sym-[5.5.5]Heterocyclophanes: Structurally well-defined, mixed π/heteroatom-donor macrobicyclic cages

Article abstract of DOI:10.1039/a805646c

Structural considerations for achieving conformational stability in cyclophanes are applied as design criteria in the synthesis of sym-[5.5.5]triaza- and sym-[5.5.5]trioxacyclophane macrobicycles. These compounds act as dynamic hosts in which the metal ion migrates between equivalent, C₃-related (η¹-C)₂N₂ coordination sites. The metal-arene interaction may alternatively be described as three centre, two-electron σ complexation to the C-H bond. Crystal structures of the copper(I) and silver(I) complexes show that little reorganization is required on the part of the ligand to accommodate the metal, and the former provides an unusual, structurally characterized example of eta-bonding of an arene to Cu¹.

Full text of DOI:10.1039/a805646c

View Article Online / Journal Homepage / Table of Contents for this issue
sym-[5.5.5]Heterocyclophanes: structurally well-defined, mixed
ð/heteroatom-donor macrobicyclic cages
Jens Hansen, Alexander J. Blake, Wan-Sheung Li and Mark Mascal*
School of Chemistry, University of Nottingham, Nottingham, UK NG7 2RD
Received 20th July 1998, Accepted 4th September 1998
Structural considerations for achieving conformational stability in cyclophanes are applied as design criteria in the
synthesis of sym-[5.5.5]triaza- and sym-[5.5.5]trioxacyclophane macrobicycles. These compounds act as dynamic
hosts in which the metal ion migrates between equivalent, C3-related (η1-C)2N2 coordination sites. The metal–arene
interaction may alternatively be described as three centre, two-electron σ complexation to the C–H bond. Crystal
structures of the copper(I) and silver(I) complexes show that little reorganization is required on the part of the ligand
to accommodate the metal, and the former provides an unusual, structurally characterized example of eta-bonding
of an arene to CuI.
The concept of the ‘cyclophane’ was introduced by Cram
in 1951,1 and the prerequisites for achieving conformational
stability in ring systems such as these were made clear by Dale
in 1966.2 In the latter work, it was demonstrated that linking
planar substructures (such as aromatic rings) diametrically by
an odd number of methylene units resulted in essentially strain-
free molecules, whereas those with an even number were
conformationally unstable.3 Despite the fact that Dale’s study
comprises the foundations of rational design in a major class of
host system where structural definition is a paramount con-
sideration, it is of interest to note that the number of cyclo-
phanes synthesized with odd-membered bridges is no greater
than that with even-membered bridges.4 Even where the odd-
number condition has been met, cyclophanes prepared for the
purpose of guest complexation have often been designed with
the heteroatoms divergent from the cavity.5 A general consider-
ation for para [n.n] or sym-[n.n.n] cyclophanes with saturated,
odd-membered linking chains is that the odd-numbered posi-
tions on the chain (≠1 or n) will converge towards the central
aromatic axis, while all even-numbered positions diverge from
the centre. This is largely supported by the examples of [n.n]-
paracyclophanes which appear in the Cambridge Structural
Database except for those where the chains contain sulfur.6
In the sym-[n.n.n] cyclophanes, the role of the aromatic rings
can be debated. These could function simply as anchor points
for the intervening chains or, like the bridgehead nitrogens in a
cryptand, involve themselves in the binding of a guest. sym-
[2.2.2], [3.3.3] and [4.4.4]cyclophane systems have been known
for some time, but no endo metal complexes appear to have
been described, even though the well known [3.3]paracyclo-
phane–chromium η12 complexes demonstrate the potential for
this type of inclusion.7 For metal ion guests to be involved in
eta-complexation the maximum value of n is likely to be 5,
which situates the rings about 4.8 Å from each other.8 This puts
the midpoint between the rings at 2.4 Å from each phenyl
centroid, i.e. well beyond the intimate Ar ؒ ؒ ؒ M distances found
in η6 or η12 species, but within the range for simple η1 bonding
to the periphery of the rings.9
C
C
27
C
9
X
X
X
X
X
1
X
C
C
18
C
1a X = NH
1b X = NMe
1c X = O
Fig. 1 Structure of 1 and cartoon where each facet represents an
independent (η1-C)2X2 ligand set.
to the centre of the trigonal plane which they define is of the
order of 3 Å, thereby ruling out the centre of the cavity as a
guest space for most metals. Therefore if neither sandwich-type
complexation nor cryptation is possible, this reduces 1 con-
ceptually to three independent, 16-membered azamacrocycles
incorporating two heteroatoms and two aromatic p orbitals as
ligating sites in an approximately square planar arrangement,
as represented in Fig. 1. Only one of these C3-related ‘facets’
can be occupied at any one time, the consequence of which is
dynamic behaviour which is dependent on the identity of the
metal. We now report in full on the synthesis and structure of
macrobicycles 1 and their interaction with metal ions.11
Results and discussion
The only previous reports of [5.5.5]cyclophane systems directly
comparable to 1 (i.e. with a heteroatom at the 3-positions of the
chains) were of a thio analogue produced from 1,3,5-
tris(bromoacetyl)benzene and sodium sulfide in 0.16% yield12
and an ester analogue by condensation of benzene-1,3,5-
triacetyl chloride with 1,3,5-tris(2-hydroxyethyl)benzene in
3.9% yield.13 Neither of these approaches seemed attractive to
us and we therefore opted for the cobalt-meditated cyclo-
trimerization method14 first used by Hubert to access the all-
hydrocarbon analogue of 1.15
The synthetic route to the aza derivative 1a is given in
Scheme 1. The starting triacid 2 was available in quantity by
Willgerodt–Kindler reaction of commercial 1,3,5-triacetyl-
benzene.16 Carbonyldiimidazole-induced coupling of 2 with 4-
aminobut-1-yne then gave the cyclization precursor 3 in high
yield. Intramolecular cyclotrimerization using cyclopentadi-
With the above considerations in mind and an in-depth study
of the conformational preferences of [n.n] paracyclophane
hydrocarbons behind us,10 we proposed a series of [5.5.5]macro-
bicycles 1 incorporating parallel aromatic rings as bridgeheads
with a heteroatom at the 3-position of each chain. In accord-
ance with the above model, the three heteroatoms are directed
towards the cavity, although the distance from each heteroatom
J. Chem. Soc., Perkin Trans. 1, 1998, 3371–3376
3371

View Article Online
H
N
O
CO2H
O
HO2C
i
HN
NH
CO2H
O
2
3
ii
Ar
Ar
OC
CO
OC
NH
iii
NH
HN
HN
NH
NH
Ar
1a + iso-1a
Ar
4 + iso-4
Scheme
1
Reagents and conditions: i, 1,1Ј-carbonyldiimidazole,
4-aminobut-1-yne, THF; ii, [CpCo(CO)2], o-xylene, heat; iii, BH3–
SMe2, THF, heat; then MeOH, heat.
enylcobalt dicarbonyl produced an inseparable mixture of 4
and its 1,2,4-regioisomer (iso-4) in a 1:1.3 ratio (by NMR) in a
net 54% yield, or 62% based on recovered 3. The mixture was
finally reduced with borane–dimethyl sulfide complex, where-
upon the desired sym-macrobicycle 1a could be isolated by
column chromatography.
