1,3,2-benzodiazaboroles with 1,3-pentafluorophenyl and tetrafluoropyridyl substituents as building blocks in luminescent compounds

Article abstract of DOI:10.1002/ejic.201300319

The reaction of N-4′-trimethylsilylphenyl-3,6-di-tert-butylcarbazole (3) or N-5′-trimethylsilylthien-2′-yl-3,6-di-tert-butylcarbazole (4) with boron tribromide and subsequently with triphenylphosphane afforded the dibromoborylphenylcarbazole-phosphane add

Full text of DOI:10.1002/ejic.201300319

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FULL PAPER
Luminescence
L. Weber,* J. Halama, L. Böhling,
A. Brockhinke,* A. Chrostowska,*
C. Darrigan, A. Dargelos,
H.-G. Stammler,
In contrast to π-donating 1,3-diethyl- and
1,3-diphenyl-1,3,2-benzodiazaboroles, de-
rivatives with fluoroaryl substituents at the
ring nitrogen atoms are potent π acceptors
B. Neumann .................................... 1–13
when connected to a carbazole donor
through suitable π-conducting spacers.
Thus, molecules of type A show low-energy
emission bands from charge-transfer (CT)
transitions with large Stokes shifts and pro-
nounced solvatochromism.
1,3,2-Benzodiazaboroles with 1,3-Penta-
fluorophenyl and Tetrafluoropyridyl Sub-
stituents as Building Blocks in Lumi-
nescent Compounds
Keywords: Boron / Diazaboroles / Per-
fluoroaryls / Photophysics / Luminescence
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DOI:10.1002/ejic.201300319
1,3,2-Benzodiazaboroles with 1,3-Pentafluorophenyl and
Tetrafluoropyridyl Substituents as Building Blocks in
Luminescent Compounds
Lothar Weber,*[a] Johannes Halama,[a] Lena Böhling,[a]
Andreas Brockhinke,*[a] Anna Chrostowska,*[b] Clovis Darrigan,[b]
Alain Dargelos,[b] Hans-Georg Stammler,[a] and Beate Neumann[a]
Dedicated to Professor Heinrich Nöth on the occasion of his 85th birthday
Keywords: Boron / Diazaboroles / Perfluoroaryls / Photophysics / Luminescence
The reaction of N-4Ј-trimethylsilylphenyl-3,6-di-tert-butyl-
carbazole (3) or N-5Ј-trimethylsilylthien-2Ј-yl-3,6-di-tert-bu-
tylcarbazole (4) with boron tribromide and subsequently with
yield). The analogous compounds 9 and 10 were obtained by
condensing precursors 5 and 6 with bis(N,NЈ-2,3,5,6-tetra-
fluoropyrid-4-yl)-o-phenylenediamine (2) in the presence of
triphenylphosphane afforded the dibromoborylphenylcarba- the piperidine derivative in 35 and 16% yield. Compounds
zole–phosphane adduct 5 or its thiophene derivative 6 as col-
orless solids. These adducts were converted into the new
benzodiazaborole derivatives 7 and 8 by treatment with
N,NЈ-bis(pentafluorophenyl)-o-phenylenediamine (1) and
2,2,6,6-tetramethylpiperidine in hot toluene (52 or 45%
7–10 were characterized by NMR spectroscopy (1H, 11B, 13C,
19F) and mass spectrometry. The molecular structure of 8 was
elucidated by X-ray diffraction analysis. The borylated sys-
tems show intense blue luminescence upon UV irradiation.
lack of close packing as a result of the sterically demanding
mesityl groups.[4] In the past decade, the chemistry of 1,3,2-
diazaboroles has developed rapidly.[5,6] Some of these com-
pounds are strongly luminescent as solids and in solution.[7]
For synthetic reasons, the 1,3-diethyl-1,3,2-benzodiazabor-
olyl group (1,3-Et2-1,3,2-N2BC6H4) has been frequently
used, and compounds with this function are moderately air-
stable.[5g,7e–7i] Calculations on 2-arylethynyl-1,3,2-diazabor-
oles disclosed the localization of the highest occupied mo-
lecular orbital (HOMO) on the diazaborole group and led
to the suggestion that this group does not function as a π
acceptor as originally anticipated but instead behaves as a
π-donor substituent.[7i] In line with these observations, it
was obvious to study the syntheses and photophysical prop-
erties of systems containing two different types of three-
coordinate boron centre, which may behave as a π donor
on the one end and as a π acceptor on the other end of a
rodlike molecule. Thereby, it was found that the π-electron-
donating capacity of the 1,3-diethyl-1,3,2-benzodiazaboro-
lyl group towards the BMes2 unit is between that of meth-
oxy and dimethylamino groups.[8] In addition to this,
chalcogenodiphenylphosphanyl and alkyldiphenylphos-
phonium functions were tested for their π-accepting proper-
ties towards B/N-heterocycles.[9] Benzodiazaboroles are also
potent π-electron donors when ligated to the carbon atoms
of o-, m-, and p-closo-dicarbadodecaboranes.[10]
Introduction
Over the last two decades, the development of fluores-
cent organic compounds for potential application in pho-
tonic devices has been a focus of continuing interest.
Among the huge number of luminescent species, molecular
three-coordinate organoboron compounds and polymers
are of emerging importance.[1] Therein, the three-coordinate
boron centre usually operates as a π acceptor owing to its
vacant p orbital. The dimesitylboryl group (BMes2, Mes =
2,4,6-Me3C6H2) is by far the most prominent boron-con-
taining substituent owing to the steric shielding of the un-
saturated boron centre by the four o-methyl groups. The π-
accepting character of the BMes2 unit is similar to those of
NO2 and CN based on UV[2] and cyclic voltammetry
data.[3] Conjugated molecules with boryl substituents dis-
play very large Stokes shifts and high quantum yields in
solution as well as in the solid state, which indicates the
[a] Fakultät für Chemie der Universität Bielefeld,
33615 Bielefeld, Germany
E-mail: lothar.weber@uni-bielefeld.de
Homepage: www.Uni-bielefeld.de
[b] IPREM, UMR 5254, Université de Pau et Pays de l’Adour,
64000 Pau, France
E-mail: anna.chrostowska@univ-pau.fr
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300319.
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At this point, we have been interested in the conditions
under which a 1,3,2-benzodiazaborolyl group may undergo
an “umpolung” inversion to a π-accepting functionality.
Here, it was conceivable to fix a powerful π donor at the
opposite end of the organic chain. For this purpose, we se-
lected carbazolyl units, but soon learned that in such species
the HOMO and lowest unoccupied molecular orbital
(LUMO) are mainly located on the organic part of the mo-
lecule, and the benzodiazaborolyl part of the molecule be-
comes a mere spectator ligand.[7b] As an alternative, the in-
troduction of powerful electron-acceptor substituents at
both nitrogen atoms of the B/N-heterocycle seems promis-
ing. The present work is focused on the role of 1,3-bis-
(pentafluorophenyl)- and 1,3-bis(2,3,5,6-tetrafluoropyridin-
4-yl)-functionalized 1,3,2-benzodiazaboroles as ligands in
N-phenyl- and N-thienylcarbazoles.
Scheme 2. Syntheses of o-phenylenediamines 1 and 2.
Results and Discussion
Basically, the synthesis of aryl-functionalized 1,3,2-
benzodiazaboroles I can be accomplished by the two dif-
ferent routes (A and B, Scheme 1).
Scheme 1. General synthetic routes to 2-(hetero)aryl-1,3,2-benzodi-
azaboroles.
