Ferrocene catalysed heteroarylation of BODIPy and reaction mechanism studies by EPR and DFT methods

Article abstract of DOI:10.1039/c6ra03705d

The C-H heteroarylations of BODIPy using heteroaryl diazoniumtetrafluoroborate and ferrocene (Fc) as catalysts were carried out. Mono and di heteroaryl BODIPy derivatives (1-8) were obtained in a cost-effective way. This method gives easy access to 4-pyri

Full text of DOI:10.1039/c6ra03705d

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Ferrocene catalysed heteroarylation of BODIPy and reaction
mechanism studies by EPR and DFT methods
Swati Dixit,a Mahendra Patil*a and Neeraj Agarwal*a
UMꢀDAE, Centre for Excellence in Basic Sciences, Health Center Building,
Kalina Campus, Santacruz (E), Mumbai, 400098, India
Eꢀmail: mahendra.patil@cbs.ac.in and na@cbs.ac.in
Abstract:
The
CꢀH
heteroarylations
of
BODIPy
using
heteroaryl
diazoniumtetrafluoroborate and ferrocene (Fc) as catalyst were carried out. Mono and di
heteroaryl BODIPy derivatives (1ꢀ8) were obtained in a costꢀeffective way. This method
gives easy access to 4ꢀpyridyl substituted BODIPy (7ꢀ8) which are useful to synthesize
water soluble derivatives for biological applications. Reaction pathway for this reaction
was studied by carrying out the spin crossꢀover experiments using electron paramagnetic
resonance (EPR) technique. A strong signal in EPR was obtained in the presence of
ferrocene and heteroaryldiazonium salt which indicates the formation of radicals during
the initial steps of reaction. In addition, we have also performed the computational
investigations on different steps of reaction to elucidate the role of ferrocene as a radical
initiator in this reaction.
Introduction
4,4’ꢀDifluoroꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene (BODIPy) is one of the most popular dye
family and has been studied extensively in past few years.1ꢀ3 BODIPy dyes are known for
their rich optical properties, photostability etc. Photophysical, electrochemical and
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morphological properties of these dyes can be tuned, almost at will, which makes
BODIPy an important fluorophore for applications in different areas.4ꢀ6 A variety of
substituted BODIPys with variable degree of conjugations, multimeric BODIPy,
conjugates of BODIPy with other fluorophores, such as porphyrins, substitution with
variety of aryl groups have been synthesized to alter the photophysical properties.7
Heteroarylation of BODIPy, has also been well explored as substitution of heteroaryls
changes the optical properties drastically.8 Even though many BODIPy derivatives
bearing various heteroaryl substituents have been reported, methods of their synthesis are
rather challenging. In general, to synthesize the heteroaryl derivatives of BODIPy one can
start with the heteroaryl substituted pyrrole. A few reports are available for the synthesis
of 3,5ꢀdiheteroaryl BODIPy in multiple steps.9 In some of these methods, 2ꢀheteroaryl
substituted pyrroles were first synthesized and further used in the synthesis of heteroaryl
BODIPy. In other approaches, transition metal catalysed coupling reactions (Suzuki
Miyaura, Stille coupling etc.) were used to synthesize the aryl BODIPy derivatives.10
These coupling reactions require expensive transition metal catalyst, heteroaryl coupling
partners and halogenated BODIPy. In these methods, purification of desired heteroaryl
BODIPy is quite tedious.
The transitionꢀmetalꢀfree processes have been realized as alternative choices to
perform various aryl CꢀC crossꢀcoupling reactions. Several such reactions have been
suggested, such as, base promoted coupling reaction between unactivated arenes and aryl
halides have been used in the presence of nitrogen heterocyclic ligands.11 In situ, metal
complex formation with ligand facilitates the singleꢀelectronꢀtransfer (SET) from metal
tertꢀbutoxides to ligands on heating or in the presence of light.12 Light absorbing metal
2

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complexes (Irꢀppy complex) or other chromophores have been used as active photoredox
catalyst in CꢀH arylation.
Recently, Dehaen et al. showed a very useful, convenient, efficient and costꢀeffective
method for CꢀH arylation of BODIPy.13 In this, phenyl BODIPy derivatives were
synthesized by the reaction of phenyldiazoniumtetrafluoroborate with BODIPy in
presence of ferrocene as catalyst. Later, alkylated BODIPy derivatives were synthesized
using alkyltrifluoroborate or boronic acids and manganese acetate as catalyst.14 Herein,
we further extend the method developed by Dehaen et al to synthesize heteroaryl
substituted BODIPy derivatives (1ꢀ8) by using convenient and costꢀeffective way.