Fig. 2 (a) Crystal structure of 1a. Displacement ellipsoids are at the
30% probability level and H-atoms (except for N-H’s) are omitted for
clarity. (b) Crystal structure of 1c. Displacement ellipsoids are at the
20% probability level.
Triaza cage 1a crystallizes as colourless tablets from hexane,
and the determination of the crystal structure [Fig. 2(a)] served
to support the above argued structural considerations, i.e. that
the rings would occupy parallel planes and the heteroatoms
would point into the cavity. The actual ring to ring separation is
4.93(3) Å and the N to (molecular) C3 axis distance is 3.08(3) Å.
An interesting feature of this structure is that the nitrogen
H-atoms occupy the cavity in preference to the lone pairs.
Simple mixing of solutions of 1a and [Cu(MeCN)4]BF4
1
results in the formation of a stable complex. The H and 13C
spectra of this material show a 2:1 desymmetrization of the
ligand resonances consistent with occupation by the metal of
one of the three (η1-C)2N2 coordination sites represented in
Fig. 1. Final confirmation of this mode of assembly came in the
form of an X-ray crystal structure (Fig. 3). The structural simi-
larity of the ligand in the complexed and uncomplexed states
indicates favourable preorganization, although the Cu–N bond
lengths (2.01 Å) are significantly closer than the midpoint
between the two nitrogens in 1a (2.67 Å) and some puckering of
the two chains involved is observed. The third chain however
remains undistorted and participates in H-bonding to a mole-
cule of water of crystallization which, along with the BF4Ϫ ion,
links the complexes together in chains (Fig. 4). The aromatic
rings stack at an interplanar distance of 3.3 Å with centres
offset 1.4–1.5 Å.
Fig. 3 Crystal structure of [Cu1a]BF4ؒH2O. Displacement ellipsoids
are at the 30% probability level. The H-atoms, counterion and water of
crystallization are omitted for clarity.
other structurally characterized examples appearing in the
literature.18
The dynamics of intramolecular exchange between the three
1
coordination sites of 1a were then examined. The H NMR
spectrum (CDCl2CDCl2) of the [Cu1a] complex shows tem-
perature dependent fluxional behaviour, with collapse of the
two aromatic signals to a single, broad peak occurring around
95 ЊC. The activation energy for this process estimated from
the coalescence temperature and the δν value is 72 kJ molϪ1.19
Migration of the copper nominally involves breaking away
from one of the nitrogens and both carbons (or C–H(σ)→
Cu bonds) of a C2N2 ligand set before regaining the same from
another set, although progression from site to site would take
place under the continuous influence of the π system. This in
effect constitutes ‘dynamic sandwich complexation’, with the
centre of gravity of the metal coinciding with the molecular C3
axis.
The relationship of the copper ion to the benzene rings in the
[Cu1a] complex is a matter of some interest. This may involve
either the metal participating in η1 bonds to C, or three centre,
two-electron σ complexation to the aromatic C–H bonds.17 The
Cu–C distances are 2.38 and 2.40 Å, and the 0.57 Å displace-
ment of the metal away from the C9–C18 axis puts the contacts
to the midpoint of the C–H bonds at 2.37 and 2.39 Å. The 0.59
1
ppm downfield shift in the H NMR of the aromatic C-H’s
associated with the Cu is indicative of electron withdrawal
from the hydrogen to the metal bond, whereas the relevant
carbon atoms are some 10 ppm upfield of those not involved
with the metal. It should be noted that eta interactions between
copper() and aryl rings are a novelty in any case, with only six
Reaction of the macrobicycle with AgOTf in THF gave the
3372
J. Chem. Soc., Perkin Trans. 1, 1998, 3371–3376

View Article Online
HO
O
R
R
i
OH
O
OH
O
R
5
6 R = OTHP
7 R = OH
8 R = Br
ii
Fig. 4 Secondary structure of [Cu1a]BF4ؒH2O showing the involve-
ment of the water molecule and counterion. The relevant distances and
angles are: N3–H1O, 1.78 Å; N3–H1O–O1W, 172Њ; O1W–H14A, 2.25
Å; O1W–H14A–N14A, 161Њ; F2–H2O, 2.18 Å, F2–H2O–O1W, 166Њ;
F4–H25A, 2.30 Å; F4–H25A–N25A, 159Њ.
iii
iv
O
Ar
Ar
v
O
O
O
O
O
1c + iso-1c
9
Scheme 2 Reagents and conditions: i, NaH, THPOCH2CH2Br, DMF,
heat; ii, HCl, MeOH; iii, methanesulfonyl chloride, TEA, CH2Cl2 then
LiBr, THF; iv, lithium acetylide–ethylenediamine complex, liq. NH3; v,
[CpCo(CO)2], o-xylene, heat.
argylic (but-3-ynylic) halides to directly produce a triyne precur-
sor to 1c were fruitless. Instead, the alkynyl substituents had to
be introduced stepwise, first by alkylation with THP-protected
bromoethanol to give 6, then hydrolysis to the alcohol 7, con-
version to the bromide 8 and finally reaction with acetylide
anion to give the cyclization precursor 9. Cyclotrimerization as
described above gave 1c and its 1,2,4-regioisomer (iso-1c) in a
1:1.7 ratio and a net 52% yield, or 72% based on conversion.
Compound 1c is crystallographically isostructural with 1a
[Fig. 2(b)]. The ring to ring separation of 4.74(3) Å is less than
in 1a, while the O to (molecular) C3 axis distance of 3.13(1) Å is
slightly greater. No characterizable metal complexes of 1c have
yet been obtained, although efforts are continuing.
