Synthetic, structural, photophysical and computational studies on π-conjugated 1,3,2-benzodiazaboroles with carbazole building blocks

Article abstract of DOI:10.1002/ejic.201000665

The reaction of the N-lithiated 3,6-di-tert-butyl-carbazole (2) with 2-bromo-1,3-diethyl-1,3,2-benzodiazaborole (1a) and 2-bromo-1,3-diphenyl-1,3,2- benzodiazaborole (1b) afforded the 2-N-carbazolyl-functionalized benzodiazaboroles 3a and 3b as colourless

Full text of DOI:10.1002/ejic.201000665

FULL PAPER
DOI: 10.1002/ejic.201000665
Synthetic, Structural, Photophysical and Computational Studies on
π-Conjugated 1,3,2-Benzodiazaboroles with Carbazole Building Blocks
Lothar Weber,*[a] Johannes Halama,[a] Vanessa Werner,[a] Kenny Hanke,[a] Lena Böhling,[a]
Anna Chrostowska,*[b] Alain Dargelos,[b] Małgorzata Maciejczyk,[b] Anna-Lena Raza,[a]
Hans-Georg Stammler,[a] and Beate Neumann[a]
Keywords: Boron / Carbazoles / Density functional calculations / Photophysics
The reaction of the N-lithiated 3,6-di-tert-butyl-carbazole (2)
with 2-bromo-1,3-diethyl-1,3,2-benzodiazaborole (1a) and 2-
bromo-1,3-diphenyl-1,3,2-benzodiazaborole (1b) afforded
the 2-N-carbazolyl-functionalized benzodiazaboroles 3a and
3b as colourless solids in 77 and 73% yield, respectively.
Synthesis of 2[5Ј-N-carbazolyl-2Ј-thienyl]-1,3-diethyl-1,3,2-
benzodiazaborole (5a) was effected by lithiation of N-(2-thi-
enyl)carbazole (4) and subsequent reaction with equimolar
amounts of 1a, and 5a was obtained in 68% yield. Similarly,
2[5Ј-N-carbazolyl-2Ј-thienyl]-1,3-diphenyl-1,3,2-benzodiaza-
borole (5b) was prepared from lithiated 4 and 1b in 62%
yield. Compounds 3a,b and 5a,b are characterized by ele-
mental analyses, IR and NMR spectroscopy (1H, 11B, 13C) and
mass spectrometry. The molecular structures of 3a and 5a
were elucidated by X-ray diffraction analysis. These bor-
ylated systems show intense blue luminescence. The spectro-
scopic results were reproduced by TD-DFT calculations at
the [B3LYP/6-311G (d,p)] level of theory.
on the syntheses and optical properties of extended π-con-
jugated systems with 1,3,2-diazaborolyl- and 1,3,2-benzodi-
azaborolyl ligands. We recently reported on the syntheses,
photophysical properties and computational studies of ben-
zene, diphenyl, 1,3,5-triphenylbenzene, thiophene and di-
thiophene cores that are functionalized by one, two or three
1,3,2-benzodiazaborole units.[10] This study was extended to
2-arylalkynyl-1,3,2-benzodiazaboroles, 2-(4Ј-X-C6H4CϵC)-
1,3-Et2-1,3,2-N2BC6H4 (X = -H, -Me, -MeO, -MeS,
Me2N).[11] These borolylated systems show intense blue/vi-
olet luminescence with Stokes shifts up to 9500 cm–1 and
quantum yields from 0.33 to 0.99. According to TD-DFT
calculations, the HOMO–LUMO transitions in the UV/Vis
spectra are assigned to π(diazaborolyl)–π*(thiophene/arene)
transitions.[10,11] Herein we report the syntheses, photophys-
ical properties and computational studies of 1,3,2-benzodi-
azaboroles with carbazole and 5Ј-carbazolyl-2Ј-thienyl sub-
stituents at the boron atom. The possibility of a push–pull
interaction between the carbazole nitrogen atom and the
borole was of particular interest.
Introduction
Conjugated molecules and polymers containing three-co-
ordinate boron have attracted considerable current interest
because of their optical and electronic properties, which
make them appropriate for use in functional materials.[1]
Three-coordinate boron generally behaves as a π acceptor
as a result of its vacant pz orbital, which stabilizes the
LUMO of an adjacent conjugated π-electron system and
thus lowers the HOMO–LUMO gap of these molecules.
The dimesitylboryl (BMes2) moiety (Mes = 2,4,6-Me3C6H2)
is the most prominent substituent in which the unsaturated
boron centre is stabilized by the steric effects of the ortho-
methyl groups. Such materials exhibit sizeable second- and
third-order nonlinear optic (NLO) coefficients[2,3] and large
two-photon absorption (TPA) cross-sections[4] and can be
used as efficient electron-transporting and/or emitting lay-
ers in organic light-emitting diodes (OLEDs)[5] or as sen-
sors for fluoride ions.[6] Recently, a number of conjugated
molecules with boryl side-groups that show very large
Stokes shifts and high quantum yields have been synthe-
sized.[7] At Bielefeld we have a long-standing interest in the
chemistry of 1,3,2-diazaboroles.[8,9] We carried out studies
Results and Discussion
Reaction of 2-bromo-1,3-diethyl-1,3,2-benzodiazaborole
(1a)[12] with a slight excess of in situ generated N-lithiated
3,6-di-tert-butylcarbazole (2)[13] in n-pentane at room tem-
perature led to the generation the 2-N-carbazolyl-1,3-dieth-
ylbenzodiazaborole (3a) as a colourless solid in 77% yield.
Similarly, the analogous 2-N-carbazolyl-1,3-diphenyl-1,3,2-
benzodiazaborole (3b) was synthesized as a colourless solid
in 73% yield (Scheme 1).
[a] Fakultät für Chemie der Univerität Bielefeld,
33615 Bielefeld, Germany
E-mail: lothar.weber@uni-bielefeld.de
[b] Equipe Chimie Physique, IPREM, UMR 5254, Université de
Pau et des Pays de l’Adour,
2 Av. du président Angot, B. P. 1155, 64013 Pau Cédex, 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.201000665.
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π-Conjugated 1,3,2-Benzodiazaboroles with Carbazole Building Blocks
Scheme 1. Syntheses of benzodiazaboroles 3a,b.
Scheme 2. Syntheses of 1,3,2-benzodiazaboroles 5a,b.
In the next step the influence of a π-conducting spacer
The 11B{1H}NMR resonance of compound 5a (δ =
between the electron-accepting benzodiazaborole unit and 25.8 ppm) is slightly shifted relative to those of thiophene-
the electron-donating carbazole system was investigated. functionalized 1,3,2-benzodiazaboroles 7 (δ = 26.2 ppm)
Thiophene was selected as a bridging π spacer because in and 8 (δ = 26.6 ppm).[10a] The 11B{1H}NMR spectrum of
the UV/Vis and fluorescence spectra of known thienyldiaza- 5b is characterized by a singlet at δ = 21.3 ppm (Figure 1).
boroles, significant bathochromic shifts were observed.[10]
Moreover, the incorporation of thienyl fragments usually
improves the thermostability of 1,3,2-diazaboroles. The syn-
thesis of 2[5Ј-N-carbazolyl-2-thienyl]-1,3-diethylbenzodi-
azaborole (5a) (Scheme 2) was effected by lithiation of (2-
thienyl)carbazole (4)[14] with n-butyllithium in ethyl ether at
20 °C and subsequent treatment of the reaction mixture
with an equimolar amount of 2-bromo-1,3-diethyl-1,3,2-
benzodiazaborole (1a).
