Synthesis, structure and photoluminescent properties of BF2 and BPh2 complexes with N,O-benzazine ligands

Article abstract of DOI:10.1016/j.jfluchem.2015.04.010

Novel N,O-bidentate BF₂ and BPh₂ complexes have been prepared in good to excellent yields through coordination of 8-hydroxy-2-methylquinolines and 2-(2-hydroxyphenyl)-3H-quinazolin-4-ones with boron trifluoride etherate or triphenylb

Full text of DOI:10.1016/j.jfluchem.2015.04.010

Accepted Manuscript
Title: Synthesis, structure and photoluminescent properties of
BF2 and BPh2 complexes with N,O-benzazine ligands
Author: Emiliya V. Nosova Tatyana N. Moshkina Galina N.
Lipunova Inna V. Baklanova Pavel A. Slepukhin Valery N.
Charushin
PII:
S0022-1139(15)00106-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2015.04.010
FLUOR 8548
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
27-2-2015
16-4-2015
18-4-2015
Please cite this article as: E.V. Nosova, T.N. Moshkina, G.N. Lipunova, I.V. Baklanova,
P.A. Slepukhin, V.N. Charushin, Synthesis, structure and photoluminescent properties
of BF2 and BPh2 complexes with N,O-benzazine ligands, Journal of Fluorine Chemistry
(2015), http://dx.doi.org/10.1016/j.jfluchem.2015.04.010
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1

BF2 and BPh2 complexes of 8-OH-2-Me-quinolines and 2-(2-HOC6H4)-quinazolinones
were prepared


Structure of complexes was confirmed by MS, 1H, 19F, 11B NMR and X-ray
2-Methyl-8-hydroxyquinolines BPh2 complexes surpass their BF2 analogs in quantum
yield

BF2 complex of 2-(2-OH-3,5-di(t-Bu)phenyl)-3Н-quinazolin-4-one exhibits the best
fluorescence
Page 1 of 22

2
Synthesis, structure and photoluminescent properties of BF2 and BPh2
complexes with N,O-benzazine ligands
Emiliya V. Nosova,a,* Tatyana N. Moshkina,a Galina N. Lipunova,b Inna V. Baklanova,b
Pavel A. Slepukhin,b Valery N. Charushina,b
a Department of Organic Chemistry, Chemical Technology Institute, Ural Federal University,
19 Mira Str., 620002 Ekaterinburg, Russia. E-mail: emily74@rambler.ru
b I. Postovsky Institute of Organic Synthesis, Ural Division of the Russian Academy of Sciences,
22 S. Kovalevskoy Str., 620219 Ekaterinburg, Russia. E-mail: lipunova@ios.uran.ru
* corresponding author
Abstract
Novel N,O-bidentate BF2 and BPh2 complexes have been prepared in good to excellent yields
through coordination of 8-hydroxy-2-methylquinolines and 2-(2-hydroxyphenyl)-3Н-quinazolin-
4-ones with boron trifluoride etherate or triphenylborane under mild conditions. All complexes
have been characterized by 1H, 11B and 19F NMR, mass-spectrometry and X-ray crystallography
data. Some complexes have been found to exhibit a significant fluorescence in acetonitrile
solutions. Electronic and site effects of substituents in both heterocyclic and phenol fragments
proved to have a profound impact on quantum yields.
Keywords: 8-hydroxy-2-methylquinoline, 8-hydroxy-6,7-difluoro-2-methylquinoline, 8-
hydroxy-2-styrylquinoline, 2-(2-hydroxyphenyl)-3Н-quinazolin-4-one, N,O-bidentate ligands,
BF2 complexes, BPh2 complexes, structural analysis, photophysical properties, fluorescence
1. Introduction
Organoboron complexes represent one of the most important types of fluorescent dyes.
Not only complexes with N,N-ligands, such as boradipyrromethene (BODIPY) [1], 2-(quinolin-
2-yl)-1Н-phenantro[9,10-d]imidazole [2], but also complexes with N,O-ligands have been
studied intensively for the last decade (Scheme 1). In particular, BF2 complexes, bearing (2-
Page 2 of 22