Fig. 5 Crystal structure of [Ag(1a)]OTf. Displacement ellipsoids
are at the 20% probability level and the H-atoms and counterion are
omitted for clarity. Only the major component of disorder affecting the
free nitrogen (N3) is shown.
corresponding complex [Ag(1a)]OTf. Unlike [Cu(1a)]BF4, the
1H NMR (CD2Cl2) of this material showed a single resonance
in the aromatic region at room temperature. Coalescence
occurred at Ϫ28 ЊC and only on cooling below Ϫ50 ЊC did two
sharp peaks (2:1) appear, separated in this case by 0.27 ppm.
This indicated a greater degree of mobility for the AgI than for
CuI, also reflected in the lower activation energy of 48 kJ
molϪ1.19 The X-ray crystal structure of [Ag(1a)]OTf (Fig. 5)
was comparable to that of [Cu(1a)]BF4, the major difference
being that only one of the two C–C–N–C–C chains needed to
distort from the ideal gauche-anti-anti-gauche conformation to
accommodate the larger silver ion (Ag–N distances, 2.32 Å).
The outward displacement of the silver from the C9–C18 axis
(0.40 Å) is slightly less than that for copper(), but the same
general NMR and structural arguments apply and either η1
complexation20 or two electron donation from the C–H bonds
can be invoked. A longer-range contact to the metal by one of
the oxygens (O2) of the triflate ion (2.92 Å) is also observed
normal to the (approximate) C2N2 plane as well as a hydrogen
bond from O1 to one of the amine hydrogens (H ؒ ؒ ؒ O distance,
2.25 Å; N–H ؒ ؒ ؒ O angle, 147Њ).
The alkylation of 1a by deprotonation with butyllithium and
treatment with methyl iodide succeeded in 66% yield to give
derivative 1b. The extreme solubility of 1b in all solvents from
methanol to hexane meant that no single crystals could be
grown for X-ray analysis. An analogous silver complex
[Ag(1b)]OTf could however be prepared whose NMR spectra
showed evidence of dynamic behaviour similar to that of the
previous complexes. Coalescence of the aromatic proton signals
in CD2Cl2 occurred at Ϫ5 ЊC, but a separation of only 0.07 ppm
was observed at complete resolution (ca. Ϫ20 ЊC). In contrast
to the other cases, this complex decomposed gradually at room
temperature and no X-ray quality crystals were obtained.
The synthetic route to the oxo derivative 1c is given in
Scheme 2. The starting triol 5 was prepared by reduction of the
acid 2.21 All attempts however to alkylate 5 with homoprop-
Experimental
Benzene-1,3,5-tris(N-but-3-ynylacetamide) 3
To a stirred solution of benzene-1,3,5-triacetic acid 216 (244 mg,
0.967 mmol) in THF (7 cm3) was added 1,1Ј-carbonyldiimid-
azole (518 mg, 3.19 mmol). The mixture was stirred for 3 h
after which a solution of 1-aminobut-3-yne (221 mg, 3.20
mmol) in THF (2 cm3) was added dropwise over a 5 min
period. Precipitation of the product was observed within 5 min
and was complete after 1 h. The solid was filtered off, washed
with THF (5 × 1 cm3) and dried to give 3 (240 mg) as colour-
less crystals. The filtrate was evaporated and the residue was
chromatographed on silica (1:1 CH2Cl2–acetone→acetone) to
give additional 3 (127 mg, total 367 mg, 94%), mp (acetone)
190–193 ЊC (Found: C, 70.94; H, 6.95; N, 10.26. C24H27N3O3
requires C, 71.09; H, 6.71; N, 10.36%); νmax/cmϪ1 (KBr) 3290
(NH, C –H), 3075, 2936, 2118 (C᎐C), 1642 (C᎐O), 1549, 1438,
᎐
᎐
sp
1345, 1251, 1160, 1065, 871 and 640; δH (400 MHz,
2
᎐
[ H ]DMSO) 2.31 (6 H, dt, J 2.6, 7.1, CH -C᎐C), 2.85 (3 H, t,
᎐
6
2
᎐
J 2.6, C᎐CH), 3.18 (6 H, app. q, NCH ), 3.36 (6 H, s, ArCH ),
᎐
2
2
7.00 (3 H, s, ArH) and 8.23 (3 H, t, J 5.5, NH); δC (100.6 MHz,
2
᎐
[ H ]DMSO) 18.9 (CH -C᎐C), 38.0 (NCH ), 42.3 (ArCH ),
᎐
6
2
2
2
᎐
᎐
72.2 (C᎐CH), 82.4 (C᎐CH), 127.9 (ArH), 136.1 (Ar) and 170.3
᎐
᎐
(C᎐O); m/z (EI) 405 (Mϩ, 18%), 366 (36), 337(8), 310 (42), 297
᎐
(9), 267 (11), 241 (27), 212 (21), 70 (100) and 53 (51).
sym-[5.5.5]Triazacyclophane amides 4 and iso-4
o-Xylene (700 cm3) was distilled from sodium–benzophenone
J. Chem. Soc., Perkin Trans. 1, 1998, 3371–3376
3373

View Article Online
directly into a flask containing pulverized triyne 3 (1.90 g, 4.69
mmol) under dry argon. The mixture was degassed by five suc-
cessive evacuation and flushing cycles with argon while stirring.
The suspension was heated at 155 ЊC and CpCo(CO)2 (0.250
cm3; technical grade) was added. After 4 h additional CpCo-
(CO)2 (0.750 cm3) was introduced by syringe pump over a 16 h
period. The mixture was allowed to come to RT and the solvent
was evaporated. The residue was triturated with boiling metha-
nol (2 × 50 cm3) and filtered. The combined filtrates were evap-
orated and the residue was dissolved in hot methanol. The solu-
tion was concentrated at the boiling point to ca. 2–3 cm3,
diluted with hot ethyl acetate (10 cm3) and immediately chrom-
atographed on silica (10:1→5:1 ethyl acetate–methanol) to
give an inseparable mixture of 4 and iso-4 in a 1:1.3 ratio (1.034
g, 54%). The yield based on recovered 3 (241 mg) was 62%.
