A convenient synthetic approach to bis-functionalised quaterfluorenes

Article abstract of DOI:10.1016/j.tetlet.2004.05.074

Ni(COD)₂ promoted coupling of bromofluorenes functionalised with boronic esters or trimethylsilyl groups proves to be an efficient method for the preparation of reactive bifluorenes, which are key intermediates for the synthesis of bis-substituted oligofluorenes. The synthetic method has been exploited as a key step for the synthesis of a chiral 2,7?-diiodo- quaterfluorene and a 2,7?-bis-amino quaterfluorene.

Full text of DOI:10.1016/j.tetlet.2004.05.074

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 5367–5370
A convenient synthetic approach to bis-functionalised
quaterfluorenes
Roberto Grisorio,a Piero Mastrorilli,a Cosimo Francesco Nobile,a Giuseppe Romanazzi,a
Gian Paolo Surannaa,* and E. W. Meijerb
aDepartment of Water Engineering and of Chemistry (DIAC), Polytechnic of Bari, via Orabona, 4I-70125 Bari, Italy
bLaboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology,
PO Box 513, 5600 MB Eindhoven, The Netherlands
Received 21 April 2004; revised 13 May 2004; accepted 17 May 2004
Abstract—Ni(COD)2 promoted coupling of bromofluorenes functionalised with boronic esters or trimethylsilyl groups proves to be
an efficient method for the preparation of reactive bifluorenes, which are key intermediates for the synthesis of bis-substituted
oligofluorenes. The synthetic method has been exploited as a key step for the synthesis of a chiral 2,7000-diiodo-quaterfluorene and a
2,7000-bis-amino quaterfluorene.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Organic p-conjugated macromolecules increasingly
attract industrial and scientific interest because of their
potential applications in optoelectronic devices.1 Their
plastic properties, unattainable with traditional inor-
ganic substances, can be exploited for the construction
of light emitting diodes (LEDs) to be used in large area
and flexible displays. In previous years synthetic efforts
have been aimed at obtaining well-defined p-conjugated
oligomers which, different from the corresponding
polymers, can be synthesised with very high purities,
indispensable for LEDs spectral stability.2 Among them,
chiral oligofluorenes are the subject of intense investi-
gations3 because of their strong blue and circularly
polarised light emission.
with the desired regioselectivity and can produce
impurities of structural isomers, often difficult to
remove,6 which can be deleterious for the final perfor-
mance of the electroluminescent device.
Here we report the use of the Yamamoto coupling
reaction for a simple and high-yielding synthesis of the
2,70-bis(trimethylsilyl)-{9,9,90,90-tetrakis[(S)-3,7-dimethyl-
octyl]-7,20-bifluorene (3) and of the 2,20-{9,9,90,90-tetra-
kis[(S)-3,7-dimethyloctyl]-2,20-bifluoren-7,70-diyl}-bis(4,
4,5,5-tetramethyl-[1,3,2]dioxaborolane) (8), which are
high-value intermediates for the preparation of new
quaterfluorene derivatives. Compound 4 has in fact been
successfully used for the synthesis of the new 2,7000-di-
iodo-9,9,90,90,900,900,9000,9000-octakis[(S)-3,7-dimethyloctyl]-
7,20;70,200;700,2000-quaterfluorene (6) whereas 8 has been
the building block for the obtainment of the new 2,7000-
bis-amino-9,9,90,90,900,900,9000,9000-octakis[(S)-3,7-dimethyl-
octyl]-7,20;70,200;700,2000-quaterfluorene (11).
In the framework of the acknowledged procedures for
the synthesis of oligofluorenes, bromination of the aro-
matic rings, usually carried out with Br2/FeCl3, is the
crucial step for further chain growth,4 because it pro-
vides suitable intermediates that can be used in Suzuki–
Miyaura and Stille cross-couplings either as such, or
after conversion into their corresponding boron or tin
derivatives.5 However, bromination may not proceed
The interest for new efficient synthetic approaches for
the obtainment of bis-functionalised oligofluorenes is
justified by the facile modulation of their optical and
charge injection properties by means of the introduction
of specific end groups.7 For instance, the presence of
reactive iodides in 6 makes it the ideal substrate for
further functionalisation in order to create cross-link-
able or supramolecular polymers, while the amines in
Keywords: Oligofluorenes; Ni(0) promoted coupling; Amines; Boronic
esters.
