Double homologation method for substituted soluble pentacenes and dimerization behaviours of pentacenes

Article abstract of DOI:10.1002/asia.200800312

A double homologation method for the formation of substituted soluble pentacenes was developed by a zirconium-mediated cyclization of tetrayne derivatives. Thermal dimerization of tetra- and octasubstituted pentacenes was observed. The dimerization behavi

Full text of DOI:10.1002/asia.200800312

FULL PAPERS
DOI: 10.1002/asia.200800312
Double Homologation Method for Substituted Soluble Pentacenes and
Dimerization Behaviours of Pentacenes
Shi Li,[a] Zhiping Li,[a] Kiyohiko Nakajima,[b] Ken-ichiro Kanno,[a] and
Tamotsu Takahashi*[a]
Abstract: A double homologation method for the formation of substituted soluble
pentacenes was developed by a zirconium-mediated cyclization of tetrayne deriva-
tives. Thermal dimerization of tetra- and octasubstituted pentacenes was observed.
The dimerization behavior was observed to be strongly related to the substituent
groups affixed to the pentacenes.
Keywords: alkynes · cyclization ·
dimerization double homologa-
tion · zirconium
·
Introduction
It was reported in 1997 that a pentacene film showed a com-
parable or higher field-effect transistor (FET) mobility com-
pared with amorphous silicon.[1] Pentacene is acknowledged
as possessing the highest FET mobility among organic thin
films. Pentacene is insoluble in organic solvents at ambient
conditions. Therefore, we proposed that soluble pentacenes
with organic substituents are attractive and important.[2a]
We have reported two methods for the construction of a
linear pentacyclic system of substituted pentacene deriva-
tives using zirconacyclopentadienes. One is homologation[2]
and the other is coupling.[3] The homologation method intro-
duces organic substituents into naphthacenes and penta-
cenes by diyne cyclization. This method can extend the aro-
matic ring system in one direction as shown in Figure 1.[2]
As a more efficient method for symmetrical pentacene for-
mation, we reported a double homologation method to
extend the aromatic ring system in both directions by tet-
rayne cyclization to prepare pentacene derivatives also
Figure 1. The concept of homologation and double homologation.
shown in Figure 1.[4a] More recently, Stone et al. also report-
ed the same reaction using the double homologation reac-
tions with zirconacycleopentadienes.[4b]
[a] Dr. S. Li, Dr. Z. Li, Dr. K.-i. Kanno, Prof. Dr. T. Takahashi
Catalysis Research Center
Four substituted patterns of pentacenes could be prepared
by the double homologation reaction as shown in Figure 2.
Compared with the homologation method, double homolo-
gation reduces the number of synthesis steps. For example,
the homologation method requires 2 steps each for alkynyla-
tion, zirconacyclopentadiene formation, and aromatic ring
formation. However, the double homologation method re-
quires only one step each. Therefore, for symmetrical penta-
cene formation, the double homologation method has the
advantage over the homologation method.
Hokkaido University, and SORST
Japan Science and Technology Agency (JST)
Kita 21, Nishi 10, Kita-ku, Sapporo 001-0021 (Japan)
Fax : (+81)11-706-9150
E-mail: tamotsu@cat.hokudai.ac.jp
[b] Prof. Dr. K. Nakajima
Department of Chemistry
Aichi University of Education
Igaya, Kariya 448-8542, Aichi (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200800312.
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Figure 2. Substituted patterns of pentacenes prepared by double homolo-
gation.
In this paper, we report in full detail the double homolo-
gation method which we have developed.
Results and Discussion
Preparation of Symmetrically Octa- and Deca-Substituted
Pentacenes by Double Homologation
Scheme 2. Synthesis of pentacene 11.
We have preliminarily reported the preparation method for
the 1,2,3,4,6,8,9,10,11,13-decasubstituted pentacene 5.[4a] It
was successfully prepared by zirconium-mediated double-
ring extension as shown in Scheme 1. The reaction of
of tetrakis(bromomethyl)benzene 6 with 1-alkynyllithium or
magnesium halide did not lead to a clean formation of the
desired tetraynes 8. Therefore, tetrabromide 6 was convert-
ed to tetraiodide 7.[5] 7 cleanly reacted with 1-alkynylmagne-
sium bromide in the presence of CuCl to give the desired
tetraynes 8 in moderate yields.[6] Similarly, the zirconium-
mediated double cyclization of tetraynes 8 with dialkyl ace-
tylenedicarboxylate proceeded in the presence of CuCl in
refluxing THF. Tetrahydropentacenes 10 were obtained via
bis(zirconacyclopentadiene) complexes 9.
Aromatization of octa-substituted tetrahydropentacenes
10 with 2 equiv of DDQ at 1508C gave the corresponding
pentacenes 11 (Scheme 2). The trimethylsilyl-substituted
pentacene 11a,c were obtained as single products in 30%
and 28% yield, respectively, from the corresponding tetra-
hydropentacenes 10a,c by using 2 equiv of DDQ at 1508C.
However, aromatization of tetrahydropentacene 10b under
the same conditions led to the corresponding pentacene 11b
and its dimer 12b formed in 36% and 16% yield, respec-
tively. The structure of pentacene dimer 12b was deter-
mined by X-ray analysis as shown in Figure 3.
Scheme 1. Synthesis of pentacene 5.
1,2,4,5-tetrakis(bromomethyl)-3,6-dimethoxybenzene 1 with
1-pentynyllithium in THF and DMPU led to the clean for-
mation of the corresponding tetrayne 2 in 42% yield. Tet-
rayne 2 was then treated with 2.5 equiv of Cp2ZrBu2 to give
bis(zirconacyclopentadiene) 3 followed by coupling with di-
methyl acetylenedicarboxylate (DMAD) in the presence of
CuCl to form the first and fifth rings of the pentacene skele-
ton. The tetrahydropentacene derivative 4 was obtained in
60% yield. Tetrahydropentacene 4 was aromatized with
2 equiv of DDQ in toluene at 1008C for 3 h. The corre-
sponding symmetrically decasubstituted pentacene 5 was ob-
tained as a blue solid in 60% yield (Scheme 1).