δH (400 MHz, [2H6]DMSO, >6 ppm only) 6.25 (1 H, t, J 5.0,
NH), 6.31 (3 H, t, J 5.1, NH), 6.55 (1 H, t, J 5.4, NH), 6.70
(3 H, s, ArH), 6.72 (2 H, s, ArH), 6.76 (1 H, dd, J 3.5, 6.9, NH),
6.85 (1 H, d, J 7.9, ArH), 6.91 (3 H, s, ArH), 6.97 (1 H, s, ArH),
6.99 (1H, d, J 8.2, ArH) and 7.12 (1 H, s, ArH); δC (100.6 MHz,
[2H6]DMSO) 28.2, 28.9, 33.1, 33.6, 35.5, 37.1, 37.2, 37.9, 43.2,
43.3, 43.5, 43.6, 124.5, 126.4, 126.9, 127.51, 127.57, 127.60,
128.0, 128.5, 134.3, 135.2, 135.7, 136.2, 136.4, 136.5, 136.7,
137.7, 169.69, 169.75 and 170.1.
less solid. Recrystallization from CH2Cl2–ether at Ϫ20 ЊC
gave [Cu1a]BF4ؒH2O as colourless crystals, mp 210–230 ЊC
(decomp.) (HRFABMS: Mϩ, 426.1962. C24H3363CuN3 requires
426.1970); νmax/cmϪ1 (CHCl3) 3266 (NH), 2925, 1600, 1457,
1076 (B-F) and 980; δH (250 MHz, [2H6]acetone) 1.58 (1 H, br s,
NH), 2.6–3.0 (20 H, m, CH2), 3.26 (4 H, m, CH2), 3.97 (2 H,
br s, CuNH), 6.75 (4 H, s, ArH) and 7.34 (2 H, s, ArH);
δC (100.6 MHz, [2H6]acetone) 33.1 (ArCH2), 35.5 (ArCH2, br),
48.9 (NCH2, br), 50.4 (NCH2), 118.1 (ArH–Cu), 128.2 (ArH),
138.1 (Ar) and 142.1 (Ar); m/z (FAB) 426 ([Cu1a], 20%) and
364 (1a ϩ H, 7).
[Ag1a]OTf complex
All operations were performed with exclusion of light. To a
solution of cyclophane 1a (18.2 mg, 50.0 µmol) in THF (1 cm3)
was added a solution of silver triflate in THF (33.5 mM, 1.50
cm3, 50.0 µmol). The solvent was evaporated giving [Ag1a]OTf
(31.0 mg, 100%) as a colourless solid. Recrystallization from
CH2Cl2–ether at Ϫ20 ЊC gave pure [Ag1a]OTf as colourless
crystals, mp 220–225 ЊC (decomp.) (Found: C, 48.13; H,
5.33; N, 6.46. C24H33N3 requires C, 48.39; H, 5.36; N, 6.77%);
νmax/cmϪ1 (CHCl3) 3269 (NH), 2924, 2859, 1597, 1454, 1282,
1028 and 638 (m); δH (400 MHz, CD2Cl2) 1.93 (3 H, br s, NH),
2.72 (12 H, t, J 5.8, ArCH2), 2.89 (12 H, br s, NCH2) and 6.86
(6 H, s, ArH); δH (400 MHz, CD2Cl2, Ϫ50 ЊC, >6 ppm only)
6.72 (4 H, s, ArH) and 6.99 (2 H, s, ArH); δC (100.6 MHz,
CD2Cl2) 34.5 (ArCH2), 50.6 (NCH2), 124.4 (br, ArH) and 139.2
(br, Ar); m/z (FAB) 620 ([Ag1a] ϩ TfOH, 7%), 470 ([Ag1a],
100) and 364 (1a ϩ H, 18).
sym-[5.5.5]Triazacyclophanes 1a and iso-1a
To a stirred suspension of the above mixture of 4 and iso-4
(1.016 g, 2.51 mmol) in THF (40 cm3) was slowly added a solu-
tion of BH3ؒSMe2 in THF (10 M, 1.65 cm3, 16.5 mmol). The
mixture was heated at reflux for 24 h and then allowed to cool
to RT. Methanol (20 cm3) was cautiously added and then evap-
orated. To the residue was added additional methanol (50 cm3)
and the mixture was heated at reflux for 12 h. The solvent was
evaporated and the residue chromatographed on silica
(10:1→3:1 CH2Cl2–methanol) giving 1a (235 mg), a mixed
fraction of 1a ϩ iso-1a (178 mg) and iso-1a (325 mg), total
738 mg (81%), as colourless solids. The mixed fraction was
rechromatographed providing additional 1a (65 mg), and the
combined mass of the desired product was recrystallized
from hexane to give pure 1a (274 mg, 30%) as colourless
crystals.
Tri-N-methyl-sym-[5.5.5]triazacyclophane 1b
To a solution of 1a (36.4 mg, 100 µmol) in THF (2 cm3) at
Ϫ78 ЊC was added a solution of n-butyllithium in hexane (1.57
M, 0.210 cm3, 330 µmol) over a 5 min period. The pale yellow
mixture was allowed to warm to Ϫ20 ЊC over a 30 min period.
After an additional 10 min the mixture was recooled to Ϫ78 ЊC
and methyl iodide (56.8 mg, 400 µmol) was added over a period
of 3 min. The reaction was warmed to RT and the solvent was
evaporated. The residue partitioned between CH2Cl2 (3 cm3)
and water (3 cm3) and the aqueous phase was extracted with
CH2Cl2 (3 × 2 cm3). The combined extracts were dried over
MgSO4 and the solvent evaporated. Chromatography on silica
(ether saturated with NH3) gave 1b (27 mg, 66%) as a waxy
white solid (HREIMS: Mϩ, 405.3142. C27H39N3 requires
405.3144); νmax/cmϪ1 (CHCl3) 2937, 2845, 2790, 1602, 1459,
1350, 1127 and 1048; δH (400 MHz, CDCl3) 2.30 (9 H, s, CH3),
2.46 (12 H, t, J 6.3, NCH2), 2.58 (12 H, t, J 6.3, ArCH2) and
6.57 (6 H, s, ArH); δC (100.6 MHz, CDCl3) 33.6 (ArCH2), 40.6
(CH3), 59.6 (NCH2), 125.9 (ArH) and 140.3 (Ar); m/z (EI) 405
(Mϩ, 24%), 116 (3) and 58 (100).