Heteroaryl diazoniumtetrafluoroborate and ferrocene along with BODIPy were reacted in
acetone at room temperature. To get the insight on the possible reaction mechanism the
electron paramagnetic resonance (EPR) experiments were carried out. Spin crossꢀover
experiments with 5,5ꢀdimethylꢀpyrroline Nꢀoxide (DMPO), in presence of ferrocene,
helped in trapping the radicals formed in reaction. Furthermore, reaction mechanism is
investigated using density functional theory (DFT) methods. The comparison of free
energies of different steps of reaction, using ferrocene and other catalysts such as CuCl
and ascorbic acid, helped to understand the role of ferrocene in this reaction. At this stage
we believe that reaction proceeds with radical formation. Absorption and emission
properties of heteroaryl BODIPys are also reported.
Results and Discussion
The heteroaryl BODIPys (1ꢀ8) were synthesized by the reaction of heteroaryl
diazoniumtetrafluoroborate and BODIPy precursor with ferrocene as catalyst (Scheme 1).
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The precursor 8ꢀanisyl BODIPy was synthesized by the literature method15 whereas the
diazonium salts of heteroaryls were synthesized by slightly modified classical method.
The unsubstituted BODIPy was reacted with 2ꢀthiadizole diazoniumtetrafluorborate, 2ꢀ
thiazole diazoniumtetrafluorborate, 2ꢀbenzothiazole diazoniumtetrafluorborate, and 4ꢀ
pyridyl diazoniumtetrafluoroborate in the presence of ferrocene to get the compounds 1ꢀ8
.
All these reactions produced a mixture of mono and diꢀheteroaryl substituted BODIPys.
The exclusive synthesis of diꢀheteroaryl BODIPy could not be achieved, irrespective of
the number of equivalents of diazonium salts. All these reactions were monitored by thin
layer chromatography and absorption spectroscopy. After about 4 h all the starting
BODIPy was found to be consumed. Purification by column chromatography afforded the
pure 1ꢀ8 in 40ꢀ70 % yields except for compound 2. For compound 2 only 4ꢀ5% yield was
observed even in the excess of 2ꢀthiadizole diazonium salt. Compounds 1ꢀ8 were
1
characterized by several spectroscopic techniques which include HꢀNMR, 13CꢀNMR,
MALDIꢀmass etc. Compounds 1ꢀ8 are fairly soluble in common organic solvents.
OCH3
OCH3
OCH3
-
Ar N2+ BF4
+
N
N
B
N
N
B
N
N
B
Ferrocene
Acetone, RT, 4h
Ar
Ar
Ar
F
F
F
F
F
F
1, 3, 5, 7
9
2, 4, 6, 8
N
N
S
S
N
Ar =
N
S
N
Scheme 1: Ferrocene catalysed synthesis of BODIPy derivatives, 1ꢀ8
.
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1
Figure 1 shows the HꢀNMR and 13CꢀNMR of compound
6
. Two doublets were
obtained for pyrrolic protons between 8.0ꢀ8.2 ppm in 1HꢀNMR. These two doublets show
the substitutions at ꢀ3,5 positions only and not at 2,6 positions in which case we expect
two singlets for pyrrolic protons. Substitutions at 3,5 positions was further confirmed with
the help of correlation spectroscopy (COSY) (see SI information). Other peaks in
aromatic region were assigned to aryl substituents.
Figure 1: 13CꢀNMR and 1HꢀNMR of BODIPy derivative
6 (only aromatic region is
shown for better clarity)
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To get an insight on the reaction mechanism we carried out a set of electron
paramagnetic resonance (EPR) experiments. The EPR spectra were recorded on X band
spectrometer (Bruker EMX series) at room temperature. Samples were degassed by
passing high purity N2 gas before recording EPR. No signal was observed when
diazonium salt and ferrocene mixture was used. This does not rules out the absence of
aryl radicals as it may be short lived or efficiently relaxing. It is well known to use 5,5ꢀ
dimethylꢀpyrroline Nꢀoxide (DMPO) as spin trapping agent for aryl radicals in spin crossꢀ
over experiments.16 Reaction mixture of diazonium salt and DMPO produced a weak
signal in EPR which shows the presence of radical formation. A sharp increase in
intensity of this signal was observed when EPR was conducted with diazonium salt,
DMPO and Fc together (Figure 2). A sharp increase in the intensity in EPR spectrum in
presence of Fc indicates the catalytic behaviour of Fc in the radical formation. Weak
signal obtained in the absence of ferrocene was attributed to the self decomposition of
diazonium salt. It will be worth to note that reaction of diazonium salt and BODIPy gives
desired product even in absence of ferrocene albeit in lesser yield and more reaction time.