* Corresponding author. Tel.: +39-0805963603; fax: +39-0805963611;
e-mail: surannag@poliba.it
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.05.074

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R. Grisorio et al. / Tetrahedron Letters 45 (2004) 5367–5370
RX
n-BuLi
Br
Si
Br
Br
Br
Br
NaOH
Me3SiCl
R
R
R
R
1 (85%)
2 (93%)
R
R
R
R
Ni(COD)2
ICl
I
I
Si
Si
R
R
R
R
3 (78%)
4 (97%)
Me3Si
B(OH)2
ICl
R
R
Si
Si
I
I
4
4
R
R
R
Pd(PPh3)4
R
5 (68%)
6 (95%)
R = H2C
Scheme 1. Synthesis of 6.
11, could facilitate, as electron-donor groups, the hole
injection by raising the HOMO energy level.8
in 97% yield. It can therefore be concluded that the
Yamamoto coupling conditions are tolerant towards
trimethylsilyl groups, which can be used as protective
moieties during C–C linkage step and easily converted
into reactive iodides. Submitting 4 to a Suzuki reaction
with two equiv of 2-trimethylsilyl-9,9-bis[(S)-3,7-di-
methyloctyl]-fluoren-7-yl-boronic acid2 and treating the
obtained quaterfluorene derivative 512 with ICl afforded
the 2,7000-diiodo-quaterfluorene derivative 6.13
The synthesis of 6 is depicted in Scheme 1 and started
from the commercially available 2,7-dibromo-fluorene,
which was reacted with (S)-3,7-dimethyloctyl-bromide
in a NaOH aqueous solution to afford 1 in 85% yield.
Minor impurities of mono-alkyl derivatives (<1%), the
presence of which may lead to keto-defects under LEDs
operating conditions, have been removed by treating 1
t
with an excess solution of BuOK in THF.9 Subsequent
We have tested the reactivity of 6 in the synthesis of 11,
which has been achieved via copper catalysed amino-
dehalogenation of 6 with potassium phthalimide14
followed by reaction with hydrazine. However, unsat-
isfactory yields in the first step (less than 10%), directed
our efforts towards an alternative approach, namely the
lithiation with one equiv of n-BuLi and reaction with
trimethylsilyl chloride yielded 2 in 93% yield. The
Ni(COD)2-promoted dimerisation of 2 gave the 2,70-
bistrimethylsilyl-bifluorene 310 in 80% yield, which was
transformed into the corresponding bis-iodide 411 by ICl
R
R
O
Ni(COD)2
nBuLi
O
O
B
B
B
O
Br
Br
Br
O
O
R
R
O
O
R
R
R
R
B O
8 (90%)
7 (51%)
1
O
O
NK
NH2NH2
NH2
Br
N
O
O
Br
Br
Br
R
R
R
R
CuI
R
R
1
10 (93%)
9 (48%)
Pd(PPh3)4
H2C
R =
H2N
NH2
4
8 + 10
R
R
11 (69%)
Scheme 2. Synthesis of 11.

R. Grisorio et al. / Tetrahedron Letters 45 (2004) 5367–5370
5369
3. Geng, Y.; Trajkovska, A.; Katsis, D.; Ou, J. J.; Culligan,
S. W.; Chen, S. H. J. J. Am. Chem. Soc. 2002, 124, 8337.
4. Ding, J.; Day, M.; Robertson, G.; Roovers, J. Macromol-
ecules 2002, 35, 3474.
Pd-catalysed Suzuki coupling reaction between the
bis(boronate) 815 and the 2-bromo-7-aminofluorene
derivative 10 (Scheme 2).