1a. Mp (n-hexane) 247–249 ЊC (Found: C, 79.43; H, 9.35;
N, 11.48. C24H33N3 requires C, 79.29; H, 9.15; N, 11.56%);
νmax/cmϪ1 (CHCl3) 3291 (NH), 2917, 2827, 2744, 1601, 1458,
1120 and 909; δH (400 MHz, CDCl3) 1.90 (3 H, br s, NH), 2.74
(12 H, t, J 5.7, ArCH2), 2.91 (12 H, t, J 5.7, NCH2) and 6.81
(6 H, s, ArH); δC (100.6 MHz, CDCl3) 35.0 (ArCH2), 49.9
(NCH2), 127.1 (ArH) and 139.7 (Ar); m/z (EI) 363 (Mϩ, 53%)
and 335 (100).
iso-1a. Mp (n-hexane) 135–140 ЊC (Found: C, 79.49; H,
9.33; N, 11.62. C24H33N3 requires C, 79.29; H, 9.15; N, 11.56%);
νmax/cmϪ1 (CHCl3) 3294 (NH), 2911, 2829, 2743, 1600, 1460 and
1120; δH (400 MHz, CDCl3) 0.09 (3 H, br s, NH), 2.45–2.91
(24 H, m, CH2), 6.54 (1 H, s, ArH), 6.75 (1 H, s, ArH), 6.79 (1H,
s, ArH), 6.83 (1 H, dd, J 1.6, 7.8, ArH), 6.86 (1 H, s, ArH) and
6.97 (1 H, d, J 7.8, ArH); δC (100.6 MHz, CDCl3) 30.4, 31.4,
34.6, 34.8, 34.9, 35.2, 48.1, 49.0, 49.6, 49.8, 50.1, 50.3, 126.09,
126.14, 126.6, 127.77, 127.84, 130.4, 135.2, 136.8, 137.2, 138.7,
139.1 and 139.6; m/z (EI) 363 (Mϩ, 100%), 335 (57), 320 (16),
244 (14), 203 (30), 172 (19), 160 (28), 145 (16), 117 (12), 91 (12)
and 42 (28).
[Ag1b]OTf complex
All operations were performed with exclusion of light. To a
solution of cyclophane 1b (8.11 mg, 20.0 µmol) in ether (1 cm3)
was added a solution of silver triflate in THF (33.5 mM, 0.596
cm3, 20.0 µmol) in THF. The solvent was evaporated and the
resulting tan solid was recrystallized from CH2Cl2–ether at
Ϫ20 ЊC giving [Ag1b]OTf (12.4 mg, 94%) as colourless crys-
tals, mp 140–180 ЊC (decomp.) (HRFABMS: Mϩ, 512.2209.
C27H39107AgN3 requires 512.2195); νmax/cmϪ1 (CHCl3) 2960,
2860, 2795, 1599, 1456, 1282, 1158, 1100, 1030 and 638; δH (400
MHz, CD2Cl2) 2.55 (9 H, br s, CH3), 2.74 (24 H, br m, CH2)
and 6.78 (6 H, s, ArH); δH (400 MHz, CD2Cl2, Ϫ20 ЊC, >6
ppm only) 6.71 (4 H, s, ArH) and 6.78 (2 H, s, ArH); δC (100.6
MHz, CDCl3, 323 K) 32.2 (ArCH2), 43.2 (br, CH3), 59.4
(NCH2), 122.8 (br, ArH) and 139.2 (br, Ar); m/z (FAB)
662 ([Ag1b] ϩ TfOH, 2%), 512 ([Ag1b], 32) and 406 (1b ϩ H,
17).
[Cu1a]BF4ؒH2O complex
To a solution of [Cu(CH3CN)4]BF4 (15.7 mg, 50.0 µmol) in
acetonitrile (0.5 cm3) was added a solution of cyclophane 1a
(18.2 mg, 50.0 µmol) in CH2Cl2 (0.5 cm3). The solvent was
evaporated giving [Cu1a]BF4ؒH2O (25.7 mg, 97%) as a colour-
3374
J. Chem. Soc., Perkin Trans. 1, 1998, 3371–3376

View Article Online
1,3,5-Tris{2-[2-(tetrahydropyran-2-yloxy)ethoxy]ethyl}benzene
1,3,5-Tris[2-(but-3-ynoxy)ethyl]benzene 9
6
Ammonia (10 cm3) was condensed in a flask containing lithium
acetylide–ethylenediamine complex (807 mg, 8.77 mmol) with
stirring at Ϫ78 ЊC. Tribromide 8 (512 mg, 0.964 mmol) was then
added over a period of 10 min. Stirring was continued at a bath
temperature between Ϫ40 and Ϫ30 ЊC for 3.5 h. The ammonia
was allowed to evaporate and the residue was partitioned
between sat. aq. NH4Cl (15 cm3) and ether (20 cm3). The
aqueous phase was extracted with ether (2 × 25 cm3) and the
combined organic extracts were washed with sat. aq. NaCl
(15 cm3) and dried over MgSO4. Chromatography on silica
(4:1→3:1 petroleum ether–ether) gave the triyne 9 (260 mg,
74%) as a colourless oil (HREIMS: Mϩ, 366.2188. C24H30O3
To a suspension of sodium hydride (60% in paraffin oil, 480 mg,
12.0 mmol) and 1,3,5-tris(2-hydroxyethyl)benzene 5 (210 mg,
1.00 mmol) in DMF (5 cm3) was added 2-(2-bromoethoxy)-
tetrahydropyran (1.89 g, 9.04 mmol). The mixture was stirred at
50 ЊC for 5 h and allowed to cool to RT. Sat. aq. NH4Cl (5 cm3)
and ether (10 cm3) were added carefully with vigorous stirring.
The aqueous phase was extracted with ether (3 × 10 cm3) and
the combined organic extracts were washed with sat. aq. NaCl
(10 cm3) and dried over MgSO4. The residue was chromato-
graphed on silica (2:1 petroleum ether–ether→ether) to give
6 (483 mg, 81%) as a colourless oil (Found: C, 66.38; H, 9.27.
C33H54O9 requires C, 66.64; H, 9.15%); νmax/cmϪ1 (neat) 2940,
2867, 1604, 1455, 1352, 1201, 1124, 1078, 1036, 987, 871 and
815; δH (400 MHz, CDCl3) 1.40–1.87 (18 H, m, THP-3,4,5-H),
2.82 (6 H, t, J 7.3, ArCH2), 3.46 (3 H, m, OCH2), 3.52–3.70
(15 H, m, OCH2), 3.83 (6 H, m. OCH2), 4.60 (3 H, t, J 3.7, 3 H,
THP-2-H) and 6.90 (3 H, s, ArH); δC (100.6 MHz, CDCl3) 19.3
(THP-C-4), 25.3 (THP-C-5), 30.4 (THP-C-3), 36.0 (ArCH2),
62.0 (OCH2), 66.5 (OCH2), 70.1 (OCH2), 72.2 (OCH2), 98.7
(THP-C-2), 127.3 (ArH) and 138.8 (Ar); m/z (EI) 333 (5%), 331
(8), 290 (4), 218 (22), 199 (15), 156 (23), 144 (100), 129 (32), 85
(65), 84 (90), 55 (83) and 41 (43).