3
quinolin-2-yl)phenol ligands, have been shown to exhibit a strong fluorescence in both organic
solvents (em 441-492 nm in CHCl3 at room temperature), and in solid state (em 454-502 nm)
[3]. Also BF2 complexes with 3-(2-oxo-2-arylethylidene)-3,4-dihydro-1H-quinoxalin-2-ones and
3-(2-oxo-2-arylethylidene)-3,4-dihydro-benzo[1,4]oxazin-2-ones demonstrate a bright and
intensive yellowish green fluorescence in THF solutions with maximum at 481-521 nm (φ =
0.59-0.87) [4, 5].
Difluoroboron complexes of 8-hydroxyquinoline derivatives have been mentioned in the
only publication [6], dealing with photoisomerization of 3,4-bis-[2-(8-hydroxyquinolin-2-
yl)vinyl-5-methylthiophen-4-yl]-2,5-dihydrothiophene taking place on treatmeant with boron
trifluoride etherate. Diphenylboron complexes of 8-hydroxyquinolines have been studied in more
detail, as analogues of 8-hydroxyquinoline aluminates with an enhanced stability comparing to
aluminium-based emitters [7] and a strong -electron accepting character of the empty pz orbital
at the boron centre [8, 9].
X
N
O
R1
R2
R3
R4
N
F
B
F
O
B
F
O
F
R
X = O, NH
Scheme 1. BF2 complexes based on N,O-ligands, described in the literature
Two main approaches to turn the emission wavelength of diphenylboron complexes are
worth to be mentioned: a) incorporation of substituents into heterocyclic ligands, thus effecting
the HUMO-LUMO energy levels and, therefore, on λem [10]; b) variation of substituents at the
boron atom, in particular, replacement of the phenyl moiety with naphthyl, thienyl or benzo-
thienyl fragments [11, 12]. 4-Fluorophenyl and C6F5 groups increase the Lewis acidity of the
boron center, effecting the HOMO-LUMO levels, while pentafluorophenyl groups also seem to
Page 3 of 22

4
contribute into stability of complexes [13]. Interaction of 8-hydroxyquinoline with tris(2-
vinylphenyl)borane has also been described [14].
Diphenylboron complex of 8-hydroxyquinoline has been modified through incorporation
of 1-naphthyl and 2-benzothienyl fragments into position 5 of the ligand [15], while the complex
of 2-methyl-8-hydroxyquinoline with BPh2 has not so far been described. Also the data on
electroluminescent properties of di(mesithyl)boron complexes of 8-hydroxyquinoline and 2-
methyl-8-hydroxyquinoline are available in the literature [16].
In this paper we wish to report the synthesis of novel BF2 and BPh2 complexes with N,O-
benzazine ligands, namely the complexes with five-membered boron chelating ring, based on 2-
methyl-8-hydroxyquinoline and 2-methyl-6,7-difluoro-8-hydroxyquinoline, as well as the
complexes with six-membered boron chelating ring, based on 2-(2-hydroxyphenyl) substituted
3H-quinazolin-4-ones.
2. Results and discussion
Treatment of 8-hydroxy-2-methylquinoline 1а and its 6,7-difluoroderivative 1b with an
excess of boron trifluoride etherate in the presence of triethylamine proved to result in the
formation of novel BF2 complexes 2a,b as yellow crystalls in good to excellent yields (Scheme
2).
Unfortunately, we have failed to isolate individual difluoroboron complexes derived from
the reaction of 2-styryl derivatives 4a,b [17, 18] with BF3·Et2O under a variety of conditions.
Nevertheless, diphenylboron complexes of 2-methyl-8-hydroxyquinolines (3a,b) and 2-styryl-8-
hydroxyquinolines (5a,b) have been obtained successfully on heating of the reaction solutions of
ligands 1a,b and 4a,b with triphenylborane in tetrahydrofuran (Scheme 2).
Page 4 of 22

5
X
X
BF3.Et2O
X
X
X
X
BPh3, THF
N
F
CH3
NEt3, C6H6
N
CH3
N
CH3
O
B
O
OH
B
1a,b
Ph
F
2a,b
Ph
3a,b
O
H
MeO
1)
Ac2O
2) HCl, 00C
3) HCl, EtOH, t
4) Et3N, EtOH
X
X
X
N
BPh3, THF
OH
4a,b
X
N
O
B
Ph
Ph
OMe
5a,b
OMe
1-5: X = H (a), F (b).
Scheme 2. Synthesis of BF2 and BPh2 complexes
with 2-methyl- and 2-styryl-8-hydroxyquinolines and their 6,7-difluoro derivatives
The evidence for the structures of 2a,b, 3a,b, and 5a,b is provided by their spectral data,
1
including the Н, 11B, and 19F NMR-spectroscopy, as well as mass-spectrometry and the
elemental analysis. In the 19F NMR spectra of compounds 2a,b the resonance signals of BF2
1
groups at 143-156 ppm have been observed, while the H NMR spectra of these compounds
show no OH signals. In spite of the fact, that compound 1b exists in the zwitter-ion form in
solution [18], an increase in the positive charge at the nitrogen atom of the complex 2b results in
1
downfield shifts for H(3), H(4) and H(5) protons in the Н NMR of the complex 2b, relative to
the corresponding signals for the ligand 1b. In the 19F NMR spectra of 6,7-difluoroderivative 2b
( -143.7 ppm) the signal of BF2 group is shifted downfield considerably in comparison with the
correspondent signal of the complex 2а ( -155.7 ppm). Also it is worth mentioning, that in the
11B NMR spectrum of compound 2a the signal at 1.01 ppm has been observed.
In the mass spectra of complexes 2a,b the peaks of molecular ions (m/z 207 and 243
respectively) with 100% relative intensivity are observed.
Page 5 of 22

