Synthesis- and oxidation of triarylamine derivatives bearing hydrogen-bonding groups

Article abstract of DOI:10.1021/jo070318a

(Chemical Equation Presented) Hydrogen-bonding triarylamines, 4-(N,N-bis(4-medioxyphenyl)amino)benzoic acid (TPA1), 5-(N,N-bis(4- methoxyphenyl)amino)isophthalic acid (TPA2), and N-(4-(1H-benz-imidazol-2-yl) phenyl)-N,N-bis(4-methoxyphenyl)amine (BImTPA),

Full text of DOI:10.1021/jo070318a

radical cations that were studied by magnetic susceptibility,
UV-vis, and electron spin resonance spectroscopy.
Synthesis and Oxidation of Triarylamine
Derivatives Bearing Hydrogen-Bonding Groups
Scheme 1 shows the methods used to make the triarylamines.
TPA1 was made by Pd2(dba)3-catalyzed coupling of N,N-bis-
(4-methoxyphenyl)amine (BMPA) with methyl 4-iodobenzoate,
followed by hydrolysis of the obtained crude ester. TPA2 was
made analogously by coupling BMPA with dimethyl 5-iodo-
isophthalate, followed by hydrolysis of the crude diester. TPA1
was then condensed with 1,2-diaminobenzene to give BImTPA.
The product amines were all satisfactorily characterized by 1H
NMR, 13C NMR, FTIR, and elemental composition.
Hidenori Murata† and Paul M. Lahti*
Department of Chemistry, UniVersity of Massachusetts,
Amherst, Massachusetts 01003
lahti@chem.umass.edu
ReceiVed February 15, 2007
Addition of SbCl5 or AgSbF6 (Figure 1) to dichloromethane
solutions of the triarylamines immediately gave deep colors
associated with the corresponding radical cations. TPA1-rc was
violet, TPA2-rc red-purple, and BImTPA-rc green. The as-
sociated UV-vis maxima were 356, 577, and 785 nm for TPA1-
rc, 365, 520, and 793 nm for TPA2-rc, and 290, 365, 401,
∼630 (shoulder), and 777 nm for BImTPA-rc. The colors per-
sisted for days in air. The similarity of the TPA1-rc and TPA2-
rc absorption spectra is consistent with their chromophoric sim-
ilarity. The transient spectroscopy of photooxidization and the
chemical oxidation of TPA1 with Br2 show absorption bands
at 750 and 590 nm that are attributed3 to the radical cation;
these are in good agreement with the present results. Part of
the spectrum of BImTPA-rc is significantly perturbed by com-
parison, with doubling of a peak found around 350-360 nm in
the other two systems (new peak at ∼400 nm) and a red shift
of the band at about 500-600 nm to about 630 nm. However,
the lowest energy, strongest peak in all is at 780-800 nm (∼1.55
eV).
Hydrogen-bonding triarylamines, 4-(N,N-bis(4-methoxyphen-
yl)amino)benzoic acid (TPA1), 5-(N,N-bis(4-methoxyphen-
yl)amino)isophthalic acid (TPA2), and N-(4-(1H-benz-
imidazol-2-yl)phenyl)-N,N-bis(4-methoxyphenyl)amine
(BImTPA), were synthesized as radical cation precursors.
TPA1 and TPA2 are readily p-doped by AgSbF6 to give
highly persistent radical cations. Poor solid-state spin yields
of the radical cation from BImTPA may be due to spin
delocalization.
Cationic doping of triarylamines is an important strategy in
organic-based magnetic materials.1 Hydrogen-bonding interac-
tions are useful to help assemble molecules in the solid state
with some degree of control, to try to control intermolecular
exchange between unpaired electrons.2 However, hydrogen-
bonded assembly has not been much used to our knowledge in
p-dopable triarylamines, although 4-(N,N-bis(4-methoxyphenyl)-
amino)benzoic acid, TPA1, was made as a synthetic intermedi-
ate for studies of photoactive and luminescent organometallic
complexes.3 To our knowledge, the solid-state hydrogen bonding
and chemical doping behavior of TPA1 has not been studied.