Path A is the base-assisted cyclocondensation between
an o-phenylene diamine II and a (hetero)aryldibromobor-
ane III, whereas path B involves the nucleophilic substitu-
tion of bromide in 2-bromobenzodiazaboroles IV by
organolithium compounds.[11]
For this work, route A proved to be more efficient and
was, thus, preferred over the alternative route B. The re-
quired N,NЈ-bis(perfluoroaryl)-o-phenylenediamines were
prepared by reacting o-phenylenediamine with 4 equiv. of
lithiumbis(trimethylsilyl)amide in tetrahydrofuran (THF) at
–78 °C followed by 2 equiv. of hexafluorobenzene[12] or
pentafluoropyridine (Scheme 2).
Scheme 3. Syntheses of 5 and 6.
The purification of crude 2 was accomplished by subli-
mation at 10–6 bar and 140 °C, whereby the product was
obtained as a pale yellow solid in 67% yield.
Compounds 3 and 4 reacted smoothly with an equivalent
amount of boron tribromide in dichloromethane within
The syntheses of (heteroaryl)dibromoboranes III were re- 16 h or 2 h, respectively. As the resulting organodibromo-
alized by treatment of the appropriate trimethylsilylarenes boranes underwent no clean cyclocondensations with the
with boron tribromide. The silylated precursors 3 and 4 re- o-phenylenediamines 1 and 2, presumably because of their
sulted from the reaction of freshly prepared organolithiums pronounced Lewis acidity, they were converted into the less
with chlorotrimethylsilane (TMSCl, Scheme 3).
reactive triphenylphosphane adducts 5 and 6. These ad-
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Scheme 4. Syntheses of 7 and 8.
Scheme 5. Syntheses of 9 and 10.
ducts react with equimolar amounts of phenylenediamine 1
and two equiv. of 2,2,6,6-tetramethylpiperidine in hot tolu-
ene (100 °C) in 15 h to afford the new benzodiazaborole
derivatives 7 and 8 as pale yellow solids in 52 and 45%
yield, respectively. The crude reaction products were sepa-
rated from triphenylphosphane by sublimation at 100–
120 °C (Scheme 4).
Similarly, adducts 5 and 6 were converted to benzodiaza-
boroles 9 (35%) and 10 (16% yield) by heating them with
equimolar amounts of 2 in the presence of 2 equiv. of
2,2,6,6-tetramethylpiperidine (Scheme 5).
Figure 1. Compounds 11 and 12.
Compound 12 has been the subject of a recent paper.[7b]
The continuous extraction of crude 9 with n-hexane over The missing link, the 1,3,2-benzodiazaborole derivative 11,
16 h furnished an analytically pure colorless solid. Crude was synthesized from N-(4Ј-bromophenyl)-3,6-di-tert-butyl-
10 was extracted with n-pentane, and the combined extracts carbazole by lithium/halogen exchange with n-butyllithium
were subsequently stirred with copper(I) iodide to remove in diethyl ether at –78 °C and the subsequent quench of
excess triphenylphosphane. In this way, pure 10 was ob- the resulting aryllithium species with 2-bromo-1,3-diphenyl-
tained as yellow crystals.
1,3,2-benzodiazaborole. The pure product was obtained as
For the validation of the utility of 1,3,2-benzodiazaboro- a colorless solid by continuous n-hexane extraction over 2 d
lyl groups with various aryl- and heteroaryl substituents at (yield 63%, Scheme 6).
the N atoms in luminescent carbazoles, the comparison of
In contrast to 11, compounds 7–10 are reasonably stable
7 and 8 with the non-fluorinated derivatives 11 and 12 was towards moisture and oxygen. They are soluble in CHCl3,
indispensable (Figure 1).
CH2Cl2, ethers, and aromatic hydrocarbons. In aliphatic hy-
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Scheme 6. Synthesis of 11.
drocarbons, the new benzodiazaborole derivatives are po-
orly soluble. In the 11B{1H}NMR spectra broad singlets
were observed at δ = 30.7 and 29.9 ppm for of 7 and 9,
respectively, and δ = 27.7 and 28.9 ppm for 8 and 10,
respectively. The incorporation of two N-C6F5 substituents
as in 7 caused only a slight deshielding of the 11B NMR
signal in comparison to that of the non-fluorinated ana-
logue 11 (δ = 29.3 ppm).
Figure 2. Crystal structure of 8.
X-ray and Computational Structural Analysis of 8
Single crystals of 8 suitable for an X-ray structural study
(Table 7) were grown from n-hexane solution at –20 °C. The
compound crystallizes in the monoclinic space group P21/c.
The molecule is constructed of three planar rings (Figure 2,
Figure 3. Compounds 13 and 14.
The thiophene ring is linked in the 2-position to the carb-
Table 1), whereby the central thiophene ring is linked to the azole fragment by a single N(3)–C(22) bond [1.405(4) Å].
benzodiazaborole unit by single bond B(1)–C(19) The respective bond lengths in 13 and 14 are 1.405(2) and
a
[1.530(5) Å], which is slightly shorted in comparison to the 1.394(3) Å. The molecule deviates from planarity as evident
B–C bond in 13 [1.557(2) Å], but matches well with that in by the interplanar angles enclosed by the central thiophene
the
5Ј-dimesitylboryl-2-N-carbazolylthiophene
[14, ring and the diazaborole plane (10.1°) or the carbazole ring
(42°). Although the latter angle is similar to that in 13
1.536(3) Å, Figure 3].
Table 1. Comparison of selected experimental and [CAM-B3LYP/6-311G(d,p)] calculated bond lengths [Å] and angles [°] for 8.
Bond
Experimental
CAM-B3LYP
Angle
Experimental CAM-B3LYP
B(1)–N(1)
B(1)–N(2)
1.440(4)
1.441(4)
1.421(4)
1.411(4)
1.415(4)
1.417(4)
1.397(4)
1.530(5)
1.729(3)
1.721(3)
1.370(4)
1.407(4)
1.361(4)
1.405(4)
1.416(4)
1.412(4)
1.397(4)
1.457(4)
1.405(4)
1.4397
1.4367
1.4072
1.4070
1.4053
1.4045
1.3978
1.5394
1.7325
1.7373
1.3701
1.4169
1.3619
1.3929
1.3980
1.3972
1.4024
1.4491
1.4026
N(1)–B(1)–N(2)
B(1)–N(1)–C(1)
B(1)–N(1)–C(7)
B(1)–N(2)–C(2)
B(1)–N(2)–C(13)
N(1)–C(1)–C(2)
N(2)–C(2)–C(1)
N(1)–B(1)–C(19)
N(2)–B(1)–C(19)
B(1)–C(19)–S(1)
B(1)–C(19)–C(20)
C(19)–S(1)–C(22)
S(1)–C(22)–C(21)
C(20)–C(21)–C(22)
S(1)–C(19)–C(20)
C(19)–C(20)–C(21)
S(1)–C(22)–N(3)
C(21)–C(22)–N(3)
C(23)–N(3)–C(34)
C(22)–N(3)–C(23)
104.5(3)
109.5(2)
127.8(3)
109.7(2)
126.9(2)
107.9(2)
108.4(2)
128.6(3)
126.8(3)
120.4(2)
130.6(3)
92.6(1)
111.6(2)
111.7(3)
108.9(2)
115.3(3)
120.0(2)
128.3(3)
107.8(2)
125.1(2)
105.41
108.79
128.11
108.90
128.12
108.45
108.44
127.66
126.89
122.32
127.48
92.14
111.17
112.44
109.95
114.23
120.70
128.12
108.25
125.58
N(1)–C(1)
N(2)–C(2)
N(1)–C(7)
N(2)–C(13)
C(1)–C(2)
B(1)–C(19)
S(1)–C(19)
S(1)–C(22)
C(19)–C(20)
C(20)–C(21)
C(21)–C(22)
N(3)–C(22)
N(3)–C(23)
N(3)–C(34)
C(23)–C(28)
C(28)–C(29)
C(29)–C(34)
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(41.4°), the diazaborole ring is clearly more twisted into the (Stokes shift 1200 cm–1), which in the more polar solvents
thiophene plane in 8 than in 13 (34.7°), which points to THF or CH2Cl2 is redshifted to λ = 395 (Stokes shift
more π interaction between the better π-accepting fluor- 4000 cm–1) and 407 nm (Stokes shift 4800 cm–1), respec-
inated borole in comparison to the N,NЈ-dialkyl derivative tively. These Stokes shifts as well as the solvatochromism
in 13. The bond lengths and angles within the benzodiaza- are consistent with an excited state of increased polarity
borole part are as usual. The bond lengths within the thio- as the result of an intramolecular charge transfer (CT). In
phene building block [S(1)–C(19) 1.729(3) Å, S(1)–C(22) contrast to this, the non-fluorinated analogue 11 shows an
1.721(3) Å]
C(19)–C(20)
1.370(4) Å,
C(20)–C(21) emission at λ = 354 nm in cyclohexane (Stokes shift
1.407(4) Å, and C(21)–C(22) 1.361(4) Å] are close to those 600 cm–1) with virtually no solvatochromism (THF: λ =
in 13 [1.735(1), 1.735(1), 1.373(2), 1.416(2), and 1.364(2) Å]. 355 nm, Stokes shift 900 cm–1; CH2Cl2: λ = 358 nm, Stokes
As also observed in 13, the exocyclic angles B(1)–C(19)– shift 1200 cm–1). A similar situation was observed with p-
S(1) [120.4(2)°] and B(1)–C(19)–C(20) [130.6(3)°] differ sig- bromophenylcarbazole 15 (λ = 350–255 nm; Stokes shift
nificantly. Similar observations were made with angles S(1)– 500–900 cm–1) These differences may be explained by the
C(22)–N(3) [120.0(2)°] and C(21)–C(22)–N(3) [128.3(3)°].
