Synthesis, characterization, and spectrophotometric studies of novel fluorescent arachno decaborane and nonaborane clusters containing aza-distyrylbenzene derivatives

Article abstract of DOI:10.1016/j.jorganchem.2007.12.028

Two aza-analogues of distyrylbenzene namely: 1,4-bis[β-(4-quinolyl)vinyl]benzene (PhQ) and 1,4-bis[β-(4-pyridyl)vinyl]benzene (PhPy) containing arachno-decaborane or arachno-nonaborane clusters have been isolated: 6,9-(PhQ)₂-arachno-B₁₀

Full text of DOI:10.1016/j.jorganchem.2007.12.028

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1065–1072
www.elsevier.com/locate/jorganchem
Synthesis, characterization, and spectrophotometric studies
of novel fluorescent arachno decaborane and nonaborane
clusters containing aza-distyrylbenzene derivatives
a,
a
b,1
*
Afaf R. Genady , Tarek A. Fayed , Detlef Gabel
a Department of Chemistry, Faculty of Science, University of Tanta, 31527 Tanta, Egypt
b Department of Chemistry, University of Bremen, P.O. Box 330440, D-28334 Bremen, Germany
Received 24 November 2007; received in revised form 28 December 2007; accepted 30 December 2007
Available online 8 January 2008
Abstract
Two aza-analogues of distyrylbenzene namely: 1,4-bis[b-(4-quinolyl)vinyl]benzene (PhQ) and 1,4-bis[b-(4-pyridyl)vinyl]benzene
(PhPy) containing arachno-decaborane or arachno-nonaborane clusters have been isolated: 6,9-(PhQ)2-arachno-B10H12 (1), N,N0-bis[9-
Me2S-arachno-B10H12-6-yl]PhQ (2), 6,9-(PhPy)2-arachno-B10H12 (3), N,N0-bis[(9-Me2S)-arachno-B10H12-6-yl]PhPy (4), N,N0-bis[arachno-
B9H13-4-yl]PhQ (5), 4-PhQ-arachno-B9H13 (6), N,N0-bis[arachno-B9H13-4-yl]PhPy (7), and 4-PhPy-arachno-B9H13 (8). These boronated
compounds were easily prepared from the displacement reactions of weaker ligand (SMe2) of bis (dimethyl sulfide) arachno-decabora-
ne(14) {6,9-(Me)2SB10H12}or dimethyl sulfide-arachno-nonaborane {4-(Me)2SB9H13} by the stronger bidentate ligands of PhQ or PhPy
in ratio (1:2). The electronic interaction between decaborane or nonaborane arachno-type unit and the bonded pyridine units has been
investigated by UV–Vis spectroscopy and by AM1 molecular orbital calculations. The resulting compounds undergo trans–cis photoiso-
merization upon excitation. The connection of boron clusters to PhQ and PhPy led to enhancing of the photoreactivity and decreasing of
the fluorescence quantum yield of the products.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Borane; NMR spectroscopy; MO-calculations; Laser dyes; Aza-distyrylbenzene
1. Introduction
a good entry to generate new fluorescent boron carriers help-
ful in detecting the accumulation of boron in tumor cells by
simple spectrophotometeric methods.
Aza-analogues of distyrylbenzene, e.g. 1,4-bis[b-(4-quino-
lyl)vinyl]benzene (PhQ) and 1,4-bis[b-(4-pyridyl)vinyl]ben-
zene (PhPy) have been reported as highly efficient blue
emitting laser dyes with good photochemical stability
(Fig. 1, ) [1,2]. Dye lasers are attractive due to their unique
feature of tunability over a wide range of wavelengths.
Recently, it was reported that PhQ can serve as a probe
for biological systems to get information about the site that
the probe molecule occupies [3]. The connection of boron
clusters to the probes such as PhQ and PhPy may constitute
The bis (dimethyl sulfide) adduct of decaborane(14) {6,9-
(Me2S)2B10H12} is one of several compounds that is easily
prepared by reacting decaborane (B10H14) and a Lewis base
[4–6]. The alcoholysis of bis (dimethyl sulfide)-arachno-deca-
borane using methanol led to the formation of dimethyl sul-
fide-arachno-nonaborane {4-Me2SB9H13} [7]. Both of these
borane clusters undergo several interesting reactions [8–15].
The open-faced arachno 10 or nine-vertex borane residues
will permit tailoring of the borane residues, for example
by the addition of metal centers as exemplified by the
reaction between {Co2(CO)8} and the monomer precursor
unit {6,9-(Et2S)2B10H12} to give {(CO)6CoB10H8(Et2S)2}
[16]. The reactions of 6,9-(Me2S)2B10H12 with 4,40-bipyridyl
*
Corresponding author. Tel.: +20 40 3297974; fax: +20 40 3350804.
