Big macrocyclic assemblies of carboranes (big MACs): Synthesis and crystal structure of a macrocyclic assembly of four carboranes containing alternate ortho- and meta-carborane icosahedra linked by para-phenylene units

Article abstract of DOI:10.1016/S0022-328X(03)00313-9

The macrocyclic compound, [1,2-C₂B₁₀ H₁₀-1,4-C₆H₄-1,7-C₂ B₁₀H₁₀-1,4-C₆H₄] ₂ (5)-a novel cyclooctaphane, was prepared by condensation o

Full text of DOI:10.1016/S0022-328X(03)00313-9

Journal of Organometallic Chemistry 680 (2003) 155ꢁ164
/
www.elsevier.com/locate/jorganchem
Big macrocyclic assemblies of carboranes (big MACs): synthesis and
crystal structure of a macrocyclic assembly of four carboranes
containing alternate ortho- and meta-carborane icosahedra linked by
para-phenylene units
Mark A. Fox *, Judith A.K. Howard, J.A. Hugh MacBride, Angus Mackinnon,
Kenneth Wade *
Chemistry Department, Durham University Science Laboratories, South Road, Durham DH1 3LE, UK
Received 28 February 2003; received in revised form 2 April 2003; accepted 17 April 2003
Dedicated to Prof. Fred Hawthorne, pioneer and world authority on carborane and borane chemistry, on the occasion of his 75th birthday
Abstract
The macrocyclic compound, [1,2-C2B10H10-1,4-C6H4-1,7-C2B10H10-1,4-C6H4]2 (5)*
condensation of the C,C?-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)-ortho-carborane. The X-ray crystal
structure of 5×C6H6×6C6H12 was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic
/a novel cyclooctaphane, was prepared by
/
/
Cs and local C2v symmetry; the macrocycle adopts a butterfly (dihedral angle 1438) conformation with the ortho-carborane units at
the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that
molecule 5 in solution inverts rapidly via the planar D2h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal
molꢀ1 higher in energy than the C2v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and
three ortho-carborane units linked by six para-phenylene units, was unsuccessful.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Macrocycle; Carborane icosahedra; Butterfly conformation
1. Introduction
macrocyclic assemblies of metallacarborane polyhedra
linked by metal or organic units [10].
Over the past decade there has been much interest in
macrocyclic assemblies of carborane polyhedra linked
In Durham, we have focused on macrocycles of more
rigidly defined geometry in which carborane icosahedra
are linked through aromatic (phenylene or pyridylene)
by organic units or metal atoms [1ꢁ9]. Hawthorne has
/
rings [6ꢁ8]. Our aim was to generate carborane assem-
/
prepared macrocycles in which ortho-carborane icosa-
hedra are linked through flexible organic linkers and has
shown how the flexibility and multiple Lewis acidity of
macrocycles with alternating ortho-carborane icosahe-
dra and mercury atoms (mercuracarborands) provides
scope for their use in molecular recognition, optical
sensors and catalysis [1]. There is also recent interest in
blies which, subjected to deboronation and metallation
reactions, would in turn afford metallacarborane assem-
blies in which the metal atoms were held close enough
together to participate in collaborative di- or tri-metallic
reactions of potential catalytic interest [8].
To date, our work has primarily concerned systems
like compounds 1ꢁ3 (Fig. 1) formally derived from the
/
known organic macrocycle 4, hexa-meta-phenylene [11],
by replacement of selected benzene rings in 4 by meta-
carborane icosahedra (and by pyridine rings in the case
of 2). That planar hexagonal organic ring systems can
formally be replaced by 3-dimensional carborane icosa-
* Corresponding authors. Tel.: ꢂ
384-4737.
E-mail
kenneth.wade@durham.ac.uk (K. Wade).
/
44-191-374-3138; fax: ꢂ
/
44-191-
addresses:
m.a.fox@durham.ac.uk
(M.A.
Fox),
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00313-9

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M.A. Fox et al. / Journal of Organometallic Chemistry 680 (2003) 155ꢁ164
/
Fig. 1. Macrocycles incorporating carboranes: relationship to cyclo-phenylenes.
hedra without excessive bond angle strain is a valuable
consequence of the similarity between the preferred
angles between bonds to substituents on a benzene
ring (60, 120, 1808 for ortho-, meta- or para-substitu-
ents, respectively) and those to the carbon atoms of the
parent icosahedral carboranes (53, 115 and 1808,
respectively) [12].
Here we report the extension of this work to macro-
cycle 5 (Fig. 1), which we believe to be the first
phenylene-linked assembly of carborane icosahedra to
contain both ortho- and meta-carborane units. We have
described this compound previously in conference
proceedings [13]. The octa(phenylene) analogue of 5,
compound 6, has not to our knowledge been reported.