The yields of desired pentacenes 11 could be improved by
the pentacene–DDQ adduct method which we have report-
ed recently (Scheme 3).[3] Tetrahydropentacene 10 reacted
with an excess of DDQ (3 equiv) at 508C to give Diels–
Alder adducts 13 in quantitative yields.[7] Once formed pen-
tacene with 2 equiv of DDQ was converted into 13 with the
third DDQ. To remove DDQ from 13, the pentacene–DDQ
adducts 13 were treated with 50 equiv of g-terpinene at
1008C in toluene to induce the retro-Diels–Alder reaction.[3]
The silyl-substituted pentacenes 11a,c were obtained as
single products in good yields. For tetrahydropentacene 10b,
the dimer 12b was also formed under the conditions used
here, but the yield of pentacene 11b was improved. Penta-
cenes 11a–c were deep blue powders with a good solubility
in a variety of organic solvents.
Synthesis of 1,2,3,4,8,9,10,11-octasubstituted pentacenes
11 proceeded from commercially available 1,2,4,5-tetrakis-
(bromomethyl)benzene 6 (Scheme 2). However, the reaction
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The solvent was evaporated,
and the resulting solid was
washed with hexane to afford
bis(zirconacycle) 9a as a yellow
solid in 87% yield. 1H NMR
spectrum of 9a in C6D6 showed
four singlet signals at 0.26, 3.44,
5.82, and 7.05 ppm assigned to
36 protons of four TMS groups,
eight protons of four CH2, 20
protons of four Cp ligands, and
two protons of the central aro-
matic
ring,
respectively.
13C NMR showed the character-
istic carbon of Cp ligand at
110.7 ppm. The sp2 carbons of
zirconacycle appeared at 140.8
and 197.6 ppm, respectively.[8]
When
the
trimethylsilyl
group in 9a was changed to a
butyl group, bis(zirconacycle)
9b was not soluble in toluene.
Therefore, the LiCl salt could
Figure 3. Structure of pentacene dimer 12b.
not be completely removed. In
order to increase the solubility
of 9b, the methylcyclopentadienyl ligand was introduced in-
stead of cyclopentadienyl ligand as shown in Scheme 4.
Compared with 9b, the solubility of bis(methylcyclopenta-
dienyl)zirconacycle 9’b is improved. Bis(zirconacycle) 9’b
was easily isolated by the same procedure in 79% yield.
Similarly, the methylcyclopentadienyl ligand was introduced
to 3. The complex bis(methylcyclopentadienyl)zirconacycle
3’ prepared from tetrayne 2 showed similar characteristic
13C NMR data as that of 9’b in C6D6 at room temperature.
Three Cp carbons appeared at 105.1, 111.9, and 123.6 ppm
and the characteristic sp2 carbon attached to zirconium
metal appeared at 186.8 ppm.[8] These spectra clearly show
that these bis(zirconacycle)s 3’, 9a, and 9’b are stable under
N2 at room temperature.
Scheme 3. Pentacene formation by pentacene-DDQ adduct method.
Formation of Bis(zirconacyclopentadiene)s as Key
Intermediates
The key intermediates, bis(zirconacyclopentadiene)s 3’, 9a,
and 9’b, were successfully observed and characterized by
NMR (Scheme 4). The tetrayne 8a was treated with
2.5 equiv of Cp2ZrBu2 (Negishiꢁs reagent), generated in situ
from zirconocene dichloride and n-butyllithium in THF at
À788C for 1 h. The reaction proceeded at room temperature
Preparation and Functionalization of Pentacene–2,3,9,10-
Tetraesters
1
for 3 h. H NMR analysis showed 9a was formed in 94%
Formation of 2,3,9,10-tetrasubstituted pentacene 11d was
shown in Scheme 5. Desilylation of 10a with 4 equiv of
Bu4NF in THF at 08C gave desilylated tetrahydropentacene
14 in 75% yield. Tetrahydropentacene 14 was aromatized
with 2 equiv of DDQ at 1508C to give a mixture of desired
pentacene 11d and its dimer 12d in 40% and 10% yield, re-
spectively. However, when tetrahydropentacene 14 was ar-
omatized by the pentacene–DDQ adduct method at 1008C,
pentacene 11d was formed as a single product in 72% yield.
The desilylated pentacene 11d still has good solubility in or-
ganic solvents. The 1H NMR of 11d recorded in CDCl3
clearly show three singlet signals at 8.36, 8.72, and 8.98 ppm
in the aromatic region assignable to ten protons of the pen-
tacene skeleton.
NMR yield. Upon changing the reaction solvent from THF
to toluene, the precipitated LiCl was removed by filtration.
Scheme 4. Formation of bis(zirconacycle)s 3’ and 9’b.
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Double Homologation Method and Dimerization of Pentacenes
Scheme 7. Dimerization of symmetrically substituted pentacenes.
converted to monomer 11b in dichlorobenzene at 1508C
(Scheme 7). Pentacene 11a did not dimerize when it was
prepared in mesitylene as described above, owing to the
bulky trimethylsilyl groups. However, it also was converted
to its dimer 12a in dodecane, although a longer reaction
time and higher temperatures were needed (2008C for
3 days, yield: 40% of dimer 12a). The less substituted penta-
cene 11d dimerized under the same conditions in 96%
yield, with high temperatures required to improve its solu-
bility in dodecane.
Scheme 5. Synthesis of pentacene 11d.
Pentacene diimide 17 also could be prepared by function-
alization and aromatization of 14 (Scheme 6). Tetraesters 14
reacted with lithium iodide in refluxing pyridine to afford
Compared with pentacene 11, no dimerization was ob-
served for decasubstituted pentacene 5 and 2,3-disubstituted
pentacene.[2b] For pentacene 5, the lack of dimerization
arises from the steric repulsion between methoxy groups in
the pentacene pair.[10]
Conclusions
Double homologation was successfully developed by a zirco-
nium mediated double ring extension of 1,2,4,5-tetrakis(pro-
pargyl)benzene derivatives. Dimerization of tetra- and octa-
substituted pentacenes was observed. Reversible conversion
between monomeric pentacene and its dimer was observed
for tetra- and octa-substituted pentacenes.
