of the
charge-transfer interaction with the paraquat-type units, as
previously observed for catenane 24‡.[24] Therefore, none of
the L14‡, L24‡, and L44‡ ligands exhibits luminescence.
Emission spectra of complexes: The [Re(CO)3(Cl)(bpy)] and
[Ru(bpy)3]2‡ model compounds (Table 4) are known to
luminesce relatively strongly, both in fluid solution at room
temperature and in a rigid matrix at 77 K, from the lowest
triplet metal-to-ligand charge-transfer (3MLCT) excited
state.[7, 8, 11] None of the complexes examined emits at room
temperature. This result is expected, since it is well known
that paraquat-type units can quench the luminescent excited
state of Re and Ru polypyridine complexes by electron
transfer.[11] In a rigid matrix at 77 K, where electron transfer is
prevented,[26] emission can be observed from the complexes
containing the L41‡ and L24‡ ligands (Figures 9 and 10, insets),
but not from those containing the catenane ligand L44‡
(Table 4). This situation shows that, in [Ru(bpy)2L4]6‡ and
Figure 10. Absorption (MeCN, 298 K) and luminescence (inset: butyroni-
trile, 77 K) spectra of the complexes [Ru(bpy)2L1]6‡ (full line),
[{Ru(bpy)2}2L2]8‡ (dotted line), and [Ru(bpy)2L4]6‡ (dashed line).
The MLCT band is found at considerably lower energy than
that in the [Re(CO)3(Cl)(bpy)] model compound.[11, 25] This
difference can be attributed to the Coulombic stabilization
offered to the MLCT excited state by the positive charges on
the paraquat-type units present in L41‡. The MLCT band of
[{Re(CO)3Cl}2L2]4‡ occurs at the same wavelength and shows
an absorption coefficient twice that of [Re(CO)3L1Cl]4‡, sug-
gesting that the two metal-based moieties do not substantially
perturb each otherÐa conclusion which is confirmed by the
electrochemical results (see below). Comparison of the ab-
sorption spectra of [Re(CO)3L1Cl]4‡ and [Re(CO)3L4Cl]4‡ in-
dicates that the latter complex displays a more intense absorp-
tion in the 300 ± 350 nm spectral region because of the bands
due to the 1/5DMN units of the crown ether, and a tail in the
400±600 nm region due to the CT band of the catenane ligand.
It is well known[7, 8] that the RuII complexes of bpy-type
ligands exhibit a MLCT band in the visible region around
450 nm. Besides the ligand-centered bands in the UV region,
the absorption spectrum of [Ru(bpy)2L1]6‡ (Figure 10) shows
a MLCT band much broader (toward lower energies) than
that of the [Ru(bpy)3]2‡ model compound.[7, 8] This is a result
of the presence of two types of ligands (bpy and L41‡) involved
in the MLCT transitions. The Ru !bpy transitions presum-
ably occur at the same energy as in the model compound, but
the transition involving the bpy moiety of L41‡ occurs at lower
energy because of the above-mentioned Coulombic stabiliza-
tion offered to the MLCTexcited state by the positive charges
on the paraquat-type units in L41‡. The MLCT band of
[{Ru(bpy)2}2L2]8‡ occurs at the same wavelength and has an
absorption coefficient twice that of [Ru(bpy)2L1]6‡. This
suggests that, as in the case of the ReI complex containing
the L42‡ ligand, the two metal-based moieties do not substan-
tially perturb each other. When the L41‡ tetracationic cyclo-
phane ligand is replaced by the L44‡ catenane ligand, the band
in the visible region is apparently shifted to lower energy
3
[Re(CO)3L4Cl]4‡, the MLCT excited state is quenched by
energy transfer to the low-energy CT excited state of the
catenane moiety. For the Re and Ru complexes of the L41‡ and
L42‡ ligands, emission is shifted to lower energies compared
with the emission of the [Re(CO)3(Cl)(bpy)] and [Ru-
(bpy)3]2‡ model compounds (Table 4) because of the stabiliz-
ing effect of the positive charges of the paraquat-type units on
the 3MLCT excited state. It can also be noted that the
emission of [{Re(CO)3Cl}2L2]4‡ is slightly red-shifted com-
pared to that of [Re(CO)3L1Cl]4‡. For both the Re and Ru
complexes containing the L41‡ and L24‡ ligands, the emission
lifetime is close to that of the corresponding model com-
pound.
In conclusion, even from the viewpoint of the emission pro-
perties, the bpy-type moieties of the L41‡, L24‡, and L44‡ ligands
behave substantially as simple bpy ligands, but the appended
paraquat-type moieties in L41‡ and L24‡ and the CT catenane
interaction in L44‡ play an important role. Particularly worth
noting, in view of the possible use of these compounds in
photodriven mechanical systems,[6d] is the photoinduced
electron-transfer process taking place at room temperature
3
from the MLCT excited state to a paraquat-type unit in the
[Re(CO)3L1Cl]4‡, [{Re(CO)3Cl}2L2]4‡, [Ru(bpy)2L1]6‡, and
[{Ru(bpy)2}2L2]8‡ complexes.
Electrochemistry of ligands: The electrochemical data for the
ligands L41‡, L24‡ and L44‡ are gathered in Table 5. Figure 11
shows schematically the relationships of the processes occur-
ring for L41‡ and L44‡. All the potential values are referred to
the SCE electrode.
In the case of L41‡, two reversible bielectronic processes are
observed at 0.29 and 0.73 V, followed by a process
because of the contribution of the CT band present in L44‡
.
In conclusion, the bpy-type moieties of the L41‡, L24‡ and L44‡
ligands behave substantially as simple bpy ligands, but the
energy of the MLCT transition involving such ligands is
moderately affected by the appended paraquat-type moieties.
(
2.10 V) near the end of the accessible potential window.
The first and second processes can be assigned to the first and
second simultaneous monoelectronic reductions of the two
paraquat-type units. The observed potentials are almost the
same as those found for the previously investigated tetraca-
tionic cyclobis(paraquat-p-phenylene).[18, 23] The third process
Emission spectra of ligands: Among the chromophoric units
of the L41‡, L42‡, and L44‡ ligands, only the dioxynaphthalene
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FULL PAPER
Table 5. Electrochemical data for ligands and complexes.[a]
units of the crown ether, one expects
i) the shift of the reduction processes to
more negative potentials and of the
oxidation processes to more positive
potentials, and ii) the splitting of the
degenerate reduction waves of L41‡. The
observed behavior (Table 5 and Fig-
ure 11) is fully consistent with the above
expectations and with the behavior of
the analogous catenane 24‡.[24, 28] Specif-
ically, on reduction, the first and third
processes can be assigned to the first and
second reduction of the alongside para-
quat-type unit, whereas the second and
fourth processes concern the first and
second reduction of the inside unit. On
oxidation, the two processes concern
Ered (V)
Eox (V)
L41‡
0.29;[b] 0.73;[b] 2.10
0.31; 0.49; 0.79; 0.86
0.29;[b] 0.68;[b] 2.03; 2.17
1.32
±
L44‡
‡ 1.36;[c] ‡1.63[c]
L42‡
±
[Re(CO)3(bpy)(Cl)][d]
[Re(CO)3L1Cl]4‡
[Re(CO)3L4Cl]4‡
[Ru(bpy)3]2‡
[Ru(bpy)2L1]6‡
[Ru(bpy)2L4]6‡
[{Re(CO)3Cl}2L2]4‡
[{Ru(bpy)2}2L2]8‡
‡ 1.36
0.28;[b] 0.70;[b] 1.33
0.27; 0.43; 0.82;[b] 1.40
1.33; 1.52; 1.78
‡ 1.43; ‡1.86[c]
‡ 1.33;[c] ‡1.40;[c] ‡2.04[c]
‡ 1.29
0.28;[b] 0.69;[b] 1.32; 1.51; 1.77
‡ 1.37
0.28; 0.44; 0.83;[b] 1.31; 1.52; 1.78 ‡ 1.37; ‡1.54[c]
0.27;[b] 0.62;[b] 1.31;[b]
0.28;[b] 0.62;[b] 1.29;[b]
‡ 1.42[b]
‡ 1.37[b]
ꢀ
1.5[e]
[a] Argon-purged MeCN solution, 298 K; halfwave potential values in V vs SCE; reversible and
monoelectronic processes, unless otherwise noted. [b] Bielectronic process. [c] Not fully reversible;
potential values estimated from DPV peaks. [d] See ref. [25b]. [e] Affected by adsorption
phenomena.
oxidation of the alongside and inside electron-donor 1/
5DMN units, respectively. The reduction of the bpy moiety
(
2.10 V for L41‡) cannot be observed in L44‡, suggesting that,
when the paraquat-type units have been reduced twice and
therefore cannot play a role as electron acceptors, the
electron-donor moieties of the crown can be involved in a
charge-transfer interaction with the bpy unit.
Electrochemistry of complexes: We have examined the
electrochemical behavior of complexes [Re(CO)3L1Cl]4‡,
[Re(CO)3L4Cl]4‡, [{Re(CO)3Cl}2L2]4‡, [Ru(bpy)2L1]6‡, [Ru-
(bpy)2L4]6‡, and [{Ru(bpy)2}2L2]8‡. The results are listed in
Table 5, where the data of the [Re(CO)3(Cl)(bpy)] and
[Ru(bpy)3]2‡ model compounds are also shown for compar-
ison purposes. Figure 11 shows schematically the relationships
of the processes occurring for the L41‡ and L44‡ ligands and for
their Re complexes, while Figure 12 shows the cyclic voltam-
Figure 11. Genetic diagram of the redox potentials of the L41‡ cyclophane
ligand, the L44‡ catenane ligand, and of their ReI complexes. For comparison
purposes, the redox potentials of the [Re(CO)3(Cl)(bpy)] model compound
and of the crown ether 1/5DN38C10, which is a component of L44‡, are also
shown. Solid symbols correspond to reduction processes centered on the
&
*
paraquat- ( ) and the bipyridine-type ( ) units. Empty symbols correspond
I
^
to oxidation processes centered on the Re metal ion ( ) and the 1/5DMN
*
units ( ).
is due to the reduction of the bpy-type unit ( 2.09 V in DMF
at 548C for 2,2'-bipyridine).[27] For the L24‡ ligand, which
contains two paraquat-type and two bpy-type units, four
processes are observed. The first two reversible processes
(
0.29 and 0.68 V) are bielectronic in nature and can be
straightforwardly assigned to the first and second simulta-
neous monoelectronic reductions of the two paraquat-type
units. The third and fourth processes (at 2.03 and about
2.2 V, respectively) can be assigned to the reduction of the
two equivalent, but apparently interacting, bpy-type units.
