Novel polymers of intrinsic microporosity (PIMs) derived from 1,1-spiro-bis(1,2,3,4-tetrahydronaphthalene)-based monomers

Article abstract of DOI:10.1016/j.tetlet.2009.08.032

The synthesis of novel monomers based upon the rigid 1,1′-spiro-bis(1,2,4,5-tetrahydro-6,7-dihydroxynaphthalene) framework is reported. These monomers can be used for the synthesis of polymers of intrinsic microporosity (PIMs) due to their reactive catech

Full text of DOI:10.1016/j.tetlet.2009.08.032

Tetrahedron Letters 50 (2009) 5954–5957
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Novel polymers of intrinsic microporosity (PIMs) derived from
1,1-spiro-bis(1,2,3,4-tetrahydronaphthalene)-based monomers
*
Mariolino Carta, Kadhum J. Msayib, Neil B. McKeown
School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
a r t i c l e i n f o
a b s t r a c t
The synthesis of novel monomers based upon the rigid 1,10-spiro-bis(1,2,4,5-tetrahydro-6,7-dihydroxy-
naphthalene) framework is reported. These monomers can be used for the synthesis of polymers of
intrinsic microporosity (PIMs) due to their reactive catechol units and nonlinear shape, which introduces
the necessary sites of contortion into the resulting PIM.
Article history:
Received 12 June 2009
Revised 22 July 2009
Accepted 17 August 2009
Available online 20 August 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Microporous materials contain interconnected pores that are
less than 2 nm in diameter and are widely used as adsorbents, het-
erogeneous catalysts and for gas separation, purification and stor-
age.1 In the past few years there has been growing interest in the
synthesis and applications of microporous materials derived from
purely organic components.2–4 Our approach involves the design
of polymers with highly rigid and contorted macromolecular struc-
tures that cannot fill space efficiently thus leaving molecular-sized
interconnected voids. These polymers of intrinsic microporosity
(PIMs) are composed of fused rings that provide rigidity, and sites
of contortion, which are provided by spiro-centres.5–10 PIMs are or-
ganic microporous materials which combine the high internal sur-
face areas of conventional microporous materials, such as zeolites
or activated carbons, with the processability of polymers and have
been studied as separation membranes,11–13 hydrogen storage
materials,14–17 adsorbents8,18 and heterogeneous catalysts.19
For example, the archetypal PIM, (PIM-1)20,21 is prepared by
the nucleophilic aromatic substitution reaction between commer-
cially available 2,3,5,6-tetrafluoroterephthalonitrile and 5,50,6,60-
tetrahydroxy-3,3,30,30-tetramethyl-1,10-spirobisindane (Scheme 1).
PIM-1 is a promising membrane material for gas and vapour sepa-
rations and therefore we are interested in making novel PIMs in or-
der to understand property-structure relationships and to optimise
their performance in this important application. One simple
modification of interest is the preparation of PIMs from a family
of monomers based upon 1,10-spiro-bis(1,2,4,5-tetrahydro-6,7-
dihydroxynaphthalene). In particular, replacement of the fused
five-membered spirocyclic rings of PIM-1 with six-membered rings
was anticipated to increase the flexibility of the polymer frame-
work, which may be beneficial to enhance solubility in a wider
range of organic solvents and to improve film formation for mem-
brane development. In analogy with the preparation of the analo-
gous 1,1-spirobisindane monomers,22 the key intermediate for the
synthesis of the spiro-bis(tetrahydronaphthalene) monomers is
the diester 1, which was prepared via the route shown in Scheme 2.
After many unsuccessful attempts with a number of different
reagents [e.g., cH2SO4 and polyphosphoric acid (PPA)], Eaton’s
reagent23 facilitated the troublesome double addition of veratrole
onto the ketone of diethyl-4-oxopimelate to give 1, which was
accompanied by partial hydrolysis of the ester groups. Hence it
proved convenient to perform the aqueous hydrolysis of crude 1
to give the diacid 2, which was isolated readily by precipitation
with aqueous acid and then perform a re-esterification to obtain
pure 1. In order to make a direct comparison with PIM-1 and the
analogous polymer containing a spirocyclic framework consisting
of six-membered rings, the tetramethyl-containing spirobis(tetra-
hydronaphthalene) precursor 4 was prepared (Scheme 3). This
was achieved by the addition of an excess of methylmagnesium
bromide to diester 1, followed by double cyclisation, in Eaton’s re-
agent, of the dehydrated open-chain compound, which was iso-
lated after acid work-up of the Grignard adduct. Demethylation
of 4 using BBr3 afforded the desired monomer 5. By an identical
route, the tetraphenyl spirobis(tetrahydronaphthalene) monomer
7 was prepared starting with the addition of phenylmagnesium
bromide to 1.
Of interest was the synthesis of a spirobis(tetrahydronaphtha-
lene) monomer containing two ketone groups that can be used
for further substitutions. This was achieved readily by treatment
of diacid 2 with PPA to force a double intramolecular Friedel–Crafts
acylation to give the desired spirocyclic diketone 9 (Scheme 4).
BBr3 facilitated the removal of the methoxy groups to give the
monomer 10.
In order to provide bulky substituents to enhance the solubility
of the resulting polymers, phenyl and spirobisfluorene groups were
joined to the spirobis(tetrahydronaphthalene) framework by the
addition of the appropriate Grignard reagent to the bisketone 9
(Scheme 5). Thus, acid work-up of the product from the addition
of phenylmagnesium bromide to 9 gave 1,10-spirobis(4-phenyl-
1,2-dihydro-6,7-dimethoxynaphthalene) 11. Similarly, addition of
* Corresponding author. Tel.: +44 (0)2920 875851; fax: +44 (0)2920 874030.
E-mail address: mckeownnb@cardiff.ac.uk (N.B. McKeown).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.08.032