This paper describes the oxidation of three hydrogen-bonding
triphenylamines: TPA1, 5-(N,N-bis(4-methoxyphenyl)amino)-
isophthalic acid (TPA2), and N-(4-(1H-benzimidazol-2-yl)-
phenyl)-N,N-bis(4-methoxyphenyl)amine (BImTPA). TPA1 and
TPA2 were crystallographically characterized, and all three were
p-doped in both solid state and solution to give highly persistent
Table 1 summarizes solution ESR hyperfine couplings for
the radical cations generated by AgSbF6 oxidation of TPA
solutions in dichloromethane at room temperature. TPA1-rc and
TPA2-rc show hyperfine coupling (hfc) from the aryl protons,
but any analogous hfc in BImTPA-rc was masked by line
broadening, despite attempts in several solvents in the temper-
ature range of 100-300 K. The ESR spectra of samples
produced by SbCl5 vapor oxidization were essentially the same.
Under no conditions or solvents attempted were ESR peaks
observed that were clearly attributable to triplet state radical
pairs, either in fluid solution or at 77 K in frozen solution.
Numerous attempts to crystallize BImTPA failed to yield
single crystals of sufficient quality for X-ray diffraction (XRD)
analysis. Its high melting point suggests strong intermolecular
interactions. FTIR shows a broad NH stretching envelope over
2800-3100 cm-1 that suggests NH‚‚‚N hydrogen bonding
(NH‚‚‚N chain formation is common for 2-substituted benz-
imidazoles). TPA1 and TPA2 crystallize well from chloroform/
methanol and were readily analyzed by single-crystal XRD.
† Present address: Department of Pure & Applied Chemistry, Faculty of Science
& Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan.
(1) (a) Ito, A.; Ino, H.; Matsui, Y.; Hirao, Y.; Tanaka, K. J. Phys. Chem.
A 2004, 108, 5715. (b) Bushby, R. J.; Gooding, D. J. Chem. Soc., Perkin
Trans. 2 1998, 1069. (c) Tyutylkov, N.; Baumgarten, M.; Dietz, F. Chem.
Phys. Lett. 2002, 353, 231. (d) Stickly, K. R.; Blackstock, S. C. J. Am.
Chem. Soc. 1994, 116, 11576. (e) Selby, T. D.; Blackstock, S. C. J. Am.
Chem. Soc. 1999, 121, 7152. (f) van Meurs, P. J.; Janssen, R. A. J. J. Org.
Chem. 2000, 65, 5712. (g) Okada, K.; Imakura, T.; Oda, M.; Murai, H.;
Baumgarten, M. J. Am. Chem. Soc. 1996, 118, 3047. (h) Sato, K.; Yano,
M.; Furuichi, M.; Shiomi, D.; Takui, T.; Abe, K.; Itoh, K.; Higuchi, A.;
Katsuma, K.; Shirota, Y. J. Am. Chem. Soc. 1997, 119, 6607. (i) Murata,
H.; Takahashi, M.; Namba, K.; Takahashi, N.; Nishide, H. J. Org. Chem.
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(2) (a) Veciana, J.; Cirujeda, J.; Rovira, C.; Molins, E.; Novoa, J. J.
Solid State Chem. 2001, 159, 440-450. (b) Maspoch, D.; Domingo, N.;
Ruiz-Molina, D.; Wurst, K.; Tejada, J.; Rovira, C.; Veciana, J. Compt. Rend.
Chim. 2005, 8, 1213. (c) Lahti, P. M. Magneto-structural Correlations in
π-Conjugated Nitroxide-based Radicals: Hydrogen-bonds and Related
Interactions in Molecular Organic Solids. In Carbon-based magnetism: An
oVerView of the magnetism of metal-free carbon-based compounds and
materials; Makarova, T., Palacio, F., Eds.; Elsevier: Amsterdam, 2006; pp
23-52.