Catenane L44‡ is formed by the interlocking of two
components, the L41‡ tetracationic cyclophane and the 1/
5DN38C10 macrocyclic polyether. The latter component
displays two not fully reversible oxidation processes at
‡1.00 and ‡1.15 V, showing that there is some interaction
between the two equivalent 1/5DMN units. In the catenane,
L41‡-localized reduction and 1/5DN38C10-localized oxidation
processes are expected to occur. In addition, considering the
perturbations caused by the charge-transfer interaction,
which also induces topological differences between the two
paraquat-type units of the cyclophane and the two 1/5DMN
Figure 12. Cyclic voltammetric behavior on reduction of 5 Â 10 4 m
[Ru(bpy)2L4]6‡ (acetonitrile solution, 298 K, potential values vs. SCE, scan
rate 50 mVs 1, glassy carbon as working electrode, 0.05m Et4NPF6 as
supporting electrolyte).
metric behavior on reduction of [Ru(bpy)2L4]6‡. Previous
investigations on ReI and RuII polypyridine complexes have
shown that, to a first approximation, the electrochemical
processes can be discussed on the basis of localized molecular
orbital configurations.[7±11]
[Re(CO)3L1Cl]4‡ (Figure 11) shows three reduction and
one oxidation processes. The first two (bielectronic) reduction
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Catenane Ligands
590±607
processes can be straightforwardly assigned to the first and
second simultaneous monoelectronic reductions of the two
paraquat-type units of the L14‡ ligand. These waves are slightly
displaced toward less negative potentials compared with
uncoordinated L41‡. The only sizeable difference is the 30 mV
displacement of the second reduction wave to less negative
values. This displacement can perhaps be attributed to some
electron donation of the bireduced paraquat-type units to the
coordinated bpy moiety. The following (monoelectronic)
wave can be assigned to the reduction of the bpy moiety
which, because of metal coordination, becomes much easier
to reduce. This process occurs practically at the same potential
as for the bpy ligand of the [Re(CO)3(Cl)(bpy)][25b] model
compound showing that, once the paraquat units have been
reduced twice, the L41‡ ligand (now reduced to L1) behaves
like a simple bpy ligand. On the oxidation side, [Re(CO)3L1-
(Cl)]4‡ exhibits the expected one-electron wave because of
metal oxidation, displaced by 70 mV toward more positive
potentials compared with [Re(CO)3(Cl)(bpy)].[25b] This dis-
placement can be attributed to the presence of a substituted
bpy ligand like L41‡, which is also responsible for the positive
charge of the complex.
In the case of [Ru(bpy)2L1]6‡ as many as six reversible
redox processes are observed. As in the case of the analogous
Re compound, the first two (bielectronic) reduction processes
can again be assigned to the first and second simultaneous
monoelectronic reductions of the two paraquat-type units of
the L41‡ ligand, slightly displaced toward less negative
potentials compared with uncoordinated L41‡ (40 mV for the
second reduction process). The three following (monoelec-
tronic) waves can be assigned to the successive one-electron
reduction of the three bpy moieties. These three processes
occur practically at the same potentials as in the [Ru(bpy)3]2‡
model compound, showing once again that, after reduction of
the paraquat units, the cyclophane ligand behaves as a simple
bpy ligand. On the oxidation side, [Ru(bpy)2L1]6‡ exhibits the
one-electron wave due to metal oxidation, displaced by
80 mV toward more positive potentials compared with
[Ru(bpy)3]2‡. This displacement can be attributed to the large
increase in the positive charge of the complex caused by the
tetracationic L41‡ ligand.
The electrochemical behavior of the [Re(CO)3L4(Cl)]4‡
(Figure 11) and [Ru(bpy)2L4]6‡ complexes, which contain
the L44‡ catenane ligand, is very interesting. In the accessible
potential window, [Re(CO)3L4(Cl)]4‡ can lose three and
accept five electrons and [Ru(bpy)2L4]6‡ can lose three and
accept seven electrons. According to these expectations, the
reduction of the two complexes shows two monoelectronic
waves and one bielectronic wave involving the paraquat-type
units, followed by the monoelectronic reduction waves of the
bpy moietiesÐone for [Re(CO)3L4Cl]4‡ and three for
[Ru(bpy)2L4]6‡ (Figure 12). For both complexes, the first
and second reduction waves of the paraquat units are
displaced toward less negative potentials compared with the
free ligand L44‡ (also compared with free L41‡). These
displacements suggest that the charge-transfer interaction
between the paraquat units of L41‡ and 1/5DN38C10 weakens
upon coordination. This outcome could be due to i) structural
constraints (imposed by the metal coordination of the bpy
unit of L44‡) that prevent optimization of the charge-transfer
interaction in the coordinated catenane, and/or ii) the
increased electron-acceptor character of the bpy moiety upon
coordination, which could partially compete with the para-
quat units for the electron donor units of the crown ether. The
presence of structural constraints could also account for the
fact that the second reduction of the two paraquat units of the
coordinated catenane occurs at the same potential, contrary
to what happens with the uncoordinated catenane. For
[Re(CO)3L4Cl]4‡, the reduction potential of the bpy-type unit
of L44‡ is clearly displaced toward more negative potentials
compared with that of [Re(CO)3L1(Cl)]4‡, an effect most
likely due to the interaction of the coordinated bpy moiety
with the electron-donating units of 1/5DN38C10, which is
expected to become stronger once the paraquat units have
been reduced (vide supra). For [Ru(bpy)2L4]6‡, the reduction
of the three bpy moieties (i.e., the two bpy ligands and the
bpy-type unit of L44‡ in an unknown sequence) occurs at
almost the same potentials, just as it does in the case of
[Ru(bpy)2L1]6‡
Upon oxidation, [Re(CO)3L4(Cl)]4‡ and [Ru(bpy)2L4]6‡ are
expected to exhibit a reversible metal-centered process and
two not fully reversible processes involving the 1/5DMN
moieties of the crown ether component of the L44‡ catenane.
[Re(CO)3L4(Cl)]4‡ actually undergoes three not fully rever-
sible processes (Table 5). Comparison with the behavior of
L44‡ and [Re(CO)3L1(Cl)]4‡ suggests that the first process is
due to the oxidation of the alongside 1/5DMN unit of the
catenane ligand and the second process to oxidation of the
metal. The oxidation of the alongside 1/5DMN unit does not
affect the potential of metal oxidation, but compromises its
reversibility because of the partial overlap of the two waves.
The third process can be assigned to the oxidation of the
inside 1/5DMN unit of the catenane ligand. [Ru(bpy)2L4]6‡
undergoes only two processes. The first process, being
reversible, is assigned to the oxidation of the metal center,
and the second one, not fully reversible, to the oxidation of the
alongside 1/5DMN unit. Such a wave is displaced toward
more positive potentials, indicating that oxidation of the metal
affects the oxidation of the external 1/5DMN unit presumably
because of a change in the structure of the catenane caused by
an increased electron donation of the bpy moiety to the
oxidized metal. The oxidation of the inside 1/5DMN unit of
the crown is displaced outside the accessible potential
window. It should also be noted that at this stage the complex
has a very large (8 ‡ ) positive charge, so that further
oxidation becomes very difficult.
All the electrochemical processes observed for the binu-
clear complexes [{Re(CO)3(Cl)}2L2]4‡ and [{Ru(bpy)2}2L2]8‡
are bielectronic in nature (Table 5), showing that i) the two
paraquat- and two bpy-type units of the L42‡ ligand behave
almost independently, and ii) the two metal-based moieties
bridged by L42‡ largely ignore each other. Thus, one expects to
observe three reduction waves and one oxidation wave for the
Re complex, and five reduction waves and one oxidation wave
for the Ru complex. In the case of [{Re(CO)3Cl}2L2]4‡, the
four expected processes are observed. On the reduction side,
the first two processes are due to the first and second
simultaneous monoelectronic reduction of the two paraquat-
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V. Balzani, J. F. Stoddart, D. J. Williams et al.
FULL PAPER
type units of the bridging ligand, slightly displaced (60 mV for
the second reduction) toward less negative potentials com-
pared with uncoordinated L42‡. The successive reduction
process, due to the bpy moieties of the L42‡ bridge, is very
close to the reduction process involving the bpy ligand of the
model compound. The simultaneous oxidation of the two Re
centers is displaced (60 mV) toward more positive potentials
compared with the model compound, that is, at practically the
same potential as for [Re(CO)3L1(Cl)]4‡. In the case of
[{Ru(bpy)2}2L2]8‡, only four reduction waves were observed.
The first two processes are again due to the first and second
simultaneous monoelectronic reductions of the two paraquat-
type units of the L42‡ ligand, slightly displaced toward less
negative potentials compared with uncoordinated L42‡. The
following wave ( 1.29 V) can be assigned to the simultaneous
one-electron reduction of two bpy moieties (either two bpy
ligands coordinated to different metals, or the bpy-type units
of the L42‡ bridge). The fourth process at about 1.5 V is
affected by adsorption phenomena, which also preclude
observation of the other expected reduction processes. On
oxidation, a bielectronic process takes place at the same
potential as for the one-electron oxidation of the mononu-
clear [Ru(bpy)2L1]6‡ compound.