nature of the transitions, which in the case of 11 and 15 are
In Table 1, the [CAM-B3LYP/6-311G(d,p)] calculated local transitions within the carbazole part, whereas a CT
geometrical parameters for 8 are compared with the experi- from the carbazole to the benzodiazaborole occurs in 7. The
mental results (see Supporting Information for the calcu- formal replacement of the phenylene spacer in 7 by the thio-
lated geometrical parameters of 7–11).
phene-2,5-diyl bridge in 8 did not change the absorptions
In comparison to the experimentally determined geomet- in the UV/Vis spectra significantly (cyclohexane: λ = 295,
rical parameters of the crystal structure of 8, the theoretic- 340 nm; THF: λ = 294, 340 nm; CH2Cl2: λ = 294, 340 nm).
ally derived gas-phase ones agree nicely and show that the Here, solvatochromism is again virtually absent. In the lu-
CAM-B3LYP method associated with 6-311G(d,p) is well minescence spectrum of 8, however, the emission band in c-
suited to the prediction and evaluation of the geometries of C6H12 is markedly redshifted to λ = 394 nm (Stokes shift
the studied molecules.
4000 cm–1). This band is more sensitive to the polarity of
the solvent and is redshifted to λ = 405 nm (Stokes shift
4900 cm–1) in THF and λ = 411 nm (Stokes shift 5300 cm–1)
in CH2Cl2.
UV/Vis and Luminescence Spectra/DFT Calculations
In the benzodiazaborole derivatives 9 and 10, the ex-
change of both N-pentafluorophenyl substituents by two
2,3,5,6-tetrafluoro-4-pyridyl groups had no significant in-
fluence on the low-energy and solvent-insensitive absorp-
tions in the UV/Vis spectra. However, the luminescence
spectra are somewhat different and merit special comments.
In c-C6H12, the phenylene-bridged species 9 displays a
Selected photophysical data for 7–10 are compiled in
Table 2; all compounds exhibit intense blue luminescence
under UV irradiation. Compounds 11 and 12 featuring 1,3-
diphenyl-1,3,2-benzodiazaborole groups and the carbazoles
15 and 16 are also considered for comparison.
The UV/Vis spectra of 7–10 (in cyclohexane) show in-
tense bands at
λ
=
294–296 nm (ε
=
20800–
single emission band at
λ = 377 nm (Stokes shift
33400 Lmol–1 cm–1) in addition to a less intense band at λ
2900 cm–1), which is bathochromically shifted in compari-
son to that of the C6F5 analogue 7. However, the two emis-
sions are recorded at λ = 354 and 418 nm in THF and λ =
356 and 414 nm in CH2Cl2. The Stokes shifts for the low-
energy emissions, which correspond to intramolecular
charge-transfer transitions, are 5300 and 5600 cm–1.
In derivative 10, which features the thiophene-based
linker, two emissions are also observed in cyclohexane at λ
= 357 nm and 410 nm. They are redshifted to λ = 366 and
428 nm in THF and λ = 367 and 431 nm in CH2Cl2. The
corresponding Stokes shifts are 5000, 6200, and 6300 cm–1.
To reach a deeper understanding of this phenomenon, the
luminescence spectra of 9 and 10 were recorded in a number
of solvents of different orientation polarization (Figure 5,
Table 3).
= 340–344 nm (ε = 11600–17000 Lmol–1 cm–1). In 11, for
comparison, absorption bands at
λ
=
297 (ε
=
11900 Lmol–1 cm–1) and 344 nm (ε = 4400 Lmol–1 cm–1)
were measured and are identical to those in the fluorinated
derivatives as well as in carbazoles 15 and 16 (Figure 4).
Figure 4. Carbazoles 15 and 16.
From inspection of the emission bands of 10 in various
The positions of these absorptions in THF and CH2Cl2 solvents, it is clear that the band at λ≈ 360 nm increased in
solutions are virtually the same. The absence of solvato- intensity with increasing polarity of the solvent, ac-
chromism points to a minor change of dipole moment of companied by a weak solvatochromism. Usually, the CT
these compounds during the absorption. This observation is emissions of known benzodiazaboroles are quenched in
in accord with local transitions without the participation of acetonitrile because of adduct formation. Here, however,
the benzodiazaborolyl unit. In the luminescence spectrum for the first time, the CT band at λ = 447 nm is clearly more
of 7 in cyclohexane, there is a strong band at λ = 358 nm prominent the high-energy band at λ = 381 nm.
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Table 2. Selected photophysical data of 7–12, 15, and 16.