(3) (a) Baranoff, E.; Dixon, I. M.; Collin, J.-P.; Sauvage, J.-P.; Ventura,
B.; Flamigni, L. Inorg. Chem. 2004, 43, 3057. (b) Flamigni, L.; Baranoff,
E.; Collin, J.-P.; Sauvage, J.-P. Chem.sEur. J. 2006, 12, 6592.
10.1021/jo070318a CCC: $37.00 © 2007 American Chemical Society
Published on Web 05/31/2007
4974
J. Org. Chem. 2007, 72, 4974-4977

SCHEME 1. Synthesis of Triphenylamines and Derived Radical Cations
TPA2 also crystallizes well from THF, but this solvent is
incorporated into the lattice.
directly probed. However, π-orbital contact between aryl units
could also give exchange between radical cations, given their
significant spin densities delocalized from the aminium centers.
In TPA1, the π-carbon ipso to the carboxylic acid group is only
3.52 Å from a π-carbon ortho to the acid group on a neighboring
molecule. For TPA2, inversion symmetry gives to an antiparallel
close contact of 3.36 Å between the phenyl-CO2H bonds
(Supporting Information). These contacts do not provide ideal
π-system overlap for inter-radical exchange, but modest re-
alignment during doping could easily improve them.
UB3LYP/6-31G* geometry optimized computations5 for the
three radical cations were carried out in order to evaluate further
their spin delocalization and to compare to the experimental
ESR hfc. Solution-phase ESR spectra of TPA1-rc and TPA2-
rc show aryl C-H hyperfine coupling consistent with the
computational 6-9% and (-)2-4% spin populations on the
phenyl π-carbons ortho and meta to the aminium nitrogen,
respectively. These delocalized spin density sites could provide
exchange sites where close contacts between doped radical
cations occur in the solid state, depending on the intermolecular
contacts between molecules in the doped form.
Powdered TPA1, TPA2, or BImTPA exposed to SbCl5 vapor
for 24 h turned blue-black, blue-black, and green-black,
respectively. The oxidized samples remained visually unchanged
after exposure to room air for weeks. Measurements of the
vapor-doped paramagnetic susceptibilities of powdered TPA1
and TPA2 showed 28 and 12% of the theoretical moments
expected if all molecules yielded S ) 1/2 spin units (Supporting
Information). Single crystals of TPA1 and TPA2 that were
doped for 24 h showed pale yellow interiors when broken,
proving that extensive diffusive doping does not occur readily
from the vapor phase.
By comparison, dichloromethane solutions of TPA1, TPA2,
or BImTPA treated with AgSbF6 immediately turned deeply
colored and could be precipitated into hexane to give dark
colored powders that were readily studied by paramagnetic
susceptibility (Figure 2). The data indicate 59, 79, and 4% yields
of spin units from this procedure, relative to a theoretical value
1
of 0.375 emu‚K/Oe‚mol for 100% generation of S ) /2 spin
carriers, and assuming that the basic spin units are monoradical
-
cations with SbF6 counterions.
Neutral TPA1 forms crystallographic dimers, a typical motif
for monocarboxylic acids.4 TPA2 forms 1-D ribbons, as is
common in isophthalic acids.4 In both, the aryl rings are
significantly twisted relative to one another. All methoxy and
some aryl groups show moderately large thermal motion
ellipsoids at room temperature, but the molecules are not
otherwise disordered. Although the hydrogen bonds hold the
amine molecules closer together than might occur without the
interaction, the crystallographic geometries found in the neutral
amines appear unlikely to assist strong exchange. The closest
N‚‚‚N distances (Supporting Information) in TPA1 are 5.8-
5.9 Å, and in TPA2, they are 6.74 Å, too large to allow strong,
direct exchange due to direct overlap of N(2p) orbitals from
the aminium radical cation centers. It seems likely that swelling
of the lattice to accommodate dopant counterions would move
the TPA radical cations further apart, although this was not
FIGURE 1. UV-vis spectra of radical cations from AgSbF6 oxidation
of neutral amines at room temperature in dichloromethane: (a) TPA1-
rc, (b) TPA2-rc, (c) BImTPA-rc.