8 directly from acetylene and 1,4-diiodobenzene (we
obtained an intractable mixture of oligomers in a similar
experiment), and that we used the dimethyl sulfide,
rather than the acetonitrile, complex of decaborane,
B10H12L2 (LꢃMe2S).
/
Ring-closing reactions in attempted syntheses of
macrocycles are notoriously prone to acyclic by-product
formation, and the final stage in our synthesis of
compound 5 (Scheme 1) proved no exception. Reaction
of the bis(iodophenyl)carborane 9 with di-copper(I)
meta-carborane 10, needing the formation of four new
carbonꢁcarbon bonds to complete the macrocycle, gave
/
a mixture of six main components from which some 9%
yield of compound 5 was isolated by a combination of
chromatography and fractional crystallisation. A by-
product compound 11 (Fig. 2) was also isolated and
characterized by NMR, IR and mass spectroscopy. The
mass spectra of the other fractions showed what we
believe were molecular ions appropriate for the masses
2. Results and discussion
2.1. Synthetic aspects
of compounds 12ꢁ15, which were not however fully
/
separated. Their structures are inferred on the assump-
tion that no unexpected reaction, particularly cleavage
The steps by which compound 5 was prepared are
shown in Scheme 1. Details are given in Section 3.
Because ortho-carborane, unlike meta or para, is only
mono-arylated when its di-copper(I) derivative reacts
with aryl iodides [14,15], it was necessary to attach the
aryl substituents to what were to become the carborane
skeletal carbon atoms before the carborane cage was
prepared from the alkyne and decaborane. 1,2-Bis(4-
iodophenyl)-ortho-carborane has been prepared pre-
viously [16,17]. Our route differs from that used by the
earlier workers in that they obtained the di-iodoarylyne
of phenylꢁ
tion, giving compound 14, could result from copper/
iodine exchange and subsequent protolysis of the arylꢁ
/
carborane bonds, has occurred. De-iodina-
/
copper links on work-up.
A further reaction explored was that between the
bis(iodophenyl) carborane 9 and the di-copper(I) deri-
vative of para-carborane 16, in the hope that the
triangular macrocycle 17 (Scheme 2), containing three
ortho- and three para-carborane icosahedra, might

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/164
157
Scheme 1. Synthesis of macrocycle 5, [1,2-C2B10H10-1,4-C6H4-1,7-C2B10H10-1,4-C6H4]2.
form. This reaction gave a complex mixture containing
at least 10 components in addition to some unchanged
starting material 9, probably all carboranes judged by
their similar fluorescent properties on thin layer chro-
matography (TLC). Mass spectrometry of the more
abundant fractions did not reveal any of the desired
product, compound 17. Two products from the reaction
were identified from mass and infra-red spectroscopy as
Fig. 2. By-products detected in the synthesis of 5.

158
M.A. Fox et al. / Journal of Organometallic Chemistry 680 (2003) 155ꢁ164
/
Scheme 2. Attempted synthesis of macrocycle 17, [1,2-C2B10H10-1,4-C6H4-1,12-C2B10H10-1,4-C6H4]3.
the iodo-compound 18 and the three cage assembly 19
(para-carborane analogues of compounds 11 and 12,
respectively).
So far, carborane macrocycles with rigid aromatic
links successfully synthesized are limited to those con-
observed NMR data indicate the macrocycle either has
planar symmetry (D2h) or apparent D2h symmetry
arising from fast equilibrium between two folded con-
formations via planar symmetry. By comparison with
the reported [20] NMR data for 1,2-diphenyl-ortho- and
1,7-diphenyl-meta-carboranes the peaks corresponding
to the cage borons and carbons in the macrocycle are
assigned.
However, assignments of the cage proton peaks in the
macrocycle here are less straightforward. It has pre-
viously been shown for the meta-carborane macrocycle
1 that the internal cage protons attached to B2 and B3
resonate at significantly lower field (higher frequency)
than those in related diaryl-meta-carboranes [6]. This
arises from the rigid aryl orientations at the cage carbon
atoms in 1 whereas the aryl groups in diaryl-meta-
carboranes are freely rotating. For the macrocycle 5,
however, the orientations of the aryl groups at the cage
carbons of the meta-carborane are different from those
in 1. As a result, the internal cage protons attached to
B2 and B3 in 5 resonate at significantly higher field
(lower frequency) than related diaryl-meta-carboranes.
Proton NMR shifts calculated from optimized geome-
tries of 1 and 5 at the GIAO-RHF/6-31G*//RHF/6-
31G* level are in agreement with the shifts observed for
taining meta-carborane links (1ꢁ
/
3 and 5) [6ꢁ8]. Our
/
unsuccessful attempts in synthesizing macrocycles con-
taining only ortho- and/or para-carborane and phenyl-
ene links here and elsewhere [18,19] suggest that these
cycles are unlikely to prove readily accessible.