E-mail address: afafgenady@hotmail.com (A.R. Genady).
Fax: +49 421 2182871.
1
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.12.028

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A.R. Genady et al. / Journal of Organometallic Chemistry 693 (2008) 1065–1072
and pyrazine (1,4-diazabenzene) resulted in the formation
of two potential pyridine-borane oligomer and polymer
building blocks and characterized by X-ray single crystal
[17].
percentage of the cis isomer formed at the photostationary
state upon irradiation.
2. Chemistry of the synthesized compounds
The molecules prepared in this work were obtained by
spontaneous displacement of weaker ligand (SMe2) from
preformed 6,9-(Me2S)2B10H12 or 4-Me2SB9H13 by stronger
ligands such as PhQ and PhPy. The preparation of these
new molecules aims to study the effect of increasing the
conjugation path connecting the arachno decaborane or
nonaborane units. Also, semiempirical AM1 molecular
orbital calculations were performed to compare the exper-
imental results with the calculated structures expressed by
the UV–Vis spectra. The study is extended to test the pho-
tochemical stability of these compounds by determining the
We have found that the exchange of the weak ligand
(SMe2) of 6,9-(Me2S)2B10H12 or 4-Me2SB9H13 by another
strong ligand such as PhQ or PhPy is a convenient route
for the formation of new N-substituted numbers of decabor-
anes or nonaboranes. Reaction of 6,9-(Me2S)2B10H12 with
PhQ and PhPy in ratios 2:1 in CH2Cl2 for one day at room
temperature followed by TLC separation gave 6,9-(PhQ)2-
arachno-B10H12 (1, faint red color, 32%), N, N0-bis[9-
Me2S-arachno-B10H12-6-yl]PhQ (2, orange color, 24%) and
6,9-(PhPy)2-arachno-B10H12 (3, faint red color, 28%), N,N0-
bis[(9-Me2S)-arachno-B10H12-6-yl]PhPy (4, orange color,
25%), respectively (Scheme 1). During the TLC separation
of these compounds a variety of orange and red colored
components were observed, most of which were unstable
in solution, probably because of ligand exchange processes.
Alternatively, the reaction of 4-Me2SB9H13 with PhQ
and PhPy under the same conditions led to the formation
of N,N0-bis[arachno-B9H13-4-yl]PhQ (5, red color, 32%),
4-PhQ-arachno-B9H13 (6, yellow color, 26%), N,N0-bis-
[arachno-B9H13-4-yl]PhPy (7, red color, 35%), and 4-PhPy-
arachno-B9H13 (8, yellow color, 24%), respectively (Scheme 2).
All of these compounds were fully characterized by ele-
mental analysis, IR, NMR, UV–Vis, fluorescence, and
N
N
PhQ
N
N
1
mass spectrometry (see Section 6). 11B and H NMR spec-
PhPy
troscopic data of the prepared compounds are listed in
Fig. 1. Structures of aza-distyrylbenzene and their abbreviations.
Fig. 2. Representation of optimized HOMO and LUMO levels of compound 7.

A.R. Genady et al. / Journal of Organometallic Chemistry 693 (2008) 1065–1072
1067
SMe2
H
H
H
H
R1
R1
Me2S
H
R1
H
B
B
B
B
B
B
B
B
B
B
B
B
H
H
H
H
H
H
B
B
B
B
B
B
R1
B
B
+
B
B
B
B
B
stirring for 2 days, CH2Cl2
B
B
H
SMe2
Me2S
H
B
B
B
B
B
B
B
1
2
H
H
B
B
B
B
B
B
H
SMe 2
H
H
H
R2
R2
R2
H
Me2SH
B
B
B
B
B
B
B
B
H
H
H
R2
B
B
B
B
B
B
H
H
H
+
B
B
B
B
B
B
stirring for 2 days, CH2Cl2
B
B
B
B
B
B
B
B
B
B
R1=
R2=
N
N
4
3
N
N
Scheme 1. Exo H atoms are omitted for clarity.
H
H
H
R1
R1
B
B
B
B
B
B
H
H
H
H
H
R1
B
B
B
B
B
B
H
+
B
B
B
B
B
B
stirring for 2 days, CH2Cl2
H
SMe2
B
B
B
B
B
B
B
B
B
B
B
H
H
5
6
B
B
B
B
B
B
H
H
H
R2
R2
B
B
B
B
B
B
H
H
H
H
H
R2
B
B
B
B
B
B
H
+
B
B
B
B
B
B
stirring for 2 days, CH2Cl2
B
B
B
B
B
B
B
B
B
B
8
7
R1=
R2=
N
N
N
N
Scheme 2. Exo H atoms are omitted for clarity.