Scheme 6. Synthesis of pentacene imide 17.
the corresponding tetracarboxylic acid 15.[9] 15 could be con-
verted to dianhydride in high yield by treatment with acetic
anhydride at 1408C. The anhydride reacted with 2-ethylhex-
ylamine in refluxing toluene. The corresponding diimide 16
was formed in 80% yield. The tetrahydropentacene 16 was
aromatized by the pentacene–DDQ adduct method at
1008C in degassed toluene to afford the corresponding pen-
tacene diimide 17 in 66% yield. The pentacene 17 could be
isolated as a stable blue solid by methanol precipitation.
Experimental Section
General
All reactions were carried out under a nitrogen atmosphere using stan-
dard Schlenk techniques. Tetrahydrofuran (THF) and toluene were dis-
tilled over sodium and benzophenone under a nitrogen atmosphere. All
of the reagents were commercially available and used as received unless
stated. 1,2,4,5-Tetrakis(bromomethyl)-3,6-dimethoxybenzene (1) was pre-
pared according to the literature.[11] 1H and 13C NMR spectra were mea-
sured in CDCl3 (containing 0.03% TMS) solutions.
Dimerization of Symmetrically Substituted Pentacenes
When tetrahydropentacene 10b was aromatized with
2 equiv of DDQ in the dark, the corresponding dimer 12b
was still formed (Scheme 7).[10] Interestingly, a reversible
conversion between pentacene monomer 11b and its dimer
12b was observed by changing the solvent. For example,
when pentacene 11b was heated in degassed dodecane solu-
tion at 1508C, the monomer 11b was converted to its dimer
12b as a white precipitate owing to the low solubility of 12b
in dodecane. The dimer 12b could also be quantitatively
Preparation of 1,2,4,5-Tetrahex-2-ynyl-3,6-dimethoxybenzene (2) from 1
To a solution of 1-pentyne (0.79 mL, 8.0 mmol) in THF (25 mL) was
added nBuLi (1.56m hexane solution, 5.13 mL, 8.0 mmol) and DMPU
(1,3-dimethyl-tetrahydro-pyrimidin-2-one, 0.96 mL, 8.0 mmol). The mix-
ture was stirred at room temperature (RT) for 1 h. Tetrabromide 1
(510 mg, 1.0 mmol) was added to the mixture and it was stirred at RT for
12 h. The reaction mixture was quenched with saturated aqueous NH4Cl
at 08C and extracted with ethyl acetate. The combined extract was
washed with water. After addition of BHT (3 mg), the solution was
washed with brine and dried over Na2SO4. After removal of the solvent,
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the residue was purified by silica gel chromatography (hexane/ethyl ace-
tate/triethylamine=50:1:1 as eluent) to afford 2 as a colorless solid
(188 mg, 42% yield).
2: 1H NMR (CDCl3, Me4Si): d=0.93 (t, J=7.2 Hz, 12H), 1.44–1.51 (m,
8H), 2.06–2.11 (m, 8H), 3.73 (t, J=2.4 Hz, 8H), 3.91 ppm (s, 6H);
13C NMR (CDCl3, Me4Si): d= 13.5, 15.9, 20.8, 22.3, 62.4, 78.0, 80.3, 130.1,
152.3 ppm; HRMS (EI) calcd for C32H42O2: 458.3185. Found: 458.3196.
Preparation of 1,2,4,5-Tetrakis(iodomethyl)benzene (7) from 6
1,2,4,5-Tetrakis(bromomethyl)benzene (449 mg, 1.0 mmol) in 25 mL of
acetone was refluxed with sodium iodide (1.8 g, 12.0 mmol) for 8 h. After
removal of the solvent, the reaction mixture was extracted with CHCl3
and treated with saturated aqueous Na2S2O3. The extract was washed
with water and brine. After evaporation of the solvent, the title com-
pound was obtained as a pale-yellow solid (592 mg, 93% yield).
1
Preparation of Bis
N
7: H NMR (CDCl3, Me4Si): d=4.50 (s, 8H), 7.28 ppm (s, 2H); 13C NMR
(3’) from 2
(CDCl3, Me4Si): d=0.2, 132.9, 138.0 ppm; HRMS (EI) calcd for C10H10I4:
637.6961. Found: 637.6962.
To
a
solution of bis(methylcyclopentadienyl)zirconium dichloride
(160 mg, 0.5 mmol) in 15 mL of toluene was added nBuLi (1.56m hexane
solution, 0.64 mL, 1.0 mmol) at À788C, and the mixture was stirred at
À788C. After 1 h, tetrayne 2 (92 mg, 0.2 mmol) was added to the solu-
tion, and it was warmed to RT by removal of the cooling bath. After stir-
Preparation of 1,2,4,5-Tetrakis(3-trimethylsilyl-2-propynyl)benzene (8a)
from 7
To a solution of 1-trimethylsilylacetylene (0.85 mL, 6.0 mmol) in 15 mL
THF was added ethylmagnesium bromide (0.97m THF solution, 6.18 mL,
6.0 mmol) at 08C. The mixture was heated to 408C for 1 h. Copper chlo-
ride (99 mg, 1.0 mmol) and tetraiodide 7 (637 mg, 1.0 mmol) were added
to the mixture and it was heated to reflux for 6 h. After cooling to 08C,
the reaction mixture was quenched with saturated aqueous NH4Cl and
extracted with ethyl acetate. The combined extract was washed with
water. After addition of BHT (3 mg), the solution was washed with brine
and dried over Na2SO4. After removal of the solvent, the residue was pu-
rified by silica gel chromatography (hexane/ethyl acetate/triethylamine=
100:1:3 as eluent) to afford 8a as colorless solid (414 mg, 80% yield).
