Iron-catalyzed synthesis, structure, and photophysical properties of tetraarylnaphthidines

Article abstract of DOI:10.3390/molecules25071608

We describe the synthesis and photophysical properties of tetraarylnaphthidines. Our synthetic approach is based on an iron-catalyzed oxidative C–C coupling reaction as the key step using a hexadecafluorinated iron–phthalocyanine complex as a catalyst and

Full text of DOI:10.3390/molecules25071608

molecules
Article
Iron-Catalyzed Synthesis, Structure, and
Photophysical Properties of Tetraarylnaphthidines
Alexander Purtsas , Sergej Stipurin , Olga Kataeva and Hans-Joachim Knölker 1,*
1
1
2
1
Faculty of Chemistry, Technische Universität Dresden, Bergstraße 66, 01069 Dresden, Germany;
alexander.purtsas@chemie.tu-dresden.de (A.P.); sergej.stipurin@chemie.tu-dresden.de (S.S.)
A. E. Arbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy
2
of Sciences, Arbuzov Str. 8, 420088 Kazan, Russia; olga-kataeva@yandex.ru
*
Correspondence: hans-joachim.knoelker@tu-dresden.de; Fax: +49-351-463-37030
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀ
ꢁꢂꢃꢄꢅꢆ
Received: 22 February 2020; Accepted: 29 March 2020; Published: 1 April 2020
Abstract: We describe the synthesis and photophysical properties of tetraarylnaphthidines.
Our synthetic approach is based on an iron-catalyzed oxidative C–C coupling reaction as the
key step using a hexadecafluorinated iron–phthalocyanine complex as a catalyst and air as the sole
oxidant. The N,N,N’,N’-tetraarylnaphthidines proved to be highly fluorescent with quantum yields
of up to 68%.
Keywords: iron catalysis; oxidative coupling; naphthidines; fluorescence
1
. Introduction
Triarylamines have been the subject of numerous studies due to their electron-rich character
and the resulting low oxidation potentials [
have induced extensive investigations towards their potential applications in organic films for
optoelectronics [ ] and as hole-transport materials in OLEDs (organic light emitting diodes) and
solar cells [ ]. Naphthidines (1,1 -binaphthalene-4,4 -diamines) have also been studied because of
their ready oxidation to radical cations [9–12]. Starting from the corresponding 1-naphthylamines by
an oxidative coupling, the synthesis of naphthidines can be induced electrochemically [ 10 13], by
1–3]. These unique properties of triarylamine derivatives
4
0
0
5–8
9, ,
stoichiometric amounts of titanium tetrachloride [11], stoichiometric amounts of iron(III) chloride [14],
chloranil [15], or (bis(trifluoroacetoxy)iodo)benzene (PIFA) [16]. It has been well-known for a long
time that naphthidines can be separated into their stable atropisomers [17].
Herein, we report a simple synthesis of N,N,N’,N’-tetraarylnaphthidines by an iron-catalyzed
oxidative coupling of the corresponding 1-(diphenylamino)naphthalene precursor using
iron(II)–hexadecafluorophthalocyanine (FePcF ) [18] as the catalyst and air as the final oxidant
16
(Figure 1). Moreover, we have investigated the photophysical properties of the obtained
naphthidine derivatives.
F
F
F
F
F
F
N
Fe
N
F
F
F
F
N
N
N
N
N
N
F
F
F
F
F
F
Figure 1. Structural formula of iron(II)–hexadecafluorophthalocyanine (FePcF ).
1
6
Molecules 2020, 25, 1608; doi:10.3390/molecules25071608
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2
. Results and Discussion
2
.1. Synthesis
Following a procedure reported by Nechaev et al. for the Buchwald–Hartwig reaction
under solvent-free conditions [19], we have achieved the coupling of diphenylamine ( ) and
1-bromonaphthalene (2) to afford 1-(diphenylamino)naphthalene (3) in high yield (Scheme 1).
1
Scheme 1. Synthesis of 1-(diphenylamino)naphthalene (3). Reagents and conditions: (a) 1 mol%
◦
Pd(OAc) , 2 mol% RuPhos, 1.2 equivalents NaOtBu, air, 110 C, 12 h, 89% compound 3.
