Preparation of soluble π-conjugated poly(5,6-dialkoxy- 1,10-phenanthroline-3,8-diyl)s. Their stacking behavior and function as a π-conjugated polymer ligand

Article abstract of DOI:10.1246/cl.2002.774

Soluble π-conjugated poly(dialkoxyphenanthroline)s were prepared by organometallic polycondensation using a Ni(0) complex. Stacking structure, optical and electrochemical properties, and Ru complex forming reactivity of the polymer have been revealed.

Full text of DOI:10.1246/cl.2002.774

7
74
Chemistry Letters 2002
Preparation of Soluble ꢀ-Conjugated Poly(5,6-dialkoxy-1,10-phenanthroline-3,8-diyl)s.
Their Stacking Behavior and Function as a ꢀ-Conjugated Polymer Ligand
ꢀ
Takakazu Yamamoto, Kazushige Anzai, and Hiroki Fukumoto
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503
(Received April 22, 2002; CL-020346)
Soluble ꢀ-conjugated poly(dialkoxyphenanthroline)s were
(1.02 g, 2.0 mmol) with a mixture of Ni(cod)2 (0.66 g, 2.4 mmol),
3
prepared by organometallic polycondensation using a Ni(0)
complex. Stacking structure, optical and electrochemical proper-
ties, and Ru complex forming reactivity of the polymer have been
revealed.
bpy (0.37 g, 2.4 mmol), and cod (1.2 cm , 10 mmol) in DMF at
ꢁ
60 C for 36 h gave a bright yellow powder of 5a in 84% yield. 5a
was worked-up by washing with aqueous solutions (e.g., that of
dimethylglyoxime) and methanol. Polymers 5b, 5c, and 5d were
7
obtained in similar ways.
1,10-Phenanthroline (phen) is a typical chelating ligand for
transition metals. Metal complexes of phen are useful as a photo
1
a
1b
sensitizer, electroluminescent material, and catalyst for
1
c,d
organic synthesis.
ꢀ-Conjugated polymers of phen are also
expected to be useful and interesting materials. Preparation and
some chemical properties of poly(1,10-phenanthroline-3,8-diyl)
(
PPhen) with a molecular weight of 6800 have already been
2
Scheme 2. Reagent and conditions: Ni(cod)2 (cod ¼
reported. However, its solubility in organic solvents is low
showing complete insolubility in non-acidic solvents such as
CHCl3 and THF, and solubilization of the polymer by introducing
appropriate substituent(s) is desired for further development of
chemistry of poly(phenanthroline)s. We now report preparation
of soluble ꢀ-conjugated poly(5,6-dialkoxy-1,10-phenanthroline-
ꢁ
1,5-cyclooctadiene), 2,2-bipyridyl, cod, DMF, 60 C, 36 h (84%
for 5a, 63% for 5b, 74% for 5c, 86% for 5d).
5
showed only a minor content of Br below 0.5%. H NMR and IR
a–d were soluble in organic solvents such as CHCl3. 5a–d
1
1
data of 5a–d agreed with their structures. The H NMR spectra
3,8-diyl)s and its basic chemical properties.
gave two broad peaks at ꢁ 9.6 and 9.0, which were assigned to
aromatic 2,9-H and 4,7-H, respectively. Peaks of ꢂ-CH2 and other
alkyl protons appeared at ꢁ 4.2–4.3 and 0.9–2.1, respectively. 5a
was soluble in hexafluoro-i-propanol, and GPCanalysis of 5a
using this solvent gave a number average molecular weight (Mn)
of 17000 (vs poly(methyl methacrylate) standards). 5b–d were
insoluble inthe solvent, and GPCanalysis of these polymers using
chloroform and DMF as the eluent was not possible presumably
The starting monomers 4a–d for new PPhens were prepared
according to procedures shown in Scheme 1. Oxidation of 3,8-
2
dibromo-phen (1) in mixed acid in the presence of KBr afforded
3
2 as a bright yellow powder in 92% yield. Reduction of 2 with
dithiooxamide gave 3 as a dark yellow solid in a quantitative
4
yield. Sodium salt of 3 easily reacted with the corresponding
5
alkyl iodide to afford 4a–d as pale yellow crystals. It was difficult
to introduce alkyl group(s), instead of the alkoxy group, at the 5,6-
positions.
1
due to interaction of the polymer with the GPCcolumn. H NMR
spectra of these polymers showed a weak aromatic peak at ꢁ 7.7
which seemed assignable to the terminal 3,8-H. From the area of
this peak, Mn’s of 5b–d were estimated at 4300–6100. 5d had
ꢂ3
ꢂ3
solubility of 0.11 g cm and 0.002 g cm in CHCl3 and THF,
respectively.