1
ring for 3 h, H NMR measurements showed 3’ was formed in 92% yield.
The precipitated LiCl was removed by filtration. The solvent was evapo-
rated, and the resulting solid was washed with hexane (20 mL) to afford
3’ as a yellow solid (153 mg, 80% yield).
3’: 1H NMR (C6D6, Me4Si): d=1.10 (t, J=7.2 Hz, 12H), 1.38–1.52 (m,
8H), 1.80 (s, 12H), 2.47–2.51 (m, 8H), 3.61 (s, 8H), 3.74 (s, 6H), 5.44–
5.45 (t, J=2.8 Hz, 8H), 5.92–5.94 ppm (t, J=2.8 Hz, 8H); 13C NMR
(C6D6, Me4Si): d=15.3, 15.5, 24.4, 27.2, 40.7, 61.5, 105.1, 111.9, 123.6,
127.3, 129.9, 149.4, 186.8 ppm; HRMS (FAB) calcd for C56H70O2Zr2:
954.3470. Found: 954.3484.
1
8a: H NMR (CDCl3, Me4Si): d=0.17 (s, 36H), 3.65 (s, 8H), 7.40 ppm (s,
Preparation of 6,13-Dimethoxy-1,4,8,11-tetrapropyl-5,7,12,14-tetrahydro-
2H); 13C NMR (CDCl3, Me4Si): d=0.1, 23.7, 87.0, 103.6, 129.9,
2,3,9,10-tetrakis(methoxycarbonyl)pentacene (4) from 2
133.3 ppm; HRMS (EI) calcd for C30H46Si4: 518.2677. Found: 518.2673.
To a solution of Cp2ZrCl2 (730 mg, 2.5 mmol) in 15 mL of THF was
added nBuLi (1.56m hexane solution, 3.2 mL, 5.0 mmol) at À788C with
constant stirring. After 1 h, tetrayne 2 (459 mg, 1.0 mmol) was added to
the solution, and it was warmed to room temperature by removal of the
cooling bath. After stirring for 3 h, CuCl (594 mg, 6.0 mmol), DMAD (di-
methyl acetylenedicarboxylate, 0.96 mL, 8.0 mmol), and DMPU
(0.97 mL, 8.0 mmol) were added to the mixture, and it was stirred for
12 h under refluxing. The mixture was quenched with 3n HCl at 08C and
extracted with ethyl acetate. The combined organic phase was washed
with water, saturated aqueous NaHCO3 solution, and brine. The solution
was dried over anhydrous Na2SO4. The solvent was evaporated, and the
resulting brown viscous oil was purified by flash chromatography (silica
gel, hexane/ethyl acetate=5:1 as eluent) to afford 4 as colorless crystals
(445 mg, 60% yield).
Preparation of Bis(dicyclopentadienylzirconacyclopentadiene) (9a) from
8a
9a (167 mg) was prepared in 87% yield of isolated product (94% NMR
yield) from 8a (1.0 mmol) by the same method as described for 3’.
1
9a: H NMR (C6D6, Me4Si): d=0.26 (s, 36H), 3.44 (s, 8H), 5.82 (s, 20H),
7.05 ppm (s, 2H); 13C NMR (C6D6, Me4Si): d=2.8, 43.7, 110.7, 123.6,
136.1, 140.8, 197.6 ppm; HRMS (FAB) calcd for C50H66Si4Zr2: 958.2336.
Found: 958.2332.
Preparation of 1,4,8,11-Tetrakis(trimethylsilyl)-5,7,12,14-
tetrahydropentacene-2,3,9,10-tetracarboxylic Acid Tetramethyl Ester (10a)
from 8a
10a (268 mg) was prepared in 33% yield of isolated product from 8a
(1.0 mmol) by the same method as described for 4.
10a: 1H NMR (CDCl3, Me4Si): d=0.41 (s, 36H), 3.80 (s, 12H), 3.97 (s,
8H), 7.18 ppm (s, 2H); 13C NMR (CDCl3, Me4Si): d=1.8, 38.1, 52.3,
124.1, 135.48, 135.52, 135.8, 145.9, 170.5 ppm; HRMS (FAB) calcd for
C42H58O8Si4Na [M+Na]+: 825.3106. Found: 825.3130.
4: 1H NMR (CDCl3, Me4Si): d=1.05 (t, J=7.4 Hz, 12H), 1.60–1.74 (m,
8H), 2.77–2.81 (m, 8H), 3.85 (s, 12H), 3.87 (s, 8H), 3.98 ppm (s, 6H);
13C NMR (CDCl3, Me4Si): d=14.5, 24.2, 26.4, 32.7, 52.3, 61.4, 128.0,
130.4, 135.8, 138.1, 150.0, 169.5 ppm; HRMS (FAB) calcd for C44H54O10
742.3717. Found: 742.3708.
:
Preparation of 6,13-Dimethoxy-1,4,8,11-tetrapropyl-2,3,9,10-
tetrakis(methoxycarbonyl)pentacene (5) from 4
Preparation of DDQ Adduct of 1,4,8,11-Tetrakis(trimethylsilyl)-5,7,12,14-
tetrahydropentacene-2,3,9,10-tetracarboxylic Acid Tetramethyl Ester (13a)
from 10a
A mixture of tetrahydropentacene 4 (60 mg, 0.08 mmol) and DDQ (2,3-
dichloro-5,6-dicyano-1,4-benzoquinone, 37 mg, 0.16 mmol) was refluxed
for 3 h in degassed toluene (5 mL). After cooling to RT, the solvent was
removed in vacuo. The remaining mixture was put into 10 mL of de-
gassed MeOH and stirred for 10 min to dissolve the hydroquinone. The
blue precipitate was collected by filtration. The blue solid was reprecipi-
tated in degassed CHCl3 (1 mL) and hexane (10 mL). 5 was afforded as a
blue solid (35 mg) in 60% yield of isolated product.