2
Then, we turned our attention to the projected iron-catalyzed oxidative homocoupling of
-(diphenylamino)naphthalene ( ). Recently, we applied our iron-catalyzed oxidative coupling
methodology to the C–C homocoupling of diarylamines, 1-, and 2-hydroxycarbazoles, as well as
to the cross coupling of tertiary anilines with hydroxyarenes [20 22]. Iron as a first-row transition
metal is environmentally safe and has become a powerful tool in synthetic organic chemistry with
many applications for selective C–H bond activation [23 26]. According to a previous report by Yang,
N,N,N’,N’-tetraphenylnaphthidine ( ) could not be prepared by oxidative coupling of compound
with stoichiometric amounts of iron(III) chloride [14]. The oxidation of compound with chloranil
provides compound only as the minor isomer in an inseparable mixture with the corresponding
benzidine derivative [15]. Based on our previous studies [20 22], we envisaged to develop an
iron-catalyzed homocoupling of the triarylamine with air as the sole oxidant. Using catalytic amounts
2 mol%) of FePcF16 and substoichiometric amounts (40 mol%) of methanesulfonic acid as an additive
at room temperature provided N,N,N’,N’-tetraphenylnaphthidine ( ) in 48% yield along with the
N,N,N’,N’-tetraarylnaphthidine as a by-product in 11% yield (Scheme 2). Obviously, compound
results from a further oxidative C–C coupling at the p-position of one of the phenyl rings of the initial
coupling product compound . The structural assignments for compounds and were based on their
H-NMR and C-NMR spectroscopic data and an X-ray analysis of compound 4 (see Section 2.2).
1
3
–
–
4
3
3
4
–
3
(
4
5
5
4
4
5
1
13
Scheme 2. Iron-catalyzed oxidative C–C coupling of 1-(diphenylamino)naphthalene (
conditions: ( ) 2 mol% FePcF16, 40 mol% MsOH, CH Cl , air, room temperature, 24 h, 48% compound
1% compound 5.
3). Reagents and
a
4,
2
2
1

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2
.2. Structure
The H-NMR, 13C-NMR, and DEPT spectra of compound
1
4
displayed signals for a highly
symmetrical compound. Signals for nine aromatic CH and five quaternary aromatic carbon atoms
were identified. The COSY experiment revealed the presence of three spin systems (Supplementary
Materials, COSY of compound 4). The first is caused by coupling of H-1 with H-2 and H-3, which
belong to the phenyl fragment. The second spin system consists of H-6 and H-7. The third system
is formed by H-10, H-11, H-12, and H-13. The assignment of all 13C-NMR signals to the respective
1
H-NMR signals could be achieved by an HSQC measurement (Figure 2 and Table S1). The constitution
of naphthidine
of compound
4
was confirmed by analysis of the HMBC spectrum (Supplementary Materials, HMBC
4
, Table S1). Characteristic HMBC signals (C-4/H-2 and C-4/H-3) led to elucidation
of the quaternary carbon atom C-4 by connecting the proton spin systems. The position of C-5 was
established based on the HMBC cross-peaks with H-6, H-7, and H-13. Accordingly, the quaternary
aromatic carbon atom C-8 was assigned based on the HMBC interactions with H-6, H-7, and H-10.
HMBC cross-peaks between C-9/H-7, H-11, H-13 and C-14/H-6, H-10, H-12 unambiguously clarified
the location of both naphthyl-based quaternary carbon atoms. The NOE interactions were exploited to
confirm the positions of H-3 and H-13 (Supplementary Materials, NOESY of compound
4). Due to
the interactions of these fjord region protons, H-13 showed a substantial downfield shift to 8.08 ppm.
15
Moreover, H-2, H-3, and H-6 exhibited an interaction with the N atom (Supplementary Materials,
1
15
H/ N HMBC of compound 4).
1
3
2
7
6
4
8
5
N
N
9
14
13
1
0
11
12
4
Figure 2. Assignment of the 13C-NMR signals of the N,N,N’,N’-tetraphenylnaphthidine (
respective H-NMR signals by the HSQC spectrum.