2.2. Spectroscopic aspects
The proton NMR spectrum of the macrocycle 5 in
CDCl3 shows two doublets, with second-order effects, in
the aromatic region at 7.26 and 7.17 ppm corresponding
to protons adjacent to ortho- and meta-carborane
substituents on the benzene ring. The observed coupling
3
constant of 8.5 Hz is expected for JHH couplings in
substituted benzenes. The boron-decoupled proton
spectrum of 5 shows five lines in the BH region, with
intensities of 1:1:6:1:1 while the proton-decoupled boron
NMR spectrum of 5 shows three broad peaks of 1:1:8
intensity ratio. Carbon-13-NMR data for 5 reveal six
peaks with four in the aromatic region. All these

M.A. Fox et al. / Journal of Organometallic Chemistry 680 (2003) 155ꢁ
/164
159
these internal cage protons. Clearly these observations
indicate the way cage proton chemical shifts in diaryl-
meta-carboranes depend on the aryl orientations. Aver-
aged cage proton chemical shifts are observed in aryl
carboranes where the aryl groups are freely rotating.
deliberately introduced at any stage of preparation, but
turned out to be present as a trace contaminant of the
cyclohexane used for chromatography and recrystallisa-
tion. In the crystal, each benzene molecule is ‘wedged’
into the concave side of the annular cavity of the
macrocycle, a cavity too small to accommodate a
cyclohexane molecule (Fig. 4).
2.3. Structural aspects
The 5×
/
C6H6 units occupy only 39% of the unit cell
volume; infinite channels, parallel to the x-axis and
The form in which macrocycle 5 crystallised from
filled with cyclohexane of crystallisation, account for
51% of the volume. Within these channels, the average
cyclohexane, as 5×
/
C6H6×
/
6C6H12, proved to have several
interesting features, some unexpected. They included the
rare space group (Cmc21, occurrence below 0.2% in the
Cambridge Crystallographic Database [21]), the high
degree of solvation, the unexpected presence of benzene
scavenged as a minor contaminant from the cyclohexane
solvent and the spacious packing mode of the cyclohex-
ane molecules.
3
volume per cyclohexane molecule (194 A ) vastly
˚
3
exceeds that in pure crystalline cyclohexane (160 A at
˚
3
195 K, 140 A at 115 K) [22]. Though spacious, this
˚
packing mode leaves no continuous residual void, large
enough for another solvent molecule, but accounts for
the relatively high displacement parameters found, and
also explains why the crystals are stable at ambient
temperature only under mother liquor, and quickly
losing solvent and crystallinity (and some of the
observed Bragg’s reflections) when exposed to air.
The para-phenylene rings lie approximately at right
angles to the overall molecular plane, face-to-face as is
usual (for steric reasons) for diaryl-ortho-carboranes
The butterfly-shaped molecule (Fig. 3) lies on a
crystallographic mirror plane, which bisects both
meta-carborane cages. Thus the asymmetric unit com-
prises half a molecule of 5, together with three cyclo-
hexane molecules of crystallisation and, unexpectedly,
half a molecule of benzene, which also lies astride the
mirror plane. It is noteworthy that benzene was not
[19,23,24]. Phenyl group orientations in Cꢁ
carboranes are usually described by their u angles, the
difference between 908 and the moduli of the cage Cꢁ
cage Cꢁaryl Cꢁaryl C torsion angles [23]. When u is
/
aryl-ortho-
/
/
/
908, the cage carbons lie in the plane of the phenyl ring
but when u is 08 they lie in a plane perpendicular to the
phenyl ring. In macrocycle 5 the u values are 1.2 and
7.68, within the values of 0.9ꢁ27.68 found for other
/
diaryl-ortho-carboranes [23,24], tilting very slightly to-
wards the benzene molecule.
The BÃ
tional for carborane cage or aryl ring systems [6,8,23ꢁ
25]. The cage C C distances in the carborane icosahe-
Á Á Á
/
B, BÃ
/
C and CÃ
/
C distances in 5 are unexcep-
/
/
/
˚
dra are 1.72 (1) A in the ortho-carborane cages and 2.67
˚
(1) A in the meta-cages.
Although in principle macrocycle 5 might be planar
(D2h) without significant bond angle strain, in the
Fig. 3. Molecules of 5 and benzene viewed in the structure of 5×
/
C6H6×
/
6C6H12, showing 30% displacement ellipsoids. Projections on the
planes (0 0 1) [top] and (0 1 0) [bottom]. Atoms, symmetrically related
˚
via mirror plane, are labelled A. Selected bond distances (A): C1ÃC2
/
1.72(1), C1Ã
1.50(1). Selected bond angles (8): C1Ã
118.4(7).