Solvent
λmax,abs [nm]
ν
[cm–1]
ε [Lmol–1 cm–1] λmax,em
ν
[cm–1]
Stokes shift [cm–1] ΦF [%]
˜
˜
max,abs
max,em
[nm]
c-C6H12
THF
296
344
297
344
297
344
33800
29100
33700
29100
33700
29100
26600
17000
18200
8300
25400
10000
358
395
407
27900
25100
24300
1200
4000
4800
79
15
26
7
8
9
CH2Cl2
c-C6H12
THF
294
340
294
340
294
340
34000
29400
34000
29400
34000
29400
23700
15600
24000
16300
17300
12000
394
405
411
25400
24500
24100
4000
4900
5300
14
9
CH2Cl2
18
c-C6H12
THF
295
344
296
344
296
344
33900
29100
33800
29100
33800
29100
20800
11600
15300
6400
25400
10400
377
26200
23600
23900
2900
5300
5600
47
7
354
418
356
414
CH2Cl2
2
c-C6H12
295
340
295
340
295
341
33900
29400
33900
29400
33900
29300
33400
11600
36500
15600
34000
15900
357
410
366
428
367
431
24400
23200
23100
5000
6200
6300
16
3
10 THF
CH2Cl2
c-C6H12
11 THF
2
297
344
297
345
297
345
33700
29100
33700
29000
33700
29000
11900
4400
21500
8400
14700
4900
353
355
358
28300
28100
27800
600
79
21
38
900
CH2Cl2
1200
c-C6H12
296
328
296
330
297
330
33800
30500
33800
30300
33700
30300
22600
9900
28600
11200
15400
10700
386
388
396
25500
25300
25000
5200
5000
5300
13
14
18
12 THF
CH2Cl2
c-C6H12
297
344
297
344
297
344
33700
29100
33700
29100
33700
29100
18700
3600
23000
4100
25100
4400
350
353
355
28600
28300
28200
500
800
900
11
12
8
15 THF
CH2Cl2
c-C6H12
296
339
296
339
296
341
33800
29500
33800
29500
33800
29300
26100
3600
20300
3200
24900
3900
356
364
370
28100
27300
26900
1400
2200
2400
3
2
2
16 THF
CH2Cl2
In the luminescence spectra of 9, a more pronounced sol- emission band of 9 in CH2Cl2 at λ = 356 nm has a lifetime
vatochromism in addition to high-energy emissions at λ = of τ = 3.69 ns and, thus, belongs to the same local transi-
354 and 356 nm were observed in THF and CH2Cl2. In tion. The single emission of 9 in cyclohexane at λ = 376 nm
contrast, in acetonitrile only one emission at λ = 360 nm and the band at λ = 414 nm in the emission spectrum of
was recorded. The high-energy emissions in 9 and 10 ap- 9 in CH2Cl2 have similar lifetimes (τ = 2.51 and 2.45 ns,
peared in the region in which the emissions of carbazoles respectively) and are assigned to the same intramolecular
15 and 16 (λ = 350–355 nm and 356–370 nm) occurred.
CT emission from the benzodiazaborole back to the carb-
The fluorescence at λ = 355 nm of carbazole 15 in azole. It is further remarkable that the CT-emission bands
CH2Cl2 (Table 4) has a lifetime of τ = 3.67 ns, which reflects of 9 in THF and CH2Cl2 have long tails in comparison to
a local transition within the carbazole. The high-energy those in the other solvents under investigation. One possible
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Figure 5. Emissions of 9 and 10 in solvents of increasing orientation polarization.
Table 3. Emission maxima [nm] of 9 and 10 in solvents of increas-
ing orientation polarity.
Table 4. Fluorescence lifetimes of 9 and 15.
Solvent
Wavelength [nm]
Lifetime [ns]
c-C6H12 Toluene CHCl3
377 400 417
10 357, 410 358, 423 365, 426 366, 428 367, 431 381, 447
THF
CH2Cl2 CH3CN
9
CyH
376
356
414
355
2.51
3.69
2.45
3.67
9
354, 420 356, 414 360
CH2Cl2
CH2Cl2
CH2Cl2
15
explanation for this could be a weak transition from the
The calculated absorption maxima from time-dependent
benzodiazaborole ring to the electron-withdrawing tetra- DFT (TD-DFT) computations on 7–11 and the dipole mo-
fluoropyridyl substituents. For example, in the fluorescence ment of ground and first excited states are displayed in
spectrum of 2-bromo-1,3-bis(tetrafluoropyridyl)-1,3,2- Table 5. The most intense absorption is calculated for 11 at
benzodiazaborole, emissions at λ = 477 nm in c-C6H12 and 281.1 nm and corresponds to the energy of the HOMO–
λ = 502 nm in CH2Cl2 of low intensity (ΦF ≈ 1%) were LUMO+1 transition. This band is observed in the UV/Vis
observed. In addition, a fluorescence spectrum of solid 9 spectrum as the most intense band at λ = 297 nm, and the
was measured by means of the integrating-sphere method, calculated small ground state dipole moment μg (0.655 D)
whereby an emission maximum appeared at λ = 386 nm. explains the observed absence of solvatochromism for this
The emission band had a large tail towards lower energies compound. For 7, the most intense absorption correspond-
and a quantum yield (ΦF) of 5%. The band is slightly red- ing to the HOMO–LUMO transition is calculated at
shifted when compared with that of 9 in cyclohexane solu- 289.7 nm for the experimentally observed λ = 296 nm, and
tion. Despite the assignment of the respective emission the change of the ground state dipole moment upon exci-
bands to local and charge-transfer transitions the occur- tation is not significant (μg = 1.043 D; μexc = 1.417 D). For
rence of the additional maxima in polar solvents such as 8, 9, and 10, this lowest-energy absorption is calculated at
THF or CH2Cl2 deserves further explanation. Therefore, the highest wavelength (302.7, 298.2, and 310.0 nm, respec-
emission spectra were recorded at varying concentrations. tively) if compared to 7 or 11. In comparison with the ex-
However, no significant changes or new bands were ob- perimental values, the measured absorption values for 7 and
served, and the formation of excimers or packing effects in 11 (in c-C6H12) are redshifted by 6.3 and 15.9 nm, respec-
the solid can be excluded. Solutions of 9 in methanol, 2- tively, whereas the calculated absorption maximum of 8, 9,
propanol, pyridine, triethylamine, and dimethylsulfide, and 10 are blueshifted by 8.7, 3.2, and 15.0 nm, respectively.
which usually react with a diazaborole, only show the high- For these three molecules, the calculated ground state di-
energy emission at λ ≈ 355 nm, which clearly agrees with pole moments μg are small (in order of increasing strength:
the quench of the CT emission. Finally, a toluene solution 8 1.005 D, 10 1.541 D, 9 1.567 D), but these dipole mo-
of 9 was combined in portions with CH2Cl2. At a toluene/ ments change significantly upon excitation of the ground
dichloromethane ration of 2:1 the emission band shifts state to the first excited state in 9 (9.593 D), 8 (9.894 D),
slightly to larger wavelengths. Thus, a Lewis acid–base ad- and 10 (10.756 D) and reflect a significant charge transfer
duct of 9 with CH2Cl2 seems unlikely. The appearance of upon excitation.
the two emissions of 9 in pure CH2Cl2 or THF are presum-
These values are obviously underestimated and deviate
ably because the polarity of the solvent cage stabilizes a significantly from the experimentally determined transition
geometry in which CT transitions from the carbazole to dipole moments by means of the Lippert–Mataga method
the benzodiazaborole and from the B/N-heterocycle to the (7 21.4 D. 8 14.7 D, 9 19.9 D, 10 20.7 D).[13] The calculated
tetrafluoropyridine are observable in addition to the local dipole moments are derived in the gas phase with solvation
π–π* transition in the N-phenylcarbazole part.
effect neglected, which may cause these deviations.
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Table 5. Comparison of [CAM-B3LYP/6-311+G(d,p)] calculated data for optimized geometries of 7–11 and observed UV absorption
maxima (in c-C6H12) [nm]; calculated values of dipole moment of ground (μg) and first excited (μexc) states [D].
Ground state di-
pole moment
(μg)
Transition dipole
moment (exp)
λmax
(calcd.)
Oscillator
strength (f) (exp)
λmax
Δλmax
(calc – exp)
Excited state di-
pole moment (μexc)
Compound.