Table 1. As can be seen, there are some minor variations in
the proton shielding as the organic moiety of the aza-ana-
logue of distyrylbenzene is changed.
changes in the UV–Vis range. The spectral behavior of
both free ligands and two of their boronated compounds
2 and 4 has been studied in CH2Cl2 and CH3CN solvents.
Fig. 4 shows the steady-state absorption and emission spec-
tra of PhPy and compound 2 in CH2Cl2 as an example,
while the corresponding data are collected in Table 3. As
can be seen, the free ligands exhibit strong absorption
around 360 nm (molar absorptivity ranges from 39500 to
3. Spectral behavior of the synthesized compounds
The electronic interaction between the diolefinic ligands
and the boron clusters leads to characteristic spectral

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A.R. Genady et al. / Journal of Organometallic Chemistry 693 (2008) 1065–1072
Table 1
200 MHz (11B, 1H) NMR data of boronated dye laser compounds 1–8 in CD3Cl at 20 °C
Compound
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10 lH, endo-H
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
1
ꢀ40.24
[0.39]
ꢀ40.18
[0.37]
ꢀ40.22
[0.39]
ꢀ40.25
[0.4]
4.52
[3.04]
4.59
[3.02]
4.55
[3.07]
4.49
ꢀ3.6
[2.28]
ꢀ40.24
[0.39]
ꢀ3.6
[2.28]
ꢀ19.91
[1.59]
ꢀ22.89
[ꢀ0.28]
ꢀ23.95
[ꢀ0.35]
ꢀ22.96
[ꢀ0.29]
ꢀ24.05
[ꢀ0.38]
ꢀ21.49
[1.97]
ꢀ19.91
[1.59]
ꢀ19.97
[1.56]
ꢀ19.96
[1.59]
ꢀ19.89
[1.54]
18.19
[4.1]
18.20
[4.18]
18.22
[4.05]
18.19
[4.18]
ꢀ19.91
[1.59]
ꢀ22.89
[ꢀ0.28]
ꢀ23.95
[ꢀ0.33]
ꢀ22.96
[ꢀ0.29]
ꢀ24.05
[ꢀ0.38]
ꢀ16.36
[1.56]
ꢀ19.91
[1.59], [ꢀ4.71]
ꢀ19.97
2a
3
ꢀ3.43
ꢀ40.22
ꢀ3.43
ꢀ19.97
ꢀ19.97
[2.25]
[0.39]
[2.25]
[1.56]
[1.56]
[1.56], [ꢀ4.68]
ꢀ19.96
ꢀ3.52
[2.27]
ꢀ40.24
[0.39]
ꢀ3.52
[2.27]
ꢀ19.96
[1.59]
ꢀ19.96
[1.59]
[1.59], [ꢀ4.68]
ꢀ19.89
4a
5a
6
ꢀ3.43
ꢀ40.25
ꢀ3.43
ꢀ19.89
ꢀ19.89
[2.27]
[0.4]
[2.27]
[1.54]
[1.54]
[1.54], [ꢀ4.71]
ꢀ39.18
[0.49]
ꢀ39.18
[0.42]
ꢀ23.64
[0.38]
ꢀ16.36
[1.56]
ꢀ21.49
[1.83]
[ꢀ3.52], [ꢀ0.0018]
[ꢀ3.51], [ꢀ0.0019]
[ꢀ3.49], [ꢀ0.0016]
[ꢀ3.57], [ꢀ0.0018]
ꢀ39.15
ꢀ39.15
ꢀ23.74
ꢀ16.35
ꢀ21.51
ꢀ21.51
ꢀ16.35
[0.47]
[0.43]
[0.39]
[1.59]
[1.95]
[1.85]
[1.59]
7a
8
ꢀ39.21
[0.48]
ꢀ39.21
[0.42]
ꢀ23.65
[0.36]
ꢀ16.57
[1.53]
ꢀ21.55
[1.89]
ꢀ21.55
[1.79]
ꢀ16.57
[1.53]
ꢀ39.12
ꢀ39.12
ꢀ23.18
ꢀ16.38
ꢀ21.41
ꢀ21.41
ꢀ16.38
[3.05]
[0.46]
[0.40]
[0.35]
[1.54]
[1.97]
[1.82]
[1.54]
a
All bands were broad.