6
The 1H NMR spectra of complexes 3 and 5 contain no signals of OH groups, however the
characteristic resonances of two phenyl residues are available. In the 11B NMR spectra of these
compounds the expected multiples in the region of 11.9-13.5 ppm are observed. The relative
intensivities of molecular ion peaks in the mass spectra of complexes 3a,b, 5a,b are in the range
of 3-6%, it should be noted that 100% peaks correspond to the ions [M-Ph]+.
Due to a similarity in the structures of complexes 3a,b, 5a,b, compounds 3a and 5a have
been selected as representatives of this family for X-ray single crystal diffraction studies, and the
data of these structural elucidations are presented in Figures 1 and 2.
The boron center in both compounds has a typical tetrahedral geometry. Five-membered
heterocycle is approximately planar, and it is in the plane of the tricyclic system. The boron atom
shows the maximal deviation from the least-squared plane of the tricyclic system (0.062 Å for
compound 3a and 0.108 Å for compound 5a). In case of compound 3a carbon atoms of Ph-
substituents demonstrate a strong thermal disordering. It has been taking into account by
introducing into the structural model of two disordering components the with occupancy
coefficients 0.5/0.5. Due to a short distance between the disordered components the thermal
ellipsoids of the disordered atoms were constrained by using commands EADP in the refinement
program XL of the SHELXTL program package.
Bond lengths B-X and angles Y-B-X of compounds are in good agreement with the data
of earlier published papers. Each boron center in both complexes is bound with two carbon
atoms of two phenyl groups. The bond angles O-B-N in complexes 3a and 5a are similar (98.56°
and 98.2(2)°) (Table 1) and close to the published data (97.6-99.6°) [15].
The bonds lengths N(1)-B(1) in compounds 3а (1.662 Å) and 5а (1.657 Å) are very close
to the published data N-B (1.618-1.646 Å); the bonds lengths O(1)-B(1) (1.514 Å and 1.524 Å)
and bonds lengths С-В (1.599-1.614 Å) are in good agreement with O-B (1.503-1.535 Å) and C-
B distances (1.578-1.606 Å), respectively [15]. The bonds lengths C-O in the heterocyclic ring
(1.340 and 1.341 Å for 3a and 5a accordingly) are in good agreement with those typical for
Page 6 of 22

7
phenols (1.36 Å [19]). Consequently, the unoccupied p-orbital of the boron atom does not have a
significant effect on electron configuration of the quinoline system.
In crystals of 3a and 5a no shortened (less then sum of V-d-W radii) intermolecular
contacts have been observed.
Fig. 1. ORTEP structure of compound 3а in accordance with the XRD data
(the disordered atoms are omitted for clarity)
Fig. 2. ORTEP structure of compound 5а according to the XRD data
2-(2-Hydroxyphenyl) substituted 3Н-quinazolin-4-ones have been chosen as the second
type of N,O-bidentate ligands, due to their structural similarity with (2-quinolin-2-yl)phenolic
ligands. Although the synthesis of quinazolinone 7b from 2-aminobenzamide and 3,5-di(tert-
Page 7 of 22

8
butyl)salicylic aldehyde has been described [20, 21], use of such oxidants as bis(acetyl-
acetonato)oxovanadium and copper oxide, reported by the authors for transformation 6b→7b,
0
require too severe reaction conditions (heating at 120 С for 15-24 h). We have suggested to
exploit copper chloride, as oxidant for the synthesis of 7b, thus enabling cyclization of
0
azomethine 6b to be carried out at 80 C for 1.5 h. In order to obtain complexes 8a,b a short-
term heating of 2-(2-hydrohyphenyl)-3H-quinazolin-4-one 7a and its derivative 7b with boron
trifluoride etherate in a mixture of toluene and acetic acid has been performed (Scheme 3).
The 19F NMR spectra of complexes 8a,b exhibit the resonance signals of BF2 groups in
the region of 136-151 ppm. Additionally, disappearance of the downfield hydroxy proton signals
1
in the Н NMR spectra of these complexes provides an additional argument for the chelation of
BF2 group with these ligands. Also, broaden singlets of the NH groups in the 1Н NMR spectra of
complexes are shifted upfield considerably relarive to the corresponding signals of the ligands.
In the 11B NMR spectra of complexes 8a,b multiplet signals at 1.10 ppm are observed. The
molecular ion peaks in the mass spectra of complexes 8a,b (m/z 286 and 398) are less intensive
(13% and 41% respectively), than those of 8-hydroxyquinoline derivatives 2a,b.
The only complex with diphenylboron, which we have managed to obtain from the ligand
7a is compound 9 which is formed on reflux of 7a with triphenylborane in tetrahydrofuran
(Scheme 3). Due to steric factors the formation of six-membered chelate rings from ligands 7
appears to be more a more difficult process, than that leading to five-membered chelates, thus
taking place with 8-hydroxyquinoline derivatives 1 and 4.
The UV-Vis absorption and fluorescence data for the complexes 2,3,5,8, and 9 are listed
in Table 2. The absorption spectra of difluoroboron complexes 2 are similar to the spectra of the
corresponding ligands 1. Transformation of ligands 1 into their diphenylboron complexes 3 is
followed by a considerable bathochromic shift. The diphenylboron complexes 3 are
characterized by the long-wave shift in absorption spectra in comparison with difluoroboron
complexes 2. 6,7-Difluoro compound 2b shows a red shift of the absorption peak relative to 2a
Page 8 of 22