J. Org. Chem, Vol. 72, No. 13, 2007 4975

TABLE 1. Solution ESR Hyperfine Coupling Constants
techniques, magnetic studies of products from both methods
showed disappointingly poor spin yields of only 4-5%.
Solutions of this radical cation also are not as color-persistent
as those from TPA1 and TPA2. The radical cation BImTPA-
rc is formed to a significant extent, however, based on the
spectroscopic results described above, as well as cyclic volta-
mmetry (CV). CV in CHCl3 shows roughly quasi-reversible
behavior, with E°′ values for (n,+) of 720, 640, and 560 mV at
10 mV/s sweep rate for TPA1, TPA2, and BImTPA, respec-
tively. In order of ease of oxidation, BImTPA > TPA2 >
TPA1. Since BImTPA is the most easily oxidized of the
triarylamines in this study, its low solid-state spin yield may
be due to increased reactivity in the solid. BImTPA-rc has spin
delocalization onto its benzimidazole unit based on its UV and
ESR spectroscopy, as well as the computational modeling
results. This could cause solid-state dimerization and other
reactions with consequent loss of spin moment.
Attachment of one carboxylic acid group to a TPA leads to
solid-state dimer formation, while attachment of an isophthalic
acid group leads to ribbon formation, both due to directional
hydrogen bonding between the carboxylic acid groups. The
hydrogen bonding between carboxylic acid groups in TPA1 and
TPA2 holds them together in motifs that were expected by
analogy to other benzenoid and isophthalic acid functionalized
systems. Use of benzimidazole as a hydrogen-bonding substitu-
ent did not yield diffraction quality crystals, but hydrogen-
bonded chains would be expected by analogy to other benzim-
idazoles. Hence, hydrogen bonding does serve to bring the
triarylamine units into close solid-state proximity. This has
potential use for the crystal assembly of dopable organic
paramagnet precursors and for bringing electron donor triary-
lamines into proximity with other molecules to act as energy
transfer or quenching agents.
TPA1-rc
a(N) ) 8.58 G
a(H) ) 1.37(6H)
a(H) ) 1.00(6H)
a(H) ) 0.56(6H)
a(N) ) 8.57 G
TPA2-rc
a(H) ) 1.38(7H)
a(H) ) 1.05(6H)
a(H) ) 0.57(4H)
a(N) ) 8.33 G
BImTPA-rc
Unresolved benzimidazole hfc in BImTPA-rc probably gives
heterogeneous line shape broadening that obscures aryl CH
hyperfine in its ESR spectrum. The UB3LYP/6-31G* computa-
tions support this, showing that (-)1.6% of spin density is
delocalized onto the benzimidazole 2-C position, 5.4% onto the
imine 3-N position, and about (()1-6% onto the benzimidazole
aryl carbons. The significant shifts in some UV-vis bands of
BImTPA-rc by comparison to those of TPA1-rc and TPA2-
rc also reflect electronic conjugation between the radical site
and the benzimidazole group.
Vapor-phase p-doping of neat powdered TPA1 and TPA2
with SbCl5 gives a surface radical cation layer that persists for
many weeks but does not perfuse the sample bulk, as explained
above. At low temperatures, the øT(T) data for vapor p-doped
samples show weak antiferromagnetic (AFM) exchange (Sup-
porting Information), so the amount of surface doping is
sufficient to give exchange interaction between radical cation
sites by proximity. The neutral amines TPA1 and TPA2 are
held in sufficient proximity in their crystal lattices that their
doped forms could show small to modest intermolecular
exchange interaction, assuming that the dimer and chain
hydrogen-bond motifs are maintained after doping.