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Figure 2: Electron paramagnetic resonance spectrum of 2ꢀbenzothiazolediazonium salt,
ferrocene and DMPO in acetone.
Having established the formation of radical intermediate in these reactions, we further
investigated the mechanism of reaction using the density functional theory (DFT)
calculations to establish the role of Fc in the reaction. The proposed steps involved in the
reaction mechanism are shown in Scheme 2. All calculations were performed using
Gaussian 09 suite of programs.17 The geometries of the reactants, intermediate structures
and transition states were optimized in the solvent phase using the M06ꢀ2X functional18
(UM06ꢀ2X functional for open shell systems) with 6ꢀ311G** basis set. The solvent effect
of acetone was taken into account by the polarizable continuum model (PCM).19 The free
energy changes of each step of the reaction are calculated and provided in table 1.
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Scheme 2: Proposed reaction steps involved in the radical mechanism.
The reaction commences with a single electron transfer (SET) from ferrocene to the
aryl diazonium salt which splits aryl diazonium salt into aryl radical and nitrogen
molecule. The 2ꢀthiazole diazoniumtertrafluroborate was taken as a model aryl diazonium
salt in the calculations. A SET from ferrocene to thiazole diazonium salt is found to be
exoergic by 10.3 kcal/mol. In the next step, thiazole radical adds to BODIPy to form
radical σ complex ArꢀBODIPy•. This step is predicted to be exoergic by 35.1 kcal/mol.
The transition state for the addition thiazole radical to BODIPy was also located at the
M062X/6ꢀ311G** level of theory. The addition of thiozole radical to the BODPy requires
an activation barrier of 9.5 kcal/mol. The resulting ArꢀBODIPy• radical transfer an
electron to the Fc+• to generate cationic σ complex ArꢀBODIPy+, this step is also found to
ꢀ
be exoergic by 7.1 kcal/mol. In final step, the ArꢀBODPy+ loses its proton to BF4 to
provide heteroaryl BODIPy.
It is quite evident from these results that the ferrocene plays crucial role in electron
transfer steps (StepꢀI and StepꢀIII) since these steps are found to be fairly exoergic. To
gain better insights on the role of ferrocene in electron transfer steps, free energies of
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these steps were calculated by replacing ferrocene with other reducing agents such as
CuCl and ascorbic acid. The free energy changes of stepꢀI and stepꢀIII involving CuCl
and ascorbic acid are provided in Table 1. Interestingly, electron transfer from CuCl and
ascorbic acid to thiazole diazonium salt is found to be endoergic by 13 kcal/mol. Thus, it
is clear that ferrocene ensure a facile electron transfer to the diazonium salt and helps to
initiate aryl radical from diazonium salt.
Table 1: The free energies (kcal/mol) of steps involved in heteroarylation of BODIPy
calculated using DFT
Step
Fc
CuCl
13.3
ꢀ
LꢀAscorbic acid
ꢀ10.3
ꢀ35.1
ꢀ7.1
13.8
StepꢀI (ꢁG1)
StepꢀII (ꢁG2)
StepꢀIII (ꢁG3)
StepꢀIV (ꢁG4)
ꢀ
ꢀ30.4
ꢀ
ꢀ31.2
ꢀ
ꢀ12.1
BODIPy derivatives 1ꢀ8 were studied by absorption and emission spectroscopies in
solution. The Figure 3 shows the absorption and emission spectra in toluene. Compounds
1ꢀ8 showed strong S0ꢀS1 (π−π∗) absorption maxima in the range of 524ꢀ632 nm. This
band is assigned to diisoindolomethene core of compounds 1ꢀ8. The absorption maxima
of this band are directly dependent on the extent of deꢀlocalization of
π electrons of
heteroaryl substituents on BODIPy core. The broad band observed in the high energy
region 414ꢀ461 nm of spectrum corresponds to the S0ꢀS2 transition of the
boradiazaindacene. Substitution of heteroaryl groups produced large bathochromic shift
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of around 20ꢀ130 nm in absorption maxima in comparison to unꢀsubstituted BODIPy.15
Molar absorption coefficients for 1ꢀ8 were high and are summarized in Table 2.
Figure 3: Absorption (above) and emission (below) spectra of 1ꢀ8 in toluene.
Emission spectra of compounds 1ꢀ8 recorded in toluene are shown in Figure 3.