Solid colourless 5a was isolated from the reaction residue
by n-hexane extraction and crystallization at 4 °C for 3 d
(yield: 68%). Similarly, reaction between lithiated thienyl-
carbazole 4 and 1b afforded 5b, which crystallized from the
n-pentane extracts of the reaction residue as an off-white
solid in 60% yield. All the compounds synthesized here are
air- and moisture sensitive. They can be stored at –5 °C un-
der an argon atmosphere for several weeks without decom-
position. In contrast to this, 5b slowly decomposed at room
temperature. Derivatives 3a,b and 5a,b are very soluble in
the common aprotic organic solvents with the exception of
alkanes (i.e. C6H6, C6H5CH3, CHCl3, CH2Cl2, thf, Et2O).
In the 11B{1H}NMR spectra of the 1,3,2-benzodiazaboroles
Figure 1. Compounds 6–8.
X-ray Structural Analysis of 3a
Single crystals of 3a, suitable for an X-ray structural
3a and 3b (CDCl3), singlets were observed at δ = 24.6 and study (Table 7), were grown from an n-pentane solution at
25.6 ppm, in agreement with the a singlet at δ = 23.1 ppm –20 °C. They crystallize in space group P21 despite the fact
(C6D6) reported for 6.[12]
that the structure is nearly centrosymmmetric, but the re-
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FULL PAPER
finement in the space group P21/a leads to poor results. The 1.362(8) Å] and compares well with that in 9 [1.412(1) Å].
asymmetric unit contains four independent molecules (I– The endocyclic bond angles in both ring systems are as ex-
IV), which differ significantly in the mutual orientation of pected (Figure 3).
the ring planes (Supporting Information). As bond lengths
and bond angles are identical within the threefold standard
deviation, only conformer I is discussed in more detail (Fig-
ure 2).
Figure 3. Compounds 9 and 10.
X-ray Structural Analysis of 5a
Single crystals of 5a suitable for an X-ray structural
study (Table 7) were grown from a dichloromethane/methyl-
cyclohexane mixture at 4 °C. The molecule is constructed
of three planar rings (Figure 4), whereby the central thio-
phene ring is linked to the benzodiazaborole unit by a single
bond B(1)–C(11) [1.557(2) Å] and to the carbazole system
by a single bond N(3)–C(14) [1.405(2) Å]. The molecule
markedly deviates from planarity as evident by the in-
terplanar angles enclosed by the central thiophene ring and
the diazaborole plane (34.7°) or the carbazole ring (41.4°).
Figure 2. Molecular structure of 3a (conformer I) in the crystal.
Selected bond lengths [Å] and angles [°]: B(1)–N(1) 1.438(6), B(1)–
N(2) 1.422(5), B(1)–N(3) 1.457(5), N(1)–C(1) 1.399(5), N(1)–C(7)
1.456(5), N(2)–C(2) 1.406(5), N(2)–C(9) 1.477(5), N(3)–C(11)
1.404(5), C(1)–C(2) 1.415(6), N(3)–C(22) 1.402(5), C(11)–C(16)
1.396(6), C(17)–C(22) 1.407(5), C(16)–C(17) 1.443(6). N(2)–B(1)–
N(1) 107.2(3), N(2)–B(1)–N(3) 127.2(4), N(1)–B(1)–N(3) 125.5(4),
C(1)–N(1)–B(1) 107.9(3), B(1)–N(1)–C(7) 129.8(3), C(2)–N(2)–B(1)
108.0(3), B(1)–N(2)–C(9) 130.4(3), N(1)–C(1)–C(2) 108.4(3), N(2)–
C(2)–C(1) 108.4(3), B(1)–N(3)–C(11) 126.0(3), B(1)–N(3)–C(22)
127.4(3), N(3)–C(11)–C(16) 110.1(3), N(3)–C(22)–C(17) 110.0(3),
C(11)–N(3)–C(22) 106.5(3), C(11)–C(16)–C(17) 107.0(3), C(16)–
C(17)–C(22) 106.3(3).
The molecule is constructed of a planar 1,3,2-benzodi-
azaborole ring and a planar carbazole ring, which are con-
nected by a B(1)–N(3) bond of 1.457(5) Å. In the remaining
conformers B–N bond lengths of 1.472(6) (II), 1.471(5) (III)
and 1.470(5) Å (IV) [av. 1.468(6) Å] are measured. For the
average bond length in a sterically unhindered acyclic ami-
Figure 4. Molecular structure of 5a in the crystal. Selected bond
lengths [Å] and angles [°]:B(1)–N(1) 1.437(2), B(1)–N(2) 1.432(2),
N(1)–C(1) 1.402(2), N(2)–C(2) 1.398(2), C(1)–C(2) 1.406(2), B(1)–
C(11) 1.557(2), S(1)–C(11) 1.735(1), S(1)–C(14) 1.735(1), C(11)–
C(12) 1.373(2), C(12)–C(13) 1.416(2), C(13)–C(14) 1.364(2), N(3)–
C(14) 1.405(2), N(3)–C(15), 1.406(2), C(15)–C(20) 1.405(2), C(20)–
noborane, a value of 1.41 Å is given in the literature.[15a]
A
particularly short BN double bond was encountered in
(CF3)2B=N (iPr)2 [1.37(1) Å].[15b] Obviously in 3a an opti-
mal π conjugation within this unit is prevented by the non-
planar orientation of both ring fragments, which enclose C(21) 1.448(2), C(21)–C(26) 1.406(2), N(3)–C(26) 1.407(2), N(1)–
C(7) 1.462(2), N(2)–C(9) 1.459(2); N(1)–B(1)–N(2) 106.7(1), B(1)–
N(1)–C(1) 107.7(1), B(1)–N(1)–C(7) 131.5(1), B(1)–N(2)–C(9)
dihedral angles of 55.9 (I), 75.5 (II), 57.2 (III) and 77.7°
(IV) (av. 66.6°). The endocyclic B–N distances [B(1)–N(1)
129.8(1), N(1)–C(1)–C(2) 108.8(1), N(2)–C(2)–C(1) 108.5(1), N(1)–
1.438(6), B(1)–N(2) 1.422(5) Å] fall in the upper region of
B(1)–C(11) 127.8(1), N(2)–B(1)–C(11) 125.4(1), B(1)–C(11)–S(1)
such values in monocyclic 1,3,2-diazaboroles [1.395(7)–
1.450(2) Å][16] and are similar to such bond lengths in com-
pound 9 [1.438(1), 1.440(1) Å].[12] The endocyclic bond
lengths N(1)–C(1) [1.399(5) Å] and N(2)–C(2) [1.406(5) Å]
also resemble those in 9 [1.398(1), 1.394(1) Å] and are typi-
cal for 1,3,2-diazaboroles. For the C–N distances in the car-
120.5(1), B(1)–C(11)–C(12) 130.3(1), C(11)–S(1)–C(14) 92.8(1),
S(1)–C(14)–C(13) 110.9(1), C(12)–C(13)–C(14) 112.2(1), S(1)–
C(11)–C(12) 109.0(1), S(1)–C(14)–N(3) 120.5(1), C(13)–C(14)–N(3)
128.4(1), C(15)–N(3)–C(26) 108.2(1), C(14)–N(3)–C(15) 126.2(1),
C(14)–N(3)–C(26) 125.2(1).