44000 Mꢀ1 cmꢀ1 depending on the solvent) and structured
fluorescence emission with a good fluorescence quantum
yield (about 0.2). The absorption and fluorescence spectral
bands of the formed compounds are broad and shifted to
longer wavelengths. Also, the fluorescence emission of the
products is quenched as indicated by the lower quantum
yield (/f = 0.12). The fluorescence quenching is accompa-
nied by enhancement of the photoreactivity as reflected
by the increase of the percentage of the less stable cis iso-
mer (x-cis) formed at the photostationary state due to the
trans–cis photoconversion. Fig. 5 displays the change of
the absorption spectra of compound 6 following irradia-
tion at 365 nm using a medium pressure Hg-lamp. Upon
irradiation of the solution at room temperature, the absor-
bance of the band at 375 nm decreases with an increase of
the absorption at 275 nm until reaching a photostationary
state. These changes are accompanied by the appearance of
an isosbestic point, indicating an equilibrium between the
trans and cis forms, and was attributed to the known
trans/cis photoisomerization. The stability of the photos-
taionary composition under irradiation for longer time
(>15 min) as well as appearance of only one isosbestic
point indicates the formation of only one photoproduct.
This is likely to be the cis isomer formed due to the isom-
erization of only one ethylenic bond as reported previously
for the free ligand [2]. The fluorescence spectrum of the
irradiated solution suffers a decrease in its intensity without
any shift or change in the band profile indicating that the
cis-isomer of the boronated compound is non-fluorescent.
Based on this fact, the extent of trans–cis conversion
(x-cis) was calculated from the fluorescence intensities mea-
sured at the emission maximum before and after irradia-
tion (I0f and Ipf ss, respectively), using the following
equation [20];
x ꢀ cis ¼ ðI0f ꢀ IfpssÞ=I0f
The value of x-cis for compound 6 in CH2Cl2 thus calcu-
lated is 0.72 which is considerably larger than that
Table 2
Energies of the highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO) for the boronated com-
pounds 1–8 calculated after geometry optimization at AM1 level
Compound kmax
1/kmax
HOMO LUMO DELUMO–
(nm)
(10ꢀ3 cmꢀ1
)
(eV)
(eV)
(eV)
HOMO
1
2
3
4
5
6
7
8
465
401
454
395
452
396
448
398
2.15
2.49
2.20
2.53
2.21
2.52
2.23
2.51
ꢀ7.57
ꢀ8.07
ꢀ7.95
ꢀ8.38
ꢀ8.66
ꢀ8.73
ꢀ8.71
ꢀ8.67
ꢀ1.59
ꢀ0.59
ꢀ1.72
ꢀ0.71
ꢀ2.35
ꢀ1.14
ꢀ2.29
ꢀ1.12
5.98
7.48
6.23
7.67
6.31
7.59
6.42
7.55
Fig. 3. Correlation of the energy differences DELUMO–HOMO with 1/kmax
for the boronated compounds 1–8.

A.R. Genady et al. / Journal of Organometallic Chemistry 693 (2008) 1065–1072
1069
1.2
1.0
0.8
0.6
0.4
0.2
0.0
4. Molecular orbital calculations
With the aim of explaining the color change of pyridine-
arachno-borane compounds as part of understanding of
this interesting and potentially important type of the com-
pounds, semiempirical AM1 theoretical calculations were
performed [18]. This type of calculation gives the HOMO
(highest occupied molecular orbital) and LUMO (lowest
unoccupied molecular orbital) energies, which we have
used for interpretation. We did not use electronic spectra
calculations that are only useful for directly comparing
measured and calculated spectra, rather than energy-level
differences, and which, therefore, do not allow any detailed
view on how the substituents may influence the absorption
maxima. At an initial empirical level, we were interested in
explaining the dependence of the color indicated by the
longest wavelength absorption band with respect to the
nature of substituent on the pyridine rings. In order to
approach this, the AM1 calculations were therefore carried
out on the 1,4-bis[b-(4-pyridyl)vinyl]benzene (PhPy) and its
4-quinolyl derivative such as PhQ. The energies of the
HOMO and LUMO levels obtained after complete geome-
try optimization are listed in Table 2 while representation
of these orbitals for compound 7 is depicted in Fig. 2.
The differences in energy (DELUMO–HOMO) show a linear
correlation with the experimental data for kmax as deter-
mined from the UV–Vis absorption spectroscopy (Fig. 3).
Analysis of the data in Table 2 reveal that there is only a
small change in the HOMO energy, therefore, the correla-
tion of DELUMO–HOMO with the absorption spectra arises
principally from the larger variation in the energy of
LUMO. Therefore, it was concluded that the principal ele-
ments of molecular orbital structure which are responsible
for the color can be constructed qualitatively from combi-
nation of fragments of the HOMO at the borane cluster
and the p-LUMO of the PhQ or PhPy. The calculated orbi-
tal-energy difference are between 5.98 and 7.59 eV which
are responsible for the absorption in the visible region.