In conclusion, the electrochemical behavior of the various
redox active units present in the L41‡, L24‡, and L44‡ ligands and
their complexes can be illustrated on the basis of Figure 11,
which explicitly refers to the L41‡ and L44‡ ligands and their
[Re(CO)3L1(Cl)]4‡ and [Re(CO)3L4(Cl)]4‡ complexes. In
going from the cyclophane L41‡ to the catenane L44‡, the
charge-transfer interaction and the fact that the two paraquat-
type units of the cyclophane and the two 1/5 DMN units of the
crown ether are no longer topologically equivalent i) shift the
reduction processes to more negative potentials and the
oxidation processes to more positive potentials, and ii) split
the two degenerate reductions of L41‡ into four separated
processes. On going from free L41‡ to its metal complexes, the
reduction potentials of the paraquat-type units are scarcely
affected, while that of the bpy moiety, which is directly
involved in the metal coordination, moves a long way toward
less negative values. In the L41‡ complexes, metal oxidation
occurs at practically the same values as in the respective
model compounds, indicating that the presence of the two
paraquat-type units is of no relevance to this process. The
changes observed in going from the free catenane ligand L44‡
to its complexes are different from those observed in the case
of L41‡, suggesting that the catenane structure changes upon
coordination. The most noticeable feature is the lack of
splitting of the second reduction of the two paraquat-type
units. Comparison between the complexes of the L41‡ and L44‡
ligands shows that the metal-centered oxidation occurs at
practically the same potential, indicating that the presence of
the crown ether does not affect metal oxidation. We can also
note that oxidation of the metal and of the alongside 1/5DMN
unit of the catenane ligand L44‡ occur at comparable
potentials. The results obtained show that oxidation of the
alongside 1/5DMN unit of the L44‡ ligand does not affect the
subsequent oxidation of the metal (in [Re(CO)3L4(Cl)]4‡),
whereas oxidation of the metal affects the successive oxida-
tion of this unit (in [Ru(bpy)2L4]6‡). Furthermore, we notice
that the oxidation of the inside 1/5DMN unit, which occurs
after metal oxidation, is strongly displaced toward more
positive potentials (400 mV for [Re(CO)3L4(Cl)]4‡, and out-
side the examined potential window for [Ru(bpy)2L4]6‡).
Conclusions
We have synthesized the tetracationic cyclophanes L41‡ and
L42‡, which contain paraquat-type units together with one and
two 2,2'-bipyridine moieties, respectively, as binding sites for
the coordination of transition metals. L41‡ has also been used
to obtain the [2]catenanes L43‡ and L44‡, made of the
tetracationic cyclophane and the macrocyclic polyethers
BPP34C10 and 1/5DN38C10, respectively. The L41‡ and L24‡
cyclophanes and the L44‡ [2]catenane ligands have then been
used to synthesize novel mono- and binuclear ruthenium(ii),
rhenium(i), silver(i), and copper(i) complexes.
The L41‡, L42‡, and L44‡ ligands and their [Re(CO)3L1(Cl)]4‡,
[Re(CO)3L4(Cl)]4‡, [{Re(CO)3(Cl)}2L2]4‡, [Ru(bpy)2L1]6‡,
[Ru(bpy)2L4]6‡, and [{Ru(bpy)2}2L2]8‡ complexes display sev-
eral redox processes that can be assigned to reduction or
oxidation of specific redox-active units: i) reduction of the
paraquat- and bpy-type moieties of the cyclophane or
catenane ligands, ii) reduction of the bpy ligands (in the Ru
complexes), iii) oxidation of the metal (in the Ru and Re
complexes) and iv) oxidation of the dioxynaphthalene moi-
eties of the 1/5DN38C10 crown ether (in the L44‡ ligand and in
its complexes).
The L41‡, L42‡, and L44‡ ligands and their [Re(CO)3L1Cl]4‡,
[Re(CO)3L4Cl]4‡, [{Re(CO)3Cl}2L2]4‡, [Ru(bpy)2L1]6‡, [Ru-
(bpy)2L4]6‡, and [{Ru(bpy)2}2L2]8‡ complexes exhibit the
absorption bands of their chromophoric subunits. Unlike the
[Ru(bpy)3]2‡ and [Re(CO)3(Cl)(bpy)] model compounds, the
RuII and ReI complexes do not exhibit any MLCT lumines-
cence at room temperature because of an electron-transfer
quenching process caused by the paraquat-type units of the
L41‡, L24‡, and L44‡ ligands. In a rigid matrix at 77 K, where
electron transfer cannot occur, emission is observed from the
complexes containing the tetracationic cyclophane ligands
L41‡ and L42‡, but not from those containing the catenane
ligand L44‡, where quenching can still occur by energy transfer
to the low-energy CT excited state.
The photoinduced electron-transfer process taking place at
room temperature from the 3MLCT excited state to a
paraquat-type unit in the [Re(CO)3L1(Cl)]4‡, [{Re(CO)3-
(Cl)}2L2]4‡, [Ru(bpy)2L1]6‡, and [{Ru(bpy)2}2L2]8‡ complexes
could be useful in the design of new types of photodriven
molecular machines.
Experimental Section
Materials and methods: Solvents were purified and dried by literature
methods.[29] Reagents were purchased from Aldrich and used as received.
BPP34C10,[18] 1/5DN38C10,[30] 1,1'-[phenylenebis(methylene)]bis-4,4'-bi-
pyridinium bis(hexafluorophosphate)[31] (6 ´ 2PF6), tetrakis(acetonitrile)
copper(i) hexafluorophosphate,[32] and 4,4'-bis(hydroxymethyl)-2,2'-bipyr-
idine[17] were prepared as described in the literature. Reactions requiring
ultrahigh pressures were carried out in a Teflon vessel by means of a
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Catenane Ligands
590±607
custom-built ultrahigh-pressure press, manufactured by PSIKA Pressure
Systems of Glossop (UK). Thin-layer chromatography (TLC) was carried
out on aluminum sheets precoated with silica gel 60F (Merck 5554) or with
alumina 60 (Merck 5550). The plates were inspected by UV light and
developed with iodine vapor. Flash column chromatography was per-
formed on silica gel H (5 ± 40 mm, Fluka 60770) with the solvents specified.
Analytical samples were dried in vacuo (0.1 Torr) at 60 ± 708C. Melting
points were determined on an Electrothermal 9200 apparatus and are not
corrected. 1H NMR spectra were recorded on a Joel 270 (270 MHz), a
Bruker AC300 (300 MHz), or a Bruker AMX400 (400 MHz) spectrometer
with either the solvent or TMS as internal standard. 13C NMR spectra were
recorded on Jeol 270, Bruker AC300, or a Bruker AMX400 spectrometer
at either 67.5, 75.5, or 100.0 MHz, respectively, using the JMOD pulse
sequence, with either the solvent or TMS as internal standard. All chemical
shifts are quoted on the d scale. Electron impact (EI) mass spectra were
recorded at 70 eV on a VG ProSpec mass spectrometer. Low-resolution
liquid secondary ion mass spectra (LSIMS) were obtained using a VG
ZabSpec mass spectrometer equipped with a cesium ion source operating
at ꢀ 30 keV. The matrix used was m-nitrobenzyl alcohol and the scan rate
5 s per decade. High-resolution mass spectra were obtained from the
ZabSpec in narrow range voltage scanning mode at ꢀ 6000 resolution and
employing a cesium/rubidium iodide reference mixture. Microanalyses
were performed by the University of Birmingham and the University of
North London Microanalytical Service. The equipment and procedures
used for the absorption, emission, and electrochemical measurements have
been described in detail in a previous paper.[24]
filtered off, washed with ice-cooled MeCN and Et2O and dried. The solid
(4.1 g) was dissolved in warm H2O (400 mL), treated with charcoal, and
filtered. The filtrate was cooled to room temperature and then a 50%
aqueous solution of NH4PF6 was added. The resulting white precipitate was
filtered off, washed with H2O and Me2CO, and dried in vacuo (708C/
0.1 Torr) to give 4.5 g (90%) of 7 ´ 2PF6, m.p. 297 ± 2988C (decomp.); 1H
NMR (400 MHz, CD3CN, 258C): d ˆ 5.87 (s, 4H; NCH2), 7.37 (dd, J ˆ 5.0,
2.0 Hz, 2H; H-5), 7.79 (dd, J ˆ 6.0, 2.0 Hz, 4H; b-CH), 8.36 (d, J ˆ 7 Hz,
4H; b'-CH), 8.50 (d, J ˆ 2 Hz, 2H; H-3), 8.74 (d, J ˆ 5 Hz, 2H; H-6), 8.85
(dd, J ˆ 6.0, 2.0 Hz, 4H; a-CH), 8.87 (d, J ˆ 7 Hz, 4H; a'-CH); 13C NMR
(75.5 MHz, CD3SOCD3): d ˆ 61.8 (CH2), 120.3, 122.1, 123.8, 126.1, 145.8,
150.4, 151.0 (CH), 140.9, 144.3, 153.2, 155.5 (Cq); MS (LSIMS): m/z ˆ 639
‡
‡
[M PF6] , 493 [M 2PF6] ; C32H26F12N6P2 (784.5): calcd C 48.99, H 3.34,
N 10.71; found C 49.25, H 3.51, N 10.80.
[2]Catenane 8 ´ 4PF6: The dibromide 5e (104 mg, 0.31 mmol), 7 ´ 2PF6
(200 mg, 0.26 mmol) and the macrocyclic polyether BPP34C10 (273 mg,
0.51 mmol) were dissolved in dry MeCN (30 mL). The solution was stirred
at room temperature for 14 d. The red solution was concentrated in vacuo
and the residue was purified by flash column chromatography (SiO2, eluent
MeOH/2m NH4Cl/MeNO2, 7:2:1) affording, after counterion exchange, 8 ´
1
4PF6 as a red solid (10 mg, 3%). H NMR (300 MHz, CD3COCD3, 258C,
TMS): d ˆ 3.37 (m, 8H; OCH2), 3.54 (m, 8H; OCH2), 3.85 (m, 8H; OCH2),
3.92 (m, 8H; OCH2), 5.63 (s, 8H; OC6H4), 6.22 (s, 8H; NCH2), 7.91 (d, J ˆ
5 Hz, 4H; PyH-5), 8.27 (d, J ˆ 7 Hz, 8H; b-CH), 8.38 (s, 4H; PyH-3), 8.82
(d, J ˆ 5 Hz, 4H; PyH-6), 9.38 (d, J ˆ 7 Hz, 8H; a-CH); MS (FAB): m/z:
‡
‡
‡
1647 [M PF6] , 1502 [M 2PF6] , 1357 [M 3PF6] .