Bond lengths and bond angles within the benzodiazabor-
bazole part N(3)–C(11) and N(3)–C(22), comparable values ole part are as usual.[10–12] The bond lengths within the
[1.404(5) and 1.402(5) Å] are measured. The double bond thiophene building block S(1)–C(11) [1.735(1) Å], S(1)–
length C(1)–C(2) [1.415(6) Å] is markedly elongated in com- C(14) [1.735(1) Å], C(11)–C(12) [1.373(2) Å], C(12)–C(13)
parison to monocyclic diazaboroles [1.315(11) to [1.416(2) Å] and C(13)–C(14) [1.364(2) Å] are close to those
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π-Conjugated 1,3,2-Benzodiazaboroles with Carbazole Building Blocks
in the central thiophene ring in molecule 10 [1.736(3);
The fluorescence spectrum of a cyclohexane solution of
the free carbazole displays a strong band at λ = 344 nm,
1.730(3); 1.379(4); 1.403(5); 1.375(4) Å][10a] (Figure 3).
As also observed in 10, the exocyclic angles B(1)–C(11)– regardless of the respective excitation wavelength (291 nm
S(1) [120.5(1)°] and B(1)–C(11)–C(12) [130.3(1)°] differ sig- or 339 nm). Thus, the transition LUMOǞHOMO gives rise
nificantly. Similar observations were made with angles S(1)– to a Stokes shift, which clearly excludes transfer of charge
C(14)–N(3) [120.5(1)°] and C(13)–C(14)–N(4) [128.4(1)°].
within the molecule by UV light absorption. The situation
is quite similar to that in 2-carbazolyl-1,3,2-benzodiazabor-
ole 3a. In the UV/Vis spectrum of a hexane solution, an
UV/Vis and Luminescence Spectra
intense band was observed at
λ = 297 nm (ε =
16676 Lmol–1 cm–1) in addition to a weak band at λ =
340 nm (ε = 2643 Lmol–1 cm–1). In the luminescence spec-
trum, a strong band was found at λ = 345 nm (Stokes shift
500 cm–1) (Figure 5). By considering the UV/Vis spectra of
2-tBuBDB and carbazole 2-H, it is obvious that absorption
and emission occur in the carbazole part of 3a without sig-
nificant contributions from B/N-heterocycle and that a no-
Table 1 lists selected photophysical data for compounds
3a,b and 5a,b, all of which exhibit intense blue luminescence
under UV irradiation. For comparison, those of 2-tert-but-
yl-1,3-diethyl-1,3,2-benzodiazaborole (2-tBuBDB) and 3,6-
di-tert-butylcarbazole (2-H) are also presented. The UV/Vis
spectrum of 2-tBuBDB displays an intense absorption band
at 294 nm in cyclohexane as well as in thf solution. This
band is assigned to the HOMO–LUMO transition. The
fluorescence spectrum of a cyclohexane solution of this
benzodiazaborole was registered at an excitation wavelength
of 285 nm and shows an intense emission at 307 nm. A
Stokes shift of 2400 cm–1 was deduced, which is in line with
the absence of a significant charge transfer during the exci-
tation. No solvatochromism was observed as absorption
(λmax = 287 nm) and emission spectra (λmax = 309 nm) in
thf gave identical values. The UV/Vis spectrum of a cyclo-
hexane solution of 3,6-di-tert-butylcarbazole (2-H) is domi-
nated by a strong absorption band at λ = 296 nm (ε =
18114 Lmol–1 cm–1) and a significantly weaker absorption
band at λ = 337 nm (ε = 2672 Lmol–1 cm–1). The same situ-
ation is encountered in the more polar thf solution.[17] Ac-
cording to the theoretical calculations, the intense band at
296 nm may be assigned to a transition from the HOMO–1
into the LUMO of the molecule, whereas that at λ = 337 nm
reflects the HOMO–LUMO transition (see also Table 3).
Figure 5. Absorption and emission spectra of 3a.
Table 1. Selected photophysical data of compounds 2-tBuBDB, 2-H, 3a,b and 5a,b.
Compound
λmax abs.
,
[nm] λmax abs.
,
[cm–1]
ε [Lmol–1 cm–1] λmax,em. [nm]
λmax em.
,
[cm–1]
Stokes Shift [cm–1] Φf[c]
2-tBuBDB[a]
2-tBuBDB[b]
2-H[a]
285
287
296
337
298
329
297
340
296
340
296
335
297
336
296
321
296
323
296
328
296
330
35100
34800
33800
29700
33600
30400
33700
29400
33800
29400
33800
29800
33700
29800
33800
31100
33800
31000
33800
30500
33800
30300
307
309
34700
34700
2400
2400
18114
2672
14890
2957
16676
2643
23080
4251
17336
1532
15895
3149
14488
9509
13661
9509
22628
9931
28555
13194
344
352
345
348
342
344
371
389
386
388
29700
29400
28900
28700
29100
29000
25800
25200
25500
25300
0
2-H[b]
3a[a]
3a[b]
3b[a]
3b[b]
5a[a]
5a[b]
5b[a]
5b[b]
1000
500
0.37
0.09
0.41
0.33
0.14
0.15
0.13
0.15
700
700
800
5300
5800
5000
5000
[a] In c-C6H12. [b] In thf. [c] Against standard POPOP Φ = 0.93.
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L. Weber, A. Chrostowska et al.
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table π conjugation between the two ring systems is absent. Table 2. Selected experimental and calculated [B3LYP/6-311G(d,p)]
bond lengths [Å] and angles [°] for molecules B, BC (3a) and BTC
(5a).
The excited state of molecule 3a is not particularly polar,
which is evidenced by similar absorption and emission
Bcalcd.
BCcalcd. BCexp.