Also, due to the localization of the LUMO level on the
complexed pyridine fragment, the color shows a depen-
dence on the pyridine substituents where a p-donor leads
to a blue shift, whereas a p-acceptors leads to a red shift.
It has been shown previously that the colors of the
6,9-bis-pyridine-arachno-decaborane {6,9-(C5H5N)2-arach-
no-B10H12} and its ring substituted derivatives vary from
a very pale yellow to a deep red, depending on the substi-
tuent group on the pyridine ligand [5,19]. In the case of
{6,9-(C5H5N)2-arachno-B10H12}and its ring-substituted
derivatives, electron-withdrawing substituents also shifted
the absorption band at the longest wavelength to the red,
whereas a p-donor substitutent led to a blue shift. The dif-
ferences of the number of boron atoms of the cluster
between 10-vertex arachno {B10} and 9-vertex arachno
{B9} would, therefore, appear to have no significant influ-
ence on the color of their pyridine complexes, because the
{B9} series shows very similar colorations to the {B10}
series [5,19].
300
400
500
600
Wavelength (nm)
Fig. 4. Normalized absorption and fluorescence emission spectra of
5 ꢁ 10ꢀ5 M of PhPy (---) and its boronated compound 4 (—) in CH2Cl2 at
room temperature.
Table 3
Spectral data of 5 ꢁ 10ꢀ5 M of PhPy, PhQ, and their boronated
compounds (2 and 4) in CH2Cl2 and CH3CN
Compound
CH2Cl2
CH3CN
ka (nm)
kf (nm)
/
ka (nm)
kf (nm)
/
f
f
PhPy
4
361
375
367
395
412,392
450
455,432
477
0.203
0.122
0.28
348
474
370
384
410
450
454
480
0.178
0.089
0.147
0.051
PhQ
2
0.069
Fig. 5. The absorption spectra of 7 ꢁ 10ꢀ5 M of compound 6 in CH2Cl2
following irradiation at 365 nm using a medium pressure Hg-lamp (time
interval = 1 min).
calculated for the free ligand (0.50). In contrast, the
absorption spectrum of the corresponding dimeric ana-
logue (compound 5) displays no changes upon irradiation
in CH2Cl2 at 365 nm for more than 10 min. This indicates
that this compound has a higher photostability, which
might be attributed to the steric hindrance caused by the
bulky boron clusters on both sides.

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A.R. Genady et al. / Journal of Organometallic Chemistry 693 (2008) 1065–1072
The results of our calculations suggest a strong depen-
were carried out on a Bruker DPX 200 spectrometer. The
chemical shifts are given in ppm relative to
dence of the absorption maxima in UV–Vis spectra on
the LUMO energy of the substituted pyridines. It seems
likely that changes in the rotamer conformation about
the B–N(pyridine) vector should not have a strong influ-
ence on the LUMO of the pyridine moiety and therefore
on the absorption maxima. Further calculations, especially
of the dependence of the rotational barrier about the
B–N(pyridine) vector, are needed to test this hypothesis.
d
N = 100 MHz for d (1H) (nominally SiMe4), N = 50 MHz
for d (13C) (nominally SiMe4), and N = 32.083 MHz for d
(11B) (nominally F3BOEt2) in CD3Cl. IR (cmꢀ1) spectra
were determined as KBr disc on a Biorad FTS-7 spectrom-
eter. Electron spray ionization (ESI) mass spectra were
recorded on a Bruker Esquire in CH3OH. Only the signal
with the highest intensity of the boron isotopic pattern is
listed. Molecular-orbital calculations [18] were carried out
with HYPERCHEM [22].
5. Conclusion
In conclusion, we have synthesized and characterized
novel fluorescent boronated aza-distyrylbenzene deriva-
tives. The presence of weak displacement ligands such
SMe2 group make compounds 2 and 4 are versatile starting
material to the synthesis of a wide variety of boron-con-
taining species. For example, further structural modifica-
tion could make the structures of compounds 2 and 4
especially attractive in the context of supramolecular
assemblies [17]. The spectroscopic data of the boronated
aza-distyrylbenzene derivatives and the molecular orbital
calculations were obtained. The presence of the two cluster
units led to a red shift in UV–Vis spectra compared with
that containing only one cluster unit. The resulting com-
pounds especially, containing one cluster unit undergo
trans–cis photoisomerization upon excitation. The connec-
tion of boron clusters to PhQ and PhPy enhanced the pho-
toreactivity and decreased the fluorescence quantum yield
of the products.