/
C29 1.50(1), C2Ã
/
C35 1.50(1), C13Ã
/
C32 1.52(1), C21Ã
/
C38
/
C2-C35 118.9(6), C2Ã
/
C1Ã
/
C29
Fig. 4. Space-filling plot of molecules of 5 and benzene. Sphere radii
are proportional to the respective van der Waals’ radii.

160
M.A. Fox et al. / Journal of Organometallic Chemistry 680 (2003) 155ꢁ164
/
crystal it adopts a butterfly conformation of approx-
imate C2v symmetry, with the ortho-carborane moieties
at the ‘wingtips’, and with a dihedral angle between the
wing planes of 1438 (calculated by the positions of the
cage carbons). The phenylene substituents subtend
angles (calculated from four cage carbons) of 58.48 at
the ortho-carborane cages and of 112.48 at the meta
carborane cages, within the ranges typical for diaryl-
carboranes [23,25].
CDCl3 solution except where stated using Varian Unity-
300 (1H, 11B, 13C), Bruker AM250 (1H, 13C) and/or
Varian Inova 500 (1H, 11B) instruments. All chemical
shifts are reported in d (ppm) and coupling constants in
Hz. 1H-NMR spectra were referenced to residual protio
impurity in the solvent (CDCl3, 7.26 ppm). 13C-NMR
spectra were referenced to the solvent resonance (CDCl3
77.0 ppm). 11B-NMR spectra were referenced externally
to Et2O.BF3, dꢃ
/
0.0 ppm. Peak assignments of cage
To clarify the relation between the butterfly confor-
mation of 5 in the solid state and the apparent D2h
symmetry from NMR data, we performed ab initio
calculations of molecule 5 (Fig. 5). The optimisation of
its geometry with an imposed C2v symmetry constraint
resulted in a butterfly conformation with the fold (inter-
wing) angle of 151.48, similar to that found in the
crystal. The optimisation with a D2h symmetry con-
straint (i.e. an imposed planarity of the macrocycle)
gave the energy only ca. 1 kcal molꢀ1 higher. Thus it is
feasible for molecule 5 in solution to undergo rapid
inversion between two opposite butterfly conformations
over the low potential barrier of the planar structure, in
agreement with NMR data.
borons, hydrogens and carbons were determined with
1
1
the aid of selective H{11B}, correlated Hꢁ13
C spectra
/
and comparison with literature values of related aryl
carboranes [19,20,27]. Mass spectra were recorded on a
VG Micromass 7070E instrument under EI conditions
at 70 eV unless otherwise stated.
All reactions (except diazotisation) were conducted
under dry nitrogen. Butyllithium refers to the solution in
hexanes of the stated concentration. TLC was con-
ducted on pre-spread silica coated sheet Merck Art. No.
5735. Chromatographic silica refers to Merck Art. No.
9385.
3.1. Bis-(4-aminophenyl)ethyne 7
4-Iodoaniline (44.0 g) in diethylamine (100 cm3) was
stirred while a solution, prepared under dinitrogen by
warming palladium chloride bis-triphenyl phosphine
(153 mg) and copper(I) iodide (54 mg) with piperidine
(8 cm3), was added by syringe. The dinitrogen supply to
the flask was replaced by acetylene (admitted above the
liquid surface) at ca. 10 cm3 minꢀ1 from a cylinder via a
bubbler charged with concentrated sulfuric acid. After
40 h the solid product was filtered off in air, washed with
3. Experimental
Dimethoxyethane was dried by distillation from
potassium. Solutions were dried over sodium sulfate
and evaporated in vacuum using a rotary evaporator.
Copper(I) chloride was purified by the method of
Whitesides et al. [26] and stored under nitrogen. Infrared
spectra were recorded as KBr discs on a PerkinꢁElmer
1600 series FTIR and NMR spectra were measured in
/
diethylamine (3ꢄ
/
20 cm3) and water (2ꢄ35 cm3) and
/
dried in vacuum at 78 8C to give a light brown powder
(11.5 g, 55%) pure enough for use in the next prepara-
tion. A sample recrystallised from ethanol had m.p.
237ꢁ240 8C, literature [28] 236 8C.
/
3.2. 1,2-Bis (4-iodophenyl) ethyne 8
The diamine 7 (11.5 g) was suspended in a warm
solution of sulfuric acid (22.0 cm3) in water (88 cm3) and
cooled in ice to ca. 2 8C. Sodium nitrite (8.2 g) in water
(40 cm3) was added dropwise with stirring, keeping the
temperature 4ꢁ6 8C, during 45 min. After a further 15
/
min the turbid solution was added in small portions to a
well-stirred solution of potassium iodide (94 g) in water
(100 cm3) contained in a large (e.g. 1.5 l) beaker to
accommodate foaming. After 2 h the precipitate was
filtered off and washed with water and with dilute
sodium bisulfite solution and dried in vacuo at 78 8C to
give the slightly impure di-iodo-compound (22.5 g, 95%)
as an ochreꢁ
/
yellow powder. Recrystallisation from
toluene (380 cm3) using charcoal gave the pure com-
Fig. 5. HF/6-31G* optimized geometries of macrocycle 5. Top
geometry A (C2v ) Bottom geometry B (D2h ).