9
(Table 2). Difluoroderivatives 3b and 5b demonstrate a blue shift of the absorption peak in
comparison with chelates 3a and 5a, bearing no fluorine atoms in the benzene ring. For instance,
absorption and emission spectra of diphenylboron complex 3a are presented at Fig. 3.
O
H
O
N
R
EtOH
NH2
NH2
O
NH2
+
R
HO
room temp, 5 h
R
HO
CuCl2
EtOH, t
R
6a,b
O
N
O
O
BPh3, THF
(R = H)
BF3.Et2O
NH
NH
NH
O
R
R
N
B
MeC6H5, CH3COOH
N
B
Ph
HO
O
9
F
Ph
7a,b
F
R
8a,b
R
6, 7: R = H (a), t-Bu (b).
Scheme 3. Synthesis of BF2 and BPh2 complexes
with 2-(2-hydrohyphenyl)-3H-quinazolin-4-ones
Unlike ligands 1 and 4, which practically don't have luminescent properties, complexes 2,
3 and 5 show fluorescence with maxima at 390-546 nm, and their intensity depends on the nature
of substituents in both the quinolone fragment and at boron atom (Table 2). The presence of
fluorine atoms in the benzene ring of the difluoroboron complex 2b leads to a substantial red
shift of the emission band (λmaxfl 392 nm for 2a and 479 nm for 2b), and enhances the quantum
yield. In case of diphenylboron complexes with the same ligands. 6,7-difluoroderivative 3b
shows a considerable short-wave shift of the emission maximum relative to non-fluorinated
analogue 3a, while λem for 3b practically coincides with λem for 2b. Diphenylboron complexes 3
with 2-methyl-8-hydroxyquinoline ligands 1 show a considerable increase in quantum yields in
comparison with difluoroboron complexes 2 (efficiency of luminescence for complex 3a is 36
times higher than that for 2a, and luminescence efficiency for 3b is 12 times higher than that for
2b). 2-Styryl derivatives 5a,b demonstrate a long-wave shift of the emission maximum and a
Page 9 of 22

10
decrease in quantum yield compared with 2-methyl analogues 3а,b. Such effect can be explained
by a better conjugation chain and an opportunity for trans-cis-photo-isomerization [22].
In the series of difluoroboron complexes of quinazolinones 8 incorporation of the tert-
butyl group into the phenol fragment leads to a long-wave shift of the emission band and
provides a considerable increase in quantum yield (φ = 9.3% for complex 8a, and φ = 36.5% for
complex 8b). Absorption and emission spectra of the difluoroboron complex 8b are presented in
Fig. 4. It has been noted [3], that in the series of BF2 complexes of (2-quinolin-2-yl)phenols
higher quantum yields are characteristic for those compounds, which bear electron-donating
groups in the phenol ring. Therefore, it has been assumed that these groups in the phenol
fragment are more influential on quantum yields than those in the benzene ring. Comparison of
BF2 and BPh2 complexes of the ligand 7a (compounds 8a and 9) shows that replacement of
fluorine atoms with phenyl groups results in the loss of luminescence properties for the complex
9 (Table 2). A similar conclusion is given in the communication [23], in which fluorescence
efficiency of the BF2 complex of 2,4-di-t-butyl-6-[(2,2,6,6-tetramethylpiperidin-4-ylimino)-
methyl]phenol has been established to be much higher, than that of BPh2 complex with the same
ligand.
Other properties are observed for complexes 2 and 3 containing a five-membered boron
chelate ring. In this case the fluorescence intensity of diphenylboron complexes 3 is much higher
than that registered for BF2 complexes 2.
Thus, a size of the boron chelate ring, as well as electronic, steric and site effects of
substituents in ligands have impact on photoluminescent properties of boron complexes.
Being compared with small values of Stokes shifts, widely observed for typical
BODIPYs [24], large shift values (88-161 nm) for the obtained complexes appear to be quite
impressive and promising for their further applications.
Page 10 of 22