5. Babudri, F.; Farinola, G.; Naso, F. J. Mater. Chem. 2004,
14, 11.
6. Zhou, X. H.; Yan, J. C.; Pei, J. Org. Lett. 2003, 5, 3543.
7. Miteva, T.; Meisel, A.; Knoll, W.; Nohofer, H. G.; Scherf,
The synthesis of 816 is depicted in Scheme 2. The lithi-
ation of 1 with 1 equiv of n-BuLi, followed by treatment
with 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane, gave the boronic ester 7, which was submitted to a
Ni(COD)2 promoted Yamamoto coupling reaction. The
Yamamoto aryl–aryl coupling is usually employed in
synthetic procedures to achieve several types of p-con-
jugated polymers; to the best of our knowledge, this is
the first example of a Yamamoto coupling reaction17 of
aryl bromides bearing boronic ester moieties.18 The
potential risks of transmetallation, and consequent
polymerisation could in fact dissuade from the use of
Ni(COD)2 in the presence of boron derivatives,19
although the fact that the Yamamoto coupling does not
involve the use of a base, encouraged our choice. The
reaction afforded 8 in 90% yield and can thus be con-
sidered a powerful and general tool for increasing the
oligomeric unit, while preserving reactive groups, like
boronates.
€
U.; Muller, D. C.; Meerholz, K.; Yasuda, A.; Neher, D.
Adv. Mater. 2001, 13, 565.
ꢀ
8. Beaupre, S.; Leclerc, M. Macromolecules 2003, 36, 8986.
9. Craig, M. R.; de Kok, M. M.; Hofstraat, J. W.; Schen-
ning, A. P. H. J.; Meijer, E. W. J. Mater. Chem. 2003, 13,
2861.
10. Synthesis of 3:
A mixture of 2 (4.80 g, 8.0 mmol),
Ni(COD)2 (2.64 g, 9.6 mmol), bipyridine (1.50 g, 9.6 mmol)
and COD (0.86 g, 8.0 mmol) in toluene (50.0 mL) was
stirred at 80 ꢁC overnight. After cooling to room temper-
ature, the solution was filtered on a Celite plug washing
the residue with petroleum ether (bp 40–60 ꢁC). After
solvent evaporation, the crude was purified by flash
chromatography (silica gel, petroleum ether bp 40–60 ꢁC)
to yield 3 (80%) as colourless oil. 1H NMR (400 MHz,
CDCl3): d 7.79–7.82 (m, 2H), 7.73–7.76 (m, 2H), 7.62–7.67
(m, 4H), 7.51–7.56 (m, 4H), 1.99–2.15 (m, 8H), 1.40–1.52
(m, 4H), 1.02–1.27 (m, 24H), 0.54–0.97 (m, 48H), 0.32 (s,
18H); 13C NMR (101 MHz, CDCl3) d 151.5, 150.1, 141.6,
140.7, 140.3, 138.9, 131.8, 127.7, 126.0, 121.5, 120.0, 119.0,
54.9, 39.2, 37.4, 36.6, 32.9, 30.6, 30.5, 27.9, 24.7 (two
overlapping signals), 22.7, 22.6, 19.6, 19.5, )0.8.
Compound 10 was obtained in two steps starting from 1
(Scheme 2). The copper catalysed amino-dehalogenation
of 1 with 1 equiv of potassium phthalimide yielded 48%
of 9,20 which was reacted with NH2NH2ÆH2O giving 1021
in 93% yield. Compound 1122 was synthesised in good
yield by reacting 2equiv of 10 with 8 in the above cited
Suzuki coupling.