4) to the
1

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The structural assignment for N,N,N’,N’-tetraphenylnaphthidine (4) was confirmed by an X-ray
crystal structure determination (Figure 3). The molecule of compound
around the central biaryl bond (C1–C11) with a torsional angle of 99.4(2) (Figure 4) according to the
4
adopts a trans conformation
◦
notation accepted for binaphthyl derivatives [27
large variations of the bond lengths is in agreement with the crystal structure of naphthalene [29
,
28]. The geometry of the naphtho fragments exhibiting
30
,
]
and its structure obtained by quantum chemical calculations [31]. The orientation of the phenyl
groups attached to the nitrogen atoms at the two sides of the molecule is different. The two phenyl
rings at N21 are symmetrically oriented respective to the bisector plane drawn through the C4–N21
bond, while the two phenyl groups at N34 have different orientations. In the crystal, the molecules of
compound
4
participate in multiple weak intermolecular C–H···π interactions between the naphtho
2
groups (Figure 5). The distances between the hydrogen atoms and the sp -carbon atoms range from
2
.7 to 2.8 Å and the angles are typical for these weak hydrogen bonds [32]. This sort of packing
with face-to-edge interactions has been observed also in naphthalene itself [29 30] and in binaphthyl
derivatives [27 28]. It is noteworthy that the naphtho groups interact mostly with each other and the
phenyl groups interact predominantly with phenyl groups, whereas naphtho–phenyl contacts are rare.
,
,
Figure 3. Molecular structure of N,N,N’,N’-tetraphenylnaphthidine (4) in the crystal (ORTEP plot
showing thermal ellipsoids at the 50% probability level). Selected bond lengths (Å): C1–C2 1.370(3),
C1–C10 1.424(2), C5–C10 1.431(2), C4–N21 1.436(2), C1–C11 1.500(2), C11–C12 1.370(2), C11–C20 1.428(2),
◦
C15–C20 1.432(2), C14–N34 1.430(2). Selected bond angles ( ): C10–C1–C11 121.4(2), C2–C1–C11 118.8(2),
C2–C1–C10 119.7(2), C1–C10–C9 122.2(2), C3–C4–N21 120.6(2), C5–C4–N21 120.0(2), C4–N21–C22
1
17.1(2), C4–N21–C28 118.3(2), and C22–N21–C28 120.6(2).

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Figure 4. Crystal structure of compound
4 with a view along the N21–C4/C1–C11/C14–N34 axis
(
ORTEP plot showing thermal ellipsoids at the 50% probability level, the N–phenyl substituents have
◦
been omitted for clarity). Torsional angle (C2–C1–C11–C12) 99.4(2) .
Figure 5. Fragment of the crystal packing of N,N,N’,N’-tetraphenylnaphthidine (
4) showing the unit
cell and C–H···π interactions (view along the a-axis of the crystal).
The connectivity in compound
the copies of the 2D-NMR spectra in the Supplementary Materials). The NMR spectra of
signals for a non-symmetrical aromatic compound. The JRES experiment revealed the absence of
5
has been secured by a full set of 2D-NMR spectra (see below and
5
display
a singlet. Thus, the additional oxidative coupling of the naphthidine
occur at positions 2, 6, 7, 11, or 12 (Supplementary Materials, JRES of compound
4
with compound
3
did not
1
5). The H-NMR
spectrum in combination with the HSQC (Figure 6) and the JRES spectra displayed signals for four
substantially downfield-shifted doublets. On the basis of the fjord region effect observed for compound
1
4
, these four downfield-shifted signals in the H-NMR spectrum of compound
5
are the naphthyl
protons H-10, H-13, H-27, and H-38. The signals of the four corresponding carbon atoms are detected
at δC = 124.66 (C-13), 124.70 (C-27), 124.71 (C-38), and 126.93 (C-10) ppm in the 13C-NMR spectrum
(HSQC in Figure 6, Table S2). The NOE interactions indicated the positions of the protons at the
phenyl groups (Supplementary Materials, NOESY of compound ). The positions of the protons at C-3,
5
C-30, and C-44 have been identified unambiguously by NOE interactions with H-13, H-27, and H-38.
Support for this assignment of the protons H-3, H-30, and H-44 is obtained from an HMBC interaction
with 15N (Supplementary Materials, H/ N HMBC of compound
1
15
5
). A strong NOE correlation of H-10
with H-16 and the presence of a spin interaction between H-16 and H-17 in the COSY (Supplementary
Materials, COSY of compound ) confirmed an oxidative coupling of compound at C-1 of naphthidine
. Further support was obtained from HMBC correlations of H-16 with the quaternary carbon atoms
5
3
4

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C-8 at
δ
C
= 138.64 ppm and C-18 at
δ
= 147.93 ppm and the HMBC correlation of H-17 with C-15 at
C
δ
= 133.51 ppm (Supplementary Materials, HMBC of compound
5). The obtained NMR data are in
C
excellent agreement with the structure assigned for compound 5.