7
289.7
302.7
298.2
310.0
281.1
0.27
0.29
0.40
0.23
0.50
296
294
295
295
297
–6.3
8.7
3.2
15.0
–15.9
1.043
1.005
1.567
1.541
0.655
1.417
9.894
9.593
10.756
2.519
21.4
14.7
19.9
20.7
–
8
9
10
11
The [CAM-B3LYP/6-311G(d,p)] calculated MO energies 11 are located at the vacant 2pz orbital of the B atom with
εKS (LUMO+2, LUMO+1, LUMO, HOMO, HOMO–1, contributions from π* of the arylene unit (phenyl in 7 and
HOMO–2) of 7–11 as well as the HOMO–LUMO gap 11 or thiophene in 8), whereas the LUMOs of 9 and 10 are
(ΔH–L) are displayed in Table 6. The LUMOs of 7, 8, and mainly located at two 2,3,5,6-tetrafluoro-4-pyridyl groups.
Table 6. [CAM-B3LYP/6-311G(d,p)] calculated MO energies εKS (LUMO+2, LUMO+1, LUMO, HOMO, HOMO–1, HOMO–2),
HOMO–LUMO gap of 7, 8, 9, 10, and 11. Contour values are plotted at Ϯ0.04 ebohr3). Element (color): H (white), B (light pink), C
(gray), N (dark blue), F (light blue), S (yellow); Ph: phenyl; th: thiophene; crb: carbazole.
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conditions. Absorption was measured with a UV/Vis double-beam
spectrometer (Shimadzu UV-2550) with the solvent as a reference.
The HOMOs in the five molecules correspond to π1(crb)
and are located on the carbazole part, whereas the HOMO–
1s are linked with the π2(crb) in 7, 8, 9, and 10. For 11,
the latter is located at the benzodiazaborole part. HOMO–
2 involves the benzodiazaborole group in 7–10 or the carba-
zole group (π2) in 11. The replacement of the phenyl substit-
uents on the benzodiazaborole nitrogen atoms in 11 by the
pentafluorophenyls in 7 leads to a significant stabilization
of all ionization energies. This effect is also found from 11
to 9, in which the phenyl groups are replaced by tetrafluo-
ropyridyls. In contrast, the replacement of the spacer from
phenyl in 7 or 9 to the thiophene in 8 or 10, respectively, is
not significant and the HOMO is only very slightly stabi-
lized in 8 (0.109 eV) and in 10 (0.114 eV) in comparison to
those of 7 and 9.
The output of a continuous Xe lamp (75 W, LOT Oriel) was wave-
length-separated by a first monochromator (Spectra Pro ARC-175,
1800 lines/mm grating, blaze 250 nm) and then used to irradiate a
sample. The fluorescence was collected by mirror optics at right
angles and imaged on the entrance slit of a second spectrometer;
astigmatism was corrected at the same time. The signal was de-
tected by a back-thinned CCD camera (RoperScientific, 1024ϫ256
pixels) in the exit plane of the spectrometer. The resulting images
were spatially and spectrally resolved. In the next step, an averaged
fluorescence spectrum was calculated from the raw images and
stored in the computer. This process was repeated for different exci-
tation wavelengths. The result is a two-dimensional fluorescence
pattern with the excitation wavelength on the y axis and the emis-
sion wavelength on the x axis. The wavelength range is λex = 230–
430 nm (in 1 nm increments) for the UV light and λem = 305–
894 nm for the detector. The time to acquire a complete excitation
emission spectrum (EES) is typically less than 15 min. Post-pro-
cessing of the EES includes subtraction of the dark current back-
ground, conversion of pixel to wavelength scales, and multiplication
with a reference file to take the varying lamp intensity as well as
grating and detection efficiency into account. The quantum yields
were determined against p-bis(5-phenyl-2-oxazolyl)benzene (PO-
POP, ΦF = 0.93) as the standard.
Conclusions
1,3,2-Benzodiazaboroles are ambiguous functionalities
when attached to extended organic π-conjugated scaffolds
and their properties depend on the nature of the substitu-
ents at the nitrogen atoms in the 1- and 3-position. With
ethyl and phenyl substituents, these heterocycles mainly ap-
pear as π donors in push–pull molecules, whereas with elec-
The solid-state fluorescence was measured by addition of an inte-
tron-withdrawing groups such as pentafluorophenyl or grating sphere (Labsphere, coated with Spectralon, Ø = 12.5 cm)
to the existing experimental setup. At the exit slit of the first mono-
chromator, the exciting light was transferred into a quartz fiber
(LOT Oriel, LLB592). It passed a condenser lens and illuminated
a 1 cm2 area on the sample in the centre of the sphere. The emission
and exciting light was imaged by a second quartz fiber on the en-
trance slit of the detection monochromator. The optics for correc-
tion of astigmatism was passed by the light in this way.
tetrafluoropyridyl at the N atoms of the benzodiazaborolyl
moieties, they experience an “umpolung” transition into π
acceptors when linked to carbazole donors through 1,4-
phenylene or 2,5-thiophenediyl spacers. In keeping with
this, the fluorescence spectra of 7–10 show low-energy emis-
sion bands resulting from CT transitions with large Stokes
shifts and pronounced solvatochromism.
The luminescence lifetimes of 9 and 15 were measured with a time-
correlated single-photon counting apparatus (TCSPC, Horiba
Jobin Yvon FluoroHub, light source: Nano-LED280, detector:
Photomultiplier TBX).
Experimental Section
General: All manipulations were performed under an atmosphere
of dry, oxygen-free argon by using Schlenk techniques. All solvents
were dried by standard methods and freshly distilled prior to use.
N,NЈ-Bis(pentafluorophenyl)-o-phenylene diamine (1)[12] and N-(4-
bromophenyl)-3,6-di-tert-butylcarbazole[14] were prepared accord-
ing to literature methods.
Computational Details: All calculations were performed by using
the Gaussian 09[15] program package with the 6-311G(d,p) basis
set, except for the calculations of UV absorptions for which the 6-
311+G(d,p) basis set was applied. DFT has been shown to predict
various molecular properties successfully.[16] All geometry optimi-
zations were performed with the CAM-B3LYP[17] functional and
were followed by frequency calculations to verify that the station-
ary points obtained are true energy minima. The TD-DFT[18] ap-
proach provides a first principals method for the calculation of
excitation energies within a density functional context taking into
account the low-lying ion calculated by ΔSCF method.
Hexafluorobenzene, pentafluoropyridine, hexamethyldisilazane,
boron tribromide, triphenylphosphane, chlorotrimethylsilane, and
n-butyllithium (1.6 m in n-hexane) were purchased commercially.
NMR spectra were recorded at room temperature with (a) a Bruker
Avance III 300 (1H: 300, 11B: 96, 13C: 75, 19F: 282 MHz) and (b) a
Bruker Avance III 500 spectrometer (1H: 500, 11B: 160, 13C: 125,
19F: 470, 31P: 202 MHz) with SiMe4 (1H, 13C), BF3·OEt2 (11B),
CFCl3 (19F), and 85% H3PO4 (31P) as external standards. Mass
spectra were obtained with a VG autospec sector field mass spec-
trometer (Micromass).
N,NЈ-Bis(tetrafluoro-4-pyridyl)-o-phenylenediamine (2): Similarly to
ref.[12], a cold THF solution (150 mL, –78 °C) of o-phenylenediam-
ine (5.0 g, 46 mmol) was lithiated and combined with pentafluo-
ropyridine (15.59 g, 10.1 mL, 92.2 mmol). After work-up, the
brown solid residue was sublimed at 1ϫ10–1 bar and 140 °C. Crude
2 was collected as a yellow sublimate and was subsequently purified
Photophysical Measurements: For all solution-state measurements,
samples were placed in quartz cuvettes of 10ϫ 10 mm (Hellma by crystallization from benzene (250 mL) to afford 12.5 g of analyt-
type 111-QS, suprasil, optical precision). Cyclohexane was used as
received from commercial sources (p. a. quality), and the other sol-
vents were dried by standard methods prior to use. The concentra-
tions varied from 20 to 70 μm according to their optical density.