11. Synthesis of 4: To a solution of 3 (2.20 g, 2.1 mmol) in
CH2Cl2 (12.0 mL), a 1.0 M ICl solution (4.5 mL, 4.5 mmol)
was slowly added at 0 ꢁC in 300, and the mixture was
stirred for a further 600 at room temperature. The reaction
was quenched with an aqueous Na2S2O3 solution
(10% wt), added dropwise until discolouration was
observed. After extraction with methylene chloride and
solvent evaporation, the crude residue was purified by
flash chromatography (silica gel, petroleum ether bp 40–
60 ꢁC) to yield 4 (97%) as colourless oil. 1H NMR
(400 MHz, CDCl3): d 7.77 (d, J ¼ 7:95 Hz, 2H), 7.69–
7.73 (m, 4H), 7.63 (d, J ¼ 7:95 Hz, 2H), 7.58 (s, 2H), 7.51
(d, J ¼ 7:63 Hz, 2H), 1.99–2.15 (m, 8H), 1.40–1.52 (m,
4H), 1.02–1.27 (m, 24H), 0.54–0.97 (m, 48H); 13C NMR
(101 MHz, CDCl3) d 153.4, 150.8, 141.1, 140.5, 139.5,
139.4, 135.9, 132.1, 126.3, 121.5, 120.0, 92.5, 55.3, 39.2,
37.5, 37.4, 36.7, 36.5, 32.8, 30.5, 27.9, 24.7, 22.7, 22.6, 19.6,
19.5.
In conclusion, we have described the synthesis of two
new quaterfluorenes. In both cases the synthesis of the
bifluorenyl ‘core’ used for the subsequent reactions with
2equiv of suitable end-cappers was achieved by a
Ni(COD)2 promoted coupling of suitable bromofluo-
renes (2 or 7). The proposed strategy represents a valid
alternative to bromination and subsequent functionali-
sation of bifluorenes and bears a high potential as a
simple and high-yielding method for the preparation of
reactive fluorene oligomers.
12. Synthesis of 5: A mixture of 4 (0.86 g, 0.6 mmol), 2-
trimethylsilyl-9,9-bis[(S)-3,7-dimethyloctyl]-fluoren-7-yl-
boronic acid (0.84 g, 1.5 mmol), Pd(PPh3)4 (60.0 mg,
5 · 10À2 mmol), toluene (14.0 mL) and 2.0 M Na2CO3
solution (5.0 mL) was stirred at 90 ꢁC for 2days. After
cooling to room temperature, petroleum ether (bp 40–
60 ꢁC) was added. The organic layer was separated and
dried over Na2SO4. After solvent evaporation, the crude
residue was purified by flash chromatography (silica gel,
petroleum ether bp 40–60 ꢁC) to yield 5 (68%) as colourless
oil. 1H NMR (400 MHz, CDCl3): d 7.76–7.82(m, 6H),
7.72(d, J ¼ 7:13 Hz, 2H), 7.60–7.68 (m, 12H), 7.48–7.53-
(m, 4H), 1.87–2.15 (m, 16H), 1.37–1.51 (m, 8H), 1.02–1.27
(m, 48H), 0.54–0.97 (m, 96H), 0.32(s, 18H); 13C NMR
(101 MHz, CDCl3) d 151.8, 151.3, 150.8, 150.5, 141.5,
140.7, 140.5, 140.2, 139.2, 138.9, 138.6, 131.8, 131.2, 128.2,
127.5, 127.0, 126.3, 125.5, 121.5, 119.9, 119.1, 118.8, 55.0,
54.8, 39.2, 37.5, 36.6, 32.8, 30.7, 30.5, 27.9, 24.7, 22.7, 22.6,
19.5, )0.9.
Acknowledgements
This work was financially supported by the FIRB pro-
ject MICROPOLYS. The authors are indebted to Dr.
Giuseppe Ciccarella (University of Lecce) for conduct-
ing the APCI-mass spectrometric measurements and to
Dr. Antonino Rizzuti for useful discussions.
References and notes
€
1. Muller, D.; Falcou, A.; Reckefuss, N.; Rojahn, M.;
Wiederhirn, V.; Rudati, P.; Frohne, H.; Nuyken, O.;
Becker, H.; Meerholz, K. Nature 2003, 421, 829, and
references cited therein.