11
Table 1
Selected bond lengths and bond angles of complexes 3a and 5a
Bond length (Å)
Complex 3a
O(1)-B(1)
Bond angle (°)
1.514(2)
1.662(2)
1.606(2)
1.613(6)
O(1)-B(1)-N(1)
O(1)-B(1)-C(11)
O(1)-B(1)-C(17)
C(11)-B(1)-N(1)
C(11)-B(1)-C(17)
C(17)-B(1)-N(1)
98.56(11)
109.25(12)
111.60(17)
111.13(12)
116.32(17)
108.6(2)
N(1)-B(1)
C(11)-B(1)
C(17)-B(1)
Complex 5a
O(1)-B(1)
N(1)-B(1)
C(20)-B(1)
C(26)-B(1)
1.524(4)
1.657(4)
1.614(5)
1.599(5)
O(1)-B(1)-N(1)
O(1)-B(1)-C(26)
O(1)-B(1)-C(20)
C(26)-B(1)-C(20)
C(26)-B(1)-N(1)
C(20)-B(1)-N(1)
98.2(2)
108.9(3)
109.3(3)
118.3(3)
110.3(3)
110.0(3)
Table 2.
Photophysical properties of ligands and complexesa
Compound
φ, %b
Stokes shift
(nm)

abs (nm)
λem (nm)
ligand
302
complex
303
392
479
502
480
546
514
421
454
430
0.5
2.5
18.2
29
89
2a
2b
3a
3b
5a
5b
8a
8b
9
293, 320
302
318
161
123
121
175
149
88
379
320
359
355, 308
355, 303
330
371, 339
365, 333,
333
8.5
3
9.3
36.5
< 1
342
355
99
330
331
a Both absorption and emission spectra were measured in MeCN solution.
b The quantum yield was obtained by using quinine bisulfate as the reference compound.
Page 11 of 22

12
Fig. 3. Absorption and emission spectra of
Fig. 4. Absorption and emission spectra of
diphenylboron complex 3a in acetonitrile
difluoroboron complex 8b in acetonitrile
3. Conclusion
In this communication we have described the synthesis, structural analysis, spectral and
photophysical properties for a number of novel BF2 and BPh2 complexes bearing 8-hydroxy-
quinoline and 2-(2-hydroxyphenyl)-3Н-quinazolin-4-one ligands. All these complexes have been
obtained in good to excellent yield under rather mild conditions, by using simple work-up
procedures. Electronic effects of substituents have been shown to play an important role for
quantum yields of the corresponding complexes. High values of quantum yields and large Stokes
shifts make these compounds to be considered as potential fluorescent dyes.
4. Experimental Section
4.1. General.
All reagents used were analytically pure, and some chemicals were further purified by
1
recrystallization. Melting points were determined by a Stuart SMP3 instrument. The Н NMR
(400.13 МHz), 19F NMR (376.45 MHz) and 11B NMR (128.4 MHz) spectra were obtained on a
Bruker Avance II DMX400 spectrometer using CDCl3 or DMSO-d6 as the solvent. The 1Н NMR
experiments were carried out using trimethylsilane as the internal standard, the 11B NMR spectra
Page 12 of 22

13
were recorded using BF3OEt2 (0 ppm) as the external standard, and the 19F NMR spectra were
recorded with CFCl3 (C6F6 was used as secondary reference, δF –162.9 ppm).
Mass spectra were recorded on a SHIMADZU GCMS-QP2010 Ultra instrument with
electron ionization (EI) of the sample. The absorption spectra in the range 220–800 nm were
recorded on a UV–2600 spectrophotometer (λ = 310 nm) produced by Shimadzu. The
fluorescence spectra were registered using a Varian Cary Eclipse spectrofluorometer (Xenon
lamp), and solutions in acetonitrile were used for spectra recording.
XRD experiments of the compounds 3a and 5a were accomplished on an Xcalibur E
diffractometer with a standard procedure (graphite-monochromated MoKα-irradiation, 295(2) K,
ω-scanning with step 1o). Using Olex2 [25], the structure was solved with the Superflip [26]
structure solution program using Charge Flipping and refined with the ShelXL [27] refinement
package using Least Squares minimization.
The results of X-ray diffraction analysis for compounds 3a and 5a were deposited with the
Cambridge Crystallographic Data Centre (CCDC 1055594 for compound 3a and CCDC
1055600 for compound 5а). These data are free and can be available at www.ccdc.cam.ac.uk.
4.2. Starting 8-hydroxyquinolines
1
2-Methyl-8-hydroxyquinoline 1а, mp. 71-73 °C (lit. 72-73 °C [28]). Н NMR (CDCl3):  2.76
(3H, s, СH3), 7.15 (1Н, d, H-3, J = 8.4), 7.39 (2Н, m, benzo), 7.41 (1Н, m, benzo), 8.06 (1Н, d,
H-4, J = 8.4), 8.4 (1H, br. s, OH).
2-Methyl-6,7-difluoro-8-hydroxyquinoline 1b was obtained from 2-amino-5,6-difluorophenol
1
using our earlier developed method [18], mp. 102-104 °C. Н NMR (CDCl3): 2.74 (3H, s,
3
4
СH3), 5.32 (1Н, br. s, HN+), 7.04 (1Н, dd, H-5, J = 10.6, J = 7.4), 7.33 (1Н, d, H-3, J = 8.4),
19
7.99 (1Н, d, H-4, J = 8.4). F{1H} NMR spectra (CDCl3): -158.84 (d, F-7, J = 19.8), -134.60
(d, F-6, J = 19.8).
Page 13 of 22