Solid sample were prepared by vacuum sublimation on quartz
plates (35ϫ 10ϫ 1 mm) by using standard Schlenk equipment and
ically pure 2 as a pale yellow solid (67% yield). 1H NMR
(300 MHz, CDCl3): δ = 6.19 (br. s, 2 H, NH), 7.16 (m, 2 H,
CH=CHCH=CH), 7.28 (m, 2 H, CH=CHCH=CH) ppm. 1H
NMR (300 MHz, C6D6): δ = 5.15 (br. s, 2 H, NH), 6.42 (m, 2 H,
CH=CHCH=CH), 6.78 (m, 2 H, CH=CHCH=CH) ppm. 13C{1H}
NMR (125 MHz, CDCl3): δ = 122.9 (s, CH=CHCH=CH), 126.4
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1
(s, CH=CHCH=CH), 132.0 (s, N2C2), 132.7 [dm, JC,F = 235 Hz, 11B{1H}NMR (C6D6): δ = –4.8 ppm. 31P NMR (C6D6): δ =
1
C5F4N], 144.1 (dm, JC,F = 240 Hz, C5F4N) ppm. 19F NMR
(282 MHz, CDCl3): δ = –155.8 (m, 4 F, o-F), –92.1 (m, 4 F, m-F)
ppm. 19F NMR (282 MHz, C6D6): δ = –155.8 (m, 4 F, 3,5-F), –92.1
(m, 4 F, 2,6-F) ppm. MS (EI): m/z (%) = 406.1 (100) [M]+, 367.1
(20) [M – 2F]+, 236.1 (31) [M – C5F4N – HF]+. C16H6F8N4
(406.23): calcd. C 47.31, H 1.49, N 13.79; found C 47.16, H 1.39,
N 13.69.
–4.1 ppm.
N-[5Ј-Dibromo(triphenylphosphonio)borato-thien-2-yl]-3,6-di-tert-
butylcarbazole (6): Analogously, the mixture of 4 (0.71 g,
1.64 mmol) and BBr3 (0.43 g, 1.7 mmol) in CH2Cl2 (30 mL) was
stirred for 2 h at ambient temperature. The volatile compounds
were removed in vacuo. The residue was dissolved in CH2Cl2
(30 mL), and a solution of PPh3 (0.446 g, 1.7 mmol) in CH2Cl2
(10 mL) was added; stirring was continued for another 2 h. Crude
6 was obtained after removal of the solvent and was directly em-
ployed for further transformations. 11B{1H} NMR (C6D6): δ = 7.0
(bs) ppm. 31P NMR (C6D6): δ = –4.2 ppm.
N-(4Ј-Trimethylsilylphenyl)-3,6-di-tert-butylcarbazole (3): A chilled
solution (–78 °C, 2-propanol/liquid N2 bath) of N-(4-bromo-
phenyl)-3,6-di-tert-butylcarbazole (1.03 g, 2.4 mmol) in THF
(20 mL) was combined with a solution of tert-butyllithium in n-
pentane (3 mL, 4.8 mmol), and the 2-propanol/liquid N2 bath was
allowed to slowly warm to 0 °C. The mixture was recooled to
–78 °C and a sample of chlorotrimethylsilane (0.32 g, 2.9 mmol)
was added dropwise. The solution was warmed to room tempera-
ture before the addition of water (10 mL) and THF (30 mL). The
organic layer was separated and washed with brine. The organic
phase was dried with Na2SO4, and the solvent was removed in
vacuo to afford pure 3 (0.98 g, 2.28 mmol, 95% yield) as a colorless
solid. 1H NMR (500 MHz, CDCl3): δ = 0.38 [s, 9 H, Si(CH3)3],
2-N-[4Ј-(3ЈЈ,6ЈЈ-Di-tert-butylcarbazolyl)phenyl]-1,3-bis(pentafluoro-
phenyl)-1,3,2-benzodiazaborole (7): A slurry of 5 (1.291 g,
1.64 mmol) in toluene (30 mL) was combined with a solution of 1
(0.609 g, 1.5 mmol) in toluene (20 mL) and 2,2,6,6-tetramethyl-
piperidine (0.494 g, 3.5 mmol). The reaction mixture was stirred for
30 h at 100 °C. The mixture was cooled to ambient temperature
and was filtered. The solvent and volatile components were re-
moved from the filtrate in vacuo. Triphenylphosphane was sepa-
rated from the residue by sublimation at 100 °C. Extraction of the
residue with n-hexane afforded 7 (0.627 g, 0.78 mmol, 52% yield).
1H NMR (500 MHz, CDCl3): δ = 1.49 [s, 18 H, C(CH3)3], 6.91 (m,
2 H, CH=CHCH=CH), 7.20, (m, 2 H, CH=CHCHCH), 7.40 (d,
3JH,H = 9 Hz, NCCHCHCB), 7.47 (d, 3JH,H = 9 Hz, tBuCCHCH),
3
1.49 (s, 18 H, tBu), 7.41 (d, JH,H = 8.6 Hz, 2 H, tBuCCHCHC),
= 8.6, 1.7 Hz, 2 H, tBuCCHCHC), 7.57 (d, JH,H
= 8.1 Hz, 2 H, NCCHCHCSi), 7.74 (d, JH,H = 8.1 Hz, 2 H,
3,4
3
7.48 (dd,
J
H,H
3
4
NCCHCHCSi), 8.16 (d, JH,H = 1.7 Hz, 2 H, tBuCCHC) ppm.
13C{1H} NMR (125 MHz, CDCl3): δ = –0.8 [s, Si(CH3)3], 32.2 [s,
C(CH3)3], 34.9 [C(CH3)3], 109.5 (s, tBuCCHCHC), 116.3 (s,
tBuCCHC), 123.7 (s, tBuCCHCHC), 125.9 (s, NCCHCHCSi),
134.9 (s, NCCHCHCSi), 138.8 (s, NCCHCHCSi), 123.5,139.22,
142.9 (3s, tBuCCHCC) ppm. MS (EI): m/z (%) = 427.3 (80) [M]+,
412.2 (100) [M – Me]+. C29H37NSi (427.70): calcd. C 81.44, H 8.72,
N 3.27; found C 81.69, H 9.07, N 3.25.
3,4
3
7.50 (dd,
J
H,H
= 9, 2 Hz, tBuCCHCH) 7.54 (d, JH,H = 9 Hz,
NCCHCHCB), 8.15 (d, JH,H = 2 Hz, tBuCCHC) ppm. 13C{1H}
NMR (125 MHz, CDCl3): δ = 31.9 [s, C(CH3)3], 34.7 [s,
C(CH3)3], 109.2 (s, CH=CHCH=CH), 110.5 (s, tBuCCHCHC),
116.2 (s, tBuCCHC), 122.0 (s, CH=CHCH=CH), 123.7 (s,
tBuCCHCHC), 126.1 (s, NCCHCHCB), 133.9 (s, NCCHCHCB),
135.9 (s, N2C2), 138.6 (s, NCCHCHCB), 123.6, 140.1, 143.3 (3s,
4
1
1
N-(5Ј-Trimethylsilylthien-2-yl)-3,6-di-tert-butylcarbazole (4):
A
tBuCCHCC), 137.0 (dm, JC,F = 256 Hz, C6F5), 140.3 (dm, JC,F
1
solution of n-butyllithium in n-hexane (6.7 mL, 10.7 mmol) was
slowly added at room temperature to a well-stirred solution of N-
(2Ј-thienyl)-3,6-di-tert-butylcarbazole (3.9 g, 10.7 mmol) in diethyl
ether (100 mL). The mixture was stirred for 1 h at 20 °C before
the addition of chlorotrimethylsilane (1.2 g, 11.0 mmol). After 16 h,
water (50 mL) and diethyl ether (80 mL) were added. The organic
layer was washed with brine and dried with Na2SO4. The solvent
was removed in vacuo, and the residue was crystallized from eth-
= 257 Hz, C6F5), 144 (dm, JC,F = 250 Hz, C6F5) ppm. 11B{1H}
NMR (160 MHz, CDCl3): δ = 30.7 ppm. 19F NMR (470 MHz,
CDCl3): δ = –144.8 (m, 4 F, 2,6-F), –154.1 (t, JF,F = 24 Hz, 2 F, 4-
F), –160.6 (m, 4 F, 3,5-F) ppm. MS (EI): m/z (%) = 803.3 (99) [M]+,
788.3 (100) [M – Me]+, 394.1 (20) [BN2C6(C6F5)2]+. C44H32BF10N3
(803.54): calcd. C 65.77, H 4.01, N 5.23; found C 65.68, H 3.91, N
5.13.