Compounds 1ꢀ8 showed emission peak at 544 ꢀ644 nm with a low intensity shoulder in
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further low energy region. Compounds 1ꢀ8 showed bathochromic shifts in emission
spectra and upto 110 nm red shifts were observed in comparison to unꢀsubstituted
BODIPy. A very small Stoke shift of ~10 nm for 1ꢀ6 was observed while for 7ꢀ8 Stoke
shift of ~ 25 nm was observed, which suggests the change occurred in the ground and
excited state geometry is minimal in 1ꢀ6. Fluorescence quantum yields of compound 1ꢀ8
were calculated with respect to either Rhodamine B (φ = 0.68 in ethanol) or tetraphenyl
porphyrin (TPP)20 (Table 2). Fluorescence life time studies of 3ꢀ6 were carried out in
toluene and data are presented in Table 2.
Table 2: Photophysical properties of 1ꢀ8 in toluene.
Φ
τ
λabs & ε
λem
[nm]
Compounds
[ns]
[nm] (log)
Std.15
503 (4.73)
521
552, 594
568
65a
60a
ꢀ
ꢀ
1
2
3
4
5
6
7
8
542 (4.76), 509 (4.37), 414(4.08)
559 (4.52), 523, 421
55a
7.7
1.8
9.5
9.1
ꢀ
558 (4.87), 522 (4.42), 416(4.15)
617 (4.83), 572 (4.45), 448(4.26)
565 (4.95), 527 (4.54), 419(4.33)
632 (4.85), 586 (4.52), 461(4.32)
524 (4.67), 414 (4.46)
568, 610
628, 681
575, 618
644, 704
544
370b
71a
410b
22a
10a
ꢀ
546 (4.22), 414 (3.6)
574
aw.r.t. Rhodamine B; bw.r.t. tetraphenyl porphyrin
Conclusion
The heteroarylation of BODIPy is achieved in moderate to good yields using diazonium
tetrafluoroborate and ferrocene as a catalyst. Furthermore, the reaction mechanism was
investigated using electron paramagnetic resonance (EPR) experiments and DFT calculations.
Spin cross over experiments on the ferrocene mediated reaction showed sharp signals in EPR
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spectrum indicating the formation of radical intermediate in the initial step of the reaction. We
also elucidated the role of ferrocene as a radical initiator in this reaction using the DFT
calculations. EPR experiments and DFT calculations support the radical mechanism for the
ferrocene mediated heteroarylation of BODIPy using diazonium salt. The absorption and
emission properties upon heteroaryl substitutions on BODIPy were studied. To the best of our
knowledge a conclusive proof for this mechanism is being reported here for the first time. We
strongly believe that knowledge on the pathway of reaction mechanism of this CꢀH arylation will
help in designing the advanced materials for various applications.
Experimental section
Chemicals and instrumentation
All general chemicals and solvents were procured from S D. Fine Chemicals, India and
SigmaꢀAldrich. Column chromatography was performed using silica gel of 100ꢀ200mesh
1
13
size. The H and CꢀNMR (δ in parts per million) spectra were recorded using a Bruker
500 MHz spectrometer. Tetramethylsilane (TMS) was used as an internal reference for
1
recording HꢀNMR spectra (residual proton; δ = 7.26 ppm) in CDCl3. The MS spectra
were recorded on Bruker MALDIꢀTOF. UV–vis spectra were acquired on Shimadzu
1800. Fluorescence measurements were carried out using Horiba Fluoromax 4. For
emission, compounds 1ꢀ8 were excited at 380 nm. Photophysical studies were carried out
in toluene (~1 X 10ꢀ6 M). The EPR spectra were recorded on X band spectrometer
(Bruker EMX series) at room temperature. Samples were degassed by passing high purity
N2 gas before recording EPR.
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Synthesis and characterization of BODIPys (1ꢀ8)
A round bottom flask was charged with BODIPy (1 eqv.), respective aryl diazonium
tetrafluoroborate (4 eqv.) and acetone. Ferrocene (0.1 eqv.) solution in acetone was added
dropwise and slowly in 15 min time at room temperature. Reaction mixture was further
stirred for 4h. A noticeable colour change of reaction mixture was observed. Reaction
mixture was extracted with dichloromethane and organic layers were washed with brine
and water. Solvents were removed and crude product obtained was purified by column
chromatography using hexane and dichloromethane to afford the compounds 1ꢀ8 (~ 40ꢀ
70% except for 2) as purple or greenish solids.
