Molecules 2006, 11, 684-692
Synthesis and Characterisation of Eight Isomeric
Brendan J. O’Keefe and Peter J. Steel*
Department of Chemistry, College of Science, University of Canterbury, Christchurch, New Zealand
* Author to whom correspondence should be addressed; E-mail: firstname.lastname@example.org
Received: 31 July 2006; in revised form: 28 August 2006 / Accepted: 29 August 2006 / Published: 13
Abstract: Eight isomeric bis(2-pyridyloxy)naphthalenes have been prepared from reactions
of 2-bromopyridine with the appropriate dihydroxynaphthalene and the products fully
characterised by 1- and 2-D NMR spectroscopy.
Keywords: N-Bridging ligands; pyridines; naphthalenes.
Over the last decade we have reported the synthesis and study of numerous compounds
characterised by the schematic representation 1[1,2]. These are comprised of a central arene core to
which are appended a number (n) of heterocyclic rings attached via spacer groups (X). Variation of the
arene core, the spacer group, the nature of the heterocycle and the number n has led to an extensive
library of bridging ligands that we have used for the construction of a diverse range of 1-, 2- and 3-D
metallosupramolecular assemblies with various topological architectures. For example, the
dimetallocyclophane 2, stabilised by internal π-π stacking of the central benzene rings, was formed by
reaction of silver nitrate with 1,4-bis(2-pyridyloxy)benzene, which has a benzene core, an ether
oxygen as spacer and (n = 2) 2-substituted pyridines as the appended heterocycles . The analogous
3-pyridyl ligand provided access to the first quadruply stranded helicate , whereas the 1,2- and 1,3-
disubstituted analogues led to a range of other interesting assemblies .
Molecules 2006, 11
n = 2-8
Disubstitution of a benzene core allows only three possible orientations (ortho, meta and para) of
the appended heterocycles. In contrast, disubstitution of a naphthalene core leads to ten isomeric
possibilities. Thus, in order to maintain greater control over the exact distance and relative orientations
of the donor substituents, we have extended this design strategy to the preparation of isomers of bis(2-
pyridyloxy)naphthalene (3). By varying the substitution pattern in the naphthalene ring system, we
expected to gain more subtle control of the distances between metal centres bridged by these bidentate
ligands. These isomeric compounds were prepared for use as synthons in metallosupramolecular
chemistry, based on previous work with related bis-ethers [3-7] and bis-thioethers [8-14]. We have
previously reported their use in regioselective double cyclopalladation reactions , but the synthetic
methodology and identification of these compounds had not been published. We now report the
synthesis and NMR characterisation of eight of the ten possible isomers of 3.
Results and Discussion
Initially, all ten isomers of 3 were viewed as targets for synthesis. Our previous syntheses of the
three isomeric bis(2-pyridyloxy)benzenes [3,5] employed a solvent-free procedure for the nucleophilic
aromatic substitution of 2-bromopyridine by the isomeric dihydroxybenzenes. This proved to be
inefficient for the corresponding dihydroxynaphthalenes, thus various experimental conditions (solvent,
base, temperature, reaction time) were explored in an effort to improve yields. No high yielding
general procedure was found for these reactions, principally because of isolation problems of these
somewhat irksome reaction products. In the end, two procedures (both using K2CO3 as base) were
found to be suitable and differed in the solvent employed (Scheme 1): method A was carried out in
DMF, whilst method B used a sulpholane/toluene solvent mixture, which was based on a previously
reported series of reactions of dihydroxynaphthalenes .
(A) K2CO3 / DMF / ∆
or (B) K2CO3 / sulpholane/ toluene / ∆
Table 1. Isolated yields for the various isomers of 3.
Method A (%)
Method B (%)
Molecules 2006, 11
18. Slater, J.W.; D’Alessandro, D.M.; Keene, F.R.; Steel, P.J. Metal-metal Interactions in Dinuclear
Ruthenium Complexes Containing Bridging 4,5-Di(2-pyridyl)imidazolates and Related Ligands.
Dalton Trans. 2006, 1954-1962.
Sample Availability: Contact the authors.
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