2[5Ј-(3ЈЈ,6ЈЈ-Di-tert-butylcarbazolyl)thien-2Ј-yl]-1,3-bis(pentafluoro-
phenyl)-1,3,2-benzodiazaborole (8): Analogously to the preparation
of 7, a mixture of adduct 6 (1.301 g, 1.64 mmol), 1 (0.609 g,
1.5 mmol), and 2,2,6,6-tetramethylpiperidine (0.594 g, 3.50 mmol)
in toluene (50 mL) was stirred for 16 h at 100 °C. The mixture was
cooled to ambient temperature and filtered. The solvent was re-
moved from the filtrate, and PPh3 was removed from the solid resi-
due by sublimation at 100 °C. The residue was triturated with n-
hexane, and the filtered n-hexane solution was evaporated to dry-
ness. A second sublimation at 120 °C was necessary to remove re-
sidual PPh3. Product 8 was obtained as a pure colorless solid
(0.546 g, 0.67 mmol, 45%). 1H NMR (C6D6): δ = 1.34 [s, 18 H,
1
anol to yield 4 (2.44 g, 5.9 mmol,55%) as pale yellow needles. H
NMR (500 MHz, CDCl3): δ = 0.46 [s, 9 H, Si(CH3)3], 1.55 (s, 18
H, tBu), 7.28 (d, 3JH,H = 3.5 Hz, 1 H, NCCHCHCS), 7.35 (d, 3JH,H
= 3.5 Hz, 1 H, NCCHCHCS), 7.56 (m, 4 H, tBuCCHCHC), 8.20
(d, JH,H = 1.7 Hz, 2 H, tBuCCHC) ppm. 13C{1H} NMR
4
(125 MHz, CDCl3): δ = –0.04 [s, Si(CH3)3], 32.1 [s, C(CH3)3], 34.8
[s, C(CH3)3], 109.8 (s, tBuCCHCHC), 116.2 (s, tBuCCHC), 123.9
(s, tBuCCHCHC), 124.7 (s, NCCHCHCS), 133.0 (s,
NCCHCHCS), 138.5 (s, NCCHCHCS), 123.5, 140.2, 143.5 (3s,
tBuCCHCC), 145.4 (s, NCCHCHCS) ppm. MS (EI): m/z (%) =
433.2 (100) [M]+, 418.2 (95) [M – Me]+. C27H35NSSi (433.72):
calcd. C 74.77, H 8.13, N 3.23; found C 74.47, H 8.16, N 3.33.
3
C(CH3)3] 6.65 (m, 2 H, CH=CHCH=CH), 6.85 (d, JH,H = 4 Hz,
1 H, NCCHCHCS), 7.03 (d, JH,H = 4 Hz, 1 H, NCCHCHCS)
3
N-[4Ј-Dibromo(triphenylphosphonio)borato-phenyl]-3,6-di-tert-but-
ylcarbazole (5): A mixture of 3 (0.71 g, 1.64 mmol) and boron tri-
bromide (0.43 g, 1.7 mmol) in CH2Cl2 (30 mL) was stirred for 16 h
at room temperature. The solvent and volatile components were
removed in vacuo, and the residue was redissolved in CH2Cl2
(30 mL). A solution of PPh3 (0.446 g, 1.7 mmol) in CH2Cl2
(10 mL) was added to this mixture and stirring was continued for
2 h at room temperature. The solvent was removed to give crude
5 as a colorless solid, which was directly used for synthesis of 7.
7.05 (m, 2 H, CH=CHCH=CH), 7.38 (s, 4 H, tBuCCHCHC) 8.20
(s, 2 H, tBuCCHC) ppm. 13C{1H} NMR (C6D6): δ = 31.6 [s,
C(CH3)3], 34.4 [s, C(CH3)3], 109.7 (s, CH=CHCH=CH), 110.5 (s,
tBuCCHCHC), 116.3 (s, tBuCCHC), 122.3 (s, CH=CHCH=CH),
124.2 (s, tBuCCHCHC), 124.5 (s, NCCHCHCS), 132.9 (s,
NCCHCHCS), 136.1 (s, N2 C2 ), 124.2, 139.9, 144.5 (3s,
1
1
tBuCCHCC), 137.0 (dm, JC,F = 255 Hz, C6F5), 140.5 (dm, JC,F
= 254 Hz, C6F5), 144.5 (dm, 1JC,F = 252 Hz, C6F5), 146.6 (s, SCN)
Eur. J. Inorg. Chem. 0000, 0–0
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/KAP1
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Pages: 13
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FULL PAPER
ppm. 11B{1H} NMR (C6D6): δ = 27.7 ppm. 19F NMR (C6D6): δ =
–145.2 (m, 4 F, 2,6-F), –153.3 (t, 2 F, 4-F), 160.6 (m, 4 F, 3,5-F)
was continuously extracted with n-hexane over 2 d, whereupon
product 11 separated as a colorless solid (0.90 g, 1.44 mmol, 63%).
ppm. MS (EI): m/z (%) = 809.3 (100) [M]+, 794.3 (82) [M – Me]+, 1H NMR (500 MHz, CDCl3): δ = 1.50 (s, 18 H, tBu), 7.10 (m, 2
738.2 (12) [M –2Me – 2HF]+. C42H30BF10N3S (809.57): calcd. C H, CH=CHCH=CH), 7.16 (m, 2 H, CH=CHCH=CH), 7.36 (m, 6
62.31, H 3.74, N 5.19; found C 60.63, H 4.06, N 4.89.
H, tBuCCHCH, NCCHCHCB), 7.46 (m, 8 H, BNPh, m-H Ph, p-
H Ph and tBuCCHCH), 7.53 (m, 4 H, BNPh, o-Ph), 8.15 (d, 4JH,H
= 1.7 Hz, 2 H, tBuCCHC) ppm. 13C{1H} NMR (125 MHz,
CDCl3): δ = 32.0 [s, C(CH3)3], 34.7 [s, C(CH3)3], 109.4 (s,
CH=CHCH=CH), 110.2 (s, tBuCCHCH), 116.1 (s, tBuCCHC),
120.1 (s, CH=CHCH=CH), 123.4 (s, tBuCCHCH), 125.2 (s,
NCCHCHCB), 126.6 (s, NCCH=CHCH), 127.9, 129.4 (2s,
NCCH=CHCH), 136.1 (s, NCCHCHCB), 123.5, 140.4, 142.9 (3s,
C-carbazole), 137.9 (s, BNC-CHCHCH), 138.5 (s, NCCHCHCB),
138.8 (s, N2C2), 144.5 (s, SCN) ppm. 11B{1H} NMR (160 MHz,
CDCl3): δ = 29.2 ppm. MS (EI): m/z (%) = 623.4 (100) [M]+, 608.2
(64) [M – CH3]+. C44H42BN3 (623.64): calcd. C 84.74, H 6.79, N
6.74; found C 84.18, H 7.17, N 6.71.