3ꢀ(2ꢀthiadizolyl)ꢀ4,4ꢀdifluoroꢀ8ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene,
1:
Purification by silica gel column chromatography using hexane and dichloromethane
ο
1
(2:8) produced
1
as brown solid. Yield: (15 mg, 40 %); M.P.: 132 C; HꢀNMR (500
MHz, CDCl3) ):
δ
9.32 (s, 1H), 8.03 (s, 1H), 7.60 (d, 2H, J = 8.55 Hz), 7.50 (d, 1H, J =
4.3 Hz), 7.11 (d, 2H, J = 8.5 Hz), 7.08 (t, 2H, J = 6.9 Hz), 6.68 (d, 1H, J = 3.6 Hz), 3.90
13
(s, 3H, OCH3); CꢀNMR (500 MHz , CDCl3):δ 154.05, 153.34, 145.45, 144.64, 139.27,
132.57, 132.49, 130.70,126.01, 121.08, 114.27, 114.21; MALDIꢀTOF mass for
C18H13BF2N4OS calcd.382.09, found 363 (MꢀF)+.
3,5ꢀBis(2ꢀthiadizolyl)ꢀ4,4ꢀdifluoroꢀ8ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene,
2
: Purification by silica gel column chromatography using hexane and dichloromethane
ο
(2:8) produced
1
as brown solid. Yield: (2 mg, 4 %); M.P.: 168 C; FTꢀIR (KBr, cmꢀ1):
ν
3090.6, 2920.7, 2851.4, 1706.9, 1525.6, 1546.3, 1503.5, 1395.9, 1370.9, 1297.2, 1253.2,
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1176.8, 1127.3, 1069.4, 1021.2, 979.2, 879.4, 795.4, 739.9, 708.4, 608.1; MALDIꢀTOF
mass for C20H13BF2N6OS2 calcd.466.63, found 446.63 (MꢀF)+.
3ꢀ(2ꢀthiazolyl)ꢀ4,4ꢀdifluoroꢀ8ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene,
3:
Purification by column chromatography using hexane and dichloromethane (2:8)
ο
produced
3
as brown solid. Yield: (20 mg, 52 %); M.P.: 184 C; FTꢀIR (KBr, cmꢀ1):
ν
3113.5, 2956.2, 2917.4, 1602.3, 1525.0, 1505.0, 1297.0, 1251.1, 1170.2, 796.8, 734.5;
1HꢀNMR (700 MHz , CDCl3):
8.04 (s , 1H), 7.97 (s, 1H), 7.66 (d, 1H, J = 3.85 Hz),
δ
7.57 (d, 2H,
1H,
CDCl3):
J
= 11.7 Hz) , 7.35 (d, 1H,
J
= 5.3 Hz), 7.09 (d, 2H,
J
= 11.9 Hz), 7.04 (d,
13
J
= 5.2 Hz), 6.99 (s, 1H), 6.61 (s, 1H), 3.94 (s, 3H OCH3); CꢀNMR (600 MHz ,
δ
162.04, 157.41 , 149.75, 144.55, 143.80, 137.26, 132.35, 130.55, 126.32,
123.74, 121.83, 113.98, 29.58; MALDIꢀTOF mass for C19H14BF2N3OS calcd. 381.2,
found 381 (M)+, 361.7 (MꢀF)+.
3,5ꢀBis(2ꢀthiazolyl)ꢀ4,4ꢀdifluoroꢀ8ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene, 4:
Silica gel column chromatography using hexane and dichloromethane (2:8) produced
4
as
ο
brownish purple solid. Yield: (25 mg, 54 %); M.P.: 204.2 C; FTꢀIR (KBr, cmꢀ1):
ν
1
3076.5, 2922.4, 2850.1, 1538.3, 1454.4, 1250.0, 1066.0, 853.6, 791.3, 734.5; HꢀNMR
(700 MHz , CDCl3):
δ
8.02 (d, 2H,
= 3.9 Hz ), 7.07 (d, 2H,
161.93, 157.48, 149.60, 146.16, 143.80, 143.49,
J
= 2.3 Hz), 7.64 (d, 2H, 2.85 Hz), 7.55 (d, 2H,
J = 8.4
Hz), 7.37 (d, 2H,
J
J
= 3.9 Hz), 6.98 (d, 2H, = 8.4 Hz), 3.94 (s,
J
13
3H); CꢀNMR (500 MHz , CDCl3):
δ
137.18, 134.76, 134.76, 132.36, 131.26, 130.70, 126.29, 123.42, 121.06, 118.83, 113.99,
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29.57; MALDIꢀTOF mass for C22H15BF2N4OS2 calcd. 464.32, found 463.9 (M)+, 444.9
(MꢀF)+.