5: M.p.: 241–2438C (dec); 1H NMR (CDCl3, Me4Si): d=1.19 (t, J=
7.2 Hz, 12H), 1.90–2.10 (m, 8H), 3.20–3.35 (m, 8H), 3.95 (s, 12H), 4.36
(s, 6H), 9.25 ppm (s, 4H); 13C NMR (CDCl3, Me4Si): d=14.7, 24.6, 32.5,
52.4, 63.9, 120.5, 123.6, 127.3, 129.8, 138.1, 149.0, 169.4 ppm; HRMS
(FAB) calcd for C44H50O10: 738.3404. Found: 738.3405. elemental analy-
sis: calcd (%) for C44H50O10: C 71.52, H 6.82; found: C 71.22, H 6.74.
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (227 mg, 1.0 mmol)
was added to a toluene solution (5 mL) of tetrahydropentacene 10a
(268 mg, 0.33 mmol). The mixture was stirred at 508C under N2. After
2 h, the reaction mixture was purified by a flash chromatography (silica
gel, CHCl3 as eluent) to afford 13a as a yellow solid (309 mg) in 90%
yield of isolated product (100% NMR yield).
13a: 1H NMR (CDCl3, Me4Si): d=0.43 (s, 18H), 0.52 (s, 18H). 3.85 (s,
6H), 3.88 (s, 6H), 5.32 (s, 2H), 8.19 (s, 2H), 8.54 ppm (s, 2H). 13C NMR
(CDCl3, Me4Si): d=2.0, 2.1, 52.6, 52.7, 55.9, 56.8, 114.1, 127.5, 127.7,
130.9, 131.9, 136.4, 136.7, 137.4, 137.5, 139.1, 139.4, 145.0, 169.9, 170.1,
178.8 ppm; HRMS (ESI) calcd for C50H54Cl2N2NaO10Si4 [M+Na]+:
1047.2130. Found: 1047.2145.
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Double Homologation Method and Dimerization of Pentacenes
Preparation of 1,4,8,11-Tetrakis(trimethylsilyl)pentacene-2,3,9,10-
tetracarboxylic Acid Tetramethyl Ester (11a) from 13a
129.4, 136.9, 168.4 ppm; HRMS (ESI) calcd for C46H54O8Na [M+Na]+:
757.3716. Found: 757.3731. elemental analysis: calcd (%) for C46H54O8:
C 75.18, H 7.41; found: C 75.04, H 7.66.
DDQ adduct 13a (277 mg, 0.27 mmol) and g-terpinene (2.2 mL,
13.5 mmol) were stirred in toluene (3 mL) at 1008C under N2. After 3 h,
the reaction mixture was cooled to RT and purified by flash chromatogra-
phy (silica gel, degassed CHCl3 as eluent) under N2 to afford 11a as a
blue solid (148 mg, 69% yield, 82% NMR yield).
Preparation of Pentacene Dimer (12b) from 10b
12b (117 mg, 0.08 mmol) was prepared in 16% yield of isolated product
from 10b (1.0 mmol) by the same method as described for 11b.
12b: M.p.: 260–2628C; 1H NMR (CDCl3, Me4Si): d=1.02 (t, J=7.2 Hz,
24H), 1.46–1.64 (m, 32H), 2.81–3.00 (m, 16H), 3.82 (s, 24H), 5.36 (s,
4H), 7.77 ppm (s, 8H); 13C NMR (CDCl3, Me4Si): d=13.9, 23.2, 29.9,
33.3, 52.1, 54.2, 123.5, 128.2, 131.2, 136.2, 141.2, 169.4 ppm; HRMS (ESI)
calcd for C92H108O16Na [M+Na]+: 1491.7535. Found: 1491.7540; elemen-
tal analysis: calcd (%) for C92H108O16: C 75.18, H 7.41; found: C 74.94,
H 7.13.
11a: 1H NMR (CDCl3, Me4Si): d=0.60 (s, 36H), 3.91 (s, 12H), 8.92 (s,
2H), 9.08 ppm (s, 4H); 13C NMR (CDCl3, Me4Si): d=2.2, 52.5, 126.7,
129.5, 129.9, 133.0, 135.9, 139.7, 170.5 ppm; HRMS (FAB) calcd for
C42H54O8Si4: 798.2896. Found: 798.2905.
Preparation of 1,2,4,5-Tetra-hept-2-ynyl-benzene (8b) from 7
8b (308 mg) was prepared in 68% yield of isolated product from 7
(1.0 mmol) by the same method as described for 8a.
8b: 1H NMR (CDCl3, Me4Si): d=0.91 (t, J=7.2 Hz, 12H), 1.37–1.55 (m,
16H), 2.17–2.23 (m, 8H), 3.56 (t, J=2.4 Hz, 8H), 7.47 ppm (s, 2H);
13C NMR (CDCl3, Me4Si): d=13.6, 18.6, 22.0, 22.5, 31.1, 77.0, 82.7, 129.2,
133.8 ppm; HRMS (EI) calcd for C34H46: 454.3599. Found: 454.3611.
Conversion of 1,4,8,11-Tetrabutyl-2,3,9,10-
tetrakis(methoxycarbonyl)pentacene (11b) to Its Dimer (12b)
A
degassed dodecane (2 mL) solution of pentacene 11b (73 mg,
0.1 mmol) was heated for 12 h at 1508C. A white precipitate was ob-
served during heating. After about 12 h, the blue color had disappeared
completely. The reaction mixture was cooled to RT and purified by silica
gel chromatography (CHCl3 as eluent) to afford compound 12b (65 mg)
as a colorless solid in 90% yield of isolated product.
Preparation of Biszirconacycle (9’b) from 8b
9’b (150 mg) was prepared in 79% yield of isolated product (85% NMR
yield) from 8b (1.0 mmol) by the same method as described for 3’.