requires 366.2195); νmax/cmϪ1 (neat) 3289 (Csp–H), 3017, 2916,
᎐
2864, 2794, 2120 (C᎐C), 1604, 1459, 1364, 1112 (C–O), 868 and
᎐
᎐
642; δ (400 MHz, CDCl ) 2.00 (3 H, t, J 2.7, C᎐CH), 2.46 (6 H,
᎐
H
3
᎐
dt, J 2.7, 6.9, CH C᎐C), 2.85 (6 H, t, J 7.2, ArCH ), 3.58 (6 H, t,
᎐
2
2
J 6.9, OCH2), 3.67 (6 H, t, J 7.3, OCH2) and 6.95 (3 H, s, ArH);
᎐
δ (100.6 MHz, CDCl ) 19.7 (CH C᎐CH), 36.0 (ArCH ), 68.8
᎐
C
3
2
2
᎐
᎐
(OCH ), 69.3 (C᎐CH), 71.8 (OCH ), 81.3 (C᎐CH), 127.4 (ArH)
᎐
᎐
2
2
and 138.8 (Ar); m/z (EI) 366 (Mϩ, 3%), 296 (5), 283 (5), 268 (5),
257 (7), 227 (12), 213 (32), 187 (20), 157 (14), 129 (12), 91 (17),
83 (20) and 53 (100).
sym-[5.5.5]Trioxacyclophanes 1c and iso-1c
1,3,5-Tris[2-(2-hydroxyethoxy)ethyl]benzene 7
o-Xylene (900 cm3) was distilled from sodium–benzophenone
into a flask under dry argon and degassed by seven successive
evacuation and flushing cycles with argon while stirring.
CpCo(CO)2 (0.700 cm3; technical grade) was added and the
mixture was heated at 155 ЊC. A solution of triyne 9 (1.49 g,
4.07 mmol) in the degassed o-xylene (20 cm3) was added via
syringe pump over an 18 h period. Additional CpCo(CO)2 (1.05
cm3) was also added over a period of 15 h, starting 3 h after the
addition of triyne was begun. The mixture was kept stirring for
further 3 h and then allowed to cool to RT. The solvent was
evaporated and the residue triturated with 1:1 ether:CH2Cl2
(20 cm3) and filtered. The solid was then washed with CH2Cl2
(3 × 5 cm3) and the combined filtrates evaporated. Chrom-
atography of the crude product on silica (4:1→1:1 petrol-
eum ether–ether) gave the starting material 9 (414 mg), a mixed
fraction of 1c:iso-1c (5:95, 466 mg) and a second mixed frac-
tion of 1c:iso-1c (86:14, 307 mg). The pure isomers could be
isolated by recrystallization from n-hexane, giving 1c (231 mg,
16%) and iso-1c (410 mg, 28%) as colourless crystals. The over-
all yield of the mixture was 52% (19% of 1c, 33% of iso-1c,
ratio: 1:1.7) or 72% based on conversion.
To a solution of the tris-THP-ether 6 (4.98 g, 8.37 mmol) in
methanol (200 cm3) was added conc. HCl (10 drops). After
standing for 14 h solid K2CO3 (1.0 g) was added. The mixture
was stirred for 0.5 h, filtered and the solvent evaporated. The
residue was chromatographed on silica (10:1→7:1 ether–
MeOH) to give 7 (2.77 g, 97%) as a colourless oil (HRFABMS:
M ϩ H, 343.2087. C18H31O6 requires 343.2121); νmax/cmϪ1
(neat) 3398 (OH), 2928, 2865, 1604, 1458, 1358, 1119, 1052,
890, 869 and 713; δH (400 MHz, CDCl3) 2.53 (3 H, t, J 6.2, OH),
2.86 (6 H, t, J 6.5, ArCH2), 3.54 (6 H, m, OCH2), 3.65 (6 H, m,
CH2OH), 3.72 (6 H, t, J 6.5, OCH2) and 6.97 (3 H, s, ArH);
δC (100.6 MHz, CDCl3) 35.9 (ArCH2), 61.4 (CH2OH), 71.7
(OCH2), 71.9 (OCH2), 127.3 (ArH) and 139.0 (Ar); m/z (FAB)
343 (M ϩ 1, 92%), 219 (53), 157 (78), 154 (100) and 136 (72).
1,3,5-Tris[2-(2-bromoethoxy)ethyl]benzene 8
To a stirred solution of triol 7 (2.745 g, 8.02 mmol) and tri-
ethylamine (9.73 g, 96.2 mmol) in CH2Cl2 (15 cm3) at Ϫ40 ЊC
was added mesyl chloride (5.51 g, 48.1 mmol) over a period of
10 min. The mixture was allowed to warm to RT. After stirring
for 20 h and then an additional 4.5 h at 45 ЊC, sat. aq. NH4Cl
(50 cm3) was added. The aqueous phase was extracted with
CH2Cl2 (2 × 75 cm3) and the combined organic extracts were
washed with sat. aq. NaCl (50 cm3), dried over MgSO4 and the
solvent evaporated. THF (50 cm3) was added to the residue
followed by LiBr (18.8 g, 216 mmol) in five portions with stir-
ring and cooling so that the temperature did not rise above
40 ЊC. After 20 h the solvent was evaporated and the residue
partitioned between sat. aq. NH4Cl (50 cm3) and ether (100
cm3). The aqueous phase was extracted with ether (3 × 100 cm3)
and the combined organic extracts were washed with sat. aq.
NaCl (50 cm3) and dried over MgSO4. Chromatography on
silica (2:1 petroleum ether–ether) gave the tribromide 8 (3.63 g,
85%) as a colourless oil (Found: C, 40.98; H, 5.41. C33H54O9
requires C, 40.71; H, 5.12%); νmax/cmϪ1 (neat) 3017, 2916, 2864,
2791, 1604, 1458, 1361, 1275, 1118 (C–O), 1043, 712 and 667;
δH (400 MHz, CDCl3) 2.87 (6 H, t, J 7.1, ArCH2), 3.46 (6 H, t,
J 6.1, CH2Br), 3.71 (6 H, t, J 7.1, OCH2CH2Ar), 3.78 (6 H, t,
J 6.1, OCH2CH2Br) and 6.97 (3 H, s, ArH); δC (100.6 MHz,
CDCl3) 30.4 (CH2Br), 36.1 (ArCH2), 70.7 (OCH2), 72.1
(OCH2), 127.5 (ArH) and 138.8 (Ar); m/z (EI) 532 (M ϩ 4,
1.1%), 530 (M ϩ 2, 1.1), 528 (Mϩ, 0.2), 405 (7), 281 (58), 157
(62) , 107 (70), 83 (41), 74 (63), 59 (100) and 45 (78).