3ꢀ(2ꢀbenzothiazolyl)ꢀ4,4ꢀdifluoroꢀ8ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene,
5
Column chromatography using hexane and dichloromethane (2:8) produced
5
as brownꢀ
ο
purple solid. Yield: (29 mg, 67 %); M.P.: 179 C; FTꢀIR (KBr, cmꢀ1):
ν 3116.4, 2918.3,
1
2844.5, 1548.4, 1496.3, 1392.8, 1128.3, 910.4, 838.4, 781.3, 723.7; HꢀNMR (500 MHz,
CDCl3):
δ
8.15 (d, 1H,
J
= 7.5 Hz ), 8.02 (s , 1H ), 7.97(d, 1H,
J
= 7.3 Hz ), 7.55–7.57 (m,
13
3H), 7.44 (s, 2H), 7.02–7.07 (m, 4H), 6.63 (s, 1H), 3.92 (s, 3H,ꢀOCH3); CꢀNMR (700
MHz , CDCl3): δ 162.12, 157.82, 153.10, 149.04, 146.80, 144.73, 137.54, 137.26, 135.13,
132.50, 131.58, 130.76, 126.47, 126.25, 125.98, 123.73, 121.78, 121.53, 119.47, 114.10,
29.67; MALDIꢀTOF mass for C23H16BF2N3OS calcd. 431.11, found 431.1 (M)+ and 411.9
(MꢀF)+.
3,5ꢀBis(2ꢀbenzothiazolyl)ꢀ4,4ꢀdifluoroꢀ8ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀs
indacene,
6
: Purification by silica gel column chromatography using hexane and
as brown solid. Yield: (37 mg, 66 %); M.P.: 254.οC;
dichloromethane (2:8) produced
FTꢀIR (KBr, cmꢀ1):
1254.4, 1118.4, 1080.3, 1022.8, 879.1, 832.1; 1HꢀNMR (700 MHz, CDCl3):
6
ν
3058.9, 2917.8, 2850.4, 1702.8, 1596.7, 1571.0, 1532.8, 1496.3,
δ
8.17 (d, 2H
= 8.33 Hz), 7.57ꢀ7.58 (m, 4H),
= 8.26 Hz) , 7.08 (d, 1H, = 4.27 Hz) , 3.96 (s,
3H, OCH3); CꢀNMR (500 MHz, CDCl3): 162.16, 157.66, 153.15, 150.29, 145.73,
,
J
= 8.12 Hz) , 8.05 (d, 2H ,
J = 7.98 Hz) , 7.62 (d, 2H , J
7.49 (t, 2H , = 7.56 Hz) , 7.12 (d, 2H ,
J
J
J
13
δ
137.94, 137.71, 132.63, 130.80, 129.75, 126.59, 126.20, 123.84, 123.11, 121.69, 114.19,
15

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DOI: 10.1039/C6RA03705D
29.6; MALDIꢀTOF mass for C30H19BF2N4OS2 calcd. 564.11, found 564.11 (M+) and
545.10 (MꢀF)+.
3ꢀ(4ꢀpyridyl)ꢀ4,4ꢀdifluoroꢀ8ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene,
7:
Column chromatography was performed using dichloromethane to purify the compound
. Yield: (19 mg, 51%); FTꢀIR (KBr, cmꢀ1):
ν 2920.9, 2850.9, 1710.9, 1631.6, 1598.3,
7
1571.7, 1539.4, 1509.8, 1462.5, 1279.2, 1175.0, 1145.5, 1069.8, 1021.6, 969.5, 810.75,
1
757.57, 740.03, 710.7, 683.4; HꢀNMR (700 MHz, CDCl3):
δ
8.7 (d, 2H ,
= 7.3, 8.5 Hz) , 7.0 (t, 3H = 8.65, 6.45 Hz) , 6.9
=5.3 Hz) , 3.9 (s , 3H, ꢀOCH3)
J = 4.1 Hz) ,
7.8 (d, 2H ,
J
= 5.0 Hz) , 7.5 (t, 3H ,
J
J
(d, 1H,
J
=4.35 Hz), 6.6 (d, 1H,
J
=3.8 Hz) , 6.4 (d, 1H, J
13CꢀNMR (500 MHz, CDCl3):
δ
149.79, 144.28, 143.23, 139.81, 132.61, 132.49, 131.79,
131.51, 131.17, 129.68, 129.10, 126.25, 123.26, 119.82, 119.22, 117.39, 114.13, 113.15,
29.69; MALDIꢀTOF mass for C21H16BF2N3O calcd. 375.14, found 375.82 (M)+ and
355.94 (MꢀF)+.