(3a) (3a)
BTCcalcd. BTCexp.
wavenumbers in thf as well as by DFT calculations [B3LYP/
6-311(d,p)] of the dipolar moments in the ground and the
excited states (0.20 and 6.22 D). Other benzodiazaboroles B(1)–N(1)
(5a)
(5a)
1.436
1.436
1.414
1.396
1.396
1.434 1.438(6)
1.435 1.422(5)
1.415 1.415(6)
1.398 1.399(5)
1.398 1.406(5)
1.468 1.457(5)
1.442
1.442
1.416
1.398
1.398
1.432(2)
1.437(2)
1.406(2)
1.402(2)
1.398(2)
B(1)–N(2)
in which the boron atom is directly attached to thienyl or
C(1)–C(2)
aryl groups display Stokes shifts of 6200–9500 cm–1. The
N(1)–C(1)
UV spectrum of 3b is similar with absorption bands at
N(2)–C(2)
B(1)–N(3)
B(1)–C(11)
C(11)–S(1)
λ = 296 nm (ε = 17336 Lmol–1 cm–1) and 335 nm (ε =
1532 Lmol–1 cm–1). Emission occurs at 342 nm, which gives
1.558
1.754
1.758
1.398
1.557(2)
1.735(1)
1.735(1)
1.405(2)
a Stokes shift of 700 cm–1.
C(14)–S(1)
The UV/Vis spectrum of derivative 5a in cyclohexane
C(14)–N(3)
solution displays prominent bands at λ = 296 nm (ε =
N(3)–C(11)
1.401 1.404(5)
1.401 1.402(5)
14488 Lmol–1 cm–1) and 321 nm (ε = 9509 Lmol–1 cm–1). In N(3)–C(22)
N(3)–C(15)
N(3)–C(26)
N(1)–B(1)–N(2)
1.405
1.403
106.6
108.0
108.1
1.406(2)
1.407(2)
106.7(1)
108.3(1)
107.7(1)
thf, only slight shifts of these absorption bands are regis-
tered. The band with the lowest energy is attributed to the
106.8
108.0
108.0
126.6
107.3 107.2(3)
107.7 108.0(3)
107.7 107.9(3)
HOMOǞLUMO transition. The HOMO–1ǞLUMO tran-
sition is attributed to the band at 296 nm (Table 6). In the
fluorescence spectrum of 5a in cyclohexane a band at λ =
371 nm is observed, which experiences a small redshift in
thf to λ = 389 nm. These data correspond to Stokes shifts
of 5300 cm–1 (c-C6H12) and 5800 cm–1 (thf).
C(2)–N(2)–B(1)
C(1)–N(1)–B(1)
N(3)–B(1)–H(1)
N(2)–B(1)–N(3)
N(2)–B(1)–C(11)
C(11)–S(1)–C(14)
C(11)–N(3)–C(22)
126.4 127.2(4)
107.0 106.5(3)
128.0
92.4
127.8(1)
92.8(1)
Similarly, in cyclohexane solutions of 5b, two bands at λ C(15)–N(3)–C(26)
108.0
108.1(1)
= 296 nm (ε = 22628 Lmol–1 cm–1) and 328 nm (ε =
N(2)–B(1)–N(3)–C(26)
63.7
55.9 (av. 66.6)
N(1)–B(1)–C(11)–S(1)
9931 Lmol–1 cm–1) were observed, which are assigned to the
S(1)–C(14)–N(3)–C(26)
–45.3
–60.2
–33.1
–39.3
HOMO–1ǞLUMO and the HOMOǞLUMO transitions.
The luminescence spectrum is characterized by an intense
emission at 386 nm, which led to Stokes shifts of 5000 cm–1
in cyclohexane as well as in thf. Again the lack of solvato-
chromism is consistent with a nonpolar excited state.
DFT Calculations
Table 2 contains selected calculated geometrical param-
eters for 1,3-diethyl-1,3,2-benzodiazaborole (B), 2-[N-3Ј,6Ј-
Figure 6. Compounds B, BC (3a) and BTC (5a).
di-tert-butylcarbazolyl]-1,3-diethyl-1,3,2-benzodiazaborole
(BC, 3a) and 2[5Ј-N-carbazolyl-2Ј-thienyl]-1,3-diethyl-1,3,2-
benzodiazaborole (BTC, 5a), in addition to the experimen-
tal structural data of 3a and 5a (Figure 6).
TD-DFT computations carried out on the optimized ge-
The geometry of benzodiazaborole ring of BC undergoes ometry of BC (3a), which is presumably not markedly dif-
no significant changes in comparison to B and agrees nicely ferent from the geometry of 3b, gave a lowest energy of
with experimental data found in numerous diazaboroles 320 nm for an allowed S1 ǟS0 electronic absorption with
and also in 3a and 5a. The calculated value of the NC bond an oscillator strength f = 0.0328, which corresponds to the
length in carbazole (1.386 Å) marginally increases in BC HOMO–LUMO transition. This calculated value differs
(1.401 Å) [exp. av. 1.403(5) Å]. The endocyclic angle NBN from the observed absorption maximum at 334 nm by
in BC [107.3°, exp. 107.2(3) Å] is more obtuse than in the 14 nm. The redshift may be due to the fact that, in solution,
free molecule B, whereas the endocyclic angle CNC in BC an ensemble of rotational isomers exists, including planar
[107.0°, exp. 108.4(3)°] is slightly compressed relative to the geometries.
calculated angle in carbazole (109.3°). Interestingly, both
In Table 3, TD-DFT [B3LYP/6-311(d,p)] calculated ion-
rings of BC are not oriented in the same plane, but instead ization energies [eV] and MOLEKEL visualizations of the
enclose a dihedral angle of 63.7° (exp. av. 66.6°), which does MOs for molecules B, C (2-H) and BC (3a) are given. The
not allow for a significant (BN) π interaction. In keeping HOMO [πI(crb)] of (BC) is assigned to the antibonding in-
with this, the bond B(1)–N(3) (1.468 Å) [exp. av. 1.468(6) Å] teraction between the sp2 carbon atoms and nitrogen lone
is markedly longer than typical BN double bonds (exp. av. pair in the π plane (6.62 eV). The corresponding HOMO
1.412 Å).[15a] Accordingly, at least in the electronic ground (7.01 eV) in the free carbazole is thus destabilized by
state, there exists no essential π-electronic communication 0.39 eV because of the positive inductive effect of the diaza-
between both ring systems.
borole fragment. The HOMO (π3–πNBN) in free B, which
5420
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5416–5425

π-Conjugated 1,3,2-Benzodiazaboroles with Carbazole Building Blocks
Table 3. TD-DFT [B3LYP/6-311G(d,p)] calculated ionization ener- 1.416(2) Å is slightly longer than the experimental one
gies, εKS and the MOLEKEL[18] MO visualization for molecules B,
[1.406(2) Å]. The same holds for the S–C bonds within the
C (carbazole 2-H) and BC (3a). (*ΔSCF values, **εKS, all values
thiophene fragment [calcd. 1.754 and 1.758 Å vs. exp.
in eV).
1.735(2) Å]. The interplanar angles between the three rings
of this molecule in the gas phase (–45.3 and –60.2°), how-
ever, differ essentially from those determined in the crystal
of 5a (–33.1 and –39.3°).