4,4'-Dicarboxy-2,2'-bipyridine (5b): The compound was prepared as
reported in the literature.[16] Yield 92%, m.p. > 3508C; the 1H NMR
spectrum was in accordance with that reported in the literature.[33] The
product was used without further purification in the next step.
[3]Catenane 9 ´ 4PF6: A mixture of 7 ´ 4PF6 (118 mg, 0.15 mmol), the
dibromide 5e (61 mg, 0.19 mmol), and the macrocyclic polyether
BPP34C10 (161 mg, 0.30 mmol) was warmed until all the solid dissolved.
A solution was transferred to a high pressure Teflon cell and subjected to
12 kbar for 3 d at room temperature. The resulting red solution was
concentrated in vacuo and the residue was purified by flash column
chromatography (SiO2, eluent MeOH/2m NH4Cl/MeNO2, 7:2:1). The
fractions containing the catenane were combined and concentrated in
vacuo. The solid residue was dissolved in H2O and treated with an excess of
50% NH4PF6 solution. The precipitate was filtered off, washed with H2O
and dried in vacuo (708C/0.1 Torr) to afford 7.0 mg (2%) [3]catenane 9 ´
4,4'-Dimethoxycarbonyl-2,2'-bipyridine (5c): The compound was prepared
following a literature procedure[17] in 84% yield, m.p. 210 ± 2118C; 1H
NMR (270 MHz, CDCl3, 258C, TMS): d ˆ 4.00 (s, 6H; CH3), 7.91 (dd, J ˆ
4.7, 1.7 Hz, 2H; PyH-5,5'), 8.87 (d, J ˆ 4.9 Hz, 2H; PyH-6,6'), 8.96 (s, 2H;
PyH-3,3'); C14H12N2O4 (272.3): calcd C 61.76, H 4.44, N 10.29; found C
61.52, H 4.39, N 10.45.
4,4'-Bis(hydroxymethyl)-2,2'-bipyridine (5d): The compound was prepared
following a literature procedure[17] in 79% yield, m.p. 170 ± 1718C; 1H
NMR (270 MHz, CD3SOCD3, 258C): d ˆ 4.7 (d, J ˆ 5.4 Hz, 4H; CH2), 5.54
(t, J ˆ 5.7 Hz, 2H; OH), 7.38 (d, J ˆ 5.2 Hz, 2H; PyH-5,5'), 8.41 (s, 2H;
PyH-3,3'), 8.61 (d, J ˆ 4.9 Hz, 2H; PyH-6,6'); 13C NMR (67.5 MHz,
CD3SOCD3, 258C): d ˆ 61.8, 117.8, 121.4, 148.9, 152.8, 155.3.
‡
‡
4PF6 as a deep red solid. MS (LSIMS): m/z ˆ 2330 [M] , 2185 [M PF6] ,
‡
‡
‡
2040 [M 2PF6] , 1894 [M 3PF6] , 1647 [M PF6 CE] , 1502 [M
‡
‡
‡
2PF6 CE] , 1357 [M 3PF6 CE] , 1111 [M PF6 2CE] , 966 [M
‡
‡
2PF6 2CE] ,
821
[M 3PF6 2CE] ;
HRMS
(LSIMS)
‡
C
100H116F12N8O20P2: [M 2PF6] calcd 2038.7537, found 2038.7590.
4,4'-Bis(bromomethyl)-2,2'-bipyridine (5e): A mixture of the diol 5d (5.0 g,
0.023 mol) and hydrobromic acid (200 mL, 48%) was heated under reflux
for 3 h before being poured onto ice and neutralized with 10n NaOH. The
white suspension was extracted with several portions of EtOAc (700 mL).
The combined extracts were dried (MgSO4) and concentrated in vacuo, and
the crude product was subjected to flash column chromatography (SiO2,
eluent CH2Cl2/EtOAc, 5:1) to afford 5e (6.5 g, 75%), m.p. 128 ± 1298C (n-
hexane/EtOAc); 1H NMR (270 MHz, CDCl3, 258C, TMS): d ˆ 4.48 (s, 4H;
CH2), 7.35 (dd, J ˆ 4.9, 1.7 Hz, 2H; PyH-5,5'), 8.44 (s, 2H; PyH-3,3'), 8.67
(dd, J ˆ 4.9, 1.7 Hz, 2H; PyH-6,6'); 13C NMR (67.5 MHz, CD3SOCD3,
258C): d ˆ 31.6, 120.5, 124.1, 147.7, 149.7, 155.2; MS (70 eV, EI): m/z (%) ˆ
Cyclophane L1 ´ 4PF6: A solution of 6 ´ 2PF6 (3.53 g, 5.0 mmol) in dry
MeCN (150 mL) and a solution of the dibromide 5e (1.62 g, 5.0 mmol) in
dry MeCN (150 mL) were added simultaneously under an atmosphere of
N2 to stirred and refluxing MeCN (300 mL) over a period of 6 h. The
reaction mixture was maintained under reflux for 4 d and then concen-
trated in vacuo. The crude product was purified by flash column
chromatography (SiO2, eluent MeOH/2m NH4Cl/MeNO2, 7:2:1). After
evaporation of the solvent, the product was dissolved in H2O and treated
with an excess of 50% NH4PF6 solution. The precipitate was filtered off,
washed with H2O and dried in vacuo (708C/0.1 Torr). Yield 1.12 g (24%),
m.p. 2688C (decomp.). 1H NMR (400 MHz, CD3CN, 258C): d ˆ 5.77 (s, 4H;
xylyl NCH2), 5.87 (s, 4H; PyNCH2), 7.56 (s, 4H; C6H4), 7.88 (dd, J ˆ 5.0,
1.0 Hz, 2H; PyH-5), 8.13 (s, 2H; PyH-3), 8.18 (d, J ˆ 7 Hz, 4H; b-CH), 8.21
(d, J ˆ 7 Hz, 4H; b'-CH), 8.83 (d, J ˆ 5 Hz, 2H; PyH-6), 8.86 (d, J ˆ 7 Hz,
4H; a-CH), 8.92 (d, J ˆ 7 Hz, 4H; a'-CH); 13C NMR (100 MHz, CD3CN,
258C): d ˆ 64.2, 65.6 (CH2), 123.9 (C-3), 127.5 (C-5), 128.5 (b-CH), 128.6
(b'-CH), 131.4 (xylyl), 146.2 (a-CH), 146.5 (a'-CH), 150.5 (C-6), 136.7,
‡
342 (100) [M] , 296 (10), 261 (21), 199 (46), 182 (38), 152 (12), 119 (13), 102
(34), 80 (12), 40 (20); C12H10Br2N2 (342.0): calcd C 42.14, H 2.95, N 8.19;
found C 42.12, H 3.04, N 8.51. A second fraction, after recrystallization
from n-hexane/EtOAc, gave 1.3 g (18%) of 4-bromomethyl-4-hydroxy-
methyl-2,2'-bipyridine, m.p. 1218C. 1H NMR (270 MHz, CDCl3, 258C,
TMS): d ˆ 4.48 (s, 2H; CH2Br), 4.81 (s, 2H; CH2OH), 5.30 (s, 1H; OH),
7.33 (dd, J ˆ 4.8, 1.6 Hz, 2H; PyH-5,5'), 8.35 (s, 1H; PyH-3), 8.40 (s, 1H;
PyH-3'), 8.63 (dd, J ˆ 4.8 Hz, 1.6 Hz, 2H; PyH-6,6'); 13C NMR (67.5 MHz,
CDCl3, 258C): d ˆ 30.7; 63.5, 118.6, 121.1, 121.5, 123.7, 147.4, 149.4, 149.6,
‡
‡
150.8, 151.2 (Cq); MS (LSIMS): m/z ˆ 1033 [M PF6] , 888 [M 2PF6] ,
‡
743 [M 3PF6] ; C40H34F24N6P4 (1178.6): calcd C 40.76, H 2.91, N 7.13;
found C 40.51, H 2.99, N 6.96.
‡
151.3, 155.5, 156.7; MS (70 eV, EI): m/z (%) ˆ 280 (88) [81Br, M] , 278 (100)
Cyclophane L2 ´ 4PF6: A solution of 7 ´ 2PF6 (0.784 g, 1.0 mmol) in dry
MeCN (75 mL) and a solution of the dibromide 5e (0.324 g, 1.0 mmol) in
dry MeCN (75 mL) were added simultaneously under an atmosphere of N2
to stirred and refluxing MeCN (80 mL) over a period of 4 h. The reaction
mixture was maintained under reflux for 4 d and then concentrated in
vacuo. The crude product was purified by flash column chromatography
(SiO2, eluent MeOH/2m NH4Cl/MeNO2, 7:2:1). After evaporation of the
solvent the product was dissolved in water and treated with an excess of
50% NH4PF6 solution. The precipitate was filtered off, washed with H2O,
‡
[79Br, M] , 199 (49), 169 (56), 119 (20), 69 (38), 40 (11); C12H11BrN2O
(279.1): calcd C 51.64, H 3.97, N 10.04; found: C 51.80, H 4.11, N 10.16.