Solution-phase doping of TPA1 and TPA2 with AgSbF6
gives precipitated products with much higher spin yields. The
exchange behaviors of these products are not necessarily related
to those of the vapor-doped TPA samples, but they do also show
øT(T) downturns at lower temperature, indicating AFM ex-
change interactions, and their 1/ø(T) versus T plots give Weiss
constants of (-)6.3 and (-)2.6 K, respectively. Solid powder
samples and solutions of the radical cations generated this way
are highly persistent under ambient conditions and retain their
characteristic deep coloration for over a year at -30 °C. The
carboxylic acid units at the para (TPA1-rc) and both meta
(TPA2-rc) positions of the non-methoxylated phenyl rings are
apparently effective steric blockading groups, limiting reactions
such as radical dimerization or oxygen trapping. However, these
samples were not readily subjected to further purification or
recrystallization. Attempts at slow evaporation from dichlo-
romethane and slow diffusion of hexane into dichloromethane
did not yield crystals of sufficient quality for single-crystal X-ray
diffraction analysis, so detailed magnetostructural analysis of
the antiferromagnetic interactions in the radical cations is not
possible at this time, but hydrogen bonding in these systems is
a major part of bringing the molecules closer together in the
neutral TPA systems and is likely to be an important contributor
to holding the radical cations in proximity in the neat solids.
Although BImTPA gives radical cations in amounts readily
detected by ESR from both vapor and solution oxidation
BImTPA exhibited only small spin yields in cationic doping
experiments, with limited persistence of its radical cation
solutions. This was attributed to spin delocalization in this
system. Cationic doping of the carboxylic acid functionalized
TPAs gives highly persistent radical cations readily characterized
by solution molecular spectroscopy. Solid-state magnetic mea-
surements of the latter radical cations show strong doping levels,
with modest antiferromagnetic exchange interactions at low
temperature. This high persistence of the carboxylic acid
functionalized radical cation systems makes them promising as
possible spin-bearing components in solid-state magnetic ma-
terials and related electronic materials.
Experimental Section
4-(N,N-Bis(4-methoxyphenyl)amino)benzoic acid (TPA1). 4-Io-
dobenzoic acid methyl ester (3.43 g, 13.1 mmol) and N,N-bis(4-
methoxyphenyl)amine6 (3.00 g, 13.1 mmol) were dissolved in
toluene (19.6 mL). Sodium tert-butoxide (1.51 g, 15.7 mmol), tri-
tert-butylphosphine (0.318 g, 1.57 µmol), and tris(dibenzylidene-
acetone)dipalladium (0.300 g, 0.328 µmol) were added, and then
the mixture was heated at 100 °C for 7 h. The reaction mixture
was neutralized with 1 N aqueous ammonia and extracted with
chloroform. The organic layer was washed with brine and evapo-
rated to give the crude product, which was added to 146 mL of
ethanol and mixed with 146 mL of 1 M aq NaOH. The mixture
was heated to reflux for 1 h and then cooled to room temperature
and concentrated. The precipitate that formed was filtered. Then
182 mL of water was added, and 182 mL of 1 M aq HCl was
(4) (a) Etter, M. C. Acc. Chem. Res. 1990, 23, 120-126. (b) Bernstein,
J.; Etter, M. C.; Leiserowitz, L. Struct. Correl. 1994, 2, 431-507.
(5) All computations in this paper were carried out using Spartan 2002
for Irix 6.5 by Wavefunction Inc., Irvine CA.
(6) Ma, D.; Cai, Q.; Zhang, H. Org. Lett. 2003, 5, 2453.