3,5ꢀBis(4ꢀpyridyl)ꢀ4,4ꢀdifluoroꢀ8ꢀ(4ꢀmethoxyphenyl)ꢀ4ꢀboraꢀ3a,4aꢀdiazaꢀsꢀindacene, 8:
A
mixture of DCM and methanol (99:1) was used as eluent to get pure
8
as brownish purple
8.70 (d, 4H,
J =8.45 Hz), 7.11 (d, 2H, J = 8.55 Hz),
solid. Yield: (18 mg, 46%); M.P.: 211 οC; 1HꢀNMR (700 MHz, CDCl3):
δ
J =
5.7 Hz), 7.70 (d, 4H,
7.00 (d, 2H, = 4.25 Hz), 6.7 (d, 2H,
MHz, CDCl3): 155.43, 149.70, 139.65, 132.46, 131.75, 123.22, 120.76, 114.05, 107.44,
J
= 5.75 Hz), 7.60 (d, 2H,
13
J
J
= 4.2 Hz), 3.9 (s, 3H, OCH3); CꢀNMR (500
δ
107.36, 96.11, 29.61; MALDIꢀTOF mass for C26H19BF2N4O calcd. 452.26, found 452.34
(M)+
Acknowledgements
16

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DOI: 10.1039/C6RA03705D
We thank, Centre for Excellence in Basic Sciences, Mumbai for providing research
facilities. Partial funding was provided by Department of Science and Technology, India
(SR/FT/CSꢀ87/2010). We thank, Tata Institute of Fundamental Research, Mumbai for
providing the NMR, EPR and mass facilities. We also thank Dr. Yatendra Chaudhary,
IMMTꢀBhubaneshwar for providing the fluorescence decay facility.
References
1 A. Loudet and K. Burgess, Chem. Rev.2007, 107, 4891.
2 R. Ziessel, G. Ulrich and A. Harriman, Angew. Chem., Int. Ed. 2008, 47, 1184
3 V. Lakshmi, M. R. Rao and M. Ravikanth, Org. Biomol. Chem, 2015, 13, 2501.
4 (a) A. B. Nepomnyashchii, M. Broering, J. Ahrens, R. Kruger and A. J. Bard, J. Phy.
Chem. C 2010, 114, 14453 (b) C. Thivierge, A. Loudet and K. Burgess, Macromolecules
2011, 44, 4012.
,
5 (a) S. ErtenꢀEla, M. D. Yilmaz, B. Icli, Y. Dede, S. Icli and E. U. Akkaya,. Org. Lett.
2008, 10, 3299 (b) J. C. T. Carlson, L. G. Meimetis, S. A. Hilderbrand and R. Weissleder,
Angew. Chem., Int. Ed., 2013, 52, 6917.
6 (a) A. A. Rachford, R. Ziessel, T. Bura, P. Retailleau and F. N. Castellano, Inorg. Chem
2010, 49, 3730. (b) T. Tachikawa, N. Wang, S. Yamashita, SꢀC Cui and T. Majima,
Angew. Chem. Int. Ed., 2010, 49, 8593.
.
7 (a) K. Rurack, M. Kollmannsberger and J. Daub, Angew. Chem., Int. Ed., 2001, 40, 385;
(b) Y. Yu, A. Descalzo, Z. Shen, H.Rohr, Q. Liu, Y. Wang, M. Spieles, Y. Li, K.Rurack
and X. You, Chem. Asian J., 2006, 1, 176 (c) E. Fron, E. CoutinoꢀGonzalez, L. Pandey,
M.Sliwa, M. Van der Auweraer, F. C. De Schryver, J.Thomas, Z.Dong, V. Leen, V. M.
17

RSC Advances
Page 18 of 21
View Article Online
DOI: 10.1039/C6RA03705D
Smet, W. Dehaen and T. Vosch, New J. Chem. 2009, 33, 1490 (d) G. Ulrich, S. Goeb, A.
De Nicola, P. Retailleau and R. Ziessel, J. Org. chem. 2011, 76, 4489 (e) T. Rohand, W.
Qin, N. Boens and W. Dehaen, Eur. J. Org. Chem. 2006, 4658 (f) M. Ravikanth, N.
Agarwal and D. Kumaresan, Chem. Lett., 2000, 836 (g) D. Kumaresan, N. Agarwal and
M. Ravikanth, J. Chem. Soc., Perkin Trans. 1, 2001, 1644.
8 (a) T. K. Khan, S. K. Jana, M. R. Rao, M. S. Shaikh and M. Ravikanth, Inorg. Chim.
Acta. 2012, 383, 257 (b) V. Leen, T. Leemans, N. Boens and W. Dehaen, Eur. J. Org.
Chem. 2011, 4386 (c) T. Rohand, W. Qin, N. Boens and W. Dehaen, Eur. J. Org. Chem.
2006,4658 (d) K. Kim, S. H.Choi, J. Jeon, H. Lee, J. O. Huh, J. Yoo, J. T. Kim, C.ꢀH.
Lee, Y. S. Lee and D. G. Churchill, Inorg. Chem. 2011, 50, 5351.