1,1'-[4,4'-Bis(methylene)-2,2'-bipyridyl]bis-4,4'-bipyridinium
bis(hexa-
fluorophosphate) (7 ´ 2PF6): solution of the dibromide 5e (2.2 g,
A
6.4 mmol) in dry MeCN (150 mL) was added dropwise over 2 h to a
stirred and refluxing solution of 4,4'-bipyridine (6.0 g, 38.4 mmol) in dry
MeCN (70 mL) under an N2 atmosphere. The reaction mixture was heated
under reflux for 2 d and then cooled in an ice bath. The precipitate was
Chem. Eur. J. 1998, 4, No. 4
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
0947-6539/98/0404-0603 $ 17.50+.25/0
603

V. Balzani, J. F. Stoddart, D. J. Williams et al.
FULL PAPER
1
and dried in vacuo (708C/0.1 Torr). Yield 0.31 g (25%), m.p. > 3008C; H
NMR (300 MHz, CD3SOCD3, 258C): d ˆ 5.97 (s, 8H; NCH2), 7.93 (d, J ˆ
5 Hz, 4H; PyH-5), 8.39 (s, 4H; PyH-3), 8.58 (d, J ˆ 7 Hz, 8H; b-CH), 8.81
(d, J ˆ 5 Hz, 4H; PyH-6), 9.55 (d, J ˆ 7 Hz, 8H; a-CH); 13C NMR
(75.5 MHz, CD3SOCD3, 258C): d ˆ 62.3 (CH2), 121.6, 125.0, 127.3, 145.4,
4H; a-CH), 8.88 (d, J ˆ 7 Hz, 4H; a'-CH); 13C NMR (75.5 MHz, CD3CN,
258C): d ˆ 63.2, 65.7 (CH2), 125.1, 126.1, 128.4, 128.6, 130.0, 131.4, 18.9,
145.9, 146.4, 152.4, 152.8, 153.7 (CH), 136.8, 141.9, 151.0, 151.3, 157.6, 158.5
‡
‡
(Cq); MS (LSIMS): m/z ˆ 1737 [M PF6] , 1592 [M 2PF6] , 1447 [M
‡
3PF6] ; C60H50F36N10P6Ru (1882.0): calcd C 38.29, H 2.68, N 7.44; found C
‡
150.8 (CH), 144.3, 149.0, 156.2 (Cq); MS (LSIMS): m/z ˆ 1111 [M PF6] ,
38.27, H 2.84, N 7.42.
‡
‡
966 [M 2PF6] , 821 [M 3PF6] ; C44H34F24N8P4 (1256.7): calcd C 42.05,
[{Ru(bpy)2}2L2](PF6)8: From [Ru(bpy)2Cl2] (53.2 mg, 0.11 mmol) and L2 ´
4PF6 (62.8 mg, 0.05 mmol) in EtOH/H2O (20 mL); yield 127 mg (97%),
m.p. 2408C (decomp.); 1H NMR (400 MHz, CD3CN, 258C, 2D COSY 45):
d ˆ 5.89 (s, 8H; NCH2), 7.39 (m, 8H; bpyH-4), 7.64 (dd, J ˆ 6.0, 2.0 Hz; 4H;
PyH-5), 7.69 (m, 8H; bpyH-3), 7.89 (d, J ˆ 6 Hz, 4H; PyH-6), 8.07 (m, 8H;
bpyH-5), 8.28 (d, J ˆ 7 Hz, 8H; b-CH), 8.30 (brs, 4H; PyH-3), 8.50 (d, J ˆ
8 Hz, 8H; bpyH-6), 8.96 (d, J ˆ 7 Hz, 8H; a-CH); 13C NMR (75.5 MHz,
CD3CN, 258C): d ˆ 63.2 (CH2), 125.2, 125.6, 128.7, 129.5, 139.0, 146.7, 152.3,
152.7, 153.6 (CH), 142.5, 157.6, 158.4 (Cq); MS (LSIMS): m/z ˆ 2519 [M
H 2.89, N 8.92; found C 42.03, H 2.81, N 8.76.
[2]Catenane L3 ´ 4PF6: The dibromide 5e (40 mg, 0.12 mmol), 6 ´ 2PF6
(75 mg, 0.11 mmol), and the macrocyclic polyether BPP34C10 (142 mg,
0.27 mmol) were dissolved in dry MeCN (30 mL). The solution was stirred
at room temperature for 14 d. The deep red solution was concentrated in
vacuo and the residue was purified by flash column chromatography (SiO2,
eluent MeOH/2m NH4Cl/MeNO2, 7:2:1) affording, after counterion
exchange, L3 ´ 4PF6 as a red solid (55 mg, 30%). M.p. > 2508C; 1H NMR
(300 MHz, CD3COCD3, 258C, TMS): d ˆ 3.51 ± 4.12 (m, 32H; OCH2), 5.23
(brs, 8H; OC6H4), 6.12 (s, 4H; NCH2), 6.18 (s, 4H; NCH2), 7.93 (d, 2H;
PyH-5), 8.04 (s, 4H; C6H4), 8.12 (m, 8H; b-CH), 8.18 (s, 2H; PyH-3), 8.92
(d, 2H; PyH-6), 9.38 and 9.43 (2 Â d, 2 Â 4H; a-CH); 13C NMR (75.5 MHz,
CD3COCD3, 258C): d ˆ 64.2, 65.5, 68.0, 68.7, 70.6, 70.8, 71.3 (CH2), 123.5,
125.0, 126.7, 126.9, 131.6, 146.0, 146.3, 151.8 (CH), 137.2, 144.2, 148.0, 159.4
‡
‡
‡
PF6] , 2375 [M 2PF6] , 2229 [M 3PF6] ; C84H68F48N16P8Ru2 (2663.4):
calcd C 37.88, H 2.57, N 8.41; found C 37.66, H 2.62, N 8.42. Single crystals
suitable for X-ray crystallography were obtained by slow evaporation of
Me2CO from a mixture Me2CO/C6H6 solution of the complex.
[Ru(bpy)2L3](PF6)6: From [Ru(bpy)2Cl2] (48 mg, 0.03 mmol) and L3 ´ 4PF6
1
(13 mg, 0.03 mmol) in EtOH/H2O (20 mL); yield 60 mg (82%). H NMR
‡
‡
(Cq); MS (LSIMS): m/z ˆ 1570 [M PF6] , 1424 [M 2PF6] .
C68H74F24N6O10P4 (1712.4): calcd C 47.61, H 4.4.32, N 4.90; found C 47.54,
H 4.39, N 4.93.
(300 MHz, CD3COCD3, 258C): d ˆ 3.3 ± 4.0 (m, 36H; OCH2 ‡ alongside
OC6H4), 6.12 (s, 4H; NCH2), 6.24 (brs, 4H; inside OC6H4), 6.24 (s, 4H;
NCH2), 7.9 ± 8.3 (m, 26H; b-CH and C6H4 and PyH), 7.5 ± 7.7 (m, 4H; PyH),
8.75 ± 8.84 (m, 6H; PyH-6), 8.96 and 9.24 (2 Â d, 2 Â 4H; a-CH); 13C NMR
(75.5 MHz, CD3COCD3, 258C): d ˆ 63.0, 65.5, 70.6, 70.8, 70.9 (CH2), 125.2,
125.4, 125.5, 125.6, 126.3, 126.9, 128.6, 128.8, 128.9, 129.2, 131.5, 131.9, 157.6,
157.8 (CH), 115.8, 139.2, 139.4, 146.7, 152.5, 152.9, 154.5, 157.9, 158.5 (Cq);
[2]Catenane L4 ´ 4PF6: The dibromide 5e (150 mg, 0.44 mmol), 7 ´ 2PF6
(282 mg, 0.4 mmol),[4] and the macrocyclic polyether 1/5DN38C10 (127 mg,
0.2 mmol) were dissolved in warm, dry DMF (7 mL). The solution was
transferred to an ultrahigh-pressure Teflon reaction vessel, which was then
compressed (12 kbar) at 208C for 3 d. After decompression of the reaction
vessel, the deep red solution was concentrated in vacuo. The residue was
purified by flash column chromatography (SiO2, eluent MeOH/2m NH4Cl/
MeNO2, 7:2:1). The fractions containing the catenane were combined and
concentrated in vacuo. The solid residue was dissolved in H2O and treated
with an excess of 50% NH4PF6 solution. The precipitate was filtered off,
washed with H2O, and dried in vacuo (708C/0.1 Torr) to afford 150 mg
(41%) [2]catenane L4 ´ 4PF6 as a deep pink solid, m.p. 2628C (decomp.). 1H
NMR (400 MHz, CD3COCD3, 243 K, 2D COSY 45): d ˆ 3.29 (d, 1H;
NpH), 3.53 ± 4.33 (m, 32H; OCH2), 4.65 (d, 1H; NpH), 5.38 (t, 1H; NpH),
5.62 (t, 1H; NpH), 5.92 ± 6.30 (m, 8H; NCH2), 6.07 (d, 1H; NpH), 6.18 (d,
1H; NpH), 6.36 (d, 1H; NpH), 6.46 (d, 1H; NpH), 7.00 (m, 3H; NpH and
PyH-5), 7.14 (d, 3H; NpH and PyH-5'), 7.33 (brs, 2H; b-CH), 7.69 (brs, 2H;
b'-CH), 7.84 (brs, 2H; b-CH), 7.98 (brs, 2H; b-CH), 8.00 (brs, 2H; C6H4),
8.15 (brs, 1H; PyH-3), 8.31 (brs, 2H; C6H4), 8.38 (brs, 1H; PyH-3'), 8.73
(brs, 1H; PyH-6), 8.79 (brs, 1H; PyH-6'), 9.04 (d, 2H; a-CH), 9.11 (brs,
2H; a-CH), 9.20 (brs, 2H; a-CH), 9.38 (brs, 2H; a-CH); 13C NMR
(100 MHz, CD3COCD3, 213 K): d ˆ 64.2, 65.6, 68.1, 68.5, 70.4, 70.6, 71.2,
72.1 (CH2), 104.6, 105.5, 106.5, 110.2, 111.1, 114.5, 125.3, 125.6, 126.3, 126.9,
131.6, 145.2, 145.5 (CH), 124.6, 124.9, 137.5, 144.0, 152.5, 154.1 (Cq); MS
‡
‡
MS (LSIMS): m/z ˆ 2273 [M PF6] , 2128 [M 2PF6] .