M.A. Fox et al. / Journal of Organometallic Chemistry 680 (2003) 155ꢁ
/164
161
pound (15.0 g, 63%) m.p. 243ꢁ
/
245 8C, literature [29]
solution was applied to a column of chromatographic
silica (120 g) and eluted with the same solvent in
fractions of 25 cm3. Fractions were examined by TLC
on silica using 2.5% v/v ethyl acetate in cyclohexane; nos
12 and 13 contained mainly the starting di-iodocom-
pound (Rf 0.75). Fractions 15 and 16 (Rf 0.55) were set
238ꢁ239 8C.
/
3.3. 1,2-Bis (4-iodophenyl)-ortho-carborane 9
The di-iodoalkyne 8 (15.0 g) was suspended in toluene
(90 cm3) and decaborane dimethylsulfide complex (12.68
g) was added. The mixture was heated slowly to bath
aside and fractions 19ꢁ29 (Rf 0.6 with an impurity Rf
/
0.45) were combined and evaporated and the residue
(530 mg containing ca. 70% of the macrocycle by
comparison (IR, TLC) with the purified compound,
corresponding with ca. 9% yield) was twice recrystallised
from cyclohexane to give small well-formed colourless
solvated crystals of macrocycle 5 (17 mg) which tend to
lose cyclohexane at r.t. A further recrystallisation from
cyclohexane with slow cooling in a Dewar of hot water
gave crystals suitable for X-ray crystallography. Found:
temperature 80ꢁ85 8C and after 2 and 4.5 h, nitrogen
/
was streamed through the flask while the upper parts
were warmed gently to remove dimethylsulfide released
in the reaction. After 22 h, TLC (eluted 2.5% v/v ethyl
acetate in cyclohexane) showed that a small proportion
of the di-iodoalkyne (Rf 0.80) remained; a further
quantity (1.22 g) of the decaborane complex was added
and heating was continued for a further 26 h. The
solvent was removed in vacuum and the cooled residue
was treated with methanol (100 cm3) in portions and
heated cautiously to reflux when the initial effervescence
had subsided. After 17 h, the solid was separated from
the cooled solution and washed with methanol to give
the almost pure carborane 9 (11.97 g, 58%) as a pale
C, 59.30; H, 9.46; C32H56B40×
/
C6H6×
/
6C6H12 requires: C,
5C6H12 requires: C,
61.03; H, 9.27 (C32H56B40×C6H6×
/
/
59.53; H, 8.96%). nmax: 2925 s, 2849 (cyclohexane CH);
2601 vs (BH); 1654 w, 1620 w, 1512 (Ar skel.); 1458,
1449 (cyclohexane CH bend); 1260; 1090; 848 (p-
phenylene o.o.p. bend); 730 (carborane skel.); 588;
1
yellow powder m.p. 215ꢁ
/
216.5 8C, literature [16] 214ꢁ
/
501. d H{11B} 7.26 (d, 8.6 Hz, aryl CH), 7.17 (d, 8.6
216 8C. This was unchanged by dissolution in warm
benzene (40 cm3), decantation to remove a little
insoluble matter and dilution with warm ethanol (60
cm3); recovery from the cooled solution was almost
Hz, aryl CH), 3.11 (2H, s, B3,6H ortho cage), 2.75 (2H,
BH), 2.50 (12H, BH), 2.35 (2H, BH), 2.29 (2H, B5,12H
meta cage). d 11B{1H} ꢀ
/
1.6 (2B, B9,12 ortho cage),
9.7 (16B). d 13C{1H}:
ꢀ
/
5.0 (2B, B5,12 meta cage), ꢀ
/
1
quantitative. d H{11B}: 7.51 (2H, d, 8.5, CH next to I
137.0 (aryl C next to meta-cage); 131.0 (aryl C next to
ortho-cage), 130.6 (aryl CH next to ortho-cage), 127.6
(aryl CH next to meta-carborane), 83.7 (ortho-cage C),
77.0 (meta-cage C resolved within the solvent triplet; in
C2D2Cl4 this resonance is unobscured at 76.9 ppm) MS
in C6H4I), 7.14 (2H, d, 8.5, CH next to cage in C6H4I),
3.15 (2H, B3,6H), 2.55 (2H, B3,6H), 2.48 (4H,
B4,5,7,11H), 2.36 (2H, B8,10H). d 11B{1H}; ꢀ
/
2.5 (2B,
B9,12), ꢀ
/
9.2 (4B, B4,5,7,11), ꢀ
/
10.5 (2B, B8,10), ꢀ11.5
/
(2B, B3,6). d 13C{1H}: 137.7 (CH next to I), 132.0 (CH
next to cage), 130.2 (aryl C next to cage), 97.5 (CI), 84.2
(cage C).