14
4.3. Synthesis of 2-methyl-8-hydroxyquinolinatoboron difluoride (2а).
To a solution of 2-methyl-8-hydroxyquinoline 1a (0.318 g, 2 mmol) in benzene (6 mL)
triethylamine (0.52 mL, 3.7 mmol) and boron trifluoride etherate (0.64 mL, 5.2 mmol) were
added. Reaction mixture was stirred at 50 0С during 2 h, then solvent was evaporated and residue
0
1
was washed with hexane. Yield of the complex 2a is 0.34 g (82%), mp. 66-68 С. Н NMR
(CDCl3):  2.74 (3Н, s, CH3), 7.15 (1Н, m), 7.30 (2Н, m), 7.40 (1Н, m), 8.04 (1Н, d, Н-4, J =
11
8.4). 19F NMR (CDCl3): 155.72 m. B NMR (CDCl3): 1.01 m. MS (m/z, Irel %): 207 [M]+
(100), 206 (29), 188 (15), 187 (87), 186 (25), 159 (40), 140 (22), 131 (46), 130 (34), 115 (10),
114 (15), 103 (25), 102 (12), 101 (14), 89 (18), 86 (46), 77 (25), 76 (10), 63 (24), 58 (16), 50
(20), 49 (11), 48 (28), 38 (17). Anal. Calc. for С10H8BF2NO, C 58.03; H 3.90; N 6.77. Found: С
57.97; H 3.86; N 6.81.
4.4. 2-Methyl-6,7-difluoro-8-hydroxyquinolinatoboron difluoride (2b)
0
1
Synthesis was acomplished by the similar method. Yield 74%, mp. > 300 C. H NMR
(CDCl3): 2.74 (3Н, s, CH3), 7.16 (1Н, dd, H-5, 3J = 10.8, 4J = 7.8), 7.60 (1Н, d, H-3, J = 8.4),
19
8.42 (1Н, d, H-4, J = 8.4). F NMR (CDCl3): 126.46 (1F, m), -143.74 (2F, m), -153.29 (1F,
m). MS (m/z, Irel %): 243 [M]+ (100), 242 (30), 224 (19), 223 (80), 222 (24), 150 (12), 121 (13),
120 (12), 119 (13), 109 (11), 104 (13), 101 (12), 99 (12), 85 (14), 80 (12), 74 (15), 73 (10), 50
(15), 49 (13), 48 (91), 47 (12), 38 (12). Anal. Calc. for C10H6BF4NO, C 49.43; H 2.49; N 5.76.
Found: С 49.38; H 2.45; N 5.80.
4.5. Synthesis of 2-methyl-8-hydroxyquinoline BPh2 complex (3а).
To a solution of quinoline 1а (79 mg, 0.5 mmol) in tetrahydrofuran (38 mL) 0.25М
solution of triphenylborane in THF (2 mL, 0.5 mmol) was added dropwise, reaction mixture was
refluxed for 12 h, solvent was evaporated and residue was washed with hexane. Yield of the
complex 3a is 0.147 g (91%), mp. 171-173 0C. 1H NMR (CDCl3): 2.56 (3H, s, CH3), 7.12 (1Н,
Page 14 of 22