Table 5 displays the MO visualization and the corre-
sponding ionization energies. As previously observed for
molecule BC (3a) (6.62 eV), the first ionization energy of
BTC (5a) (6.54 eV) corresponds to the HOMO πI(crb),
which is located on the carbazole part. Thus, the formal
insertion of the thiophene spacer between the diazaborole
and carbazole fragments leads to only a small destabiliza-
tion (0.08 eV).
Table 5. TD-DFT [B3LYP/6-311 G(d,p)] calculated ionization en-
ergies, εKS and the MOLEKEL[18] MO visualization for molecules
B, TC and BTC (5a). (* ΔSCF values, **εKS, all values in eV).
corresponds to the antibonding combination of the orbitals
of the sp2 carbon atoms, and the bonding NBN π orbital
(7.63 eV) is destabilized to 7.32 eV by the carbazole because
of a +M effect, albeit to a slightly smaller extent (0.31 eV).
The intense absorption band in the experimental UV/Vis
spectrum at 296 nm can be assigned to a transition from
the HOMO–1 (πII) (7.15 eV), which is also centred on the
carbazole part, to the LUMO of the molecule, with an os-
cillator strength of 0.1424. In line with the two observed
transitions, the calculated corresponding energy of the
HOMO–LUMO transition is 3.88 eV (319.70 nm), whereas
that between HOMO–1 and LUMO is 4.40 eV (218.84 nm).
In Table 4, the calculated and observed electronic transi-
tions are compiled (for calculated values of the HOMO–
LUMO gap of studied compounds see the Supporting In-
formation).
The HOMO–1 πII(crb) of 3a (7.15 eV), which is a part
of the more complex molecule 5a, is destabilized to 7.06 eV
Table 4. Calculated [B3LYP/6-311G(d,p)] UV spectrum for BC
and becomes the HOMO–2 in this species. The HOMO–1
(3a).
[π3–πNBN–nNπ(crb)] of 5a is ionized by an energy of 7.01 eV.
E
λ
f
Transition
This is an antibonding combination of π3 of benzene with
the two adjacent nitrogen atom lone pairs delocalized to
the p orbital of the boron atom in interaction with the car-
bazole nitrogen atom lone pair.
The low-energy HOMO–LUMO transition of 340.35 nm
(3.64 eV, f = 0.3107) corresponds to a charge transfer from
the carbazole part to the thiophene unit of the molecule.
The next observed absorption at 312.78 nm is assigned to
the HOMO–1 to LUMO transition (3.96 eV, f = 0.1187)
and reflects a charge transfer from the benzodiazaborole
part to the central thiophene ring. In Table 6, the calculated
3.88
4.40
4.42
4.53
4.77
4.94
4.95
5.07
5.15
5.19
319.70
281.84
280.54
273.45
259.86
250.97
250.31
244.44
240.70
238.69
0.0328
0.1424
0.0061
0.2108
0.0002
0.1026
0.2133
0.2404
0.0099
0.0004
HOMOǞLUMO
HOMO–1ǞLUMO
HOMO–2ǞLUMO
HOMOǞLUMO+1
HOMO–3ǞLUMO
HOMO–2ǞLUMO
HOMOǞLUMO+2
HOMO–2ǞLUMO+1
HOMO–3ǞLUMO+1
HOMOǞLUMO+4
For compound BTC (5a), the experimentally determined electronic transitions of 5a are presented. Because of the
bond lengths and valence angles (Table 2) are not signifi- opposite directions of the charge-transfer processes, no sig-
cantly different from those calculated with the exception nificant net increase in the dipole moments results. This
of the C(1)–C(2) bond, where the calculated value of idea is underlined by the lack of solvatochromism.
Eur. J. Inorg. Chem. 2010, 5416–5425
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5421

L. Weber, A. Chrostowska et al.
FULL PAPER
sodium tert-butanolate (0.244 g, 2.54 mmol) and palladium acetate
(0.190 g, 0.848 mmol) were combined with toluene (20 mL), and
the slurry was heated for 1 h at 80 °C. Homogenization of the sus-
pension was achieved in an ultrasound bath over 5 min; o-dibro-
mobenzene (20.0 g, 84.7 mmol), aniline (16.5 g, 17.8 mmol), so-
dium tert-butanolate (24.4 g, 254.0 mmol) and the catalyst solution
were then poured into toluene (150 mL). The obtained mixture was
heated to boil for 5 h. After cooling to room temperature, a satu-
rated aqueous NH4Cl solution (30 mL) was added, followed by the
dropwise addition of glacial acetic acid (10 mL). The organic layer
was separated, washed twice with brine (20 mL) and then evapo-
rated to dryness. The solid residue was recrystallized from meth-
anol. The obtained crystalline product was washed with ethanol
(5ϫ10 mL) and n-hexane (2ϫ30 mL) and then dried in vacuo.
N,NЈ-diphenyl-o-phenylene diamine was obtained as a light-violet
solid. Yield: 19.19 g (87%). 1H NMR (C6D6): δ = 5.12 (s, 2 H,
NH), 6.70 (d, JHH = 8.0 Hz, 4 H, NH–C=CH–CH=CH), 6.78 (t,
JHH = 7.8 Hz, 2 H, NH–C=CH–CH=CH), 6.84 (m, 2 H, NH–
C=CH–CH), 7.06 (t, JHH = 7.8 Hz, 4 H, NH–C=CH–CH=CH),
7.18 (m, 2 H, NH–C=CH–CH) ppm. 13C{1H} NMR (C6D6): δ =
117.5 (s, NH–CH=CH–CH=CH), 120.9 (s, NH–CH=CH–
CH=CH), 123.4 (s, p-PhC), 128.4 (s, o-PhC), 129.7 (s, m-PhC),
135.5 (s, PhC-N), 144.5 (s, N2C2) ppm. MS/EI: m/z = 260.1 [M]+.
Table 6. Calculated [B3LYP/6-311G(d,p)] of BTC (5a).
E [eV]
λ calcd. [nm]
f
Transition
3.64
3.87
3.96
4.12
4.31
4.37
4.41
4.77
4.83
4.96
340.35
320.19
312.78
301.13
287.46
283.45
281.30
259.80
256.71
249.93
0.3107
0.0958
0.1187
0.0012
0.0022
0.0119
0.1534
0.0446
0.0005
0.1080
HOMOǞLUMO
HOMOǞLUMO+1
HOMO–1ǞLUMO
HOMO–2ǞLUMO
HOMO–1ǞLUMO+1
HOMO–3ǞLUMO
HOMO–2ǞLUMO+1
HOMOǞLUMO+2
HOMO–3ǞLUMO+1
HOMO–1ǞLUMO+2
Conclusions
1,3,2-Benzodiazaboroles with N-carbazolyl substituents
of the boron atom, 3a,b, have nonplanar geometries in the
crystalline phase, as evidenced by X-ray crystallography, as
well as in the gas phase, according to DFT calculations.