1c. Mp (n-hexane) 185–186 ЊC (Found: C, 78.47; H,
8.25. C24H30O3 requires C, 78.65; H, 8.25%); νmax/cmϪ1 (KBr)
3016, 2934, 2896, 2852, 2789, 1605, 1459, 1360, 1256, 1229,
1128 (C–O), 1046, 836 and 700; δH (250 MHz, CDCl3) 2.68 (12
H, t, J 5.5, ArCH2), 3.69 (12 H, t, J 5.5, OCH2) and 6.66 (6 H, s,
ArH); δC (100.6 MHz, CDCl3) 35.7 (ArCH2), 70.4 (OCH2),
126.1 (ArH) and 138.6 (Ar); m/z (EI) 366 (Mϩ, 100%).
iso-1c. Mp (n-hexane) 117–119 ЊC (Found: C, 78.74; H, 8.52.
C24H30O3 requires C, 78.65; H, 8.25%); νmax/cmϪ1 (KBr) 3014,
2905, 2859, 2785, 1603, 1458, 1360, 1258, 1121 (C–O), 1040,
820 and 704; δH (500 MHz, CDCl3) 2.38–2.48 (2 H, m, ArCH2),
2.60–2.75 (6 H, m, ArCH2), 2.79 (2 H, m, ArCH2), 2.85–2.95
(2 H, m, ArCH2), 3.29 (1H, m, OCH2), 3.44 (1 H, m, OCH2),
3.52–3.58 (2 H, m, OCH2), 3.62 (2 H, m, OCH2), 3.75 (2 H, m,
OCH2), 3.77–3.86 (2 H, m, OCH2), 3.92–3.98 (2 H, m, OCH2),
6.48 (1 H, s, ArH), 6.63 (1 H, s, ArH), 6.84 (1 H, d, ArH),
6.85 (1 H, s, ArH), 6.89 (1 H, s, ArH) and 6.94 (1 H, dd, ArH);
δC (125.8 MHz, CDCl3) 30.4, 31.8, 35.8, 35.9, 36.3, 37.0
(ArCH2), 69.6, 70.2, 70.5, 71.0, 71.8, 72.5 (OCH2), 125.0, 126.2,
126.7, 127.3, 127.8, 128.0 (ArH), 135.7, 136.7, 137.7, 138.8,
139.26 and 139.33 (Ar); m/z (EI) 366 (Mϩ, 100%), 348 (4), 321
J. Chem. Soc., Perkin Trans. 1, 1998, 3371–3376
3375

View Article Online
(11), 204 (32), 186 (67), 175 (50), 174 (48), 159 (72), 156 (80),
145 (74), 131 (59), 129 (67), 117 (58), 105 (27) and 91 (69).
References
1 D. J. Cram and H. Steinberg, J. Am. Chem. Soc., 1951, 73, 5691.
2 J. Dale, Angew. Chem., Int. Ed. Engl., 1966, 5, 1000.
3 This naturally assumes that the linking chains provide for a
sufficient separation between the two π-systems. For methylene
groups, the first odd number to satisfy this condition is 5.
4 A literature search for [n.n]paracyclophanes and sym-[n.n.n]cyclo-
phanes from n = 5 to 12 was performed where the atoms could be
any non-metal with any substituent, but with the condition
that the bridging atoms participate in single bonds only. This
query produced an equal number of [odd.odd] and [even.even]
paracyclophanes (92 each), and 19 [odd.odd.odd] versus 16
[even.even.even] sym-[n.n.n]cyclophanes.
5 For example, the [-CH2N(CH2)3NCH2-]-bridged- (K. E. Krakowiak
and J. S. Bradshaw, J. Heterocycl. Chem., 1996, 33, 1) and [-N-
(R)CH2CH2OCH2CH2N(R)-]-bridged- (P. L. Anelli, L. Lunazzi,
F. Montanari and S. Quici, J. Org. Chem., 1984, 49, 4197) sym-
[7.7.7]cyclophanes.
6 Cambridge Structural Database Ver. 5.15 (181309 structures, April
1998 release): F. H. Allen and O. Kennard, Chemical Design
Automation News, 1993, 8, 31. Note here that no examples of sym-
[n.n.n]cyclophanes with saturated bridges occur in the Database.
7 R. Benn, N. E. Blank, M. W. Haenel, J. Klein, A. R. Koray,
K. Weidenhammer and M. L. Ziegler, Angew. Chem., Int. Ed. Engl.,
1980, 19, 44.
Single crystal structure determination of 1a
C24H33N3, M = 363.53, colourless tablet 0.50 × 0.50 × 0.30
mm3, monoclinic, space group P21/c (No. 14), a = 12.736(6),
b = 15.371(6), c = 10.676(5) Å, β = 94.12(8)Њ, U = 2084.7(16) Å3,
Z = 4, Dc = 1.158 g cmϪ3, µ(Mo-Kα) = 0.068 mmϪ1, T = 150(2)
K. Data were collected on a Stoe Stadi-4 four-circle diffracto-
meter using graphite-monochromated Mo-Kα radiation
(λ = 0.71073 Å) and ω/θ scans to 2θmax = 50Њ. Of a total of 5202
reflections measured, 3683 were unique (Rint = 0.092): of these
2412 had Fo у 4σ(Fo) and 3680 were used in all calculations.
No crystal decay was observed and no corrections were applied
for absorption. The structure was solved by automatic direct
methods (all non-H atoms)22 and refined23 by full-matrix least-
squares on F2 with all non-H atoms assigned anisotropic dis-
placement parameters. Amine H atoms were located from ∆F
syntheses; other hydrogen atoms were placed geometrically,
thereafter these were refined freely and constrained to ride on
their parent C atoms, respectively. The weighting scheme wϪ1
=
2
2
2
1
2
2
–
[σ (Fo ) ϩ (0.062P) ϩ 1.03P], P = [MAX(Fo ,0) ϩ 2Fc ], gave
3
8 This is shown by molecular mechanics simulations (MACRO-
MODEL ver. 4.0 with the MM3 force field: F. Mohamadi, N. G.