1
2
4
3
N
5
6
7
1
4
13
12
9
8
46
1
15
6
10
11
4
5
17
3
5
34
21 20
4
4
43
18
3
3
22
N
N
3
6
19
29
30
42
23
3
7
28
3
8
41 24
25
27
26
3
1
39
40
3
2
5
Figure 6. Assignment of the 13C-NMR signals of the N,N,N’,N’-tetraarylnaphthidine (
H-NMR signals by the HSQC spectrum.
5
) to the respective
1

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2
.3. Photophysical Studies
On irradiation with UV-light (λex = 254 nm) in methanolic solution, 1-(diphenylamino)naphthalene
) and the resulting N,N,N’,N’-tetraarylnaphthidines and show a strong blue fluorescence (Figure 7).
Therefore, we investigated the photophysical properties of compounds , and in more detail.
The UV absorption and fluorescence emission data for all three compounds are listed in Table 1 and the
normalized fluorescence emission spectra are displayed in Figure 8. The fluorophores , and exhibit
large Stokes shifts of 149 to 162 nm. While the UV absorption maxima are identical, the fluorescence
emission maxima show a bathochromic shift of only 7 nm for N,N,N’,N’-tetraphenylnaphthidine (
and 14 nm for compound , as compared to 1-(diphenylamino)naphthalene ( ). Previously, even larger
(3
4
5
3,
4
5
3,
4
5
4)
5
3
Stokes shifts have been observed for N,N-dimethylaminonaphthalenes [33] and strong bathochromic
shifts have been reported for substituted triarylamines [34].
Figure 7. Fluorescence of the compounds
=
3
(left),
4 (center), and 5 (right) in methanol (concentration c
2 mg mL 1) by excitation with UV light (λex = 254 nm).
−
Table 1. UV absorption and fluorescence emission data of the compounds 3, 4, and 5 in methanol.
(nm) a
abs
ε (M cm ) b
−1
−1
λem (nm) c
∆λ (nm) d
Compound
λ
aminonaphthalene 3
naphthidine 4
290
291
291
15,700
11,400
6000
439
446
453
149
155
162
naphthidine 5
a
UV absorption maximum; molar extinction coefficient; c fluorescence emission maximum (excitation at
b
λex = 291 nm); d Stokes shift, ∆λ = λem − λabs.
Figure 8. Normalized fluorescence emission spectra of 1-(diphenylamino)naphthalene (3) (blue),
N,N,N’,N’-tetraphenylnaphthidine (4) (orange), and naphthidine 5 (green) in methanol (excitation at
λex = 291 nm).

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For the naphthidines
4
and
5, the UV absorption and fluorescence emission maxima along with
fluorescence quantum yields, fluorescence lifetimes, and CIE-coordinates were determined (Table 2).
Table 2. Photophysical data of the naphthidines 4 and 5.
(nm) a
ε (M cm ) b
−1
−1
λem (nm) c
d,e
Φ
fl
т(ns) f,e
CIE-coord. (x; y) g,e
Compound
λ
abs
naphthidine 4
naphthidine 5
294
294
32,000
25,600
449
453
0.68
0.65
4.2
3.6
(0.153; 0.054)
(0.152; 0.062)
a
; b molar extinction coefficient in CH
; c fluorescence emission maximum
UV absorption maximum in CH
2
Cl
2
2
Cl
2
d
e
f
in CH
2
Cl
2
(
λex = 294 nm); fluorescence quantum yield (λex = 310 nm); in a 2% PMMA film; fluorescence lifetime
g
(λex = 360 nm); Commission internationale de l’éclairage (CIE) (λex = 310 nm).