Obviously, there exists no appreciable π communication be-
tween both ring units in the molecule. In keeping with this,
no marked charge transfer was observed during excitation
with UV light. Small Stokes shifts and the absence of solva-
tochromism are in accord with electron transitions within
the carbazole part of the molecules. In N-carbazolylthienyl-
benzodiazaborole 5a, it was calculated that the low-energy
HOMO–LUMO transition of 340.35 nm (3.64 eV) corre-
sponds to a charge transfer from the carbazole part to the
thiophene unit, while the absorption band at 312.78 nm
(3.96 eV) is assigned to the HOMO–1ǞLUMO transition
and reflects a charge transfer from the benzodiazaborole
fragment to the central thiophene ring. Experimental values
for these transitions in 5a (λ = 323; 296 nm) are slightly
blueshifted. Emission was observed at λ = 371 nm (in c-
C6H12), which results in a Stokes shift of 5300 cm–1. In thf,
this value increases to 5800 cm–1.
Step 2, Path A: Solution of boron tribromide (6.40 g, 25.4 mmol)
in toluene (40 mL) and N,NЈ-diphenyl-o-phenylene diamine (6.01 g,
23.1 mmol) in toluene (40 mL) were slowly added to a chilled slurry
(0 °C) of calcium hydride (2.94 g, 69.8 mol) in toluene (75 mL). Af-
ter completion, the slurry was stirred for 3 h at room temperature
and filtered. The filtrate was freed from solvent and volatiles. The
remaining dark-brown oil was purified by short-path distillation at
10–6 bar to afford 1b as a clear, colourless, viscous oil. Yield: 7.89 g
(98%). Path B: A solution of n-butyllithium in n-hexane (11.3 mL
of a 1.6 m solution, 18.0 mmol) was added dropwise to a chilled
solution (–78 °C) of N,NЈ-diphenyl-o-phenylene diamine (2.08 g,
8.0 mmol) in toluene (30 mL). After completion, the reaction mix-
ture was stirred for 1 h at –78 °C and then for 1 h at 70 °C, whereby
a yellow solid precipitated. It was cooled to 0 °C, before boron
tribromide (2.12 g, 8.5 mmol) was added by syringe. The mixture
was stirred continuously at room temperature overnight. It was fil-
tered, and the filtercake was washed with toluene (2ϫ10 mL). The
filtrate was evaporated to dryness, and the remaining brown oil was
purified as described above. Yield: 2.01 g (72%). 1H NMR
(CDCl3): δ = 7.06 (m, 2 H, CH=CH–CH=CH), 7.14 (m, 2 H,
CH=CH–CH=CH), 7.42 (t, JHH = 7.3 Hz, 2 H, p-Ph–CH), 7.49
(d, JHH = 7.5 Hz, 4 H, o-Ph–CH), 7.55 (t, JHH = 7.7 Hz, 4 H, m-
Ph–CH) ppm. 13C{1H} NMR (CDCl3): δ = 110.4 (s, CH=CH–
CH=CH), 120.6 (s, CH=CH–CH=CH), 126.8 (s, p-PhC), 127.2 (s,
o-PhC), 129.3 (s, m-PhC), 136.9 (s, PhC-N), 138.8 (s, N2C2) ppm.
11B{1H} NMR (CDCl3): δ = 23.8 (s) ppm; (C6D6): δ = 24.0 (s)
ppm.
Experimental Section
All manipulations were performed under an atmosphere of dry,
oxygen-free argon by using standard Schlenk techniques. All sol-
vents were dried by standards methods and freshly distilled prior
to use. The compounds 2-bromo-1,3-diethyl-1,3,2-benzodiazabor-
ole (1a),[12] 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride[19a]
and N-(2-thienyl)-3,6-di-tert-butyl-carbazole[14] were prepared ac-
cording to literature methods. The protocol for N,NЈ-diphenyl-o-
phenylenediamine reported in ref.[19b] was modified. 1,2-Dibro-
mobenzene, aniline, palladium acetate and NaOC(CH3)3 were pur-
chased commercially (Aldrich). NMR spectra were recorded at
room temperature on a Bruker AM Avance DRX 500 spectrometer
2-N-(3Ј,6Ј-Di-tert-butylcarbazolyl)-1,3-diethyl-1,3,2-benzodiaza-
borole (3a): An n-pentane solution of tert-butyllithium (1.6 m,
3.8 mL, 6.08 mmol) was added dropwise with stirring at room
temperature to the slurry of 3,6-di-tert-butylcarbazole (1.70 g,
6.08 mmol) in n-pentane (60 mL). After 1 h of stirring at room tem-
perature, the slurry was treated with a sample of 2-bromo-1,3-di-
ethyl-1,3,2-benzodiazaborole (1.54 g, 6.08 mmol). The slurry was
stirred for 2 h at room temperature. It was filtered, and, after 15 h
at –20 °C, colourless crystals of 3a separated from the filtrate.
(1H, 11B, 13C) by using TMS and BF3 Et2O as external standards.
·
Mass spectra were taken with a VG autospec sector field mass spec-
trometer (Micromass). The UV/Vis spectra were recorded on a
Thermo Evolution 300 UV/Vis spectrometer and the emission spec-
tra on a Hitachi F-4500 Fluorescence spectrometer. From the
microanalyses, low C values were repeatedly obtained with different
samples, which may be due to boron carbide formation during the
combustion process.
1
Yield: 2.12 g (77%). H NMR (CDCl3): δ = 1.20 (t, JHH = 6.9 Hz,
2-Bromo-1,3-diphenyl-1,3,2-benzodiazaborole (1b)
6 H, NCH2CH3), 1.50 (s, 18 H, tBu), 3.70 (q, JHH = 6.9 Hz, 4
Step 1, N,NЈ-Diphenyl-o-phenylenediamine: A mixture of 1,3-bis- H, CH3CH2N), 7.17 (m, 2 H, CH=CH–CH=CH), 7.26 (m, 4 H,
(2,6-diisopropylphenyl)imidazolium chloride (0.721 g, 1.70 mmol), CH=CH–CH=CH and tBu-CCH–CH), 7.48 (d, JHH = 8.2 Hz, 2
5422
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Eur. J. Inorg. Chem. 2010, 5416–5425

π-Conjugated 1,3,2-Benzodiazaboroles with Carbazole Building Blocks
H, tBu-C–CH–CH), 8.18 (d, JHH = 1.9 Hz, C–CH–C) ppm. δ = 25.8 (s) ppm. IR (ATP, diamond): ν = 3037 (w), 2960 (s), 2926
˜
13C{1H} NMR (CDCl3): δ = 15.7 (s, CH3CH2N), 32.0 [s, (m), 1678 (m), 1602 (s), 1549 (s), 1488 (m), 1469 (s), 1397 (s), 1363
C(CH3)3], 34.7 [s, C(CH3)3], 37.4 (s, CH3CH2N), 109.5, (s,
(s), 1263 (m), 1233 (s), 1045 (m), 880 (w), 809 (s), 735 (s), 730 (s),
CH=CH-CH=CH), 111.0 (s, tBu-C–CH–CH), 116.2 (s, tBu-C– 653 (m), 614 (m), 510 (m) cm–1. MS/EI: m/z = 533.3 (100) [M+]+,
CH–C), 119.1 (s, CH=CH–CH=CH), 123.6 (s, tBu-C–CH–CH), 518.35 (36) [M – CH3]+. C34H40BN3S (533.58): calcd. C 76.53, H
125.0, 141.0 142.6 (3s, C-carbazole), 136.6 (s, N2C2) ppm. 11B 7.56, N 7.88; found C 74.56, H 7.74, N 7.50.