[Ru(bpy)2L4](PF6)6: From [Ru(bpy)2Cl2] (24.2 mg, 0.05 mmol) and L4 ´
4PF6 (100 mg, 0.054 mmol) in EtOH/H2O (40 mL); yield 118 mg (82%);
m.p. 2018C (decomp.); 13C NMR (100 MHz, CD3CN, 318C): d ˆ 62.9, 66.0,
68.9, 69.1, 69.2, 69.4, 70.2, 70.4, 70.7, 71.1, 71.2, 71.5, 72.0, 72.2, 72.6 (CH2),
105.5, 106.5, 106.9, 106.9, 110.4, 111.4, 114.7, 115.0, 124.4, 124.5, 125.5, 125.6,
125.6, 125.7, 126.4, 126.6, 127.0, 127.2, 127.7, 128.9, 129.0, 129.1, 131.7, 131.9,
132.0, 139.5, 139.7, 145.0, 146.2, 152.4, 152.4, 152.6, 152.8, 155.1, 155.2 (CH),
137.8, 137.9, 142.4, 153.3, 154.2, 154.8, 157.7, 157.8, 158.0, 158.0, 158.1 (Cq);
‡
‡
‡
MS (LSIMS): m/z ˆ 2373 [M PF6] , 2229 [M 2PF6] , 2084 [M 3PF6] ;
C96H94F36N10O10P6Ru (2518.7): calcd C 45.78, H 3.76, N 5.56; found C 45.87,
H 3.85, N 5.49.
General procedure for synthesis of ReI complexes [Re(CO)3ClL1](PF6)4,
[Re(CO)3Cl]2L2](PF6)4, and [Re(CO)3ClL4](PF6)4: A mixture of [Re-
(CO)5Cl] and the appropriate ligand (L1 ´ 4PF6, L2 ´ 4PF6, or L4 ´ 4PF6) in
anhydrous MeOH was heated under reflux and under an atmosphere of N2
for 24 h. After cooling in a refrigerator, the yellow precipitate was filtered
off, washed with THF and Et2O, and dried in vacuo.
[Re(CO)3ClL1](PF6)4: From [Re(CO)5Cl] (80 mg, 0.22 mmol) and L1 ´ 4PF6
(236 mg, 0.20 mmol) in of MeOH (25 mL); yield 234 mg (79%), m.p. 2688C
(decomp.). 1H NMR (300 MHz, CD3CN, 258C): d ˆ 5.79 (s, 4H; xylyl
NCH2), 5.96 (s, 4H; Py NCH2), 7.64 (s, 4H; C6H4), 7.96 (dd, J ˆ 6.0, 2.0 Hz;
2H; PyH-5), 8.22 (d, J ˆ 7 Hz, 4H; b-CH), 8.25 (d, J ˆ 7 Hz, 4H; b'-CH),
8.94 (d, J ˆ 7 Hz, 4H; a-CH), 9.02 (brs, 2H; PyH-3), 9.15 (d, J ˆ 6 Hz, 2H;
PyH-6), 9.34 (d, J ˆ 7 Hz, 4H; a'-CH); 13C NMR (75.5 MHz, CD3CN,
258C): d ˆ 63.4, 65.7 (CH2), 126.5, 128.4, 128.6, 130.2, 131.5, 146.0, 147.2,
‡
‡
‡
(LSIMS): m/z ˆ 1814 [M] , 1669 [M PF6] , 1524 [M 2PF6] , 1379 [M
‡
3PF6] ; C76H78F24N6O10P4 (1815.4): calcd C 50.28, H 4.33, N 4.63; found C
50.39, H 4.19, N 4.82. Single crystals suitable for X-ray crystallography were
grown by vapor diffusion of iPr2O into a 1:1 MeCN/MeNO2 solution of L4 ´
4PF6.
General procedure for synthesis of bis-heteroleptic RuII complexes
[Ru(bpy)2L1](PF6)6, [Ru(bpy)2]2L2](PF6)8, [Ru(bpy)2L3](PF6)6, [Ru-
(bpy)2L4](PF6)6: A mixture of [Ru(bpy)2Cl2] ´ 2H2O and the appropriate
ligand (L1 ´ 4PF6 ± L4 ´ 4PF6) in EtOH/H2O (3:1, v/v) was heated under
reflux under an N2 atmosphere for 48 h. The solvent was removed in vacuo,
and H2O was added to the residue and filtered (to remove an excess of the
ligand). The filtrate was treated with 50% aqueous solution NH4PF6, the
resulting precipitate was filtered off, washed with H2O and Et2O, and dried
in vacuo (608C/0.1 Torr). The compounds were further purified by
precipitation after vapor diffusion of iPr2O into MeCN solutions of the
complexes.
ˆ
155.1 (CH), 136.9, 145.1, 151.0, 151.4, 157.2 (Cq), 198.3 (C O); MS
‡
‡
‡
(LSIMS): m/z ˆ 1339 [M PF6] , 1194 [M 2PF6] , 1049 [M 3PF6] ;
C43H34ClF24O3P4Re (1484.3): calcd C 34.80, H 2.31, N 5.66; found C 34.61, H
2.24, N 5.87. Single crystals suitable for X-ray crystallography were
obtained by vapor diffusion of benzene into
a MeNO2 solution of
[Re(CO)3ClL1](PF6)4.
[Re(CO)3Cl]2L2](PF6)4: From [Re(CO)5Cl] (40.0 mg, 0.11 mmol) and L2 ´
4PF6 (64.0 mg, 0.05 mmol) in MeOH (25 mL); yield 62 mg (66%), m.p. >
3008C (decomp.); 1H NMR (300 MHz, CD3SOCD3, 258C): d ˆ 6.12 (s, 8H;
NCH2), 8.15 (d, J ˆ 5 Hz, 4H; PyH-5), 8.73 (d, J ˆ 5.5 Hz, 8H; b-CH), 8.89
(brs, 4H; PyH-3), 9.20 (d, J ˆ 5 Hz, 4H; PyH-6), 9.59 (d, J ˆ 6 Hz, 8H; a-
[Ru(bpy)2L1](PF6)6: From [Ru(bpy)2Cl2] (73 mg, 0.15 mmol) and L1 ´ 4PF6
(194 mg, 0.165 mmol) in EtOH/H2O (35 mL); yield 222 mg (94%), m.p.
‡
‡
CH); MS (LSIMS): m/z ˆ 1723 [M PF6] , 1578 [M 2PF6] , 1433 [M
1
2388C (decomp.); H NMR (300 MHz, CD3CN, 258C, 2D COSY 45): d ˆ
‡
3PF6] ; C50H36Cl2F24O6P4Re2 (1868.1): calcd C 32.15, H 1.94, N 6.00; found
5.79 (s, 4H; xylyl NCH2), 5.81 (s, 4H; PyNCH2), 7.38 (m, 4H; bpyH-4), 7.63
(s, 4H; C6H4), 7.63 ± 7.67 (m, 6H; bpyH-3 and PyH-5), 7.90 (d, J ˆ 6 Hz, 2H;
PyH-6), 8.06 (t, J ˆ 8 Hz, 4H; bpyH-5), 8.17 (d, J ˆ 8 Hz, 8H; b-CH and b'-
CH), 8.33 (s, 2H; PyH-3), 8.50 (d, J ˆ 8 Hz, 4H; bpyH-6), 8.84 (d, J ˆ 7 Hz,
C 32.06, H 1.92, N 5.93.
[Re(CO)3ClL4](PF6)4: From [Re(CO)5Cl] (12.0 mg, 0.033 mmol) and L4 ´
4PF6 (54.4 mg, 0.030 mg) in MeOH (10 mL). After 24 h under reflux, the
604
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Chem. Eur. J. 1998, 4, No. 4

Catenane Ligands
590±607
reaction mixture was concentrated in vacuo to about one third of its
original volume. Addition of Et2O precipitated the product, which was
treated with 50% aqueous NH4PF6, washed with H2O and dried in vacuo;
yield 52.1 mg (82%), m.p. 2618C (decomp.); 1H NMR (100 MHz, CD3CN,
313 K, 2D COSY 45): d ˆ 3.08 (d, 1H; NpH), 3.6 ± 4.2 (m, 32H; OCH2),
5.7 ± 6.1 (m, 8H; NCH2), 6.05 (d, 1H; NpH), 6.28 (d, 1H; NpH), 6.38 (d,
1H; NpH), 6.51 (t, 1H; NpH), 6.63 (d, 1H; NpH), 6.95 ± 7.15 (m, 8H; b-CH
and b'-CH), 7.02 (t, 1H; NpH), 7.07 (d, 1H; NpH), 7.23 (t, 1H; NpH), 7.31
(d, 1H; NpH), 7.95 (brs, 4H; C6H4), 8.01 (d, 2H; PyH-5), 8.27 (brs, 2H;
PyH-3), 8.37 (m, 4H; a-CH), 8.74 (m, 4H; a'-CH), 9.36 (d, 2H; PyH-6);
[Cu(L4)2](PF6)9: From L4 ´ 4PF6 (72.6 mg, 0.04 mmol) and [Cu-
(MeCN)4]PF6 (7.45 mg, 0.02 mmol) in MeCN (10 mL); yield 72.8 mg
(95%), m.p. 2098C (decomp.); 13C NMR (100 MHz, CD3CN, 318C): d ˆ
65.9, 69.0, 70.7, 71.1, 71.5, 71.7, 71.9, 72.2, 72.6 (CH2), 105.5, 106.9, 111.2,
114.7, 114.9, 125.6, 126.3, 126.6, 126.9, 127.4, 131.8, 145.1, 145.5, 145.7 (CH),
96.4, 125.0, 137.7, 143.5, 146.6, 152.8, 153.7, 154.2, 154.7 (Cq); MS (LSIMS):
‡
‡
‡
m/z ˆ 3693 [M PF6] , 3549 [M 2PF6] , 3403 [M 3PF6] , 3258 [M
‡
4PF6] ; C152H156CuF54N12O20P9 (3839.2): calcd C 47.55, H 4.10, N 4.38;
found 47.77, H 3.91, N 4.49.
X-ray crystallography: Table 6 summarizes the crystal data, data collection,
and refinement parameters for the complexes [Re(CO)3(Cl)L1](PF6)4,
[Ag(L1)2](PF6)9, [{Ru(bpy)2}2L2](PF6)8, and for the [2]catenane L4 ´ 4PF6.
All four structures were solved by direct methods and were refined by full
matrix least-squares based on F2. In [Re(CO)3ClL1](PF6)4, [Ag(L1)2](PF6)9,
and L4 ´ 4PF6, the cationic complexes were ordered and were refined
anisotropically. In [{Ru(bpy)2}2L2](PF6)8, however, the centrosymmetric
complex was found to exhibit 50/50 disorder in the orientation of the two
chelating bipyridyl ligands, giving rise to both D and L configurations at the
unique ruthenium center; all of these half-occupancy atoms, together with
the full-occupancy atoms of the ordered macrocyclic ligand and the
ruthenium center, were refined anisotropically. In [Ag(L1)2](PF6)9 and
[Re(CO)3ClL1](PF6)4, there was found to be a mixture of both full and
partial occupancy PF6 anions, the major occupancy atoms of which were
refined anisotropically, the minor occupancy atoms isotropically. In L4 ´
4PF6, the PF6 and Cl anions were ordered and refined anisotropically. In
[{Ru(bpy)2}2L2](PF6)8, two of the PF6 anions were ordered and were
refined anisotropically, another was found to be disordered over two partial
occupancy sites (the major occupancy orientation of which was refined
anisotropically), and the remaining anion was found to be ordered but of
only half occupancy, and was refined isotropically. The included benzene
solvent molecules in [Ag(L1)2](PF6)9 were ordered and refined anisotropi-
cally; the MeCN molecules were distributed over multiple partial-
occupancy sites and were refined isotropically. In [Re(CO)3ClL1](PF6)4,
the benzene molecules were ordered (with one molecule sited on a center
of symmetry) while the MeNO2 molecules were distributed over a mixture
of full and partial occupancy sites; the benzene molecules and major
occupancy atoms of the nitromethane molecules were refined anisotropi-
cally, the minor occupancy atoms isotropically. The included MeCN
molecules of L4 ´ 4PF6 were also distributed over both full- and partial-
occupancy positions, the full-occupancy atoms being refined anisotropically
and the partial-occupancy atoms isotropically. In [{Ru(bpy)2}2L2](PF6)8, the
two acetone molecules were found to be distributed over a mixture of three
full- and partial-occupancy sites, with only the major occupancy atoms
being refined anisotropically. The hydrogen atoms of all the structures were
placed in calculated positions, assigned isotropic thermal parameters,
U(H) ˆ 1.2Ueq(C) [U(H) ˆ 1.5Ueq(C ± Me)], and allowed to ride on their
parent atoms. Computations were performed with the SHELXTL PC
program system.[34] Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication
no. CCDC-100691. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (Fax: (‡
44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
‡
‡
‡
MS (LSIMS): m/z ˆ 2120 [M] , 1975 [M PF6] , 1830 [M 2PF6] , 1685
‡
[M 3PF6] ; C79H78ClN4O13P4F24 (2121.0): calcd C 44.74, H 3.71, N 3.96;
found C 44.55, H 3.97, N 4.10.
General procedure for synthesis of AgI complexes [Ag(L1)2](PF6)9,
[Ag(L3)2](PF6)9, and [Ag(L4)2](PF6)9: A solution of silver(i) triflate in
dry MeCN was added to a stirred solution of the appropriate ligand (L1 ´
4PF6, L3 ´ 4PF6, and L4 ´ 4PF6) in dry MeCN under an atmosphere of N2 at
room temperature. After 8 h of stirring in the dark, the solvent was
removed in vacuo, and the residue was treated with a 50% aqueous
solution of NH4PF6. The precipitate was filtered off, washed with H2O and
Et2O, and dried in vacuo.
[Ag(L1)2](PF6)9: From L1 ´ 4PF6 (118 mg, 0.1 mmol) and AgCF3SO3
(13.0 mg, 0.05 mmol) in 12 mL MeCN; yield 112 mg (82%), m.p. 2808C
(decomp.); 1H NMR (300 MHz, CD3CN, 258C): d ˆ 5.75 (s, 8H; xylyl
NCH2), 5.83 (s, 8H; PyNCH2), 7.55 (s, 8H; C6H4), 7.73 (d, J ˆ 4 Hz, 4H;
PyH-5), 8.11 (s, 4H; PyH-3), 8.20 (m, 16H; b-CH and b'-CH), 8.76 (d, J ˆ
5 Hz, 4H; PyH-6), 8.88 (d, J ˆ 6.6 Hz, 8H; a-CH), 9.00 (d, J ˆ 6.6 Hz, 8H;
a'-CH); 13C NMR (75.5 MHz, CD3CN, 258C): d ˆ 64.1, 65.4 (CH2), 123.4,
126.7, 128.3, 128.4, 131.2, 145.9, 146.2, 151.6 (CH), 136.6, 144.2, 150.7, 151.0,
‡
‡
155.7 (Cq); MS (LSIMS): m/z ˆ 2465 [M PF6] , 2320 [M 2PF6] , 2212
‡
‡
‡
[M Ag 2PF6] , 2176 [M 3PF6] , 2067 [M Ag 3PF6] , 1923 [M
Ag 4PF6] ; C80H68AgF54N12P9 (2610.1): calcd C 36.81, H 2.63, N 6.44;
‡
found
C 36.91, H 2.58, N 6.46. Single crystals suitable for X-ray
crystallography were obtained by vapor diffusion of benzene into a MeCN
solution of [Ag(L1)2](PF6)9.
[Ag(L3)2](PF6)9: From L3 ´ 4PF6 (13 mg, 0.04 mmol) and AgCF3SO3
(2.1 mg, 0.02 mmol) in MeCN (10 mL); yield 72 mg (93%); 1H NMR
(300 MHz, CD3CN, 258C): d ˆ 3.44 ± 3.92 (m, 36H; OCH2 and inside
OC6H4), 6.10 (s, 4H; NCH2), 6.25 (brs, 4H; alongside OC6H4), 6.39 (s, 4H;
NCH2), 7.99 (m, 6H; C6H4 and PyH-4), 8.15 (m, 8H; b-CH), 8.65 (s, 2H;
PyH-6), 9.18 (d, 2H; PyH-3), 9.00 and 9.32 (2 Â d, 2 Â 4H; a-CH); 13C
NMR (75.5 MHz, CD3COCD3, 258C): d ˆ 63.3, 65.5, 70.6, 70.9, 71.3, 73.7
(CH2), 118.4, 120.9, 131.6, 137.3, 139.2, 141.5, 146.1, 146.4, 147.4 (CH), 148.6,
‡
148.7, 150.7, 151.5 (Cq); MS (LSIMS): m/z ˆ 3538 [M 2PF6] , 3393 [M
‡
‡
‡
2PF6] , 3248 [M 3PF6] , 3103 [M 4PF6] .
[Ag(L4)2](PF6)9: From L4 ´ 4PF6 (72.6 mg, 0.04 mmol) and AgCF3SO3
(5.1 mg, 0.02 mmol) in MeCN (10 mL); yield 72 mg (93%), m.p. 2678C
(decomp.); 13C NMR (100 MHz, CD3CN, 318C): d ˆ 64.4, 65.9, 68.9, 70.8,
71.3, 72.1 (CH2), 106.8, 114.8, 123.6, 125.6, 125.8, 126.3, 1216.8, 131.8, 145.2,
145.5, 152.6 (CH2), 137.5, 144.0, 159.2 (Cq); MS (LSIMS): m/z ˆ 3485 [M
‡
‡
‡
Ag 2PF6] , 3340 [M Ag 3PF6] , 3195 [M Ag 4PF6] , 3051 [M
‡
Ag 5PF6] ; C152H156AgF54N12O20P9 (3883.5): calcd C 47.01, H 4.05, N 4.33;
found C 46.85, H 4.12, N 4.43.
Acknowledgments: This research was supported by the Engineering and
Physical Sciences Research Council in the United Kingdom and by the
University of Bologna (Funds for Selected Research Topics) and CNR
(Progetto Strategico Tecnologie Chimiche Innovative) in Italy, and by the
EU (TMR grant FMRX-CT96-0076).
General procedure for synthesis CuI complexes [Cu(L1)2](PF6)9 and
[Cu(L4)2](PF6)9: A solution of [Cu(MeCN)4] PF6 in dry MeCN was added
by means of a syringe to a stirred solution of the appropriate ligand (L1 ´
4PF6 or L4 ´ 4PF6) in dry MeCN under an atmosphere of N2 in a Schlenk
flask at room temperature. The solution immediately became brown. After
4 h, the solution was concentrated in vacuo to about a third of its volume.
Addition of Et2O precipitated the product, which was filtered off, washed
with Et2O, and dried in vacuo.
Received: September 10, 1997 [F817]
[Cu(L1)2](PF6)9: From L1 ´ 4PF6 (118.0 mg, 0.1 mmol) and [Cu(-
MeCN)4]PF6 (18.0 mg, 0.05 mmol) in MeCN (10 mL); yield 106 mg
(83%), m.p. 2398C (decomp.); 1H NMR (300 MHz, CD3SOCD3, 258C):
d ˆ 5.83 (s, 8H; xylyl NCH2), 5.92 (s, 8H; PyNCH2), 7.67 (s, 8H; C6H4), 7.90
(s, 4H; PyH-5), 8.24 (s, 4H; PyH-3), 8.59 (brs, 16H; b-CH and b'-CH), 8.77
(s, 4H; PyH-6), 9.44 (brs, 8H; a-CH), 9.51 (s, 8H; a'-CH); MS (LSIMS): m/
[1] a) J. S. Lindsey, New J. Chem. 1991, 15, 153 ± 180; b) G. M. Whitesides,
J. P. Mathias, C. T. Seto, Science 1991, 254, 1312 ± 1319; c) D. Philp, J. F.
Stoddart, Synlett 1991, 445 ± 448; d) D. B. Amabilino, J. F. Stoddart,
New Scientist 19 Feb. 1994, No. 1913, pp. 25 ± 29; e) J.-M. Lehn,
Supramolecular Chemistry, VCH, Weinheim, 1995; f) D. Philp, J. F.
Stoddart, Angew. Chem. 1996, 108, 1242 ± 1286; Angew. Chem. Int. Ed.
Engl. 1996, 35, 1154 ± 1196.
‡
‡
‡
z ˆ 2420
[M PF6] ,
2274
[M 2PF6] ,
2130
[M 3PF6] ;
C80H68CuF54N12P9 (2565.7): calcd C 37.45, H 2.67, N 6.55; found C 37.67,
H 2.51, N 6.72.
[2] a) J.-M. Lehn, A. Rigault, J. Siegel, J. Harrowfield, B. Chevrier, D.
Moras, Proc. Natl. Acad. Sci. USA 1987, 84, 2565 ± 2569; b) E. C.
Chem. Eur. J. 1998, 4, No. 4
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
0947-6539/98/0404-0605 $ 17.50+.25/0
605

V. Balzani, J. F. Stoddart, D. J. Williams et al.
FULL PAPER
Table 6. Crystal data, data collection, and refinement parameters.[a]
[Re(CO)3ClL1](PF6)4
[Ag(L1)2](PF6)9
[{Ru(bpy)2}2](PF6)7
L4 ´ 4PF6
Formula
Solvent
C43H34N6O3ClRe ´ 4PF6
5MeNO2 ´ 1.5PhH
1906.7
yellow/orange prisms
0.33 Â 0.27 Â 0.27
monoclinic
P21/c, 14
293
C80H68N12Ag ´ 9PF6
4PhH ´ 4MeCN
3086.7
pale yellow needles
0.67 Â 0.30 Â 0.18
monoclinic
C2/c, 15
C84H68N16Ru2 ´ 7PF6
4Me2CO
2750.8
C76H78N6O10 ´ 2PF6 ´ 2Cl
6MeCN
1842.6
Formula weight
Color, habit
Crystal size (mm)
Lattice type
Space group
T (K)
orange/red plates
0.80 Â 0.77 Â 0.10
triclinic
red prisms
0.30 Â 0.30 Â 0.17
triclinic
Å
Å
P1, 2
P1, 2
198
203
173
a (Š)
b (Š)
c (Š)
a (8)
b (8)
g (8)
V (Š3)
13.415(1)
22.407(2)
26.524(3)
±
103.32(1)
±
7758(1)
4
1.632
45.182(3)
15.942(2)
18.252(3)
13.465(2)
13.776(2)
22.115(4)
88.05(1)
73.61(1)
68.33(1)
3646(1)
1[c]
11.951(1)
15.165(1)
26.185(2)
97.48(1)
90.57(1)
106.12(1)
4514.8(5)
2
98.11(1)
±
13015(3)
4[b]
Z
3
1calcd (gcm
F(000)
Radiation
)
1.575
6224
1.253
1.355
3796
CuKa
5.26
1383
CuKa
1920
CuKa
[d]
[d]
[d]
CuKa
1
m (mm
)
3.47
3.29
1.74
q range
2.6±55.0
9746
6649
semiempirical
0.23, 0.13
1073
0.059
0.154
0.084, 10.668
0.76, 0.37
2.0±60.0
9624
7428
semiempirical
0.60, 0.29
896
0.093
0.256
0.185, 39.944
0.83, 1.04
3.7±55.0
8391
5031
empirical
0.84, 0.45
998
0.124
0.346
0.298, 2.770
1.82, 0.53
1.7± 57.0
12147
7963
±
±
1133
0.088
0.212
0.133, 6.440
0.62, 0.45
No. of unique reflns measured
No. of unique reflns observed, j Fo j> 4s( j Fo j )
Absorption correction
Maximum, minimum transmission
No. of variables
[e]
R1
[f]
wR2
Weighting factors a, b[g]
3
Largest difference peak, hole (eŠ
)
[a] Details in common: graphite-monochromated radiation, w-scans, Siemens P4 diffractometer, refinement based onF 2. [b] The molecule has
crystallographic C2 symmetry. [c] The molecule has crystallographic Ci symmetry. [d] Rotating anode source. [e] R1 ˆ S j jFo j j Fc j j/S j Fo j . [f] wR2 ˆ
p
{S[w(Fo2 Fc2)2]/S[w(Fo2)2]}. [g] w ˆ s2(Fo2) ‡ (aP)2 ‡ bP.
1
Constable, Tetrahedron 1992, 48, 10013 ± 10059; c) R. Krämer, J.-M.
Lehn, A. De Cian, J. Fischer, Angew. Chem. 1993, 105, 764 ± 767;
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E. R. Heirtzler, M. Neuburger, M. Zhender, Supramol. Chem. 1995, 5,
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706 ± 712.
[6] a) V. Balzani, F. Scandola, Supramolecular Photochemistry, Ellis
Horwood, Chichester (UK), 1991; b) A. P. de Silva, C. P. McCoy,
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[3] a) C. O. Dietrich-Buchecker, J.-P. Sauvage, Bioorganic Chemistry
Frontiers, Vol. 2, Springer, Berlin, 1991, 197 ± 248; b) J.-P. Sauvage,
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Soc. Chem. Commun. 1994, 28, 2231 ± 2233; c) C. O. Dietrich-
Buchecker, J.-P. Sauvage, N. Armaroli, P. Ceroni, V. Balzani, Angew.
Chem. 1996, 108, 1190 ± 1193; Angew. Chem. Int. Ed. Engl. 1996, 35,
1119 ± 1121.
Â
Â
Balzani, S. E. Boyd, A. Credi, M. T. Gandolfi, M. Gomez-Lopez, S.
Iqbal, D. Philp, J. A. Preece, L. Prodi, H. G. Ricketts, J. F. Stoddart,
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1134; Angew. Chem. Int. Ed. Engl. 1993, 32, 1075 ± 1077; b) S. Serroni,
S. Campagna, A. Juris, M. Venturi, V. Balzani, G. Denti, Gazz. Chim.
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[14] While this work was in progress, the compound [Ru(bpy)2L3](PF6)6
was mentioned in the literature; see: A. C Benniston, A. Harriman, in
Physical Supramolecular Chemistry (Eds.: L. Echegoyen, A. E.
Kaifer), NATO ASI Series, Kluwer Academic, Dordrecht (the
Netherlands), 1996, pp. 179 ± 197Ðand subsequently its synthesis
606
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Chem. Eur. J. 1998, 4, No. 4

Catenane Ligands
590±607
was described, as well: A. C. Benniston, P. R. Mackie, A. Harriman,
Tetrahedron Lett. 1997, 38, 3577 ± 3580; finally, a communication
dealing with photoinduced electron transfer processes in the com-
pounds [Ru(bpy)2L1]6‡ and [Ru(bpy)2L3]6‡ has also appeared recent-
ly; see: A. C. Benniston, P. R. Mackie, A. Harriman, Angew. Chem.
1998, 110, 376 ± 378; Angew. Chem. Int. Ed. 1998, 37, 354 ± 356.
[15] S. Gould, G. F. Strouse, T. J. Meyer, B. P. Sullivan, Inorg. Chem. 1991,
30, 2942 ± 2949.
[22] The absence of an eighth counterion in the final difference electron
density map forces us to conclude that the structure contains a mixture
of RuI and RuII oxidation states.
Å
[23] This disorder is not a consequence of the choice of P1 as the space
group. Attemps to resolve the structure into molecules of one chirality
only and refining them in P1 still produced 50:50 superimposed
images of both chiralities.
[24] P. R. Ashton, R. Ballardini, V. Balzani, A. Credi, M. T. Gandolfi,
Â
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[17] L. D. Ciana, W. J. Dressick, A. von Zelewsky, J. Heterocycl. Chem.
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L. Prodi, M. V. Reddington, A. M. Z. Slawin, N. Spencer, J. F.
Stoddart, C. Vicent, D. J. Williams, J. Am. Chem. Soc. 1992, 114,
193 ± 218.
D. J. F. Marquis, S. Menzer, L. Perez-Garcia, L. Prodi, J. F. Stoddart,
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11171 ± 11197.
[25] a) M. Wrighton, D. L. Morse, J. Am. Chem. Soc. 1974, 96, 998 ± 1003;
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[26] G. L. Gaines, III, M. P. OꢁNeil, W. A. Svec, M. P. Niemczyk, M. R.
Wasielewski, J. Am. Chem. Soc. 1991, 113, 719 ± 721; b) P. Chen, T. J.
Meyer, Inorg. Chem. 1996, 35, 5520 ± 5524.
Â
[19] D. B. Amabilino, P. R. Ashton, L. Perez-García, J. F. Stoddart, Angew.
[27] S. Roffia, M. Marcaccio, C. Paradisi, F. Paolucci, V. Balzani, S. Serroni,
S. Campagna, G. Denti, Inorg. Chem. 1993, 32, 3003 ± 3009.
[28] Upon oxidation, the catenane 24‡ shows two not fully reversible
processes at ‡1.30 V and ‡1.55 V, which can be attributed to
the alongside and inside 1/5DMN units of the crown ether, respec-
tively.
[29] D. D. Perrin, W. F. L. Armarego, Purification of Laboratory Chem-
icals, Pergamon, Oxford, 1989.
[30] P. R. Ashton, E. J. T. Chrystal, J. P. Mathias, K. P. Parry, A. M. Z.
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[32] G. J. Kubas, Inorg. Synthesis 1971, 19, 90 ± 92.
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[20] The kinetic and thermodynamic data were calculated using two
procedures: a) the coalescence method, where values for the rate
constant kc at the coalescence temperature (Tc) were calculated (I. O.
Sutherland, Annu. Rep. NMR Spectrosc. 1971, 4, 71 ± 235) from the
approximate expression kc ˆ p(DnÄ)/(2)1/2, where DnÄ is the limiting
chemical shift difference (Hz) between the coalescing signals in the
absence of exchange; b) the exchange method, where values of kex
were calculated (J. Sandström, Dynamic NMR Spectroscopy, Aca-
demic Press, London, 1982; Ch. 6) from the approximate expression
kex ˆ p(DnÄ), where DnÄ is the difference (Hz) between the line width at
a temperature Tex, where exchange of sites occurs, and the line width in
the absence of exchange. The Eyring equation was subsequently
ˆ
ˆ
employed to calculate DGc or DGex values at Tc or Tex, respectively.
[21] M. S. Henry, M. Z. Hoffman, J. Phys. Chem. 1979, 83, 618 ± 625;
A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amster-
dam, 1984, Ch. 5, p. 296.
[34] SHELXTL PC version 5.03, Siemens Analytical X-Ray Instruments,
Madison, WI, 1994.
Chem. Eur. J. 1998, 4, No. 4
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