M. Carta et al. / Tetrahedron Letters 50 (2009) 5954–5957
5955
Scheme 1. PIM-1 synthesis.
Scheme 2. Reagents and conditions: (i) Eaton’s reagent, 20 °C (7 d, 32%); (ii) aq NaOH (20%), MeOH (2 h, 95%).
Scheme 3. Reagents and conditions: (i) MeMgBr, THF, reflux; (ii) 10% HCl (1 h, 91% for 3 and 1 h, 75% for 6) and (iii) Eaton’s reagent (overnight, 20% for 4 and 73% for 7); (iv)
BBr3, CH2Cl2 (1 h, 94% for 5 and 4 h, 73% for 8).
Scheme 4. Reagents and conditions: (i) PPA, 80 °C (3 h, 68%) and (ii) BBr3, CH2Cl2 (2 h, 73%).
2-biphenylmagnesium bromide to 9, followed by treatment of the
crude product with Eaton’s Reagent,24,25 gave the spiro-fused bis-
fluorene derivative 12 together with a mono-fluorene containing
derivative 13 originating from the single addition of the Grignard
reagent to 9. Removal of the methoxy groups from 11, 12 and 13
gave the desired biscatechol monomers 14, 15 and 16, respectively.
Polymers were prepared from the monomers by reaction with
2,3,5,6-tetrafluoroterephthalonitrile (Scheme 6) using the opti-
mised procedure developed for the synthesis of PIM-1.20
The method of purification of the crude polymers was depen-
dent on their solubility, with the soluble polymers being reprecip-
itated from a good solvent (e.g., CHCl3 or THF) into a poor solvent
(e.g., MeOH or acetone) and the insoluble polymers being washed
sequentially in refluxing solvents (THF, acetone, then MeOH). The
physical properties of the novel polymers along with the relevant
physical properties of the analogous spirobisindane-containing
polymers are given in Table 1. With one exception (the polymer
of the bisketone monomer 10, which might preferentially undergo

5956
M. Carta et al. / Tetrahedron Letters 50 (2009) 5954–5957
Scheme 5. Reagents and conditions: (i) appropriate Grignard reagent, THF, reflux; (ii) 10% HCl (24 h, 78% for 11); (iii) Eaton’s reagent (3 d, 19% for 12, 3 d, 50% for 13) and (iv)
BBr3, CH2Cl2 (6 h, 88% for 14, 1 h, 90% for 15 and 2 h, 85% for 16).
Scheme 6. Reagents and conditions: (i) DMF, K2CO3, 65 °C (typically 3 d, yields between 74% and 90%).
Table 1
Summary of the physical properties of PIMs
Surface area (m2/g)
Mw /103 (g/mol)
Tonset (°C)
Solubility
b
Polymer from
5
8
10
14
15
16
432 (780)c
395
22
93
490
495
445
466
495
486
+ (THF, CHCl3)
+ (THF)
—
—
+ (THF, CHCl3)
—
a
713 (501)c
203 (560)c
590 (895)c
300 (656)c
—
—
a
16
a
—
a
b
c
Not soluble therefore incompatible with characterisation by gel permeation chromatography.
Onset of degradation temperature measured by thermogravimetric analysis.
Comparison of the surface area of the parent spiro bisindane polymers.22
a base-catalysed aldol reaction during polymerisation resulting in
extensive cross-linking), it should be noted that the Brunauer, Em-
mett and Teller (BET) surface areas of the polymers in their pow-
dered form, calculated from the nitrogen adsorption isotherms
obtained at 77 K, are in each case lower than the analogous spiro-
bisindane-containing polymers.22 This might be expected due to
the greater flexibility of the six-membered spirocyclic ring unit.
Nevertheless, each polymer demonstrated significant microporos-
ity with the fluorene-containing polymer derived from monomer
facilitate membrane fabrication. A full assessment of the mem-
brane properties of these polymers is in progress.
Acknowledgement
We thank EPSRC (Grants: G01244X and D074312) for funding.
Supplementary data
15 demonstrating
a very respectable BET surface area of
Supplementary data (synthesis of compounds 1–16 and the
polymers derived from monomers 5, 8, 10, 14, 15 and 16) associ-
590 m2 gꢀ1 and excellent solubility in organic solvents, which will

M. Carta et al. / Tetrahedron Letters 50 (2009) 5954–5957
5957
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