{1H}NMR (CDCl ): δ = 24.6 ppm. IR (ATP, diamond): ν = 2960
˜
3
5Ј-N-(3Ј-6Ј-Di-tert-butylcarbazolyl-2Ј-thienyl)-1,3-diphenyl-1,3,2-
benzodiazaborole (5b): An n-hexane solution of n-butyllithium
(1.6 m, 1.5 mL, 2.4 mmol) was added in one portion to a solution
of N-2Ј-thienyl-3,6-tert-butylcarbazole (0.88 g, 2.4 mmol) in ethyl
ether (50 mL) at room temperature. After 1 h, a solution of 2-
bromo-1,3-diphenyl-1,3,2-benzodiazaborole (6.30 g, 2.4 mmol) was
added. The solution was stirred for 16 h, and then all the volatile
compounds were removed in vacuo. The residue was suspended in
n-pentane (40 mL) and filtered. Crystals were grown from the fil-
trate after 30 min at 4 °C. They were collected and recrystallized
from n-pentane (30 mL). After two days at 4 °C, product 5b was
obtained as an off-white solid (0.94 g, 1.5 mmol, 62% yield). 1H
NMR (CDCl3): δ = 1.47 (s, 18 H, tBu) 6.90 (d, JHH = 3.8 Hz, 1
H, S–C–CH–CH), 6.96 (m, 3 H, CH=CH–CH=CH, and S–C–CH–
CH), 7.04 (m, 2 H, CH=CH–CH=CH), 7.32 (d, JHH = 8.7 Hz, 2
H, tBu-C–CH–CH), 7.45 (dd, JHH = 8.7, 1.7 Hz, 2 H, tBu-C–CH–
CH), 7.47 (m, 2 H, p-H-Ph), 7.53 (m, 4 H, m-H-Ph), 7.57 (m, 4 H,
o-H-Ph), 8.08 (d, JHH = 1.7 Hz, 2 H, tBu-C–CH–C) ppm. 13C{1H}
NMR (CDCl3): δ = 32.0 [s, C(CH3)3], 34.7 [s, C(CH3)3], 109.7 (s,
CH=CH–CH=CH), 110.0 (s, tBu-C–CH–CH), 116.1 (s, tBu-C–
CH–C), 120.0 (s, CH=CH–CH=CH), 123.7 (s, tBu-C–CH–CH),
125.4 (s, SC–CH–CH–CN), 127.4 (s, NC–CH=CH–CH), 128.6,
129.9 (2s, NC–CH=CH–CH), 135.9 (s, S–C–CH–CH–N), 123.4,
140.1, 143.4 (3s, C-carbazole), 138.4 (s, N2C2), 144.5 (s, S–C–N)
ppm. 11B {1H}NMR (CDCl3): δ = 21.3 ppm. IR (ATP, diamond):
(s), 2901 (m), 2865 (m), 1604 (m), 1488 (m), 1469 (s), 1450 (s), 1420
(s), 1376 (m), 1360 (m), 1324 (w), 1301 (m), 1259 (s), 1231 (m),
1200 (w), 1083 (s), 1016 (s), 875 (m), 794 (s), 732 (s), 642 (w), 620
(m), 600 (w), 552 (w), 466 (m) cm–1. MS/EI: m/z = 451.5 (95)
[M]+, 436.5 (100) [M – CH3]+. C30H38BN3 (451.47): calcd. C 79.76,
H 8.48, N 9.30; found C 79.21, H 8.50, N 8.44.
2-N-(3Ј,6Ј-Di-tert-butylcarbazolyl)-1,3-diphenyl-1,3,2-benzodiaza-
borole (3b): A slurry of 3,6-di-tert-butylcarbazole (0.90 g,
3.2 mmol) in n-pentane (50 mL) was combined at 20 °C with an n-
hexane solution of n-butyllithium (1.6 m, 3.2 mmol) and stirred for
2 h. A solution of 2-bromo-1,3-diphenyl-1,3,2-benzodiazaborole
(7.50g, 3.2 mmol) in benzene (50 mL) was then added. After stir-
ring for 15 h, all the volatile components were removed in vacuo,
and the residue was continuously extracted (3 h) with n-hexane
(70 mL). After this, the volatiles were removed in vacuo, and the
colourless residue was crystallized from toluene (25 mL) at 4 °C to
yield 1.28 g (2.3 mmol, 73%) of 3b as a colourless microcrystalline
1
solid. H NMR (CDCl3): δ = 1.41 (s, 18 H, tBu), 7.04 (d, JHH
=
8.6 Hz, 2 H, tBu-CCH–CH), 7.13 (m, 2 H, p-H-Ph), 7.16 (dd, JHH
= 8.6, 1.7 Hz, 2 H, tBu-C–CH–CH), 7.19 (m, 2 H, CH=CH–
CH=CH), 7.25 (m, 8 H, o-, m-H Ph), 7.45 (m, 2 H, CH=CH–
CH=CH), 7.99 (d, JHH = 1.7 Hz, 2 H, C CH–C-tBu) ppm. 13C{1H}
NMR (CDCl3): δ = 31.9 [s, C(CH3)3], 34.6 [s, C(CH3)3], 110.5 (s,
CH=CH–CH=CH), 111.6 (tBuCCH–CH), 115.6 (CCH–C-tBu),
120.6 (s, CH=CH–CH=CH), 123.6 (s, tBu-C–CH–CH), 125.7 (s, o-
, m-PhC), 126.0 (s, p-PhC), 125.2, 140.2, 142.5 (3s, C-carbazole),
136.3 (s, N2C2), 139.2 (s, PhC-N) ppm. 11B {1H} NMR (CDCl3):
ν = 3037 (w), 2959 (s), 2898 (m), 1589 (s), 1541 (s), 1456 (m), 1362
˜
(s), 1228 (s), 1063 (m), 880 (w), 839 (s), 740 (s), 697 (m), 510 (m)
cm–1. MS/EI: m/z = 629.3 (100) [M]+, 614.2 (36) [M – CH3]+.
C42H40BN3S (629.68 g/mol): calcd. C 80.11, H 6.40, N 6.67; found
C 77.60, H 6.19, N 6.46.
δ = 25.6 ppm. IR (ATP, diamond): ν = 3037 (w), 2958 (m), 2860
˜
(w), 2360 (m), 2342 (m), 1585 (m), 1499 (m), 1485 (m), 1469 (s),
1411 (m), 1380 (s), 1330 (w), 1257 (m), 1229 (s), 1185 (w), 1071
(w), 1026 (w), 878 (w), 811 (s), 742 (s), 695 (s), 648 (m), 614 (m),
510 (m) cm–1. MS/EI: m/z = 547.3 (100) [M]+, 532.2 (83) [M –
CH3]+. C38H38BN3 (547.54): calcd. C 83.36, H 7.00, N 7.67; found
C 82.57, H 7.06, N 7.68.