4976 J. Org. Chem., Vol. 72, No. 13, 2007

FIGURE 2. (a) Paramagnetic susceptibility øT versus temperature plots for solution doped samples of TPA1 (2), TPA2 (B), and BImTPA (O)
at 1000 Oe; (b) Curie-Weiss plot for TPA1; (c) Curie-Weiss plot for TPA2.
added dropwise while the reaction was stirred. The resulting yellow
precipitate was filtered, washed with water, and dried. Chroma-
tography of the solid (silica gel, ethyl acetate) yielded TPA1 (2.75
g, 60%), which was recrystallized as yellow rhombi from chloroform/
methanol: mp 204-206 °C; 1H NMR (CDCl3) δ 7.85 (d, 2H, J )
9.0 Hz), 7.11 (d, 4H, J ) 9.0 Hz), 6.87 (d, 4H, J ) 9.0 Hz), 6.81
(d, 2H, J ) 9.0 Hz), 3.81 (s, 6H); 13C NMR (CDCl3) δ 171.1,
157.0, 153.4, 139.3, 131.6, 127.9, 119.0, 116.8, 115.0, 55.5; IR
(KBr pellet, cm-1) 2958 (OH str), 1669 (CdO str); MS (EI, m/z)
calcd for C21H19NO4 349, found 349.4. Anal. Calcd for C21H19-
NO4: C, 72.19; H, 5.48; N, 4.01. Found: C, 72.09; H, 5.39; N,
3.94. Single-crystal X-ray structural analysis results were submitted
to the Cambridge Structural Database, deposition number 636280.
5-(N,N-Bis(4-methoxyphenyl)amino)isophthalic acid (TPA2).
5-Iodoisophthalic acid dimethyl ester7 (2.50 g, 7.81 mmol) and N,N-
bis(4-methoxyphenyl)amine6 (1.79 g, 7.81 mmol) were dissolved
in toluene (11.7 mL). Sodium tert-butoxide (0.901 g, 9.37 mmol),
tri-tert-butylphosphine (0.158 g, 781 µmol), and tris(dibenzylide-
neacetone)dipalladium (0.165 g, 180 µmol) were added, and the
mixture was heated at 100 °C for 7 h. The reaction mixture was
neutralized with 1 N aq ammonia and extracted with chloroform.
The organic layer was washed with brine and evaporated to give
the crude product, to which was added 87 mL of ethanol then 87
mL of 1 M aq NaOH. The mixture was heated to reflux for 1 h
and then cooled to room temperature and concentrated. The resulting
precipitate was filtered and suspended in 108 mL of water, then
108 mL of 1 M aq HCl was added dropwise with stirring. The
resulting yellow precipitate was filtered, washed with water, and
dried. Chromatography of the solid (silica gel, ethyl acetate) yielded
TPA2 (2.15 g, 70%), which crystallized as yellow rhombi from
122.3, 120.4, 118.9, 114.8, 114.4, 55.4; IR (KBr pellet, cm-1) 2930
(NH str); MS (EI, m/z) calcd for C27H23N3O2 421, found 421.5.
Anal. Calcd for C27H23N3O2: C, 76.94; H, 5.50; N, 9.97. Found:
C, 76.69; H, 5.60; N, 9.71.
Oxidation of TPA1 with AgSbF6. A solution of AgSbF6 (53.9
mg, 157 µmol) in dichloromethane (5 mL) was added dropwise to
a solution of TPA1 (50.0 mg, 143 µmol) in dichloromethane (2.5
mL); the reaction instantly turned from yellow to deep violet. The
solution was then filtered and evaporated to give the crude product,
which was dissolved in a small amount of dichloromethane and
poured into excess hexane to precipitate the radical cation as a
deeply colored violet-black solid (44.2 mg, 53%) that was dried
under vacuum for ESR and magnetism studies.
Oxidation of TPA2 with AgSbF6. A solution of AgSbF6 (95.9
mg, 279 µmol) in dichloromethane (9 mL) was added dropwise to
a solution of TPA2 (100 mg, 254 µmol) in dichloromethane (2.5
mL); the reaction instantly turned from yellow to red-purple. The
solution was then filtered and evaporated to give the crude product,
which was dissolved in a small amount of dichloromethane and
poured into excess hexane to precipitate the radical cation as a
darkly purple colored solid (66.0 mg, 41%) that was dried under
vacuum for ESR and magnetism studies.