6.2. General procedure for preparation of compounds 1–8
A solution of 6,9-(Me2S)2B10H12 or 4-Me2SB9H13,
(2.0 mmol) was added to a solution of phenylene-1,4-dieth-
ylene-bis-4-quinoline (PhQ) or its 4-pyridyl derivative
(PhPy) (1.0 mmol) in 10 ml of dry CH2Cl2. The reaction
was stirred for two days at room temperature then the solu-
tion was filtered off. All volatile components of the filtrate
were removed under vacuum at room temperature and the
resulting substance was chromatographed on silica gel
using CH2Cl2 as eluent to yield a variety of orange and
red components.
6.2.1. Compound 1: (Yield: 32%, 152 mg, faint red color,
Rf = 0.25)
1H NMR (CDCl3): d 6.75 (d, J = 5.0 Hz, 4 H, CHphenyl),
7.08 (d, J = 7.0 Hz, 4H, CH@CHaliphatic), 7.16 (d,J =
8.0 Hz, 8H, CHphenyl), 7.27 (d, J = 8.0 Hz, 4H, CH@
CHaliphatic), 7.32 (d, J = 7.0 Hz, 4H, CH@CHpyridine),
7.54 (d, J = 6.5 Hz, 4H, CHphenyl), 7.68 (d, J = 6.5 Hz,
4H, CHphenyl), 8.5 (d, J = 7.0 Hz, 4H, CHphenyl), 8.70 (d,
J = 5.0 Hz, 2H, CH@Npyridine), 8.91 (d, J = 7.0 Hz, 2H,
CH@Npyridine); 13C NMR (CDCl3): 117.74 (2CHpyridine),
121.28, 121.68 (2CHpyridine), 124.42, 125.83, 128.05,
128.63 (20CHphenyl), 129.05 (4CH@CH), 130.12, 131.25
(8CHphenyl), 132.57, 133.56 (4Cphenyl), 135.34, 137.56
(4CH@ CH),146.68, 147.45 (4C@N), 149.12 (4CH@N),
150.62 (4Cpyridine); MS (ESI): m/z: 890 ([M]+, 57%); IR
mmax (KBr disc)/cmꢀ1: 2516s (BH), 1619s (C@C), 1452s
(BN),1151s (C–N). Anal. Calc. B10C56H52N4 requires: C,
75.65; H, 5.89; N, 6.3. Found: C, 75.43; H, 5.61; N, 6.13%.
6. Experimental
6.1. Materials and methods
The diolefinic ligands PhQ and PhPy were prepared and
characterized as described previously [2]. Steady-state
absorption and emission spectral measurements were
carried out using a Shimadzu UV-3101PC scanning spec-
trophotometer and a Perkin–Elmer LS 50B spectrofluo-
rometer, respectively. The samples were excited at 365 nm
while recording the fluorescence spectra. The fluorescence
quantum yields (/f) were measured using 9,10-diphenylan-
thracene as a standard (/f = 0.96) (optical densities at the
excitation wavelength is less than 0.2) [21]. 6,9-
(Me2S)2B10H12 and 4-Me2SB9H13 were prepared by litera-
ture methods [4–7] and all other reagents were obtained
commercially. Reactions were carried out in dry solvents
under dry nitrogen but subsequent manipulation and sepa-
ration procedures were carried out in open air. Preparative
thin layer chromatography (TLC) was carried out using
0.75 mm layers of silica gel G (Merck, GF254) made from
water slurries on glass plates of dimensions 20 ꢁ 20 cm2,
followed by drying in air at 100 °C. Elemental analyses
were performed by a Perkin–Elmer 2400 automatic elemen-
tal analyzer. All compounds gave elemental analysis within
6.2.2. Compound 2: (Yield: 24%, 12 mg, orange color,
Rf = 0.31)
1H NMR (CDCl3): d 2.54 (s, 12H, SMe2), 6.72 (d,
J = 7.0 Hz, 2H, CH@CHaliphatic), 7.08 (d, J = 5.0 Hz, 2H,
CHphenyl), 7.24 (d, J = 6.0 Hz, 2H, CHphenyl), 7.32 (d,
J = 4.5 Hz, 2H, CH@CHaliphatic), 7.45 (d, J = 6.5 Hz, 2H,
CHpyridine), 7.59–7.74 (m, 6H, CHphenyl), 8.53 (d,
J = 7.0 Hz, 2H, CHphenyl), 8.93 (d, J = 6.0 Hz, 2H,
CH@Npyridine); 13C NMR (CDCl3): 27.22, 27.36 (SMe2),
117.56 (2CHpyridine), 122.19, 122.98 (2CHphenyl), 125.83,
126.12 (2Cphenyl), 127.02, 127.31 (6CHphenyl), 127.64
(2CHaliphatic), 128.47, 131.97 (4CHphenyl), 137.41, 138.04
(2Cphenyl), 145.21, 147.16 (2C@N), 150.51 (2CH@N),
1
0.4%. The measurements for NMR (11B, H and 13C)

A.R. Genady et al. / Journal of Organometallic Chemistry 693 (2008) 1065–1072
1071
152.21 (2Cpyridine); MS (ESI): m/z: 752 ([M]+, 43%); IR
max(KBr disc)/cmꢀ1: 1032, 993, 968 (SMe2), 2533s (BH),
1618s (C@C), 1465s (BN),1149s (CN). Anal. Calc. for
B20C32H56N2S2 requires: C, 51.30; H, 7.53; N, 3.74. Found:
C, 51.03; H, 7.16; N, 3.47%.