J. Richards, W. C. Guida, R. Liskamp, M. Lipton, C. Caufield, G.
Chang, T. Hendrickson and W. C. Still, J. Comput. Chem., 1990,
11, 440). The next conformationally stable homologue, the [7.7.7]
cyclophane, has an Ar ؒ ؒ ؒ Ar separation some 3 Å greater than the
[5.5.5] system.
satisfactory agreement analyses and final R1 [Fo у 4σ(Fo)] =
0.0585, wR2 (all data) = 0.1578, S(F2) = 1.04, for 253 refined
parameters. The final ∆F synthesis showed no features outside
the range 0.21 e ÅϪ3.
Single crystal structure determination of 1c
9 On the nature of arene η1 and η2 complexes in the solid state,
M. Mascal, submitted for publication.
C24H30O3, M = 366.48, colourless hexagonal tablet 0.47 × 0.47 ×
0.19 mm3, monoclinic, space group P21/c (No. 14), a =
12.592(7), b = 15.123(13), c = 10.737(7) Å, β = 95.50(7)Њ, U =
2035(2) Å3, Z = 4, Dc = 1.196 g cmϪ3, µ(Mo-Kα) = 0.077 mmϪ1,
T = 150(2) K. Data were collected on a Stoe Stadi-4 four-
circle diffractometer using graphite-monochromated Mo-Kα
X-radiation (λ = 0.71073 Å) and ω/θ scans. Of a total of 4266
10 M. Mascal, J.-L. Kerdelhué, A. S. Batsanov and M. J. Begley,
J. Chem. Soc., Perkin Trans. 1, 1996, 1141.
11 Preliminary communication: M. Mascal, J. Hansen, A. J. Blake and
W.-S. Li, Chem. Commun., 1998, 355.
12 F. Vögtle and R. G. Lichtenthaler, Angew. Chem., Int. Ed. Engl.,
1972, 11, 535.
13 M. Kanishi, J. Kunizaki, J. Inanaga and M. Yamaguchi, Bull. Chem.
Soc. Jpn., 1981, 54, 3828.
reflections measured to 2θmax = 50Њ, 3552 were unique (Rint
=
14 Review: K. P. C. Vollhardt, Angew. Chem., Int. Ed. Engl., 1984, 23,
539.
15 A. J. Hubert, J. Chem. Soc. (C), 1967, 6.
0.059), giving 2673 with F у 4σ(F) and 3552 which were
retained in all calculations. No crystal decay was observed and
no corrections were applied for absorption. The structure was
solved by automatic direct methods (all non-H atoms),22 and
refined by full-matrix least squares23 with all non-H atoms
anisotropic; hydrogen atoms were introduced at geometrically
calculated positions and thereafter constrained to ride on their
parent C with Uiso(H) = 1.2Ueq(C). The weighting scheme
16 M. S. Newman and H. S. Lowrie, J. Am. Chem. Soc., 1954, 76, 6196.
17 Review: R. H. Crabtree, Angew. Chem., Int. Ed. Engl., 1993, 32, 789.
18 Cambridge Structural Database refcodes: CELKEJ(01),
ENCCBP10, GALTUI, JOBVUR, KAHBIE(10), LEDTIX. The
conditions for eta complexation were met when a (generalized)
metal was closer to a single carbon atom of an arene ring than to the
midpoint of the bond connecting that carbon to the adjacent ring
carbon (eta-1), or when the metal was closer to the midpoint of an
arene carbon–carbon bond than to either of the carbon atoms
between which the bond is made (eta-2). The metal to carbon (or
metal to bond midpoint) distance was limited to 3.0 Å and the
metal–carbon (or midpoint)–aryl centroid angle was limited to the
range 80–100Њ.
2
2
2
1
2
2
wϪ1 = [σ (Fo ) ϩ (0.027P) ϩ 1.38P], P = [MAX(Fo ,0) ϩ 2Fc ]
–
3
gave satisfactory agreement analyses. Final R1[F у 4σ(F)] =
0.0493, wR2 [all data] = 0.1139, S[F2] = 1.18 for 245 refined
parameters. An extinction correction refined to 0.0045(6) and
the final ∆F synthesis showed no features outside the range
0.20 e ÅϪ3.
Full crystallographic details, excluding structure factor
tables, have been deposited at the Cambridge Crystallographic
Data Centre (CCDC). For details of the deposition scheme, see
‘Instructions for Authors’, J. Chem. Soc., Perkin Trans. 1, avail-
able via the RSC Web page (http://www.rsc.org/authors). Any
request to the CCDC for this material should quote the full
literature citation and the reference number 207/261.
Fig. 2–5 were produced using SHELXTL/PC.24
19 The equation ∆G‡ = RTc [(22.96 ϩ ln (Tc/δν)] was used: R. K.
Harris, Nuclear Magnetic Resonance Spectroscopy—A Physico-
chemical Approach, Pitman, London, 1983.
20 Eta-1 complexation to silver has been discussed (K. Shelly, D. C.
Finster, Y. J. Lee, R. Scheidt and C. A. Reed, J. Am. Chem. Soc.,
1985, 107, 5955), and a good structural analogy can be drawn
between [Ag(1a)]OTf and the (η1)3-silver-deltaphane (1,2,4,5-
[2.2.2.2.2.2]cyclophane) complex (H. C. Kang, A. W. Hanson,
B. Eaton and V. Boekelheide, J. Am. Chem. Soc., 1985, 107, 1979).
21 W. P. Cochrane, P. L. Paulson and T. S. Stevens, J. Chem. Soc. (C),
1968, 630.
For the crystal data for [Cu1a]BF4ؒH2O and [Ag1a]OTf
consult ref. 11.
22 G. M. Sheldrick, SHELXS-96. Acta Crystallogr., Sect. A, 1990, 46,
467.
23 G. M. Sheldrick, SHELXL-96. University of Göttingen, Germany,
1996.
24 G. M. Sheldrick, SHELXTL/PC ver. 5.03, Siemens Analytical
Instrumentation Inc., Madison, WI, USA, 1994.
25 The United Kingdom Chemical Database Service: D. A. Fletcher,
R. F. McMeeking and D. Parkin, J. Chem. Inf. Comput. Sci., 1996,
36, 746.
Acknowledgements
This research was supported by a grant from the European
Commission (to J. H.), and we would like to thank Professor
Martin Schröder for helpful discussions. The use of the
EPSRC’s Chemical Database Service at Daresbury is also
acknowledged.25
Paper 8/05646C
3376
J. Chem. Soc., Perkin Trans. 1, 1998, 3371–3376