The first members of the octasubstituted naphthalene spider-host series with type i (abababab) conformation: Gateway to new nano-host gas storage materials

Article abstract of DOI:10.1039/c0cc00655f

Octakis(m-tolyloxymethyl)naphthalene, the first Type I spider host produced, crystallises from tetraglyme forming a novel channel structure with the host molecule attaining exact D₂ symmetry. The (flexible) channel structure is retained for guest CS₂, the host now only having exact C₂ symmetry. The octa-sulfone octakis(m-tolylsulfonylmethyl) naphthalene is also of Type I in its triclinic DMSO clathrate. DNMR establishes a substantial difference in molecular flexibilities in solution.

Full text of DOI:10.1039/c0cc00655f

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The first members of the octasubstituted naphthalene spider-host series
with type I (abababab) conformation: gateway to new nano-host gas
storage materialsw
Louis J. Farrugia,* James H. Gall, David D. MacNicol* and Ross MacSween
Received 29th March 2010, Accepted 16th June 2010
First published as an Advance Article on the web 28th June 2010
DOI: 10.1039/c0cc00655f
Octakis(m-tolyloxymethyl)naphthalene, the first Type I spider
host produced, crystallises from tetraglyme forming a novel
channel structure with the host molecule attaining exact D2
symmetry. The (flexible) channel structure is retained for guest
CS2, the host now only having exact C2 symmetry. The
octa-sulfone octakis(m-tolylsulfonylmethyl)naphthalene is also
of Type I in its triclinic DMSO clathrate. DNMR establishes a
substantial difference in molecular flexibilities in solution.
Among the first candidate molecules prepared in good yieldy
were the octakis(aryloxymethyl)naphthalenes 2 and 3. The
structures of 2–7 were established from 1H and 13C NMR,
MS and microanalytical data: for 3 and 7 also by single crystal
X-ray diffraction. Compound 2, recrystallised from a wide
variety of aromatic and non-aromatic solvents, revealed a
complete absence of inclusion behaviour. However, meta-
substitution of the side-chain aromatic rings as in
3
transformed the situation completely. Compound 3 is a very
versatile host, forming many crystalline inclusion compounds
with non-stoichiometric host–guest ratios, e.g. benzene
(1 : 1.32), toluene (1 : 1.50), 1,4-dioxane (1 : 1.69), anisole
(1 : 0.96), THF (1 : 1.1), tetraglyme (1 : 0.71) and squalene
There continues to be intense interest in the design of new
crystalline inclusion compounds, in particular those formed by
families of organic host molecules.1,2 The spider host series,3
devised in Glasgow, features conformational versatility and
exhibits an extraordinarily wide range of inclusion behaviour;
from the uniquely specific inclusion of well-ordered acetone in
octakis(4-(2-phenylpropan-2-yl) phenylthio)naphthalene4 to
the very general inclusion of many guests by octakis-
(3,4-dimethylphenylthio)naphthalene.5
1
(1 : 0.32), all ratios determined by H NMR. The tetraglyme
adduct was found to be tetragonal, space group P4/ncc. The
host molecule 3, illustrated in Fig. 1, is located on a point of
222 symmetry and so is constrained to be exactly D2 symmetric.
It possesses the desired Type I (abababab) conformation and
features a modest non-planarity of the central naphthalenecore;
the twist angle around the naphthalene central bond is
14.38(16)1. A view of the packing of 3 is shown in Fig. 2(a),
looking down the c-axis. There are two four-fold symmetric
channels running through the unit cell. The long axis of the
naphthalene is oriented exactly along the crystallographic
c-axis, unlike the situation for octakis(m-tolylthio)naphthalene
(which has a D2 symmetric Type II (aabbaabb) conformation)
where the long molecular axis lies exactly normal to the
c-axis.6 The tetraglyme guest in 3 was non-commensurately
disordered and not located.
Fourteen host-molecule conformations have been classified,6
corresponding to trans arrangements for peri-related groups.
Although several of these have been encountered, ranging in
symmetry from D2 to C1, the attractive Type I (abababab) host
conformation of D2 symmetry has remained elusive until now.
Seeking to access this previously unknown Type I conformation,
we prepared suitably designed two-atom link spider hosts, the
first atom corresponding to a methylene group directly
attached to the central naphthalene core of the molecule.z
Such molecules proved readily accessible by persubstitution
of octakis(bromomethyl)naphthalene7
1 (itself obtained
by bromination of octamethylnaphthalene)8 by judiciously
chosen nucleophiles.
Department of Chemistry, University of Glasgow, Glasgow G12 8QQ,
Scotland, UK. E-mail: davemcn@chem.gla.ac.uk;
Fax: +44 (0)141 330 4888; Tel: +44 (0)141 330 4378
w Electronic supplementary information (ESI) available: CIF files
containing full crystallographic details, labelled ORTEP plots and
stereoplots of solvent accessible voids. CCDC 771696–771698. See
DOI: 10.1039/c0cc00655f
Fig. 1 Molecular structure of 3, showing the Type I (abababab)
conformation. H atoms omitted for clarity.
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Fig. 3 A view looking approximately along the central naphthalene
C–C bond of host 7 in its DMSO clathrate, H atoms and DMSO
omitted for clarity. The chiral host molecule has non-crystallographic
C2 symmetry.
of these compounds with hydrogen peroxide in glacial acetic
acid gave sulfones 6 and 7, respectively. Again highlighting3
the power of meta-substitution to promote inclusion behaviour,
compound 6 was devoid of host properties whilst 7 formed a
crystalline inclusion compound from DMSO, with a host/
guest ratio of 1 : 2. This true clathrate is triclinic. Two
centrosymmetrically related host molecules occupy general
positions in the unit cell, but nonetheless possess the Type I
conformation shown in Fig. 3. An unusual feature of this
conformation is that two peri-related m-tolyl rings point
inwards and lie roughly parallel to the central naphthalene
core of the molecule. Two crystallographically independent
DMSO guests, one disordered, are accommodated in a
moderately large closed void.
Fig. 2 Space-filling views of the unit cell packing for compound 3
looking down the c axis in (a) the tetraglyme inclusion compound and
(b) the CS2 inclusion compound. Guest molecules are not shown to
emphasise the differing channel shapes.
From carbon disulfide solution, unexpectedly, an ortho-
rhombic adduct was formed with host–guest ratio of 1 : 3.28
and space group Pccn. The host packing is shown in Fig. 2(b)
again looking down the c-axis but now that of the orthorhombic
cell. Two channels per cell still exist but these now possess only
two-fold rotational symmetry, rather than the four-fold
symmetry of the tetragonal adduct. Three crystallographically
independent CS2 guest molecules, one on a C2 axis, were
located, appearing almost like chock blocks in the molecularly
comprised chimney. The presence of these channels, especially
in view of the retention of the volatile guest CS2 component
(bp 46 1C), is interesting and brings to mind the elegant study
by Sozzani and coworkers of CH4 absorption by tris(o-phenyl-
enedioxy)cyclotriphosphazene.9 This suggests that gas absorption
by 3 may well merit study, though it is not yet known whether
the channel structure is stable in the absence of guest molecules.
However it is worth noting that the isomorphous octakis-
(m-tolylthio)naphthalene mentioned above retains enclathrated
CH4 for months3 and that the same ‘open’ host packing is
present in the stable empty-cage form. Interestingly, in this
case small windows of approximately 2 A diameter exist at the
top and bottom of each cage, thus presenting an opportunity
for the possible pressure and temperature-dependent reversible
storage of molecular hydrogen. Atwood and coworkers have
stressed the importance10 of thermal motion of the host in
allowing small guest species to pass through thermally enlarged
apertures in the low density polymorph of p-tert-butylcalix[4]-
arene. In order to expand the Type I family members, we
analogously prepared octathioethers 4 and 5 from 1. Oxidation
The situation in solution is of conformational interest. The
observation of two sharp AB quartets [centred at dH 4.28
and 4.66, with nAB and JAB 29.2, 16.0 and 247.1, 15.6 Hz,
respectively] for the diastereotopic protons of the two non-
equivalent methylene groups in the 400 MHz 1H NMR
spectrum of 7 in CCl2DCCl2D at 373 K is consistent with
the presence and slow enantiomerisation, on the NMR time-
scale, of the chiral Type I conformation in solution. From the
absence of detectable lifetime broadening, one may place
a lower limit on the free energy of activation for enantio-
merisation of 7 at ca. 19.5 kcal molꢁ1. This raises the intriguing
possibility of optically resolving 7 or analogues with even
bulkier side-chains, for use as potential chiral ligands. It may
be noted that transition metal complexes of 5, for example
(even when a single metal atom is coordinated), will be
expected to have much higher barriers since all side chains
must undergo a 1801 rotation to produce the enantiomeric
form. Interestingly, the topomerisation barrier shows a
marked dependence upon the effective bulkiness of the
side-chain groups, and coalescences11 of AB quartets observed
for 3 and 5 allow measurement of DG# values (k = 21), namely
10.5 ꢂ 0.3 kcal molꢁ1 (at 231 K) for 3 (in CDCl3) and
14.3 ꢂ 0.2 kcal molꢁ1 (at 313 K) for 5 (in CCl4). Thus formal
replacement of oxygen by the larger sulfur atom leads to an
approximately 4 kcal molꢁ1 increase in DG#. For our starting
material 1, featuring a bulky bromine side-chain atom, we find
a value for DG# of 15.8 ꢂ 0.2 kcal molꢁ1 (at 342 K) in CCl4, in
accordance with an independent literature finding for 1 in
CCl2DCCl2D solution.z
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Finally, it may be noted that compounds described above
are the first examples of two-atom link spider hosts; their
synthesis represents a significant expansion of this conforma-
tionally fascinating host series. We thank the University of
Glasgow (Loudon Bequest) for financial support (to RM).
138.3, 135.1, 134.9, 131.9, 130.5, 130.2, 128.2, 128.0, 60.2, 56.3; MS
(FAB+) [m + 2H] 1362.6, C66H56O16S8 [plus two hydrogens], calc. as
1362.1. Compound 7 was prepared analogously from 5, in 72% yield,
mp 268–270 1C: 1H NMR (400 MHz, CDCl3) d 7.41 (m, 32H), 5.46
(d, J = 15.6 Hz, 4H), 4.80 (d, J = 15.6 Hz, 4H), 4.67 (d, J = 16.0 Hz,
4H), 4.47 (d, J = 16.0 Hz, 4H), 2.37 (s, 12H), 2.26 (s, 12H); MS
(FAB+) m/z 1473.7 [m + H], C74H73O16S8, calc. 1473.3. Crystal data
for 3 (tetraglyme adduct): C74H72O8, M = 1089.32, colourless prism,
0.5 ꢃ 0.46 ꢃ 0.32 mm, tetragonal, space group P4/ncc, a = 16.5680(2),
Notes and references
c = 26.0484(4) A, V = 7150.25(16) A3, Z = 4, Dc = 1.012 g cmꢁ3
,
z Interestingly the ordering of the two-atom link components appears
to be crucial. For example, when the sulfur atom is directly bonded to
the naphthalene, as in octakis(3,4-dichlorobenzylthio)naphthalene, no
evidence for Type I behaviour has been found (C. S. Frampton, D. D.
MacNicol, R. MacSween, unpublished results). This molecule has,
however, significant host properties and X-ray analysis of its triclinic
p-chlorotoluene adduct (host/guest ratio 2 : 3) has revealed a not
uncommon Type III (abbabaab) (C2h) host conformation. Promotion
of the Type I conformation may, in part at least, reflect a more
favourable juxtapositioning of hydrogen atoms between adjacent
methylene groups directly attached to the naphthalene core when
the side-chains adopt an anti-arrangement.
F000 = 2320, Nonius KappaCCD, Mo-Ka radiation, l = 0.71073 A,
T = 150(2) K, ymax = 26.02, 86 187 reflections collected, 3522 unique
(Rint = 0.0483). Final GooF = 1.124, R1(obs) = 0.0789, wR2(all)
0.2709, with I 4 2s(I), refinement on F2, 188 parameters, 0 restraints.
The tetraglyme solvent molecules were not located crystallographically
and their contribution to the structure factors were estimated using the
SQUEEZE algorithm in PLATON (A. L. Spek, J. Appl. Crystallogr.,
2003, 26, 7). Crystal data for 3: C76H72O8ꢄ3.27(CS2), M = 1339.01,
colourless prism, 0.7 ꢃ 0.7 ꢃ 0.5 mm, orthorhombic, space group
Pccn,
a = 15.7611(9), b = 17.0636(9), c = 26.4663(15) A,
V = 7117.9(7) A3, Z = 4, Dc = 1.250 g cmꢁ3, F000 = 2817.8, Nonius
KappaCCD, Mo-Ka radiation, l = 0.71073 A, T = 150(2) K, ymax
=
y Experimental procedure for the preparation of 2:
1 (0.25 g,
26.08, 45 331 reflections collected, 6960 unique (Rint = 0.056). Final
GooF = 1.145, R1(obs) = 0.0777, wR2(all) 0.2134, with I 4 2s(I),
refinement on F2, 440 parameters, 0 restraints. Crystal data for 7:
C74H72O16S8ꢄ2(C2H6OS), M = 1630.05, colourless prism, 0.42 ꢃ 0.25
0.29 mmol, 1 eq.) in DMF (5 mL) was added to sodium phenolate
in ethanol, prepared from phenol (0.229 g, 2.44 mmol) and sodium
(0.056 g, 2.44 mmol, 8.5 eq.). The reaction mixture was stirred at
50 1C, with diethyl ether (5 mL) and water (5 mL) added after
30 minutes. The organic layer was dried and the solvent removed to
give the crude solid. After recrystallisation from diethyl ether/
iso-propanol, product 2 was obtained as a solid (0.157 g, 56%), mp
170–174 1C: 1H NMR (400 MHz, CDCl3) d 7.12 (m, 8H), 6.97 (m,
8H), 6.88 (m, 12H), 6.71 (m, 12H), 5.41 (s, 8H), 5.39 (s, 8H); 13C NMR
(100 MHz, CDCl3) d 159.0, 157.9, 138.1, 137.0, 133.9, 129.8, 129.5,
121.6, 121.3, 115.2, 114.7, 65.3, 64.1; MS (FAB+) m/z 976.9 [M+]
C66H66O8, calc. as 976.4. Compound 3 was prepared analogously in
68% yield, mp 154–155 1C: 1H NMR (400 MHz, CDCl3) d 7.02 (m,
4H), 6.89 (t, J = 7.8 Hz, 4H), 6.69 (d, J = 7.5 Hz, 4H), 6.56 (m, 8H),
6.54 (m, 8H), 6.47 (s, 4H), 5.38 (s, 8H), 5.35 (s, 8H), 2.18 (s, 12H), 2.07
(s, 12H); 13C NMR (100 MHz, CDCl3) d 159.1, 157.9, 139.8, 139.4,
138.1, 137.0, 133.9, 129.5, 129.1, 122.4, 122.0, 116.0, 115.2, 112.3,
112.1, 65.3, 64.1, 21.76, 21.70; MS (FAB+) m/z 1089.0 [M+],
C74H72O8, calc. as 1088.5. Experimental procedure for the preparation
of 4: 1 (0.25 g, 0.29 mmol, 1 eq.) was added to the lithium salt of
thiophenol (0.253 g, 2.30 mmol, 8 eq.) and 2.5 M n-butyl lithium
(1.1 mL, 2.30 mmol, 8 eq.) at 0 1C, in dry THF (5 mL). The reaction
mixture was stirred at room temperature, and after 2 hours water
(2 mL) and chloroform (5 mL) were added. The organic layer was
dried and the solvent removed, to give the product 4 (0.40 g, 32%), mp
177–178 1C: 1H NMR (400 MHz, CDCl3) d 7.17 (m, 40H), 5.10 (broad
s, 8H), 4.52 (broad s, 8H); 13C NMR (100 MHz, CDCl3) d 136.4,
136.2, 135.5, 131.8, 130.7, 129.2, 129.0, 128.8, 126.8, 126.2, 37.1, 33.7;
MS (FAB+) m/z [M+] 1104.7, C66H56S8, calc. as 1104.2. Compound
5 was prepared analogously to 4, in 40% yield, mp 128–130 1C:
1H NMR (400 MHz, CDCl3) d 7.01 (m, 32H), 5.22 (broad s, 8H),
4.52 (broad s, 8H), 4.56 (broad s, 8H), 2.19 (s, 24H); 13C NMR
(100 MHz, CDCl3) d 138.8, 138.5, 137.0, 136.4, 136.2, 135.7, 131.9,
131.1, 129.3, 128.8, 128.6, 127.7, 127.6, 127.0, 125.7, 36.7, 33.8, 21.3,
21.2; MS (FAB+) m/z 1216.6 [M+], C74H72S8, calc. as 1216.3.
Experimental procedure for the preparation of 6: compound 4
(0.144 g, 0.130 mmol, 1 eq.) was added to a solution of hydrogen
peroxide (30% in water) (2.03 mL) and acetic acid (20.0 mL) and the
reaction mixture was refluxed with water (2 mL) added after 2 hours.
Filtration afforded the solid product 6 (0.144 g, 81%), mp 4 294 1C:
1H NMR (400 MHz, CDCl3) d 7.92 (d, J = 7.3 Hz, 8H), 7.71 (m, 4H),
7.51 (m, 28H), 7.44 (m, 8H), 5.56 (d, J = 15.6 Hz, 4H), 4.87 (m, 8H),
4.50 (d, J = 16.0 Hz, 4H); 13C NMR (100 MHz, CDCl3) d 139.6,
ꢀ
ꢃ 0.15 mm, triclinic, space group P1, a = 15.3025, b = 15.9172(6),
c
= 17.7176(5) A, a = 92.3101(18), b = 97.8882(19), g =
115.8882(16)1, V = 3836.4(2) A3, Z = 2, Dc = 1.411 g cmꢁ3
,
F000 = 1712, Nonius KappaCCD, Mo-Ka radiation, l = 0.71073
A, T = 150(2) K, ymax = 26.11, 54 852 reflections collected, 14 970
unique (Rint = 0.0611). Final GooF = 1.049, R1(obs) = 0.074,
wR2(all) 0.2089, with I 4 2s(I), refinement on F2, 966 parameters,
0 restraints.
z See S. Simaan, V. Marks, H. E. Gottlieb, A. Stanger and S. E. Biali,
J. Org. Chem., 2003, 68, 637. The authors and C. S. Frampton have
also shown by single-crystal X-ray analysis of 1 at 100 K the
completely regular alternation of Br atoms above and below the mean
plane of 1. Refinement in space group Fdd2 gives a final R1 value of
3.7%.
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Chem. Commun., 2010, 46, 5241–5243 | 5243