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Synthesis of poly(anthra-9,10-quinone-2,6-diyl)
Gerald Power, Philip Hodge,*† Ian D. Clarke, Michael A. Rabjohns and Ian Goodbody
Chemistry Department, University of Manchester, Oxford Road, Manchester, UK M13 9PL
The synthesis, via a precursor polymer, of poly(anthra-
OAc
9
,10-quinone-2,6-diyl) 1 is described and some of its
OAc
X
Br
properties are reported.
X
Poly(anthra-9,10-quinone-2,6-diyl) 1 is of interest for several
reasons. For example, it is expected to have novel redox
properties and these might lead to applications of the polymer in
Br
CO2Me
CO2Me
AcO
OAc
electrochromic displays and/or as charge injection layers in
9
electroluminescent displays. A previous attempt1,2 to synthesise
6 X = Br
1 X = H
1
polymer 1 directly from 2,6-dichloroanthraquinone 2, by
nickel(0)-mediated couplings, led only to very small oligomers
because of the extremely low solubilities of compounds of this
general type in all common organic solvents. Even the dimer 3
–
+
+
OAc
O Na
3
has very low solubilities. We now report a synthesis of polymer
1
, via the soluble precursor polymer 4, which produces a
n
n
–
OAc
O Na
product with a number average molecular weight corresponding
to an average degree of polymerisation, DP, of 13.
10
12
Very dark green
O
O
sation of the latter, convert it into polymer 1. Thus, commercial
,6-diaminoanthraquinone 7 was converted into 2,6-dibro-
X
2
6
moanthraquinone 8, mp 282–283 °C (lit., 289–290 °C) (60%
yield) using a Sandmeyer reaction.7 Reductive acetylation of
,8
n
X
2
quinone 8 by treatment with zinc dust, Ac O and NaOAc at
O
O
reflux temperature gave the anthracene 9, mp 310 °C (de-
comp.)‡ (81% yield), and treatment of this with an excess of
maleic anhydride in xylene at reflux temperature for 18 h gave
the Diels–Alder adduct. The latter was treated with MeOH at
reflux temperature to give the half esters. These reacted
1
2 X = Cl
X = NH2
X = Br
7
8
O
O
O
O
smoothly with ethereal CH
95–200 °C (decomp.)‡, (35% overall yield of recrystallised
product from compound 9).
Treatment of compound 6 in DMA at 80 °C with 1.2 equiv.
2 2
N to give compound 6, mp
O
1
Me
0
of Ni [cod]
2
2
in the presence of cod (1.0 equiv.) and
3
,2A-bipyridyl (1.2 equiv.)2
,8–11
gave precursor polymer 4‡ in
O
n
82% yield. The polymer was highly soluble in many organic
5
1
OAc
solvents including CHCl and THF. The infrared and H NMR
3
spectra of the product were consistent with structure 4. By gel
permeation chromatography polymer 4 had, relative to polysty-
rene standards, a number average molecular weight M
690, a weight average molecular weight M , of 8980 and a
value corresponds
n
, of
n
5
w
CO2Me
CO2Me
AcO
p n
peak molecular weight M , of 6830. The M
to a DP of 13.
4
Heating polymer 4 to 240 °C did not bring about a clean retro-
Diels–Alder reaction to give polymer 10 even though analogous
reactions in syntheses of related polymers proceed cleanly.
8
,12
Quinone-containing polymers have been described be-
fore,1 but most are electron-transfer polymers. The latter are
,2,4
4
However, model studies showed that the dimethyl maleate-
9,10-diacetoxyanthracene Diels–Alder adduct 11‡ reacts read-
ily with 5 equiv. of NaOEt and EtOH in NMP at 20 °C under
nitrogen to give a deep red solution of the disodium salt of
9,10-dihydroxyanthracene, and that exposure of this to air
rapidly gives anthra-9,10-quinone in essentially 100% yield.
We suggest that the key steps in this overall conversion are,
successively, (i) a retro-aldol reaction, (ii) a retro-Michael
reaction and (iii) an esterolysis (see Scheme 1). Treatment of
polymer 4 with NaOEt under similar conditions to those used
above gave a very dark green solution which we attribute to the
formation of polymer 12. Passage of air through the green
solution precipitated polymer 1, as a pale brown solid, in 95%
overall yield from the precursor polymer 4.
usually crosslinked polymers with quinone-containing pendant
groups. Very few quinone-containing polymers that have been
5
described actually have the quinone moiety in the main chain
and conjugated with the p-electron systems of the neighbouring
units. The work most relevant to the present is the synthesis of
poly(2-methylanthra-9,10-quinone-1,4-diyl) 5 and several very
closely related polymers by nickel(0)-mediated couplings of
dichloroquinones.1 For steric reasons, the neighbouring an-
thraquinone moieties in these polymers are essentially orthogo-
nal to each other.
,2
The basic strategy of the present synthesis was to prepare
Diels–Alder adduct 6, carry out a nickel(0)-mediated coupling
to give the soluble precursor polymer 4, then, after characteri-
Chem. Commun., 1998
873
Power, Gerald