(EI, DCI): 850ꢁ
/
875, 872.55 and 873.57 12.8%: [Mꢂ];
441, 435.23
564ꢁ
/
586, 580.39 100%, C18H40B3ꢂ0; 426ꢁ
/
38.8% C10H29B2ꢂ0 and 433.14ꢁ
/435.23 (5 peaks)
C32H56B
(M2ꢂ); 278.10ꢁ
/291.67 (28 peaks)
2ꢂ
40
2ꢂ
3.4. The macrocycle 5
C18H40B . No m.p. was observed in a glass capillary
30
up to 360 8C and DSC of a solvated sample sealed in air
showed multiple endothermic peaks between 60 and 958
(desolvation) but no melting endotherm before onset of
an exothermic reaction at 450 8C.
A solution of meta-carborane (1.44 g; 10 mmol) in
1,2-dimethoxyethane (80 cm3) was stirred at room
temperature (r.t.) and butyllithium (9.0 cm3, 2.71 M in
hexanes; 24.4 mmol) was added. After 5 min pyridine
(6.0 cm3) was added to the warm turbid solution, which
became yellow. This was followed after a further 5 min
by copper(I) chloride (3.12 g; 31.5 mmol). The mixture,
which soon turned black, was stirred at r.t. for 1 h,
heated to 60 8C for 15 min and 1,2-bis(4-iodophenyl)-
ortho-carborane 9 (5.45 g; 9.9 mmol) was added. The
solution, which turned dark red, was heated under
reflux for 12 days, cooled, and diluted with ether (400
cm3). After standing for 24 h the precipitate was
separated and the solution was washed with dilute
Fractions 15 and 16 were combined and extracted,
after evaporation, with hot propan-2-ol (ca. 10 cm3)
with separation of insoluble matter. The solution was re-
filtered after cooling to r.t. and allowed to evaporate
spontaneously to ca. 3 cm3 with formation of a
gelatinous white precipitate which was washed with
the same solvent and dried in vacuum at r.t. to give the
iodo-compound 11 (250 mg, 4.4%). Found: C, 33.8; H,
5.24; C16H29B20I requires: C, 34.0; H, 5.18%. nmax: 3060
(carborane CH); 2599 vs (BH); 1579, 1511, 1486 (Ar
skel.); 1406; 1391; 1084; 1008; 880; 865; 852 and 830 (p-
phenylene o.o.p. bend); 728 (carborane skel.) 585; 494. d
1H{11B}: 7.49 (2H, d, 8.5, CH next to I in C6H4I), 7.29
(2H, d, 8.6, CH next to meta cage in cage-C6H4-cage),
7.21 (2H, d, 8.6, CH next to ortho cage in cage-C6H4-
hydrochloric acid (200 cm3, 2 M) and water (4ꢄ
500
/
cm3), dried and evaporated. The residue was warmed
with cyclohexane containing 1% v/v of ethyl acetate (30
cm3), insoluble material (376 mg) was separated and the

162
M.A. Fox et al. / Journal of Organometallic Chemistry 680 (2003) 155ꢁ164
/
cage), 7.09 (2H, d, 8.5, CH next to cage in C6H4I), 3.12
(2H, B3,6H ortho cage), 3.05 (1H, CH meta cage), 2.86
(2H, B2,3H meta cage), 2.52 (3H, BH), 2.47 (5H, BH),
2.34 (4H, BH), 2.26 (2H, B8,11H, meta cage), 2.19 (2H,
Fractions nos 5, 6 and 7 contained mainly the three-
cage compound 19 (Rf 0.70, 97 mg, 1.5%) nmax: 3067
(carborane CH); 2610 vs (BH); 1511 (Ar skel.); 1405;
1091; 1009; 887; 855 (p-phenylene o.o.p. bend); 738
(carborane skel.); 589; 505. MS: [RMM of C18H40B30
B4,6H, meta cage). d 11B{1H}; ꢀ
cage), ꢀ4.0 (1B, B5 meta cage), ꢀ
(2B, B8,11 meta cage), ꢀ15.2 (2B, B2,3 meta cage). d
/
2.1 (2B, B9,12 ortho
10.3 (13B), ꢀ13.2
/
/
/
580.83] 573ꢁ
586, 580.28 (100%, [Mꢂ]).