9 (a) Y. M. Poronik, V. P. Yakubovskyi, M. P. Shandura,Y. G. Vlasenko, A. N. Chernega
and Y. P. Kovtun, Eur. J. Org. Chem. 2010, 2746 (b) E. Yu. Schmidt, B. A. Trofimov, A.
I. Mikhaleva, N. V. Zorina, N. I Protzuk, K. B. Petrushenko, I. A.Ushakov, M. Yu.
Dvorko, R. MéalletꢀRenault, G. Clavier,T. T. Vu, H. T. T. Tran and R. B. Pansu, Chem.
Eur. J. 2009, 15, 5823
10(a) V. Lakshmi and M. Ravikanth, J. Org. Chem .2013, 78, 4993 (b) M. Vincent, E.
Beabout, R. Bennett and P. Hewavitharanage, Tetrahedron Lett. 2013, 54, 2050 (c) I.
Esnal, J. Banuelos, I. Lopez Arbeloa, A. Costela, I. GarcíaꢀMoreno, M. Garzon, A. R.
Agarrabeitia and M. Jose Ortiz, RSC Adv. 2013,
3, 1547 (d) P. Gautam, B. Dhokale, S.
M. Mobin and R. Misra, RSC Adv. 2012, , 12105 (e) A. Coskun and E. U. Akkaya,
2
Tetrahedron Lett. 2004, 45, 4947 (f) G. Ulrich, C. Goze, S. Goeb, P. Retailleau and R.
Ziessel, New J. Chem. 2006, 30, 982 (g) V. P. Yakubovskyi, M. P. Shandura and Y. P.
Kovtun,. Eur. J. Org. Chem. 2009, 3237 (h) J.ꢀY. Liu, H.S. Yeung, W. Xu, X. Li and D.
18

Page 19 of 21
RSC Advances
View Article Online
DOI: 10.1039/C6RA03705D
K. P. Ng, Org. Lett .2008, 10, 5421 (i) D. Lakhe, K. K. Jairaj, M. Pradhan, U. Ladiwala
and N. Agarwal, Teterahedron Lett, 2014, 55, 7124.
11(a) S. Yanagisawa, K. Ueda, T. Taniguchi and K. Itami, Org. Lett. 2008, 10, 4673−4676
(b) W.ꢀC., Chen, Y.ꢀC. Hsu, W.ꢀC. Shih, C.ꢀY. Lee, W.ꢀH. Chuang, Y.ꢀF.Tsai, P. P.ꢀY.
Chen and T.ꢀG. Ong, Chem. Commun. 2012, 48, 6702ꢀ6704. (c) Y. Cheng, X. Gu and P.
Li, Org. Lett. 2013, 15, 2664ꢀ2667. (d) J. M. R. Narayanam and C. R. J. Stephenson,
Chem. Soc. Rev, 2011, 40, 102ꢀ113.
12(a) M. E. Budén, J. F. Guastavino and R. A. Rossi, Org. lett. 2013, 15, 1174−1177. (b) Y.
Cheng, X. Gu and P. Li, Org. Lett. 2013, 15, 2664−2667.
13B. Verbelen, S. Boodts, J. Hofkens, N. Boens and W. Dehaen, Angew. Chem. Int. Ed.
2015, 54, 4612.
,
14B. Verbelen, L. C. D. Rezende, S. Boodts, J. Jacobs, L. V. Meervelt, J. Hofkens and W.
Dehaen, Chem. Eur. J., 2015, 21: 12667.
15R. W. Wagner and J. S. Lindsey, Pure & Appl. Chem.1996, 68, 1373.
16A. Bosnjakovic and S. Schlick, J. Phys. Chem. B , 2004, 108, 4332.
17M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li,
H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M.
Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J.
Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K.
Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.
M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
19

RSC Advances
Page 20 of 21
View Article Online
DOI: 10.1039/C6RA03705D
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J.
Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J.
Cioslowski, and D. J. Fox, Gaussian 09, Revision C.01, Gaussian, Inc., Wallingford CT,
2009.
18Y. Zhao and D. G. Truhlar, Theor. Chem. Acc., 2008, 120, 215.
19(a) M. Cossi, V. Barone, R. Cammi and J. Tomasi, Chem. Phys. Lett., 1996, 255, 327ꢀ335
(b) E. Cances, B. Mennucci and J. Tomasi, Chem. Phys., 1997, 107, 3032 (c) M. Cossi,
G. Scalmani, N. Rega and V. Barone, Chem. Phys., 2002, 117, 43.
20R. F. Kubin, A. N. Fletcher, Journal of Luminescence 1983, 27, 455.
20

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Graphical abstract