The UV absorption maximum for the naphthidines
whereas the fluorescence emission maximum of compound
compared with compound . The fluorescence quantum yields of compounds
high and in the same range (68% and 65%, respectively, by excitation at 310 nm). Compound
a shorter fluorescence lifetime of 3.6 ns as compared with 4.2 ns for N,N,N’,N’-tetraphenylnaphthidine
). The CIE-coordinates for the blue light emissions of compounds and are indicative of a blue
light which could be useful for applications in OLEDs [35 39]. The fluorescence quantum yields are
very comparable with compounds already investigated as blue fluorescent OLEDs [37 39]. It has
been demonstrated for other naphthalene fluorophores that a bathochromic shift of the emission
can be achieved by increasing the size of the -system and by the introduction of appropriate
substituents [40 41]. Thus, application of these tools should easily allow an optimization of the present
4
and
shows a bathochromic shift of 4 nm as
and are relatively
exhibits
5 is at the same wavelength (294 nm),
5
4
4
5
5
(4
4
5
–
–
π
,
fluorophoric system.
In addition, we investigated the absorption and fluorescence properties of
N,N,N’,N’-tetraphenylnaphthidine (4) in various nonpolar and polar solvents. The fluorescence
behavior of compound on excitation at 254 nm was demonstrated in isohexane, dichloromethane,
4
ethyl acetate, THF, and methanol (Figure 9). The corresponding UV absorption and fluorescence
emission spectra are shown in the Supplementary Materials. The corresponding photophysical data of
compound
4 are summarized in Table 3. For a series of N,N-dimethylaminonaphthalene fluorophores,
Brummond et al. observed a significant red shift of the fluorescence emission maxima by increasing
the solvent polarity [33], whereas in other systems the solvent dependency of the emission was
significantly lower [37]. For N,N,N’,N’-tetraphenylnaphthidine (4), this solvatochromic shift is much
less pronounced (about 21 nm in dichloromethane as compared with the corresponding value in
isohexane) (Table 3).
Figure 9. Fluorescence of N,N,N’,N’-tetraphenylnaphthidine (4) by excitation with UV light
−
1
(
λex = 254 nm) in different solvents (concentration c = 2 mg mL and from left to right, isohexane,
dichloromethane, ethyl acetate, THF, and methanol).

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Table 3. UV absorption and fluorescence emission data of the naphthidine 4 in different solvents.
Isohexane
CH Cl
Ethyl Acetate
THF
Methanol
2
2
λ
(nm) a
291
428
294
449
291
439
292
445
291
446
abs
b
λem (nm)
a
UV absorption maximum and b fluorescence emission maximum (for each solvent λex = λabs).
3
. Materials and Methods
3
.1. General
All reactions were performed in oven-dried glassware using anhydrous solvents under argon,
unless stated otherwise. Pd(OAc) was recrystallized from glacial AcOH. All other chemicals were used
2
as received from commercial sources. The iron(III)-catalyzed reactions were carried out in non-dried
solvents under air. Iron(II)–hexadecafluorophthalocyanine was prepared following a procedure
reported previously [18]. Flash chromatography was performed using silica gel from Acros Organics
(0.035 to 0.070 mm). Automated flash chromatography was performed on a Büchi Sepacore system
equipped with an UV monitor on silica gel (Acros Organics, 0.035 to 0.070 mm). The TLC was
performed with TLC plates from Merck (60 F254) using UV light for visualization. The melting points
were measured on a Gallenkamp MPD 350 melting point apparatus. Ultraviolet spectra were recorded
on a PerkinElmer 25 UV/Vis spectrometer. The fluorescence spectra were measured on a Varian Cary
Eclipse spectrophotometer. The IR spectra were recorded on a Thermo Nicolet Avatar 360 FT-IR
spectrometer using the ATR method (attenuated total reflectance). The NMR spectra were recorded on
Bruker DRX 500 and Avance III 600 spectrometers. The chemical shifts δ were reported in ppm with
the solvent signal as internal standard. Standard abbreviations were used to denote the multiplicities
of the signals. EI mass spectra were recorded by GC/MS-coupling using an Agilent Technologies 6890
N GC System equipped with a 5973 Mass Selective Detector (70 eV). The ESI-MS spectra were recorded
on an Esquire LC using an ion trap detector from Bruker. Positive and negative ions were detected.
Elemental analyses were measured on a EuroVector EuroEA3000 elemental analyzer. The X-ray crystal
structure analyses were performed with a Bruker–Nonius Kappa CCD and with a Bruker AXS Smart
APEX diffractometer equipped with a 700 series Cryostream low temperature device from Oxford
Cryosystems. SHELXS-97 [42], SADABS version 2.10 [43], SHELXL-97 [44], POV-Ray for Windows
version 3.7.0.msvc10.win64, and ORTEP-3 for Windows [45] were used as software.