UV-vis spectra of CHCl3 solutions of the polymers exhibited
ꢀ
the lowest energy ꢀ-ꢀ absorption peak in a range of 350–
360 nm, which were shifted from those (ca. 290 nm) of the
corresponding monomers 4a–d. Films of the polymers showed
UV-vis absorption peaks at a longer wavelength (e.g., 369 nm for
a) than the CHCl3 solution, suggesting the presence of certain
5
8
intermolecular interaction due to stacking of the polymer in the
solid. The polymers exhibited photoluminescence in CHCl3 with
a peak in a range of 468–504 nm. The photoluminescence peak in
film is shifted by 30–60 nm to a longer wavelength, suggesting
formation of an excimer-like adduct in the solid, similar to cases
Scheme 1. Reagent and conditions: i) conc. H2SO4 conc. HNO3,
ꢁ
ꢁ
KBr, 130 C, 3 h (92%). ii) dithiooxamide, EtOH, 110 C, 12 h.
ꢁ
ꢁ
iii) a) NaH, DMSO, 60 C, 12 h, b) RI, 60 C, 16 h (46% for 4a,
28% for 4b, 40% for 4c, 39% for 4d).
6
2
of poly(pyridine) and PPhen.
Cyclic voltammograms of cast polymer films in an CH3CN
solution containing [Bu4N]PF6 showed a redox cycle with
Poly(5,6-dialkoxy-1,10-phenanthroline-3,8-diyl), 5a–d, was
prepared by dehalogenative polycondensation of 4a–d (Scheme
þ
cathodic and anodic peaks at about ꢂ2:2 V and ꢂ1:9 V vs Ag /
2;6
2
).
For example, dehalogenative polycondensation of 4a
Ag, respectively. However, the polymer film was inert in an
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
775
þ
11
oxidation region above 0 V vs Ag /Ag. These data reveal that the
polymer is susceptible to reduction and inert to oxidation and
behaves as an n-type conductor. Isolation of Na-doped polymer
was not possible due to solubility of the polymer in THF, in which
the polymer complex. The Ru-complex forming reactivity of 5a
was considerably higher than that of unsubstituted PPhen.
Examples of metal complexes of ꢀ-conjugated polymer ligands
1
are still limited. H-NMR analysis revealed quantative complex
formation of the phen unit of 5a. The Ru complex showed a
broadened MLCT peak at 440 nm in CHCl3 due to the presence of
6
Na-doping is usually carried out. Non-doped polymers did not
show electrical conductivity.
XRD patterns of the polymers are shown in Figure 1. The
ꢀ
10
a wide ꢀ band in 5a and gave an electrochemical reduction
þ
peak at ꢂ2:1 V vs Ag /Ag.
References and Notes
1
a) H. Sugihara, L. P. Singh, K. Sayama, H. Arakawa, Md. K.
Nazeeruddin, and M. Gr a¨ tzel, Chem. Lett., 1998, 1005. b) M. R.
Robinson, M. B. O’Regan, and G. C. Bazan, Chem. Commum.,
2
000, 1645. c) I. E. Mark o´ , P. R. Giles, M. Tsukazaki, S. M.
Brown, and C. J. Urch, Science, 274, 2044 (1996). d) S. S. Stahl,
J. L. Thorman, R. C. Nelson, and M. A. Kozee, J. Am. Chem.
Soc., 123, 7188 (2001).
2
3
a) S. Saitoh and T. Yamamoto, Chem. Lett., 1995, 785. b) T.
Miyamae, N. Ueno, S. Hasegawa, Y. Saito, T. Yamamoto, and
K. Seki, J. Chem. Phys., 110, 2552 (1999).
1
2: H NMR (CDCl3, 400 MHz) ꢁ: 9.14 (d, 2.8 Hz, 2H), 8.61 (d,
2
4
.8 Hz, 2H). Anal. Found: C, 39.17; H, 1.10; N, 7.61; Br,
3.43%. Calcd for C12H4Br2N2O2: C, 38.49; H, 0.89; N, 7.49;
Br, 43.68%.
W. Paw and R. Eisenberg, Inorg. Chem., 36, 2287 (1997).
4a: H NMR (CDCl3, 400 MHz) ꢁ: 9.09 (d, 2.4 Hz, 2H), 8.68 (d,
Figure 1. Powder XRD patterns of (a) 5d,
(b) 5c, (c) 5b, (d) 5a and (e) PPhen.
4
5
1
2
(
.4 Hz, 2H), 4.23 (t, 7.2 Hz, 4H), 1.90 (quin., 7.2 Hz, 4H), 1.52
m, 4H), 0.98 (t, 7.2 Hz, 6H). Anal. Found: C, 51.78; H, 5.14; N,
peaks observed at a low angle region (e.g., the peak with
ꢀ
5.49; Br, 31.32%. Calcd for C22H26Br2N2O2: C, 51.68; H, 4.92;
N, 5.49; Br, 31.46%. 4b: H NMR ꢁ: 9.09 (d, 2.4 Hz, 2H), 8.68
d ¼ 18:3 A for5a) are related to a distance between polymermain
1
chains separated by the long alkoxy groups. The d value increases
with the length of the alkoxy group, and Figure 2 depicts plots of
(
1
d, 2.4 Hz, 2H), 4.23 (t, 7.2 Hz, 4H), 1.89 (quin., 7.2 Hz, 4H),
.53 (m, 4H), 1.45–1.25 (m, 16H), 0.90 (t, 7.2 Hz, 6H). Anal.