9’b: 1H NMR (C6D6, Me4Si): d=1.07 (t, J=7.2 Hz, 12H), 1.36–1.54 (m,
16H), 1.80 (s, 12H), 2.41–2.46 (m, 8H), 3.48 (s, 8H), 5.44–5.45 (t, J=
2.8 Hz, 8H), 5.92–5.94 (t, J=2.8 Hz, 8H), 7.07 ppm (s, 2H); 13C NMR
(C6D6, Me4Si): d=14.6, 15.3, 24.2, 33.3, 34.0, 37.7, 105.2, 111.8, 123.6,
124.3, 128.3, 136.8, 186.1 ppm; HRMS (FAB) calcd for C58H74Zr2:
950.3885. Found: 950.3877.
Conversion of 1,4,8,11-Tetrabutyl-2,3,9,10-
tetrakis(methoxycarbonyl)pentacene Dimer (12b) to Its Monomer (11b)
A
degassed 1,2-[D4]dichlorobenzene (0.5 mL) solution of pentacene
dimer 12b (5 mg) was heated for 6 h at 1508C in the dark. The colour of
the reaction mixture changed from colorless to blue. Pentacene monomer
11b was formed in quantitative NMR yield.
Preparation of 1,4,8,11-Tetrabutyl-2,3,9,10-tetrakis(methoxycarbonyl)-
5,7,12,14-tetrahydropentacene (10b) from 8b
Preparation of Pentacene Dimer (12a) from 11a
A
degassed dodecane (2 mL) solution of pentacene 11a (798 mg,
10b (310 mg) was prepared in 42% isolated yield from 8b (1.0 mmol) by
the same method as described for 4.
1.0 mmol) was heated for 3 d at 2008C. Although formation of a white
precipitate was observed, the blue color of 11a remained. The reaction
mixture was cooled to RT and purified by silica gel chromatography
(CHCl3 as eluent) to afford compound 12a (320 mg) as a colorless solid
in 40% yield of isolated product.
12a: M.p.:>3008C; 1H NMR (CDCl3, Me4Si): d=0.35 (s, 72H), 3.78 (s,
24H), 5.28 (s, 4H), 7.92 ppm (s, 8H); 13C NMR (CDCl3, Me4Si): d=2.5,
52.3, 54.2, 127.8, 135.4, 136.1, 138.1, 140.1, 170.5 ppm; HRMS (FAB)
calcd for C84H108O16Si8Na [M+Na]+: 1619.5689. Found: 1619.5682; ele-
mental analysis: calcd (%) for C84H108O16Si8: C 63.12, H 6.81; found:
C 63.10, H 6.86.
1
10b: H NMR (CDCl3, Me4Si): d=0.98 (t, J=7.2 Hz, 12H), 1.41–1.58 (m,
16H), 2.74–2.80 (m, 8H), 3.84 (s, 12H), 3.92 (s, 8H), 7.27 ppm (s, 2H);
13C NMR (CDCl3, Me4Si): d=13.9, 23.0, 30.3, 32.6, 32.9, 52.2, 125.6,
130.2, 134.4, 135.6, 138.5, 169.5 ppm; HRMS (EI) calcd for C46H58O8:
738.4132. Found: 738.4131.
Preparation of DDQ Adduct of 1,4,8,11-Tetrabutylpentacene-2,3,9,10-
tetracarboxylic acid tetramethyl ester (13b) from 10b
13b (298 mg) was prepared in 93% yield of isolated product (100%
NMR yield) from 10b (1.0 mmol) by the same method as described for
13a.
Preparation of 1,4,8,11-Tetrakis(trimethylsilyl)-5,7,12,14-
tetrahydropentacene-2,3,9,10-tetracarboxylic Acid Tetraethyl Ester (10c)
from 8a
13b: 1H NMR (CDCl3, Me4Si): d=0.99 (t, J=4.8 Hz, 6H), 1.00 (t, J=
4.8 Hz, 6H), 1.45–1.67 (m, 12H), 1.70–1.79 (m, 4H), 2.96–3.06 (m, 4H),
3.10–3.20 (m, 4H), 3.90 (s, 6H), 3.91 (s, 6H), 5.38 (s, 2H), 8.05 (s, 2H),
8.43 ppm (s, 2H). 13C NMR (CDCl3, Me4Si): d=13.9 (Two peaks were
overlapped.), 23.1, 23.2, 30.0, 30.2, 33.6, 33.7, 52.5, 52.7, 56.0, 57.2, 114.0,
123.68, 123.72, 129.9, 130.3, 132.2, 132.3, 132.7, 133.2, 137.2, 137.3, 144.4,
168.9, 168.1, 179.0 ppm; HRMS (ESI) calcd for C54H55Cl2N2O10 [M+H]:
961.3234. Found: 961.3256.
The compound 10c (250 mg) was prepared by the same method as de-
scribed for 4 in 30% yield from 8a (518 mg, 1.0 mmol).
1
10c: H NMR (CDCl3, Me4Si): d=0.42 (s, 36H), 1.33 (t, J=7.2 Hz, 12H),
3.96 (s, 8H), 4.24 (q, J=7.2 Hz, 8H), 7.17 ppm (s, 2H); 13C NMR
(CDCl3, Me4Si): d=1.9, 13.8, 38.2, 61.5, 124.1, 135.5, 135.6, 135.8, 145.8,
170.1 ppm; HRMS (ESI) calcd for C46H66O8Si4Na [M+Na]+: 881.3732.
Found: 881.3705.
Preparation of 1,4,8,11-Tetrabutyl-2,3,9,10-
tetrakis(methoxycarbonyl)pentacene (11b) from 10b
Preparation of 1,4,8,11-Tetrakis(trimethylsilyl)pentacene-2,3,9,10-
tetracarboxylic Acid Tetraethyl Ester (11c) from 10c
A mixture of tetrahydropentacene 10b (148 mg, 0.2 mmol) and DDQ
(2,3-dichloro-5,6- dicyanobenzoquinone, 91 mg, 0.4 mmol) was heated in
degassed mesitylene (2 mL) for 3 h at 1508C. After cooling to room tem-
perature, the reaction mixture was purified by silica gel chromatography
under N2 (degassed CHCl3 as eluent) to afford 11b as a blue solid
(52 mg) in 36% yield of isolated product.