3
.2. Photoluminescence Measurements
The 2 wt% emitter films were prepared by doctor blading a solution of an emitter in a 10 wt%
poly(methyl methacrylate) solution in dichloromethane on a quartz substrate with a 60 µm doctor blade.
The film was dried, and the emission measured under nitrogen atmosphere. Excitation was conducted
in a wavelength range of 250–400 nm (Xe lamp with monochromator), and the emission was detected
with a calibrated quantum yield detection system (Hamamatsu, model C11347-01). The fluorescence
lifetime was measured with an Edinburgh Instruments mini-
Edinburgh picosecond Pulsed Light Emitting Diode) (360 nm, 20 kHz) and time-resolved photon
counting (TCSPC).
τ by excitation with pulses of an EPLED
(
3
.3. Procedures
3
.3.1. N,N-Diphenylnaphthalen-1-amine (1-(Diphenylamino)naphthalene) (3)
Compound was prepared following a literature procedure [19]. To a screw-cap vial were
added 1-bromonaphthalene (2) (307 µL, 455 mg, 2.20 mmol), diphenylamine (1) (338 mg, 2.00 mmol),
3
Pd(OAc) (5.4 mg, 24
µ
mol), RuPhos (19 mg, 41
µ
mol), and powdered NaOtBu (236 mg, 2.46 mmol).
2
◦
The reaction mixture was stirred at 110 C for 12 h. After cooling to room temperature, the mixture
was dissolved in CH Cl /H O (1:1). The aqueous layer was extracted twice with dichloromethane
2
2
2

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(
5 mL). The combined organic layers were dried over MgSO , the solvent was evaporated in vacuo,
4
and the crude product was purified by chromatography on silica gel with isohexane/dichloromethane
◦
(
30:1) to afford compound
3
(523 mg, 1.77 mmol, 89%) as a colorless solid. M.p. 132.5 C; UV (MeOH)
λ
= 219, 290, and 336 nm; fluorescence (MeOH) λex = 291 and λem = 439 nm; IR (ATR)
ν = 3036, 1934,
1
740, 1586, 1563, 1488, 1389, 1341, 1290, 1272, 1176, 1087, 1026, 1014, 891, 798, 773, 749, 693, and 624
−
1 1
cm ; H-NMR (500 MHz, CDCl )
δ
= 6.93 (t, J = 7.5 Hz, 2H), 7.03 (dd, J = 8.7, 0.8 Hz, 4H), 7.15–7.22
3
(
(
m, 4H), 7.30–7.38 (m, 2H), 7.42–7.50 (m, 2H), 7.77 (d, J = 8.2 Hz, 1H), 7.88 (d, J = 8.2 Hz, 1H), and 7.94
d, J = 8.5 Hz, 1H); 13C-NMR and DEPT at
◦
θ = 135 (125 MHz, CDCl ) δ = 121.76 (2 CH), 121.97 (4 CH),
3
1
24.41 (CH), 126.25 (CH), 126.48 (CH), 126.51 (CH), 126.56 (CH), 127.39 (CH), 128.51 (CH), 129.21 (4
+
CH), 131.41 (C), 135.41 (C), 143.71 (C), 148.58 (2 C); MS (EI): m/z (%) = 295 (100, [M] ), 294 (45), 293 (11),
2
17 (23), and 77 (10); elemental analysis calcd. for C H N, C 89.46, H 5.80, and N 4.74; found, C 89.61,
22 17
H 6.05, and N 4.76.
3
.3.2. Iron-Catalyzed Oxidative C−C Coupling
Dichloromethane (9 mL) was added to a mixture of iron(II)–hexadecafluorophthalocyanine
15.7 mg, 18.3 mol, mol%), methanesulfonic acid (34.8 mg, 362 mol) and
-(diphenylamino)naphthalene ( ) (265 mg, 897 mol). A 100 mL splash head was attached on the flask
(
1
µ
2
µ
3
µ
to prevent evaporation of the solvent, while ensuring sufficient gas exchange. The resulting solution was
stirred at room temperature for 24 h under air. Then, 10 mL of a saturated aqueous solution of sodium
hydrogen carbonate was added. The aqueous layer was extracted three times with dichloromethane.