Found: C, 56.58; H, 6.44; N, 4.71; Br, 26.88%. Calcd for
1
C28H38Br2N2O2: C, 56.38; H, 6.31; N, 4.70; Br, 26.53%. 4c: H
NMR ꢁ: 9.09 (d, 2.4 Hz, 2H), 8.67 (d, 2.4 Hz, 2H), 4.23 (t,
7
(
.2 Hz, 4H), 1.89 (quin., 7.2 Hz, 4H), 1.53 (m, 4H), 1.45-1.20
m, 32H), 0.88 (t, 7.2 Hz, 6H). Anal. Found: C, 61.19; H, 7.70;
N, 3.96; Br, 22.62%. Calcd for C36H54Br2N2O2: C, 61.23; H,
1
7.85; N, 4.00; Br, 22.38%. 4d: H NMR ꢁ: 9.09 (d, 2.4 Hz, 2H),
8.67 (d, 2.4 Hz, 2H), 4.23 (t, 7.2 Hz, 4H), 1.89 (quin., 7.2 Hz,
4H), 1.54 (m, 4H), 1.45-1.20 (m, 48H), 0.88 (t, 7.2 Hz, 6H).
Anal. Found: C, 64.54; H, 8.62; N, 3.42; Br, 19.52%. Calcd for
C44H70Br2N2O2: C, 64.84; H, 9.01; N, 3.48; Br, 20.22%.
T. Yamamoto, T. Maruyama, Z.-H. Zhou, T. Ito, T. Fukuda, Y.
Yoneda, F. Begum, T. Ikeda, S. Sasaki, H. Takezoe, A. Fukuda,
and K. Kubota, J. Am. Chem. Soc., 116, 4832 (1994).
6
7
5a: Anal. Found: C, 70.35; H, 7.72; N, 7.56; Br, 0%. Calcd for
C22H26N2O2ꢃ1.3H2O: C, 70.68; H, 7.71; N, 7.49. 1,10-
Phenanthroline forms hydrated products, and PPhen was also
Figure 2. Plots of d value vs. number of
carbons in the alkyl chain.
2a
hydrated. 5b: Anal. Found: C, 74.29; H, 8.88; N, 6.51; Br,
0
.20%. Calcd for C28H38N2O2ꢃ0.8H2O: C, 74.90; H, 8.89; N,
the d value vs number of carbons in the alkyl chain. The plots give
ꢀ
a straight line with a slope of 1.43 A/carbon, which is larger than
ꢀ
the height of the CH2 group (1.25 A/carbon). Based on these
results, the polymer is considered to take an end-to-end packing
mode with a stacked ꢀ-conjugated main chain, similar to cases of
6.24. 5c: Anal. Found: C, 77.75; H, 9.71; N, 5.35; Br, 0%. Calcd
for C H N O ꢃ0.5H O: C, 77.79; H, 9.97; N, 5.04. 5d: Anal.
36 54
2
2
2
Found: C, 77.37; H, 10.13; N, 4.57; Br, 0.50%. Calcd for
C44H70N2O2ꢃH2O: C, 78.06; H, 10.72; N, 4.14.
8
T. Yamamoto, D. Komarudin, M. Arai, B.-L. Lee, H.
Suganuma, N. Asakawa, Y. Inoue, K. Kubota, S. Sasaki, T.
Fukuda, and H. Matsuda, J. Am. Chem. Soc., 120, 2047 (1998).
Y. Muramatsu and T. Yamamoto, Polymer, 40, 6607 (1999).
0 N. Hayashida and T. Yamamoto, Bull. Chem. Soc. Jpn., 72,
0
0
poly(3-alkylthiophene-2,5-diyl)s, poly(4,4 -dialkyl-2,2 -bithia-
0
zole-5,5 -diyl)s,
and
poly(5,8-dialkoxyanthraquinone-1,4-
9
1
8;9
diyl).
Reaction of 5a with RuCl2(bpy)2 in an aqueous solution gave
a water-soluble [Ru(bpy)2]2 -coordinated complex of 5a, similar
to the case of a reaction of poly(2,2 -bipyridine-5,5 -diyl) and
RuCl2(bpy)2. Addition of NH4PF6 gave a yellow precipitate of
1
1 Data from elemental analysis roughly agreed with a formation
153 (1999).
þ
1
0
0
of [C H N O ꢃRu(bpy) ꢃ2PF ꢃ(H O)] : C, 47.06; H, 4.14; N,
2
2
26
2
2
2
6
2
n
6;10
7.84; F, 21.27%. Found: C, 46.31; H, 3.93; N, 8.20; F, 20.61.