2. Geng, Y.; Culligan, S.; Trajkovska, A.; Wallace, J.; Chen,
S. H. Chem. Mater. 2003, 15, 542.
13. Synthesis of 6: To a solution of 5 (1.00 g, 0.5 mmol) in
CH2Cl2 (4.0 mL), a 1.0 M ICl solution (1.0 mL, 1.0 mmol)

5370
R. Grisorio et al. / Tetrahedron Letters 45 (2004) 5367–5370
was slowly added at 0 ꢁC in 300, and the resulting mixture
crude residue was purified by flash chromatography (silica
gel, petroleum ether bp 40–60 ꢁC/CH2Cl2 ¼ 100:0, 75:25
was stirred for a further 600 at room temperature. The
reaction was quenched with an aqueous Na2S2O3 solution
(10% wt), added dropwise until discolouration was
observed. After extraction with methylene chloride and
solvent evaporation, the crude residue was purified by
flash chromatography (silica gel, petroleum ether bp 40–
60 ꢁC) to yield 6 in 95% as pale yellow oil. 1H NMR
(400 MHz, CDCl3): d 7.31–7.87 (m, 24H), 1.90–2.14 (m,
16H), 1.34–1.50 (m, 8H), 1.00–1.27 (m, 48H), 0.56–0.98
(m, 96H).
1
then 50:50) to yield 9 (48%) as pale yellow oil. H NMR
(400 MHz, CDCl3): d 7.97–8.02(m, 2H), 7.78–7.85 (m,
3H), 7.59–7.63 (d, J ¼ 8:58 Hz, 1H), 7.43–7.52(m, 4H),
1.99–2.15 (m, 4H), 1.40–1.52 (m, 2H), 1.02–1.27 (m, 12H),
0.54–0.97 (m, 24H); 13C NMR (101 MHz, CDCl3) d 167.3,
153.3, 151.0, 139.7, 139.4, 134.4, 131.8, 130.9, 130.1, 126.2,
125.1, 123.7, 121.5, 121.3, 121.1, 120.1, 55.5, 39.2, 37.5,
37.2, 36.7, 36.5, 32.9, 32.8, 30.6, 30.4, 27.9, 24.6, 24.5, 22.7,
22.6, 19.5; IR (CsI): m [cmÀ1] 2927, 2867, 1778, 1728, 1612,
1456, 1372, 1230, 813, 715.
14. Lindley, J. Tetrahedron 1984, 40, 1433.
15. Any attempt aimed at obtaining the corresponding bis-
trimethylstannyl or bis-boronic acid derivatives by means
of lithiation of 4 and subsequent reaction with Me3SnCl or
B(OiPr)3, respectively, was unsuccessful because of diffi-
culties in removing byproducts.
21. Synthesis of 10: To a solution of 9 (0.98 g, 1.5 mmol) in
ethanol (60.0 mL), NH2NH2ÆH2O (73.0 mg, 1.5 mmol) was
added in one portion. The mixture was refluxed for 3 h.
After cooling to room temperature, the solution was
filtered. After solvent evaporation, the residue was purified
by passage through a short silica gel plug using CH2Cl2 as
eluent, to yield 10 (93%) as a pale yellow oil. 1H NMR
(400 MHz, CDCl3): d 7.37–7.48 (m, 4H), 6.62–6.70 (m,
2H), 3.85 (s, 2H), 1.99–2.15 (m, 4H), 1.40–1.52 (m, 2H),
1.02–1.27 (m, 12H), 0.54–0.97 (m, 24H); 13C NMR
(101 MHz, CDCl3) 152.3, 152.0, 146.2, 140.7, 131.4,
129.7, 125.7, 120.6, 119.6, 119.0, 114.1, 109.6, 54.9, 39.2,
37.8, 37.7, 36.6, 32.9, 30.4, 27.9, 24.6, 24.5, 22.7, 22.6, 19.5;
IR (CsI): m [cmÀ1] 3477, 3382, 2927, 2867, 1733, 1616,
1456, 1373, 1215, 809.