The combined organic layers were dried (magnesium sulfate). The solvent was evaporated and the
residue was purified by automated flash chromatography (silica gel, isohexane/dichloromethane,
0
0
2
0% to 50% in 1.5 h) to provide N,N,N ,N -tetraphenylnaphthidine (
colorless solid (less polar fraction) and naphthidine (29.5 mg, 33.4
more polar fraction). Crystallization of compound from isohexane afforded colorless crystals which
were suitable for X-ray analysis.
4
) (128 mg, 217
µmol, 48%) as a
5
µmol, 11%) as a colorless solid
(
4
4
4
4
4
0
0
N ,N ,N ’,N ’-Tetraphenyl-[1,1’-binaphthalene]-4,4’-diamine (N,N,N ,N -Tetraphenylnaphthidine) (
4): M.p.
◦
2
49–250 C; UV (MeOH)
λ
= 217, 291, and 361 nm; fluorescence (MeOH) λex = 291 and λem = 446 nm;
IR (ATR)
ν
= 3058, 3034, 1931, 1740, 1582, 1488, 1458, 1420, 1397, 1376, 1266, 1153, 1075, 1053, 1025, 920,
−
1 1
8
36, 746, 691, and 624 cm ; H-NMR (600 MHz, CDCl3)
δ = 6.98 (t, J = 7.3 Hz, 4H), 7.14 (dd, J = 8.7, 1.1
Hz, 8H), 7.23–7.28 (m, 8H), 7.31 (ddd, J = 8.4, 6.9, 1.3 Hz, 2H), 7.36 (ddd, J = 8.4, 6.9, 1.3 Hz, 2H), 7.44 (d,
13
J = 7.3 Hz, 2H), 7.50 (d, J = 7.9 Hz, 2H), 7.52 (d, J = 7.3 Hz, 2H), and 8.08 (d, J = 8.1 Hz, 2H); C-NMR
◦
and DEPT at
θ
= 135 (150 MHz, CDCl )
δ
= 121.93 (4 CH), 122.17 (8 CH), 124.67 (2 CH), 126.35 (2 CH),
3
1
1
26.43 (2 CH), 126.81 (2 CH), 127.32 (2 CH), 128.71 (2 CH), 129.32 (8 CH), 131.40 (2 C), 134.72 (2 C),
36.76 (2 C), 143.55 (2 C), and 148.70 (4 C); MS (ESI, +10 V) m/z = 589.3 [M + H] ; elemental analysis
+
calcd. for C H N , C 89.76, H 5.48, and N 4.76; found, C 89.61, H 5.63, and N 4.73.
44
32
2
Crystallographic data for N,N,N’,N’-tetraphenylnaphthidine (
4
): C H N , crystal size 0.100
×
0.102
44
32
2
3
−1
×
0.522 mm , M = 588.71 g mol , orthorhombic, space group P2 2 2 , a = 7.6835(4), b = 12.5020(6), c =
1
1 1
3
−3
, µ
−1
3
3.1785(18) Å, V = 3187(3) Å , Z = 4,
ρ
= 1.227 g cm
= 0.071 mm , T = 150(2) K,
λ
= 0.71073 Å,
calcd.
◦
θ
range 2.04–28.34 , 50987 reflections collected, 7939 independent (R = 0.0473), and 415 parameters.
int
2
The structure was solved by direct methods and refined by full-matrix least-squares on F ; R = 0.0391
1
−
3
and wR = 0.0890 [I > 2σ(I)]; maximal residual electron density 0.172 e Å . The absolute structure was
2
not determined. CCDC 1983355.