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m, H-5), 7.23 (1Н, m, H-7), 7.24-7.33 (6H, m, Ph), 7.39 (1Н, d, H-3, J = 8.3), 7.44 (4H, m, Ph),
7.60 (1Н, m, H-6), 8.32 (1H, d, H-4, J = 8.3). 11B NMR (CDCl3): 12.20 m. MS (m/z, Irel %):
323 [M]+ (6), 247 (17), 246 [M-Ph]+ (100), 245 (29), 115 (25). Anal. Calc. for С22H18BNO, C
81.76; H 5.61; N 4.33. Found: С 81.68; H 5.72; N 4.29.
4.6. 2-Methyl-6,7-difluoro-8-hydroxyquinoline BPh2 complex (3b).
0
1
Synthesis was acomplished by similar method. Yield 92%, mp. 206-208 C. H NMR
(CDCl3): 3.56 (3Н, s, CH3), 7.01 (1Н, m, Н-5), 7.29 (6H, m, Ph), 7.40 (4H, m, Ph), 7.42 (1Н,
d, Н-3, J = 8.4), 8.28 (1Н, d, Н-4, J = 8.4). 19F NMR {1H} (CDCl3): -157.88 (1F, d, F-7, J =
18.5), -128.46 (1F, d, F-6, J = 18.5). 11B NMR (CDCl3): 13.34 m. MS (m/z, Irel, %): 359 [M]+
(4), 283 (19), 282 [M-Ph]+ (100), 281 (28), 107 (13). Anal. Calc. for С22H16BF2NO, C 73.57; H
4.49; N 3.90. Found: С 73.50; H 4.56; N 3.85.
4.7. (E)-2-[2-(4-methoxyphenyl)vinyl]-8-hydroxyquinoline BPh2 complex (5а).
0
1
Synthesis was acomplished by similar method. Yield 86%, mp. 308-310 C. H NMR
(CDCl3): 3.81 (3Н, s, MeО), 6.83 (2Н, d, Н-3’, Н-5’, J = 8.5), 7.08 (1Н, m, Н-5), 7.21 (1Н, m,
Н-7), 7.28 (2Н, d, Н-2’, Н-6’, J = 8.5), 7.31 (6H, m, Ph), 7.35 (1Н, d, СН=, J = 16.0), 7.44 (4H,
m, Ph), 7.46 (1Н, d, СН=, J = 16.0), 7.53 (1Н, m, Н-6), 7.89 (1Н, d, Н-3, J = 8.7), 8.26 (1Н, d,
Н-4, J = 8.7). 11B NMR (CDCl3): 11.91 m. MS (m/z, Irel %): 441 [M]+ (3), 365 (27), 364 [M-
Ph]+ (100), 363 (25), 244 (12), 243 (14). Anal. Calc. for С30H24BNO2, C 81.65; H 5.48; N 3.17.
Found: С 81.58; H 5.56; N 3.12.
4.7. (E)-2-[2-(4-methoxyphenyl)vinyl]-6,7-difluoro-8-hydroxyquinoline BPh2 complex
(5b).
Synthesis was acomplished by the similar method. Yield 86%, mp. 311-313 0C. 1H NMR
(CDCl3): 3.85 (3Н, s, MeО), 6.87 (2Н, d, Н-3’, Н-5’, J = 8.5), 6.96 (1Н, m, Н-5), 7.21 (2Н, d,
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Н-2’, Н-6’, J = 8.5), 7.27 (1Н, d, СН=, J = 16.0), 7.28 (6H, m, Ph), 7.30 (4H, m, Ph), 7.48 (1Н,
d, СН=, J = 16.0), 7.93 (1Н, d, Н-3, J = 8.7), 8.24 (1Н, d, Н-4, J = 8.7). 19F NMR {1H} (CDCl3):
-158.36 (F-7, d, J = 18.5), -128.84 (F-6, d, J = 18.5). MS (m/z, Irel %): 477 [M]+ (3), 401 (26),
400 [M-Ph]+ (100), 399 (25), 322 (13), 280 (11), 279 (15). Anal. Calc. for С30H22BF2NO2, C
75.49; H 4.65; N 2.93. Found, %: С 75.43; H 4.73; N 2.89.
4.8. Starting quinazolinones
2-(2-Hydroxyphenyl)-3Н-quinazolin-4-one 7а. Compound was obtained using method
1
described [29], mp. 272-274 0C. H NMR (DMSO-d6): 6.94 (2Н, m), 7.41 (1Н, m), 7.51 (1Н,
m), 7.71 (1Н, m), 7.83 (1Н, m), 8.17 (1Н, m), 8.24 (1Н, m), 12.5 (1H, br.s, OH), 13.9 (1H, br. s,
NH).
2-(2-Hydroxy-3,5-di(t-butyl)phenyl)-3Н-quinazolin-4-one 7b. To a solution of 2-
aminobenzaide (0.7 g, 5.1 mmol) in ethanol (12.5 mL) 3,5-di(t-butyl)salicilic aldehyde (1.193 g,
5.1 mmol) was added, reaction mixture was stirred during 5 h, and solvent was evaporated.
Residue was washed with hexane, azomethine 6b was dissolved in ethanol (8 mL), CuCl2 (0.36
g) was added and reaction mixture was refluxed for 1.5 h. After cooling the formed
quinazolinone 7b was filtered and recrystallized from DMSO. Yield 1.41 g (79%), mp. 288-290
1
0С. H NMR (DMSO-d6): 1.33 (9H, s, (CH3)3), 1.44 (9H, s, (CH3)3), 7.36 (1Н, d, H-4’, J =
2.1), 7.48 (1H, m, benzo), 7.69 (1H, m, benzo), 7.80 (1H, m, benzo), 7.97 (1Н, d, H-2’, J = 2.1),
7.69 (1H, m, Н-8), 12.6 (1Н, br. s, ОН), 14.8 (1Н, br. s, NН). Anal. Calc. for С22Н26N2O2, С
75.40; H 7.48; N 7.99. Found: С 75.38; Н 7.45; N 8.03.
4.9. Synthesis of 2-(2-hydroxy-3,5-di(t-butyl)phenyl)-3Н-quinazolin-4-onatoboron
difluoride (8b).