11b: M.p.: 232–2358C (dec); 1H NMR (1,2-[D4]dichlorobenzene, Me4Si):
d=1.20 (t, J=7.2 Hz, 12H), 1.74–1.82 (m, 8H), 2.03–2.16 (m, 8H), 3.47–
3.57 (m, 8H), 4.05 (s, 12H), 9.16 (s, 4H), 9.17 ppm (s, 2H). 13C NMR
(CDCl3, Me4Si): d=13.0, 22.3, 29.2, 32.3, 51.3, 124.8, 125.9, 126.8, 129.0,
Tetrahydropentacene 10c (858 mg, 1.00 mmol) was treated with DDQ by
the same way as described for 13a to afford the corresponding DDQ
adduct 13c (1.00 g) in 93% yield of isolated product.
13c: 1H NMR (CDCl3, Me4Si): d=0.44 (s, 18H), 0.53 (s, 18H), 1.36 (t,
J=7.2 Hz, 6H), 1.38 (t, J=7.2 Hz, 6H), 4.26–4.34 (m, 8H), 5.29 (s, 2H),
8.19 (s, 2H), 8.53 ppm (s, 2H). 13C NMR (CDCl3, Me4Si): d=2.1, 2.2,
13.72, 13.76, 55.9, 56.9, 61.9, 62.1, 114.3, 127.4, 127.6, 130.9, 131.9, 136.3,
136.6, 137.6, 137.7, 138.8, 139.0, 144.7, 169.5, 169.7, 179.0 ppm.
Chem. Asian J. 2009, 4, 294 – 301
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www.chemasianj.org
299

T. Takahashi et al.
FULL PAPERS
DDQ adduct 13c (1.08 g, 1.0 mmol) was treated with g-terpinene by the
same method as described for 11a to afford pentacene 11c (589 mg) in
69% yield of isolated product.
11c: M.p.:>3008C; 1H NMR (CDCl3, Me4Si): d=0.62 (s, 36H), 1.43 (t,
J=7.2 Hz, 12H), 4.35 (t, J=7.2 Hz, 8H), 8.92 (s, 2H), 9.08 ppm (s, 4H);
13C NMR (CDCl3, Me4Si): d=2.3, 13.9, 61.8, 126.6, 129.5, 129.8, 133.0,
136.2, 139.3, 170.1 ppm; HRMS (EI) calcd for C46H62O8Si4: 854.3522.
Found: 854.3510; elemental analysis: calcd (%) for C46H62O8Si4: C 64.59,
H 7.31; found: C 64.73, H 7.20.
3 mL of CHCl3 and added to 10 mL of MeOH. The resulting precipitate
was collected by filtration, and dried in vacuo to afford 15 as a pale-
yellow solid (389 mg, 85% yield).
1
15: H NMR ([D6]DMSO, Me4Si): d=3.97 (s, 8H), 7.26 (s, 2H), 7.63 ppm
(s, 4H); 13C NMR ([D6]DMSO, Me4Si): d=34.6, 126.2, 127.3, 130.7, 133.5,
139.8, 168.7 ppm; HRMS (FAB, negative) calcd for C26H17O8 [MÀH]:
457.0923. Found: 457.0917.
Preparation of 5,7,12,14-Tetrahydropentacene Diimide (16) from 15
Tetraacid 15 (457 mg, 1.0 mmol) was heated in acetic anhydride (10 mL)
at 1408C for 3 h. After cooling to RT, the solvent was removed in vacuo.
The corresponding dianhydride (450 mg) was obtained in quantitative
yield. In a 50 mL flask fitted with a water separator and a refluxing con-
denser were placed anhydride, 2-ethylhexylamine (1.62 mL, 10.0 mmol)
and toluene (20 mL). The flask was heated to maintain a vigorous reflux
for 6 h. After cooling to RT, the mixture was washed with aqueous 3m
HCl, saturated aqueous NaHCO3 solution, and brine, then dried over
Na2SO4. After evaporation of the solvent, the resulting residue was puri-
fied by flash chromatography (silica gel, CHCl3 as eluent) to afford the
16 as a pale-yellow solid (515 mg, 80% yield).
16: 1H NMR (CDCl3, Me4Si): d=0.87 (t, J=7.2 Hz, 6H), 0.90 (t, J=
7.2 Hz, 6H), 1.21–1.38 (m, 16H), 1.80–1.86 (m, 2H), 3.54 (d, J=7.2 Hz,
4H), 4.05 (s, 8H), 7.28 (s, 2H), 7.73 ppm (s, 4H); 13C NMR (CDCl3,
Me4Si): d=10.4, 14.0, 22.9, 23.8, 28.5, 30.5, 36.5, 38.2, 41.9, 122.2, 126.3,
130.4, 133.6, 143.6, 168.8 ppm; HRMS (FAB) calcd for C42H49O4N2
[M+H]: 645.3692. Found: 645.3681.
Preparation of 5,7,12,14-Tetrahydropentacene-2,3,9,10-tetracarboxylic
Acid Tetramethyl Ester (14) from 10a
To a solution of 1,4,8,11-tetrakis(trimethylsilyl)-5,7,12,14-tetrahydropen-
tacene-2,3,9,10-tetracarboxylic acid tetramethyl ester 10a (802 mg,
1.0 mmol) in 15 mL of THF was added tetrabutylammonium fluoride
(1.0m THF solution, 4.0 mL, 4.0 mmol) at 08C, and the mixture was
stirred for 1 h. The mixture was then quenched with 3m HCl at 08C and
extracted with ethyl acetate. The combined organic phase was washed
with water, saturated aqueous NaHCO3 solution, and brine. The solution
was dried over anhydrous Na2SO4. The solvent was evaporated, and the
resulting brown viscous oil was purified by flash chromatography (silica
gel, CHCl3 as eluent) to afford 14. 14 was obtained as a pale-yellow solid
(386 mg, 75% yield) by washing with methanol (3 mL).