6.2.6. Compound 6: (Yield: 26%, 182 mg, yellow color,
Rf = 0.22)
1H NMR (CDCl3):
m
d
6.92 (d, J = 6.4 Hz, 2H,
CH@CHaliphatic), 7.05 (d, J = 3.7 Hz, 2H, CHphenyl), 7.19
(d, J = 5.5 Hz, 2H, CHphenyl), 7.24 (d, J = 3.5 Hz, 2H,
CH@CHaliphatic), 7.32 (d, J = 7.0 Hz, 2H, CHpyridine),
7.49–7.65 (m, 6H, CHphenyl), 8.49 (d, J = 5.0 Hz, 2H,
CHphenyl), 8.94 (d, J = 3.0 Hz, 2H, CH@Npyridine); 13C
NMR (CDCl3): 117.35 (2CHpyridine), 121.55, 122.65
(2CHphenyl), 125.07, 126.52 (2Cphenyl), 127.18, 127.72,
128.46 (6CHphenyl), 129.23 (2CHaliphatic), 130.67 132.62
(4CHphenyl), 135.84, 136.95 (2Cphenyl), 143.96, 147.97
(2C@N), 149.56, 150.36 (2CH@N), 152.78, 153.11
(2Cpyridine); MS (ESI): m/z: 496 ([M]+, 52%); IR mmax(KBr
disc)/cmꢀ1: 2526s (BH), 1633s (C@C), 1455s (BN),1157s
(C–N). Anal. Calc. for B9C28H33N2 requires: C, 67.96; H,
6.72; N, 5.66. Found: C, 67.71; H, 6.36; N, 5.41%.
6.2.3. Compound 3: (Yield: 28%, 181 mg, faint red color,
Rf = 0.23)
1H NMR (CDCl3):
d 7.17 (d, J = 8.0 Hz, 4H,
CH@CHaliphatic), 7.27 (d, J = 7.0 Hz, 8H, CH@CHphenyl),
7.68 (d, J = 8.0 Hz, 8H, CH@CHpyridine), 8.02 (d, J =
8.0 Hz, 4H, CH@CHaliphatic), 8.79 (d, J = 7.0 Hz, 4H,
CH@Npyridine), 8.91 (d, J = 7.0 Hz, 4H, CH@Npyridine);
13C NMR (CDCl3): 121.16, 121.98 (8CHpyridine), 123.96,
125.38 (8CHphenyl), 129.72 (4CH@CH), 131.47 (4CH@CH),
136.54, 137.05 (4Cphenyl), 145.46, 146.17 (4Cpyridine),
152.87, 153.12 (8CH@N); MS (ESI): m/z: 670 ([M]+,
61%); IR mmax(KBr disc)/cmꢀ1: 2521s (BH), 1624s (C@C),
1459s (BN),1145s (C–N). Anal. Calc. for B10C40H44N4
requires: C, 69.74; H, 6.44; N, 8.13. Found: C, 69.49; H,
6.15; N, 7.86%.
6.2.7. Compound 7: (Yield: 35%, 196 mg, orange color,
Rf = 0.34)
1H NMR (CDCl3): d 7.0 (d, J = 5.0 Hz, 2H, CH@
CHaliphatic), 7.20 (d, J = 3.0 Hz, 4H, CH@CHphenyl),
7.29–7.38 (m, 4H, CH@CHpyridine), 7.98 (d, J = 4.0 Hz,
2H, CH@CHaliphatic), 8.56–8.93 (m, 4H, CH@N); 13C
NMR (CDCl3):121.54, 122.21 (4CHpyridine), 123.87, 124.98
(4CHphenyl), 127.25, 128.34, 131.45, 132.47 (4CH@CH),
136.12, 137.65 (2Cphenyl), 145.21, 146.99 (2Cpyridine),
151.67, 151.98 (4CH@N); MS (ESI): m/z: 508 ([M]+,
32%); IR mmax(KBr disc)/cmꢀ1: 2526s (BH), 1627s (C@C),
1451s (BN),1158s (C–N). Anal. Calc. for B18C20H42N2
requires: C, 47.55; H, 8.38; N, 5.55. Found: C, 47.37; H,
8.04; N, 5.27%.