/
/
13C{1H} 137.6 (CH next to I in C6H4I), 137.3 (aryl C
next to meta cage), 132.0 (CH next to cage in C6H4I),
131.0 (aryl C next to ortho cage in cage-C6H4-cage),
130.5 (CH next to ortho cage in cage-C6H4-cage), 130.2
(aryl C next to cage in C6H4I), 127.8 (aryl CH next to
meta cage), 97.3 (CI), 84.2 (ortho cage C next to C6H4I),
83.8 (ortho cage C), 77.0 (meta cage C), 55.2 (meta cage
3.6. X-ray structure determination
Single crystals of the 5×C6H6×
were grown from cyclohexane, which contained 6 mg
lꢀ1 of benzene (from UV). The X-ray diffraction
/
/
6C6H12 composition
experiment Tꢃ
SMART 3-circle diffractometer with a 1 K CCD area
detector, using graphite monochromated MoꢁKa radia-
0.71073 A) and a Cryostream open-flow N2
cryostat [30]. Crystal data: C32H66B40×C6H6×6C6H12,
Mꢃ1456.21, orthorhombic, space group Cmc21 (no.
36), aꢃ
/
150 K was carried out at on a Bruker
CH). MS: [RMM of C16H29B20I 564.51] 559ꢁ
565.10. 47.9%, [Mꢂ].
Mass spectra of the latter (some incompletely sepa-
rated) fractions showed ions of masses: 552ꢁ586,
strongest 580.60, C18H40B3ꢂ0 (compound 12 [RMM of
C18H40B30 580.83]), 986ꢁ1013, strongest 1000.80,
C32H57B40Iꢂ (compound 13 [RMM of C32H57B40I
1001.11]), 859ꢁ
880 strongest 875.59, C32H58B4ꢂ0 (com-
/
558,
/
˚
¯
tion (
/
l
/
ꢃ
/
/
/
/
/
˚
/
33.018(10), bꢃ
/
22.574(6), cꢃ
/
12.266(3) A, Uꢃ
/
/
3
˚
9142(4) A , Zꢃ
/
4, Dcalc
ꢃ
/
1.058 g cmꢀ3, mꢃ
/0.05
mmꢀ1. Over a hemisphere of the reciprocal space was
scanned by 4 series of narrow v-scans (0.38), each series
at different 8 and/or 2u angle settings. Intensities of
32 922 reflections (including 5572 symmetrically inde-
pendent ones and 4651 of their Friedel equivalents,
/
pound 14 [RMM of C18H40B30 875.21]) and 996ꢁ1023,
/
strongest 1016.31, C34H68B5ꢂ0 (compound 15 [RMM of
C34H68B50 1017.41]).
Rint
ꢃ0.158) were integrated using SAINT program [31].
/
The structure was solved by direct methods and refined
by full-matrix least-squares against F2 of all data, using
SHELXTL software [32]. The refinement of 526 para-
meters (non-H atoms in anisotropic approximation, all
3.5. Attempted synthesis of macrocycle 17
A solution of para-carborane (1.52 g; 10.5 mmol) in
1,2-dimethoxyethane (80 cm3) was stirred at r.t. and
butyllithium (9.0 cm3, 2.71 M in hexanes; 24.4 mmol)
was added. After 5 min pyridine (6.0 cm3) was added to
the warm turbid solution, which became yellow. This
was followed after a further 5 min by copper(I) chloride
(2.50 g; 25 mmol). The mixture, which soon turned
black, was stirred at r.t. for 1 h, heated to 60 8C for 15
min and 1,2-bis(4-iodophenyl)-ortho-carborane 9 (6.06
g; 11 mmol) was added. The solution, which turned pink
with a white precipitate, was heated under reflux for 3
days, cooled, and diluted with ether (200 cm3). After
standing for 20 h the precipitate was filtered and the
solution was washed with dilute hydrochloric acid (200
H atoms in ‘riding’ model) converged at Rꢃ
/
0.081 [on
1762 unique reflections with F2ꢀ2s(F2)], wR(F2)ꢃ
/
/
0.289 (all data). Crystal packing was analysed using
PLATON programs [33].
3.7. Computations
All ab initio computations were carried out with the
GAUSSIAN 94 or 98 packages [34,35]. The two geometries
of macrocycle 5 were optimized at the HF/3-21G level
then at the HF/6-31G* level with the relevant symmetry
constraints, C2v for A and D2h for B. Absolute energies
cm3, 2 M) and water (3ꢄ
/
250 cm3), dried and evapo-
(au) at HF/6-31G* are ꢀ
/
2232.02768 and ꢀ2232.02604
/
rated. The glassy residue was warmed with cyclohexane
containing 2% v/v of ethyl acetate (30 cm3) and the
solution was applied to a column of chromatographic
silica (90 g) and eluted with the same solvent in fractions
of 38 cm3. Fractions were examined by TLC on silica
using 2% v/v ethyl acetate in cyclohexane; fraction 8
contained crude iodo-compound 18 (Rf 0.60, 116 mg,
2%). nmax: 3054 (carborane CH); 2609 vs (BH); 1582,
1511, 1487 (Ar skel.); 1405; 1392; 1091; 1008; 889; 854
and 830 (p-phenylene o.o.p. bend); 729 (carborane
skel.); 668; 587; 493. MS: [RMM of C16H29B20I
for A and B, respectively. The geometry of macrocycle 1
was fully optimized without symmetry constraints at the
HF/6-31G* level (absolute energy of ꢀ
Theoretical 11H chemical shifts were referenced to TMS
with the conversion d (11H)ꢃ s(11H) at the
32.78ꢀ
RHF/6-31G*//RHF/6-31G* level.