1
14: H NMR (CDCl3, Me4Si): d=3.90 (s, 12H), 3.97 (s, 8H), 7.22 (s, 2H),
7.65 ppm (s, 4H); 13C NMR (CDCl3, Me4Si): d=35.5, 52.6, 126.5, 128.1,
129.8, 133.4, 140.2, 168.2 ppm; HRMS (EI) calcd for C30H26O8: 514.1627.
Found: 514.1613.
Preparation of DDQ Adduct of Pentacene Diimide (13e) from 16
Preparation of DDQ Adduct of 2,3,9,10-Tetracarboxylic Acid Tetramethyl
Ester Pentacene (13d) from 14
The compound 13e (780 mg) was prepared by the same method as de-
scribed for 13a (90% yield, 100% NMR yield) from 16 (644 mg,
1.0 mmol).
The compound 13d (555 mg) was prepared by the same method as de-
scribed for 13a in 90% yield (100% NMR yield) from 14 (514 mg,
1.0 mmol).
13d: 1H NMR (CDCl3, 323 K, Me4Si): d=3.94 (s, 6H), 3.96 (s, 6H), 5.32
(s, 2H), 7.85 (s, 2H), 8.19 (s, 4H), 8.30 ppm (s, 2H). 13C NMR (CDCl3,
323 K, Me4Si): d=52.81, 52.89, 55.4, 56.9, 113.9, 126.66, 126.74, 129.9,
130.3, 130.4, 130.8, 133.1, 133.4, 133.7, 134.5, 144.9, 167.2, 167.5,
178.5 ppm; HRMS (ESI) calcd for C38H22Cl2N2NaO10 [M+Na]+:
759.0549. Found: 759.0574.
1
13e: H NMR (CDCl3, 323 K, Me4Si): d=0.87 (t, J=7.2 Hz, 3H), 0.88 (t,
J=7.2 Hz, 3H), 0.93 (t, J=7.2 Hz, 3H), 0.94 (t, J=7.2 Hz, 3H), 1.19–1.62
(m, 16H), 1.51–1.62 (m, 1H), 1.84–1.94 (m, 1H), 3.64 (d, J=7.2 Hz, 2H),
3.67 (d, J=7.2 Hz, 2H), 5.41 (s, 2H), 8.01 (s, 2H), 8.29 (s, 2H), 8.36 (s,
2H), 8.41 ppm (s, 2H). 13C NMR (CDCl3, 323 K, Me4Si): d=10.4, 10.5,
13.9 (2 C), 23.0 (2 C), 24.07, 24.15, 28.58, 28.61, 30.7, 30.8, 38.4, 38.5,
42.57, 42.59, 55.2, 56.8, 113.8, 124.2, 124.6, 128.1, 128.2, 129.8, 130.2,
134.2, 134.9, 135.4, 135.7, 145.0, 167.4, 167.7, 178.2 ppm; HRMS (ESI)
calcd for C50H45Cl2N4O6 [M+H]: 867.2716. Found: 867.2732.
Preparation of 2,3,9,10-Tetracarboxylic Acid Tetramethyl Ester Pentacene
(11d) from 13d
Preparation of Pentacene Diimide(17) from 13e
The compound 17 (422 mg) was prepared by the same method as de-
scribed for 11a (66% yield) from 13e (866 mg, 1.0 mmol).
The compound 11d (367 mg) was prepared by the same method as de-
scribed for 11a in 72% yield from 13d (736 mg, 1.0 mmol).
17: M.p.:>3008C; 1H NMR (1,1,2,2-[D2]tetrachloroethane, 419 K,
Me4Si): d=0.99 (t, J=6.8 Hz, 6H), 1.06 (t, J=7.2 Hz, 6H), 1.33–1.58 (m,
16H), 1.99–2.10 (m, 2H), 3.77 (d, J=7.2 Hz, 4H), 8.50 (s, 4H), 8.94 (s,
4H), 9.11 ppm (s, 2H); 13C NMR (1,1,2,2-[D2]tetrachloroethane, 419 K,
Me4Si): d=10.6, 13.6, 22.8, 24.7, 28.8, 31.3, 38.8, 42.9, 125.9, 127.4, 128.5,
131.1, 131.5, 132.1, 167.3 ppm; HRMS (FAB) calcd for C42H45N2O4
[M+H]: 641.3379. Found: 641.3364; elemental analysis: calcd (%) for
C42H44N2O4: C 78.72, H 6.92, N 4.37; found: C 78.61, H 7.04, N 4.28.
11d: M.p.:>3008C; 1H NMR (CDCl3, Me4Si): d=3.99 (s, 12H), 8.36 (s,
4H), 8.72 (s, 4H), 8.98 ppm (s, 2H); 13C NMR (CDCl3, Me4Si): d=52.7,
127.7, 128.2, 129.0, 130.2, 131.0, 132.0, 167.9 ppm; HRMS (EI) calcd for
C30H22O8: 510.1315. Found: 510.1328; elemental analysis: calcd (%) for
C30H22O8: C 70.58, H 4.34; found: C 70.53, H 4.04.
Preparation of Pentacene Dimer (12d) from 11d
12d (490 mg) was prepared in 96% yield of isolated product from 11d
(510 mg, 1.0 mmol) by the same method as described for 12a.
12d: M.p.:>3008C; 1H NMR (CDCl3, Me4Si): d=3.87 (s, 24H), 5.21 (s,
4H), 7.52 (s, 8H), 7.94 ppm (s, 8H); 13C NMR (CDCl3, Me4Si): d=52.6,
53.5, 126.6, 128.4, 129.5, 132.1, 142.1, 168.0 ppm; HRMS (FAB) calcd for
C60H44O16Na [M+Na]+: 1043.2527. Found: 1043.2521; elemental analysis:
calcd (%) for C60H44O16: C 70.58, H 4.34; found: C 70.53, H 4.48.
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2,3,9,10-Tetrakis(methoxycarbonyl)-5,7,12,14-tetrahydropentacene
14
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ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: August 12, 2008
Published online: December 15, 2008
Chem. Asian J. 2009, 4, 294 – 301
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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301