To a suspension of quinazolinone 7b (0.138 g, 0.34 mmol) in toluene (0.51 mL) glacial
0
acidic acid (0.51 mL) was added, mixture was warmed up to 60 С, then boron trifluoride
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etherate (0.22 mL) was added, and mixture was refluxed for 5 min. After cooling Et2O (10 mL)
was added, solvents were evaporated partially (until 1/3 of initial volume), and light-yellow solid
was filtered and washed with hexane. Yield of complex 8b is 0.118 g (87%), mp. 268-270 0С. 1H
NMR (CDCl3): 1.43 (9H, s, (CH3)3), 1.54 (9H, s, (CH3)3), 7.65 (1H, m, benzo), 7.72 (1Н, d, H-
4’, J = 2.0), 7.76 (1Н, d, H-2’, J = 2.0), 7.97 (1H, m, benzo), 8.38 (1H, m, benzo), 8.59 (1H, m,
benzo), 11.4 (1Н, br, s, NН). 19F NMR (CDCl3): -136.01 m. 11B NMR (CDCl3): 1.10 m. MS
(m/z, Irel %): 398 [M]+ (41), 397 (11), 384 (18), 383 (79), 382 (19), 364 (23), 363 (100), 362 (26),
347 (14), 335 (12), 307 (17), 160 (20), 57 (35), 41 (18). Anal. Calc. for С22Н25BF2N2O2, С
66.35; H 6.33; N 7.03. Found: С 66.40; H 6.39; N 6.97.
4.10. 2-(2-Hydroxyphenyl)-3Н-quinazolin-4-onatoboron difluoride (8a).
Synthesis was accomplished by similar method. After reaction completion the mixture
was cooled, the colourless solid was filtered and washed with methanol (6 mL) and Et2O (4 mL).
0
1
Yield 76%, mp. > 300 C. H NMR (CDCl3): 7.17 (1Н, m), 7.29 (1Н, m), 7.34 (1Н, m), 7.68
(2Н, m), 7.96 (1Н, m), 8.39 (1Н, m), 8.59 (1Н, m), 11.1 (1H, br. s, NH). 19F NMR (CDCl3):
150.74 m. MS (m/z, Irel %): 286 [M]+ (13), 266 (30), 265 (16), 238 (17), 237 (11), 148 (10),
139 (21), 130 (12), 119 (38), 113 (19), 102 (78), 92 (56), 91 (34), 90 (100), 99 (16), 87 (12), 77
(13), 76 (39), 75 (37), 74 (17), 65 (20), 64 (67), 63 (85), 62 (26), 52 (12), 51 (17), 50 (23), 49
(34), 48 (26), 38 (60), 37 (23). Anal. Calc. for С14Н9BF2N2O, С 58.79; H 3.17; N 9.79. Found: C
58.84; H 3.21; N 9.73.
4.11. 2-(2-Hydroxyphenyl)-3Н-quinazolin-4-one BPh2 complex (9).
To a solution of quinazolinone 7а (200 mg, 0.84 mmol) in tetrahydrofurane (46 mL)
0.25М solution of triphenylborane in THF (3.4 mL, 0.84 mmol) was added dropwise, reaction
mixture was refluxed during 12 h, solvent was evaporated and residue was washed with hexane.
Yield of complex 9 is 0.28 g (84%), mp. > 300 0C. 1H NMR (CDCl3): 7.04 (1Н, m), 7.15 (1Н,
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m), 7.43-7.48 (2H, m), 7.52-7.56 (4H, m), 7.62 (2H, m), 7.76-7.80 (3H, m), 7.84 (1H, m), 8.28
(3H, m), 8.35 (1Н, m), 10.3 (1H, br. s, NH). 11B NMR (CDCl3): 29.96 m. Anal. Calc. for
С26Н19BN2O2, С 77.63; H 4.76; N 6.96. Found: C 77.70; H 4.82; N 6.93.
Acknowledgments
This work was supported by the Russian Foundation for Basic Research (grant 14-03-00340),
Ural Division of Russian Academy of Sciences (project 15-21-3-7) and the Grants Council of the
President of the Russian Federation (grant NSh-3656.2014.3).
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Novel N,O-bidentate BF2 and BPh2 complexes have been prepared in good to excellent yields
through coordination of 8-hydroxy-2-methylquinolines and 2-(2-hydroxyphenyl)-3Н-quinazolin-
4-ones with boron trifluoride etherate or triphenylborane under mild conditions. All complexes
have been characterized by 1H, 11B and 19F NMR, mass-spectrometry and X-ray crystallography
data. Some complexes have been found to exhibit a significant fluorescence in acetonitrile
solutions. Electronic and site effects of substituents in both heterocyclic and phenol fragments
proved to have a profound impact on quantum yields.
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X
X
X
X
N
F
CH3
N
CH3
O
O
B
B
Ph
F
Ph
X = H, F
O
X
NH
X
N
R
N
B
F
O
B
F
Ph
O
Ph
R
OMe
R = H, t-Bu
Page 22 of 22