6.2.4. Compound 4: (Yield: 25%, 142 mg, orange color,
Rf = 0.37)
1H NMR (CDCl3): d 2.42 (s, 12H, SMe2), 7.01 (d,
J = 9.0 Hz, 2H, CH@CHaliphatic), 7.23 (d, J = 2.0 Hz, 4H,
CH@CHphenyl), 7.32–7.41 (m, 4H, CH@CHpyridine), 8.01
(d, J = 6.0 Hz, 2H, CH@CHaliphatic), 8.55–8.82 (m, 4H,
CH@N); 13C NMR (CDCl3): 27.3, 27.58 (SMe2), 121.95,
122.47 (4CHpyridine), 124.87, 125.94 (4CHphenyl), 128.65,
129.03, 131.98, 132.67 (4CH@CH), 136.86, 137.27 (2Cphenyl),
144.54, 146.65 (2Cpyridine), 151.35, 151.92 (4CH@N); MS
(ESI): m/z: 652 ([M]+, 39%); IR mmax(KBr disc)/cmꢀ1
:
6.2.8. Compound 8: (Yield: 24%, 157 mg, yellow color,
Rf = 0.21)
1035s, 993s, 984 (SMe2), 2525s (BH), 1618s (C@C), 1448s
(BN),1162s (C–N). Anal. Calc. for B20C24H52N2S2
requires: C, 44.41; H, 8.08; N, 4.32. Found: C, 44.18; H,
7.79; N, 4.02%.
1H NMR (CDCl3):
d 7.01 (d, J = 7.0 Hz, 2H,
CH@CHaliphatic), 7.18 (d, J = 6.3 Hz, 4H, CH@CHphenyl),
7.29–7.38 (m, 4H, CH@CHpyridine), 8.04 (d, J = 4.0 Hz,
2H, CH@CHaliphatic), 8.55 (d, J = 5.0 Hz, 2H, CH@N),
8.92 (d, J = 3.0 Hz, 2H, CH@N); 13C NMR (CDCl3):
121.44, 122.26 (4CHpyridine), 123.76, 124.99 (4CHphenyl),
127.45, 128.63, 131.79, 132.52 (4CH@CH), 136.24, 137.55
(2Cphenyl), 145.32, 146.87 (2Cpyridine), 151.74, 152.17
(4CH@N); MS (ESI): m/z: 396 ([M]+, 29%); IR mmax(KBr
disc)/cmꢀ1: 2528s (BH), 1624s (C@C), 1456s (BN),1156s
(C–N). Anal. Calc. for B9C20H29N2 requires: C, 60.85; H,
7.4; N, 7.10. Found: C, 60.51; H, 7.12; N, 6.89%.
6.2.5. Compound 5: (Yield: 32%, 231 mg, orange color,
Rf = 0.29)
1H NMR (CDCl3): d 7.07 (d, J = 4.0 Hz, 2H, CHphenyl),
7.09 (d, J = 4.7 Hz, 2H, CH@CHaliphatic), 7.21
(d,J = 6.0 Hz, 4H, CHphenyl), 7.23 (d, J = 4.5 Hz, 2H,
CH@CHaliphatic), 7.33 (d, J = 5.4 Hz, 2H, CH@CHpyridine
)
7.51 (d, J = 7.5 Hz, 2H, CHphenyl), 7.71 (d, J = 4.0 Hz,
2H, CHphenyl), 8.51 (d, J = 3.8 Hz, 2H, CHphenyl), 8.92 (d,
J = 7.0 Hz, 2H, CH@Npyridine); 13C NMR (CDCl3):
117.19, 121.52, (2CHpyridine), 122.27, 125.04, 126.01,
127.93, 128.56 (10CHphenyl), 129.42 (2CH@CH), 130.24,
131.05 (4CHphenyl), 132.61, 135.89 (2Cphenyl), 136.46,
137.15 (2CH@CH), 144.92 (2C@N), 147.78 (2CH@N),
152.32 (2Cpyridine); MS (ESI): m/z: 608 ([M]+, 37%); IR
Acknowledgement
The authors are grateful to Dr. Tobias Borrmann,
Department of Chemistry, University of Bremen, Ger-
many, for helping us in the MO-calculations.
m
max(KBr disc)/cmꢀ1: 2525s (BH), 1631s (C@C), 1457s
(BN),1153s (C–N). Anal. Calc. for B18C28H46N2 requires:
C, 55.56; H, 7.66; N, 4.63. Found: C, 55.21; H, 7.31; N,
4.31%.
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