16. Synthesis of 8:
A mixture of 7 (2.20 g, 3.4 mmol),
Ni(COD)2 (1.20 g, 4.0 mmol), bipyridine (0.63 g, 4.0 mmol)
and COD (0.36 g, 3.4 mmol) in toluene (20.0 mL) was
stirred at 80 ꢁC overnight. After cooling to room temper-
ature, the solution was filtered on a Celite plug with
petroleum ether as eluent. Upon evaporating off the
solvent, the residue was purified with a short silica gel plug
with CH2Cl2 as eluent to yield 8 in 90% as colourless oil.
1H NMR (400 MHz, CDCl3): d 7.74–7.89 (m, 8H), 7.58–
7.67 (m, 4H), 1.99–2.15 (m, 8H), 1.40–1.52 (m, 28H), 1.02–
1.27 (m, 24H), 0.54–0.97 (m, 48H); 13C NMR (101 MHz,
CDCl3) d 152.1, 150.3, 144.1, 141.0, 140.0, 133.8, 128.5,
126.2, 121.7, 120.3, 119.0, 83.7, 55.0, 39.2, 36.6, 36.5, 32.9,
30.6, 27.1, 24.9, 24.6, 22.7, 19.6, 19.5.
22. Synthesis of 11: a mixture of 8 (0.51 g, 0.45 mmol), 10
(0.49 g, 0.90 mmol), Pd(PPh3)4 (0.10 g, 9 · 10À2 mmol),
toluene (5.0 mL), ethanol (1.0 mL) and a 2.0 M Na2CO3
solution (2.0 mL) was refluxed for 2 days. After the
solution was cooled to room temperature, diethyl ether
was added. The organic layer was separated, washed with
water and dried over Na2SO4. After solvent evaporation,
the residue was purified by flash chromatography (silica
gel, petroleum ether/CH2Cl2 ¼ 2:1) to yield 11 in 69% as
17. Yamamoto, T.; Wakabayashi, S.; Osakada, K. J. Orga-
nomet. Chem. 1992, 428, 223.
18. Recently, it has been demonstrated that the Yamamoto
coupling can also tolerate unprotected arylamine func-
€
tions: Guntner, R.; Asawapirom, U.; Forster, M.; Schmitt,
1
C.; Stiller, B.; Tiersch, B.; Falcou, A.; Nothofer, H.-G.;
Scherf, U. Thin Solid Films 2002, 417, 1.
pale yellow oil. H NMR (400 MHz, CDCl3): d 7.79–7.86
(m, 4H), 7.51–7.71 (m, 16H), 6.70–6.75 (m, 4H), 1.88–2.19
(m, 16H), 1.39–1.50 (m, 8H), 1.02–1.26 (m, 48H), 0.56–
0.99 (m, 96H); 13C NMR (101 MHz, CDCl3) d 152.9,
151.7, 150.4, 140.8, 140.4, 140.2, 139.9, 138.9, 126.0, 121.5,
121.0, 120.6, 119.8, 118.4, 114.1, 109.9, 55.0, 54.7, 39.3,
37.4, 36.7, 32.9, 30.6, 27.8, 24.7, 22.6, 19.6; IR (CsI): m
[cmÀ1] 3476, 3364, 2926, 2867, 1716, 1619, 1585, 1461,
1366, 1261, 1040, 812, 740; MS (APCI): m=z calculated:
1809.54, found: 1810.6 (Mþ + H).
19. Tang, Z. Y.; Hu, Q. S. J. Am. Chem. Soc. 2004, 126, 3058.
20. Synthesis of 9: A mixture of 1 (5.00 g, 8.3 mmol), CuI
(1.58 g, 8.3 mmol) and potassium phthalimide (1.53 g,
8.3 mmol) in DMA (130.0 mL) was refluxed for 2days.
After cooling to room temperature, water was added to
the reaction mixture and the products extracted with
petroleum ether. The organic phase was washed with brine
and dried over Na2SO4. After solvent evaporation, the