2-N-[4Ј-(3ЈЈ,6ЈЈ-Di-tert-butylcarbazolyl)phenyl]-1,3-bis(tetrafluoro-
pyridyl)-1,3,2-benzodiazaborole (9): A mixture of 5 (1.291 g,
1.64 mmol), 2 (0.609 g, 1.50 mmol), and 2,2,6,6-tetramethylpiper-
idine (0.494 g, 3.5 mmol) in toluene (50 mL) was stirred for 48 h at
100 °C. After similar work-up, the colorless residue was continu-
ously extracted with n-hexane over 16 h, whereby product 9 precipi-
tated from the extract as a colorless solid (0.404 g, 0.53 mmol,
35%). 1H NMR (500 MHz, C6D6): δ = 1.39 [s, 18 H, C(CH3)3],
6.55 (m, 2 H, CH=CHCH=CH), 7.01, (m, 4 H, CH=CHCH=CH
3
and NCCHCHCB), 7.17 (d, JH,H = 4 Hz, 2 H, NCCHCHCB),
7.26 [d, 3JH,H = 8.6 Hz, tBuCCHCH], 7.35 (dd, 3JH,H = 8.6, 1.8 Hz,
4
tBuCCHCH), 8.31 (d, JH,H = 1.8 Hz, tBuCCHC) ppm. 13C{1H}
Further details of the crystallographic data for 8 are given in
Table 7. CCDC-925364 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
NMR (125 MHz, CDCl3): δ = 30.0 [s, C(CH3)3], 34.7 [s,
C(CH3)3], 109.8 (s, CH=CHCH=CH), 111.4 (s, tBuCCHCHC)
116.5 (s, tBuCCHC), 122.9 (s, CH=CHCH=CH), 124.0 (s,
tBuCCHCHC), 125.7 (s, NCCHCHCB), 133.9 (s, NCCHCHCB),
1
135.4 (s, N2C2), 138.6 (dm, JC,F = 263 Hz, C5F4N), 144.3 (dm,
1JC,F = 240 Hz, C5F4N), 124.1, 139.6, 143.0 (3s, tBuCCHCC) ppm.
11B{1H} NMR (160 MHz, C6D6): δ = 29.4 ppm. 19F NMR
(470 MHz, C6D6): δ = –87.7 (m, 4 F, 3,5-F), 145.1 (m, 4 F, 2,6-F)
ppm. MS (EI): m/z (%) = 769.3 (89) [M]+, 754.3 (100) [M – Me]+,
698.2 (16) [M –2Me – 2HF]+.
Table 7. Crystallographic data for 8.
Empirical formula
C42H30BF10N3S
Mr [gmol–1]
Crystal dimensions [mm]
Crystal system
Space group
a [Å]
809.56
0.08ϫ0.07ϫ0.06
monoclinic
P 21/c
12.9805(4)
23.2787(10)
12.7744(5)
98.854(2)
3814.0(3)
4
2-[5Ј-(3ЈЈ,6ЈЈ-Di-tert-butylcarbazolyl)thien-2Ј-yl]-1,3-bis(tetrafluoro-
pyridyl)-1,3,2-benzodiazaborole (10): Prepared analogously to 9
from 6 (1.301 g, 1.64 mmol), 2 (0.609 g, 1.50 mmol), and 2,2,6,6-
tetramethylpiperidine (0.494 g, 3.50 mmol) in toluene (50 mL) for
72 h at 100 °C, crude product 10 was obtained. The solid was re-
moved in vacuo (1ϫ10–6 bar), and the solid was extracted with n-
pentane (2ϫ40 mL). The combined extracts were stirred for 1 d in
the presence of CuI (2 g). After filtration, the solution was concen-
trated to ca. 20 mL and stored at –20 °C. Within 2 d, product 10
b [Å]
c [Å]
β [°]
V [Å3]
Z
ρcalcd. [gcm–3]
1.410
0.169
μ [mm–1]
1
separated as yellow crystals (0.200 g, 0.26 mmol, 16%). H NMR
F (000)
1656
Θ [°]
3–25
44982
6692
0.113
4014
520
1.009
0.0520
(500 MHz, C6D6): δ = 1.34 [s, 18 H, C(CH3)3], 6.47 (m, 2 H,
CH=CHCH=CH), 6.74 (d, 3JH,H = 4 Hz, 1 H, NCCHCHCS), 6.86
Reflections collected
Unique reflections
R(int)
Reflections [IϾ2σ(I)]
Refined parameters
GOF
RF [I Ͼ2σ(I)]
wRF2 (all data)
Δρmax/min [eÅ–3]
3
( d , J H , H = 4 H z , 1 H , N C C H C H C S ) , 6 . 9 6 ( m , 2 H ,
3
CH=CHCH=CH), 7.35 (d, JH,H = 8.7 Hz, 2 H, tBuCCHCHC),
3,4
3
7.42 (dd,
J
H,H
= 8.7, 1.2 Hz, 2 H, tBuCCHCHC), 8.20 (s, JH,H
= 1.2 Hz, 2 H, tBuCCHC) ppm. 13C{1H} NMR (125 MHz, C6D6):
δ = 30.6 [s, C(CH3)3], 34.4 [s, C(CH3)3], 108.6 (s, CH=CHCH=CH),
110.0 (s, tBuCCHCHC), 115.3 (s, tBuCCHC), 121.9 (s,
CH= CHCH= CH), 1 2 3 . 3 ( s, t B uCCH C H C ) , 1 2 4 . 7 ( s,
NCCHCHCS), 133.9 (s, NCCHCHCS), 138.6 (dm, 1JC,F = 263 Hz,
C5F4N), 144.0 (dm, 1JC,F = 231 Hz, C5F4N), 138.7 (s, N2C2), 123.5,
0.1230
0.242/–0.240
139.1, 143.2 (3s, tBuCCHCC), 146.0 (s, SCN) ppm. 11B{1H} NMR Supporting Information (see footnote on the first page of this arti-
(160 MHz, C6D6): δ = 28.9 ppm. 19F NMR (282 MHz, C6D6): δ =
–87.4 (m, 4 F, 3,5-F), –144.7 (m, 4 F, 2,6-F) ppm. MS (EI): m/z (%)
= 775.5 (100) [M]+, 760.5 (94) [M – Me]+.
cle): Tables of atomic coordinates for [CAM-B3LYP/6-311G(d,p)]
optimized geometries, values of total energies and Lippert–Mataga
plots of 7–10.
2-N-[4Ј-(3ЈЈ,6ЈЈ-Di-tert-butylcarbazolyl)phenyl]-1,3-diphenyl-1,3,2-
benzodiazaborole (11): A chilled solution (–78 °C) of N-(4-bromo-
phenyl)-3,6-di-tert-butylcarbazole (1.00 g, 2.30 mmol) in diethyl
ether (50 mL) was treated with an equimolar amount of n-butyllith-
ium dissolved in n-hexane (1.6 m, 1.44 mL, 2.3 mmol). The reaction
mixture was warmed to 0 °C, and was then recooled to –78 °C be-
fore a solution of 2-bromo-1,3-diphenyl-1,3,2-benzodiazaborole
(0.91 g, 2.3 mmol) in benzene (15 mL) was added. The mixture was
stirred for 16 h at ambient temperature, and the solvent and volatile
components were removed in vacuo. The obtained solid residue
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Date: 21-06-13 10:49:00
Pages: 13
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FULL PAPER
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Received: March 8, 2013
Published Online: ᭿
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim