Synthesis of m-terphenyl derivatives for potential use as tectons in crystal engineering

Article abstract of DOI:10.1016/S0040-4039(03)01832-X

Treatment of 4,4-biphenyldiboronic acid with suitably substituted iodo-m-terphenyls provide easy access to the precursors for the synthesis of two rigid m-terphenyl derivatives bearing, H-bonding groups, for potential use as tectons in crystal engineering

Full text of DOI:10.1016/S0040-4039(03)01832-X

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 7129–7132
Synthesis of m-terphenyl derivatives for potential use as tectons
in crystal engineeringꢀ
Ryan S. Wright and Thottumkara K. Vinod*
Department of Chemistry, Western Illinois University, Macomb, IL 61455, USA
Received 1 June 2003; revised 26 July 2003; accepted 28 July 2003
Abstract—Treatment of 4,4-biphenyldiboronic acid with suitably substituted iodo-m-terphenyls provide easy access to the
precursors for the synthesis of two rigid m-terphenyl derivatives bearing, H-bonding groups, for potential use as tectons in crystal
engineering.
Published by Elsevier Ltd.
1. Introduction
required directionality and symmetry properties of the
functional groups aiding the self-assembly process, has
enabled synthetic chemists to prepare suitable tectons
(building blocks)6a for the construction of molecular
solids.6b–e
The rational design of molecular solids with desired
network topologies is an area of considerable practical
applications and interest to chemists and material scien-
tists alike.1 Organic molecular solids with large and
well-defined cavities are expected to find use as molecu-
lar sieves, analogous to zeolites. Microporous organic
solids capable of selective intracavity incorporation of
dienes and dienophiles have shown to promote stereose-
lective Diels–Alder reactions.2 Proper alignment of
reactants in organic solids via supramolecular assembly
have enabled successful realization of unique
topochemical reactions.3 A highly desirable and vigor-
ously sought out goal in the synthesis (construction) of
nanoporous molecular solids is the ability to predict the
shape and size of the cavities in the solid state struc-
tures of organic and organometallic compounds.4 Crys-
tal engineering, a relatively new area of study, addresses
this question by trying to establish a reliable set of rules
and paradigms that relate molecular structures of
organic and organometallic substances to the crystal
(supramolecular)5 structures of these compounds. A
library of weak, but directional, intermolecular interac-
tions have been identified by crystal engineers as the
glue that holds the molecular entities in their respective
crystal lattice.5 A knowledge of these weak intermolecu-
lar forces, coupled with an understanding of the
2. Results and discussion
In this communication, we report the synthesis of two
rigid m-terphenyl derivatives 1 and 2 carrying phenolic
and carboxylic acid functional groups. The conven-
tional OH···O hydrogen bonding possible with these
functional groups is the most commonly used
supramolecular glue in the generation of predictable
networks in crystal engineering.1,5b The choice of 1 and
2 as potential tectons was guided by the consideration
of the following expected structural features of these
compounds. The positioning of the functional groups
on the outer rings of the top and bottom m-terphenyl
units of these structures will place these H-bonding
functional groups pointing in opposite directions, albeit
not orthogonal to each other when R=H as in 1 and 2.
Such H-bonding functional groups, mounted on a con-
formationally rigid molecular scaffold pointing in
opposite directions is likely to favor interaction direc-
tionality over close packing in the crystal structures of
1 and 2. The use of a biphenyl spacer to connect the
top and bottom m-terphenyl units allows one to tune
the angle between the functional groups by introducing
bulky ortho-substituents (R"H) on the biphenyl
spacer. Such a tuning of the angle between the func-
tional groups will also provide a degree of control over
the extent of voids in the eventual lattice. Finally, the
synthetic approach (Scheme 2, vide infra) allows us to
Keywords: tectons; m-terphenyl derivatives; Suzuki coupling reaction;
crystal engineering.
ꢀ Supplementary data associated with this article can be found at
doi:10.1016/S0040-4039(03)01832-X
* Corresponding author. Tel.: 309-298-1379; fax: 309-298-2180;
e-mail: mftkv@wiu.edu
0040-4039/$ - see front matter. Published by Elsevier Ltd.
doi:10.1016/S0040-4039(03)01832-X

7130
R. S. Wright, T. K. Vinod / Tetrahedron Letters 44 (2003) 7129–7132
use other linear polyphenyls as the spacer between the
m-terphenyl units allowing another degree of control
over the void space in the final lattice.
Our approach to the synthesis of 1 and 2 relies on
Suzuki coupling7 reactions between appropriately sub-
stituted m-terphenyl derivatives with 4,4-biphenydi-
boronic acid (8)8 to mount the m-terphenyl caps on the
4,4% positions of biphenyl, thereby yielding the rigid
molecular framework of 1 and 2 (Scheme 2). Hart’s
tandem aryne generation-nucleophilic capture sequence
for the one-pot preparation of m-terphenyls9 was used
for the synthesis of 2%-iodo-m-terphenyl derivatives, 6
and 7 required in the crucial Suzuki coupling reaction
(Scheme 1). Treatment of 2,6-dichloroiodobenzene (3)
with 3.0 equivalence of 4-methoxyphenylmagnesium
bromide (4) followed by an iodine quench of the reac-
tion mixture prior to aqueous work-up afforded 6 in
83% yield. The synthesis of 7 was similarly carried out
and was isolated in 76% yield by using 3.0 equivalence
of 4-methoxymethylphenylmagensium bromide (5).
Though Suzuki cross-coupling reaction between aryl
halides and arylboronic acids has emerged as one of the
most reliable protocols for biaryl synthesis, coupling
involving sterically demanding substrates (boronioc
acid, halide, or both) requires the use of specialized
Scheme 1.
Scheme 2.

R. S. Wright, T. K. Vinod / Tetrahedron Letters 44 (2003) 7129–7132
7131
Scheme 3.
sity AA%BB% set in the case of 2 appeared upfield (l 6.54
and l 6.84) than the corresponding signals of 1 (l 7.18
and l 7.74) which bear electron withdrawing carboxylic
acid groups on the outer m-terphenyl rings.
catalysts and reaction conditions and the yields are
often variable.10 The sterically demanding nature of
halides 6 and 7, with the iodine site (C2%) flanked by
two phenyl rings on the ortho carbons, was a concern
for us before we attempted the necessary coupling with
4,4-biphenydiboronic acid (8). To our surprise, we
found that employing the original Suzuki reaction con-
ditions,11 namely the use of Pd[P(Ph)3]4 as the catalyst
and aq. Na2CO3 as the base in the coupling of 6 and 7
with 8, afforded the coupled products 9 and 10 in 82
and 79% yield, respectively.12,13 We consider these
yields remarkable, as the coupled products 9 and 10
result from a two-fold Suzuki coupling reaction involv-
ing sterically demanding aryl halides. Demethylation of
9 using BBr3 provided the desired tetraphenol, 1, in
94% yield.14 Demethylation of 10 provided the expected
tetrakis-bromomethyl derivative 11, which we hoped to
directly oxidize to the desired tetracarboxylic acid 2.
However, our attempts at this direct oxidation proved
difficult with intractable mixture resulting from our
oxidation attempts. We were thus forced to adopt a
circutous but a sequence of high yielding reactions
shown in Scheme 3 to obtain 2. Benzylic bromination
of 11 using excess NBS in benzene yielded the octabro-
mide 12 in 82% yield which was subsequently
hydrolyzed to the tetraformyl derivative, 13, in presence
of silver nitrate in THF–H2O mixture.15 The final oxi-
dation of 13 to the tetracarboxylic acid derivative, 2,
was easily accomplished with KMnO4 in acetone–water
mixture.16 The precipitation of the product, in essen-
tially pure form upon acidification and decolorization
of the reaction mixture, made the product isolation
easy. The structures of 1 and 2 are readily discernible
from their respective 1H NMR spectra. Both com-
pounds show two sets of AA%BB% signals with an inten-
sity ratio of 2:1 in their 1H NMR spectra for the
protons on the outer rings of m-terphenyl caps and
biphenyl unit respectively. As expected due to the pres-
ence of electron donating OH groups, the higher inten-
In conclusion, we have found an easy route to assemble
m-terphenyl capped biphenyl derivatives, which by
virtue of having suitably positioned H-bonding groups,
are likely to find use in crystal engineering as tectons.
The ready availability of suitably substituted and func-
tionalized m-terphenyls via Hart’s one-pot procedure
and the ease of coupling of these derivatives with
4,4-biphenyldiboronic acid as demonstrated by the cur-
rent work should facilitate the synthesis of many struc-
turally analogous derivatives of 1 and 2. Work on
elucidation of solid state structures of 1 and 2 (recrys-
tallized from DMSO) and synthesis of derivatives of 1
and
laboratory.
2 (R"H) are currently underway in our
Acknowledgements
Support of this work by the University Research Coun-
cil of Western Illinois University and the Petroleum
Research Fund of the American Chemical Society
(34866-B4) is gratefully acknowledged. We also grate-
fully acknowledge the support of the National Science
Foundation (ILI grant no. DUE –9851569) and West-
ern Illinois University for funding the NMR spectrome-
ter used in this study.
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