Oxidation of BImTPA with AgSbF6. A solution of AgSbF6
(17.9 mg, 52.2 µmol) in dichloromethane (2 mL) was added
dropwise to a solution of the BImTPA (20 mg, 47.5 µmol) in
dichloromethane (5 mL); the reaction instantly turned from yellow
to green. The solution was then filtered and evaporated to give the
crude product, which was dissolved in a small amount of dichlo-
romethane and poured into excess hexane to precipitate the radical
cation as a deeply colored green-to-black solid (17.9 mg, 57%)
that was dried under vacuum for ESR and magnetism studies.
1
chloroform/methanol: mp 304-306 °C; H NMR (acetone-d6) δ
8.11 (s, 1H), 7.16 (d, 4H, J ) 8.8 Hz), 7.69 (s, 2H), 6.97 (d, 2H,
J ) 8.8 Hz), 3.81 (s, 6H); 13C NMR (acetone- d6) δ 166.1, 157.1,
149.8, 139.7, 131.8, 127.4, 123.0, 121.4, 115.1, 54.8; IR (KBr,
cm-1) 2930 (OH str), 1693 (CdO str); MS (EI, m/z) calcd for
C22H19NO6 393, found 393.4. Anal. Calcd for C22H19NO6: C, 67.17;
H, 4.87; N, 3.56. Found: C, 67.04; H, 4.79; N, 3.54. Single-crystal
X-ray structural analysis results were submitted to the Cambridge
Structural Database, deposition number 636282 (and 636281 for a
THF solvent incorporated structure).
Acknowledgment. This work was supported by the National
Science Foundation under Grant CHE-0415716. The University
of Massachusetts Mass Spectrometry Facility, Nanomagnetic
Characterization Facility, X-ray Structural Characterization
Laboratory, and EPR Facility are also supported in part by the
National Science Foundation.
Supporting Information Available: General methods used,
crystallographic summaries for TPA1 and TPA2 and TPA2‚THF,
including full details in CIF format; computational spin density
summaries for radical cations; solution ESR spectra and hyperfine
simulations for radical cations, FTIR spectra for neutral amines;
characterization NMR spectra, summary of Curie and Weiss
constants from doping experiments, cyclic voltammetry for TPA1,
TPA2, and BImTPA. This material is available free of charge via
the Internet at http://pubs.acs.org.
N-(4-(1H-Benzimidazol-2-yl)phenyl)-N,N-bis(4-methoxyphen-
yl)amine (BImTPA). A mixture of TPA1 (200 mg, 572 µmol),
o-phenylenediamine (61.9 mg, 572 µmol), and phosphoric acid (561
mg, 572 µmol) was dissolved in ethylene glycol (0.46 mL), stirred
at 160 °C for 14 h under nitrogen, cooled to room temperature,
and concentrated. Chromatography of the resulting solid (silica gel,
ethanol) yielded BImTPA (96.4 mg, 40%) as a yellow powder:
1
mp 225-226 °C; H NMR (methanol-d) δ 7.68 (d, 2H, J ) 6.8
JO070318A
Hz), 7.37 (m, 2H), 7.03 (m, 2H), 6.92 (d, 4H, J ) 6.8 Hz), 6.77
(d, 2H, J ) 6.8 Hz), 6.69 (d, 4H, J ) 6.8 Hz), 3.62 (s, 6H); 13C
NMR (methanol-d) δ 156.4, 152.3, 150.4, 140.0, 127.5, 127.3,
(7) Boomgaarden, W.; Vogtle, F.; Nieger, M.; Hupfer, H. Chem.sEur.
J. 1999, 5, 345.
J. Org. Chem, Vol. 72, No. 13, 2007 4977