X-ray Crystallography: Single crystals of 3a and 5a were coated
with a layer of hydrocarbon oil, attached to a glass fibre and cooled
to 100 K for data collection. Crystallographic data were collected
with a Nonius Kappa CCD diffractometer with Mo-Kα radiation
(graphite monochromator), λ = 0.71073 Å. Crystallographic pro-
grams used for the structure solution and refinement were from
SHELX-97.[20] The structure was solved by direct methods and was
refined by using full-matrix least-squares on F2 of all unique reflec-
tions with anisotropic thermal parameters for all non-hydrogen
atoms, with the exception of the disordered solvent in 3a. Hydrogen
atoms were included at calculated positions with U(H) = 1.2Ueq
for CH2 groups and U(H) = 1.5Ueq for CH3 groups. Crystal data
for the compounds are listed in Table 7. CCDC-780597 (3a) and
-780598 (5a) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from
Cambridge Crystallographic Data Centre via www.ccd.cam.ac.uk/
data_request/cif or as ESI.
5Ј-N-(Carbazolyl-2Ј-thienyl)-1,3-diethyl-1,3,2-benzodiazaborole
(5a): A solution of N-2Ј-thienyl-3,6-tert-butylcarbazole (1.20 g,
3.3 mmol) in ethyl ether (50 mL) was slowly combined with an n-
hexane solution of n-butyllithium (1.6 m, 2.1 mL, 3.4 mmol) at
room temperature. After 1 h, 2-bromo-1,3-diethyl-benzodiazabor-
ole (1a) (0.85 g, 3.36 mmol) was added in one portion. After 20 h
of stirring at room temperature, all volatile compounds were re-
moved in vacuo, and n-hexane (40 mL) was added. The obtained
slurry was filtered. After 3 d, product 5a was separated from the
chilled filtrate (4 °C) as an off-white solid (1.20 g, 2.2 mmol, 68%
yield). 1H NMR (CDCl3): δ = 1.48 (t, JHH = 7.2 Hz, 6 H,
NCH2CH3), 1.54 (s, 18 H, tBu), 4.08 (q, JHH = 7.2 Hz, 4 H,
NCH2CH3), 7.14 (m, 2 H, CH=CH–CH=CH), 7.21 (m, 2 H,
CH=CH–CH=CH), 7.40 (d, JHH = 4.6 Hz, 1 H, S–C–CH–CH–
CN), 7.56 (d, JHH = 4.6 Hz, 1 H, S–C–CH–CH–CN), 7.59 (s, 4H
Computational Methods: All calculations were performed by using
the Gaussian 03[21] program package with the 6-311G(d,p) basis
tBu-C–CH–CH), 8.20 (s, 2 H, C–CH–C) ppm. 13C{1H} NMR set. DFT has been shown to predict various molecular properties
(CDCl3): δ = 16.3 (s, CH3CH2N), 32.0 [s, C(CH3)3], 34.8 [s, successfully.[22] All geometry optimizations were carried out with
C(CH3)3], 38.0 (s, CH3CH2N), 108.9 (s, CH=CH–CH=CH), 109.7 the B3LYP[23] functional and were followed by frequency calcula-
(s, tBu-C–CH–CH), 116.2 (s, tBu-C–CH–C), 119.0 (s, CH=CH– tions in order to verify whether the stationary points obtained were
CH=CH), 123.9 (s, tBu-C–CH–CH), 124.6 (s, SC–CH–CH–CN), true energy minima. Ionization energies (IE) were calculated with
132.9 (s, S–C–CH–CH–N), 123.6, 140.1, 143.6 (3s, C-carbazole), ΔSCF–DFT, which means that separate SCF calculations were per-
137.1 (s, N2C2), 143.8 (s, S–C–N), ppm. 11B {1H}NMR (CDCl3):
formed to optimize the orbitals of the ground state and the appro-
Eur. J. Inorg. Chem. 2010, 5416–5425
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5423

L. Weber, A. Chrostowska et al.
FULL PAPER
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Table 7. Crystallographic data for 3a and 5a.
3a
5a
Empirical formula
C30H38BN3 +
C5H12
523.59
C34H40BN3S
Mr [gmol–1]
533.56
Crystal dimensions [mm] 0.30ϫ0.30ϫ0.05 0.26ϫ0.22ϫ0.12
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
P21
monoclinic
P21/c
12.3812(1)
31.5523(3)
16.8248(1)
99.5623(5)
6481.4(1)
8
1.073
0.062
2288
21.0380(5)
13.0890(3)
10.9130(3)
94.7240(12)
2996.5(2)
4
1.183
0.135
1144
3–30
57361
8648
0.063
6276
360
1.030
0.0494
0.1237
0.407/–0.272
β [°]
V [Å3]
Z
ρcalcd. [gcm–1]
μ [mm–1]
F(000)
[3]
[4]
Z. Yuan, C. D. Entwistle, J. C. Collings, D. Albesa-Jove, A. S.
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θ [°]
3–25
No. reflections collected 126296
No. unique reflections
R(int)
11617
0.047
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No. reflections [IϾ2σ(I)] 10443
Refined parameters
GOF
Rf [I Ͼ2σ(I)]
wRF2(all data)
Δρmax/min [eÅ–3]
1343
1.044
0.0577
0.1621
0.894/–0.468
priate ionic state (IE = Ecation – Eneutral). The advantages of the
most frequently employed ΔSCF–DFT method of calculations of
the first ionization energies have been demonstrated previously.[24]
The TD-DFT[25] approach provides a first principal method for the
calculation of excitation energies within a density functional con-
text by taking into account the low-lying ion calculated by the
ΔSCF method. Finally, the so-called “corrected” IEs were evalu-
ated by applying a uniform shift, x = –IEv
– εKSHOMO, where
exp.
εKS
is the B3LYP/6-311G(d,p) Kohn–Sham energy of the
HOMO
[5]
highest occupied MO of the molecule in the ground state and IEv
is the lowest-calculated ionization energy of this species, as was
suggested previously by Stowasser and Hoffmann[26] and in our
studies on different methods for the calculation of IEs.[27]
MOLEKEL[18] has been used as a visualization tool for MOs.
Supporting Information (see footnote on the first page of this arti-
cle): Tables of atomic coordinates for [B3LYP/6-311G(d,p)] opti-
mized geometries, values of total energies, optimized geometrical
parameters and ionization energies (IEs) of B, C, T, BC, TC and
BTC are presented.
Acknowledgments
This work was financially supported by the French Ministry of
Research and High School Education Grant for M. M. and the
Deutsche Forschungsgemeinschaft, Bonn, Germany.
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Received: June 17, 2010
Published Online: October 25, 2010
A minor change has been made since publication in Early View.
Eur. J. Inorg. Chem. 2010, 5416–5425
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5425