4
4
4
4
N -(4-(4-(Diphenylamino)naphthalen-1-yl)phenyl)-N ,N ’,N ’-triphenyl-[1,1’-binaphthalene]-4,4’-diamine (
5):
◦
M.p. 272–275 C; UV (MeOH)
λ
= 215, 291, and 367 nm; fluorescence (MeOH) λex = 291 and λem = 453
nm; IR (ATR)
ν
= 3061, 3035, 2952, 2920, 2851, 1727, 1585, 1488, 1457, 1420, 1377, 1265, 1174, 1154, 1074,
−
1 1
1
026, 952, 920, 827, 748, 692, and 625 cm ; H-NMR (600 MHz, CDCl )
δ = 6.94 (t, J = 7.3 Hz, 2H), 6.99
3
(
(
t, J = 7.3 Hz, 2H), 7.03 (t, J = 7.3 Hz, 1H), 7.06–7.11 (m, 4H), 7.13–7.17 (m, 4H), 7.19–7.30 (m, 12H), 7.32
t, J = 8.1 Hz, 3H), 7.34–7.39 (m, 4H), 7.40–7.48 (m, 6H), 7.49–7.61 (m, 5H), 8.03 (d, J = 8.3 Hz, 1H), 8.09

Molecules 2020, 25, 1608
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(
t, J = 7.7 Hz, 2H), and 8.18 (d, J = 8.7 Hz, 1H); 13C-NMR and DEPT at
θ = 135 (150 MHz, CDCl ) δ =
◦
3
1
1
1
1
21.40 (2 CH), 121.78 (2 CH), 121.95 (2 CH), 122.00 (4 CH), 122.19 (4 CH), 122.28 (CH), 122.54 (2 CH),
24.66 (CH), 124.70 (CH), 124.71 (CH), 126.19 (CH), 126.31 (CH), 126.39 (CH), 126.45 (CH), 126.46 (CH),
26.57 (CH), 126.82 (CH), 126.93 (CH), 127.03 (CH), 127.05 (CH), 127.31 (CH), 127.41 (CH), 127.55 (CH),
28.74 (CH), 128.79 (CH), 129.23 (4 CH), 129.33 (4 CH), 129.44 (2 CH), 131.07 (2 CH), 131.41 (C), 131.51
(
C), 131.67 (C), 133.51 (C), 133.72 (C), 134.72 (C), 134.80 (C), 136.72 (C), 137.03 (C), 138.64 (C), 142.80 (C),
1
43.39 (C), 143.61 (C), 147.93 (C), 148.46 (C), 148.61 (2 C), and 148.70 (2 C); MS (ESI, +10 V) m/z = 882.5
+
[
M + H] ; elemental analysis calcd. for C H N , C 89.87, H 5.37, and N 4.76; found, C 89.56, H 5.31,
66
47
3
and N 4.79.
4
. Conclusions
In conclusion, we have developed a two-step synthesis of N,N,N’,N’-tetraphenylnaphthidine
). Starting from diphenylamine ( ), Buchwald–Hartwig coupling with 1-bromonaphthalene ( ) and
subsequent iron-catalyzed oxidative homocoupling of the resulting 1-(diphenylamino)naphthalene (
provides compound as the major product and as a minor product compound , resulting from an
(4
1
2
3
)
4
5
additional oxidative C–C coupling. Thus, we could demonstrate that our method of iron-catalyzed
oxidative C–C coupling with air as the final oxidant can be applied to the regioselective homocoupling
of triarylamines. Compounds
up to 68% and fluorescence lifetimes of 4.2 and 3.6 ns, for compounds
structural changes of the N,N,N’,N’-tetraarylnaphthidines by extension of the
4
and
5
exhibit a strong blue-light fluorescence with quantum yields of
and , respectively. Further
-system or modification
4
5
π
of the substitution pattern could lead to improved photophysical properties and fluorophores for
various potential applications.
Supplementary Materials: The following data are available online. Copies of the H-NMR, 13C-NMR, DEPT (
1
θ
=
◦
1
35 ), UV, and fluorescence spectra of the compounds
3,
4
, and
5; copies of the 2D-NMR spectra (COSY, HSQC,
1
15
HMBC, NOESY, H/ N-HMBC, JRES) of the compounds 4 and 5.
Author Contributions: A.P. performed the chemical synthesis and characterized the compounds; A.P. and H.-J.K.
designed the experiments and analyzed the data; S.S. determined the fluorescence quantum yields and the
fluorescence lifetimes; O.K. performed the X-ray analysis; A.P. and H.-J.K. wrote the paper. All authors have read
and agreed to the final version of the manuscript.
Funding: We thank the Deutsche Forschungsgemeinschaft (DFG) for the financial support of our project “Green
and Sustainable Catalysts for Synthesis of Organic Building Blocks” (DFG grant KN 240/19-2).
Acknowledgments: We are indebted to Dr. Tilo Lübken (NMR facility, TU Dresden) for the measurement and
assignment of the NMR spectra. We are grateful to Maximilian Georgi (Physical Chemistry, TU Dresden) for his
support when taking the fluorescence pictures (Figures 7 and 9).
Conflicts of Interest: The authors declare no conflict of interest.
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©
2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).