/
1674.06199 au).
/
/
Calculated proton NMR data (GIAO-RHF/6-31G*//
RHF/6-31G*) for geometry A (C2v) of macrocycle 5:
7.49 (aryl CH next to ortho cage), 7.20 (aryl CH), 3.37
(B3,6H, ortho cage), 2.97 (B9,12H, ortho cage), 2.84
(B5,12H, meta cage), 2.77 (B2,3H, meta cage), 2.76
(B4,6,8,11H, meta cage), 2.61 (B4,5,7,11H, ortho cage),
564.51] 559ꢁ
568, 563.77 (100%, [Mꢂ]).
/

M.A. Fox et al. / Journal of Organometallic Chemistry 680 (2003) 155ꢁ
/164
163
Bachas, Anal. Chem. 72 (2000) 4249;
(o) I.H.A. Badr, M. Diaz, M.F. Hawthorne, L.G. Bachas, Anal.
Chem. 71 (1999) 1371;
2.59 (B8,10H, ortho cage), 2.50 (B9,10H, meta cage).
Similar shifts were obtained for geometry B, D2h.
Calculated proton NMR data (GIAO-RHF/6-31G*//
RHF/6-31G*) for optimized geometry of macrocycle 1:
8.29 (aryl CH inward pointing), 7.44 (2H, aryl CH), 7.28
(1H, aryl CH), 3.80 (B2,3H), 3.28 (B5,12H), 2.78
(B4,6,8,11H), 2.59 (B9,10H). Observed for 1 in CDCl3:
8.14 (aryl CH inward pointing), 7.34 (2H, aryl CH), 7.21
(1H, aryl CH), 3.59 (B2,3H), 2.87 (2H, BH), 2.54 (4H,
B4,6,8,11H), 2.37 (2H, BH).
(p) H. Lee, C.B. Knobler, M.F. Hawthorne, Angew. Chem. Int.
Ed. Engl. 40 (2001) 2124;
(q) H. Lee, C.B. Knobler, M.F. Hawthorne, J. Am. Chem. Soc.
123 (2001) 8543.
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Chem. 34 (1995) 432.
[3] C. Songkram, R. Yamasaki, A. Tanatani, K. Takaishi, K.
Yamaguchi, H. Kagechika, Y. Endo, Tetrahedron Lett. 42
(2001) 5913.
[4] R.N. Grimes, Angew. Chem. Int. Ed. Engl. 32 (1993) 1289.
[5] (a) M.F. Hawthorne, in: W. Siebert (Ed.), Advances in Boron
Chemistry, The Royal Society of Chemistry, 1997, p. 261;
(b) M.F. Hawthorne, in: M.G. Davidson, A.K. Hughes, T.B.
Marder, K. Wade (Eds.), Contemporary Boron Chemistry, The
Royal Society of Chemistry, 2000, p. 197.
4. Supplementary material
Crystallographic data for 5×
/
C6H6×
/
6C6H12 have been
[6] W. Clegg, W.R. Gill, J.A.H. MacBride, K. Wade, Angew. Chem.
Int. Ed. Engl. 32 (1993) 1328.
deposited with the Cambridge Crystallographic Data
Centre, Dep. no. CCDC 204970. Copies of this in-
formation may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
[7] W.R. Gill, P.L. Herbertson, J.A.H. MacBride, K. Wade, J.
Organomet. Chem. 507 (1996) 249.
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Baxter, D.J. Williams, in: M.G. Davidson, A.K. Hughes, T.B.
Marder, K. Wade (Eds.), Contemporary Boron Chemistry, The
Royal Society of Chemistry, 2000, p. 59.
UK (Fax: ꢂ44-1223-336033; e-mail: deposit@ccdc.ca-
/
m.ac.uk or www: http://www.ccdc.cam.ac.uk).
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M.F. Hawthorne, J. Am. Chem. Soc. 115 (1993) 6981;
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Acknowledgements
We thank EPSRC for an Advanced Research Fellow-
ship (M.A.F., AF/98/2454) and Dr A.S. Batsanov for
helpful discussions on X-ray crystallography.
[10] (a) H. Yao, M. Sabat, R.N. Grimes, F. Fabrizi de Biani, P.
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