Polymethoxyphenyl-substituted [2-(5-chloro-2-hydroxy-4-methylphenyl)-2- phenylvinyl]phosphine oxides: Synthesis and complexation with Eu(TTA) 3

Article abstract of DOI:10.1134/S1070428014040186

New di- and trimethoxyphenyl-substituted phosphorus-containing ligands, (Z)-[2-(5-chloro-2-hydroxy-4-methylphenyl)-2-phenylvinyl]bis(3,4-di- and 3,4,5-trimethoxyphenyl)phosphine oxides, have been synthesized, and their adducts with europium(III) 2-thenoyl

Full text of DOI:10.1134/S1070428014040186

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2014, Vol. 50, No. 4, pp. 547–551. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © R.R. Zairov, D.A. Tatarinov, N.A. Shamsutdinova, A.R. Mustafina, I.Kh. Rizvanov, V.V. Syakaev, V.F. Mironov, A.I. Konovalov, 2014,
published in Zhurnal Organicheskoi Khimii, 2014, Vol. 50, No. 4, pp. 558–562.
Polymethoxyphenyl-Substituted [2-(5-Chloro-2-hydroxy-
4-methylphenyl)-2-phenylvinyl]phosphine Oxides:
Synthesis and Complexation with Eu(TTA)3
R. R. Zairov, D. A. Tatarinov, N. A. Shamsutdinova, A. R. Mustafina, I. Kh. Rizvanov,
V. V. Syakaev, V. F. Mironov, and A. I. Konovalov
Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences,
ul. Arbuzova 8, Kazan, 420088 Tatarstan, Russia
e-mail: rustem@iopc.ru
Received February 14, 2014
Abstract—New di- and trimethoxyphenyl-substituted phosphorus-containing ligands, (Z)-[2-(5-chloro-2-hy-
droxy-4-methylphenyl)-2-phenylvinyl]bis(3,4-di- and 3,4,5-trimethoxyphenyl)phosphine oxides, have been
synthesized, and their adducts with europium(III) 2-thenoyltrifluoroacetonate have been obtained. High
luminescence intensity of the synthesized complexes suggests prospects in using them for the design of various
materials possessing unique photophysical properties.
DOI: 10.1134/S1070428014040186
The synthesis of new ligands and their coordination
compounds with lanthanide ions, which exhibit
efficient luminescence, constitutes a topical problem in
modern chemistry [1–3]. For instance, β-diketonate
complexes of lanthanides are known as components
of luminescent materials [4–6]. In this connection,
europium(III) 2-thenoyltrifluoroacetonate Eu(TTA)3
attracts much interest due to its unique photophysical
properties which in turn may be improved via forma-
tion of ternary complexes with other ligands. Studies
on mixed-ligand europium(III) complexes based on
europium β-diketonates, including Eu(TTA)3, have
been reported in many publications [7–9]. Introduction
of an additional ligand possessing some chromophoric
properties into the coordination sphere of Eu(III) ion
leads to luminescence sensitization [8, 9]. We previ-
ously described the synthesis of a new ternary complex
of Eu(TTA)3 with (Z)-2-(5-chloro-2-hydroxyphenyl)-2-
phenylethenyl)bis(2-methoxyphenyl)phosphine oxide
(IIa), which showed strong luminescence at λ 612 nm
(5D0→7F2) [10]. It was found that both β-diketonate
and phosphine oxide ligands exert an antenna effect on
the luminescence of europium(III); as a result, the
luminescence intensity of the ternary complex con-
siderably exceeded the luminescence intensity of
Eu(TTA)3. Phosphine oxide IIa ensured more efficient
luminescence sensitization of Eu(III) complexes, as
compared to its analogs with methyl and 2-methyl-
phenyl substituents on the phosphorus atom. There-
fore, a positive effect of electron-donor methoxy group
in the aromatic ring on the phosphorus atom was in-
ferred [10]. Methoxy group is a strong electron donor
toward benzene ring, and introduction of two or three
methoxy group is expected to enhance the donor power
of the aromatic fragment and hence increase the basic-
ity of the phosphoryl group. Taking the above stated
Scheme 1.
O
Me
Cl
O
Me
Cl
OH
P
Cl
P(O)R2
THF
+
RMgX
Ph
Ph
I
IIa–IIc
R = 2-MeOC6H4 (a), 3,4-(MeO)2C6H3 (b), 3,4,5-(MeO)3C6H2 (c).
547

ZAIROV et al.
Eu(TTA)3, and photoluminescence intensity of the
548
3
12
resulting mixed-ligand complexes we have synthesized
both previously described phosphine oxide IIa [10]
and new (Z)-diaryl[2-(5-chloro-2-hydroxy-4-methyl-
phenyl)-2-phenylethenyl]phosphine oxides IIb and
IIc. The reaction of substituted 1,2-benzoxaphos-
phinine I with organomagnesium compounds derived
from 3,4-dimethoxy- and 3,4,5-trimethoxyphenyl
bromides was accompanied by a weak exothermic
effect, and the products were the corresponding phos-
phine oxides IIb and IIc (yield 70–80%; Scheme 1).
The isolation of compounds II by recrystallization
from diethyl ether or acetone took a long time (up
to several days).
10
8
4
2
6
4
2
1
0
580
600
620
640 λ, nm
Fig. 1. Emission spectra of (1) Eu(TTA)3 (c = 2.5× 10–5 M)
and its 1:1 adducts with phosphine oxides (2) IIa, (3) IIb,
and (4) IIc in acetonitrile.
The structure of phosphine oxides II was deter-
mined on the basis of their spectral data. In the
1H NMR spectra of II, the signal from the methyl
group in the hydroxyphenyl substituent appeared in
a strong field (δ ~2 ppm), while methoxy protons
resonated in a weaker field (δ ~4 ppm). Phosphine
oxide IIc displayed two signals from the three me-
thoxy groups with an intensity ratio of 2:1. The most
upfield signals in the aromatic region were those
belonging to protons in the ortho position to the
phenolic hydroxy group (δ ~6.0–6.5 ppm). The proton
into account, it seems reasonable to synthesize new di-
and trimethoxyphenyl-substituted phosphine ligands
and their complexes with europium(III) 2-thenoyltri-
fluoroacetonate.
With a view to get a deeper insight into the rela-
tions between the structure of phosphorus-containing
ligand, peculiar features of its complexation with
2
3
(a)
F
8
1
6
4
5
7
S
F
F
O
O
3
2
1
6′
3′
1′
2′
(b)
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
δ, ppm
Fig. 2. 1H NMR spectrum of Eu(TTA)3 (1 mM, CD3CN, 600 MHz, 303 K) (a) before and (b) after addition of an equimolar amount
of phosphine oxide IIb. Primed locants refer to the free ligand.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 4 2014

POLYMETHOXYPHENYL-SUBSTITUTED [2-(5-CHLORO-2-HYDROXY-...
1037.2
549
(a)
1.25
1.00
0.75
0.50
0.25
0.00
876.5
1319.1
1300
850
900
950
1000
1050
1100
1150
1200
1250
m/z
(b)
1037.1
1.5
1.0
0.5
0.0
1379.1
876.5
900
930.2
1220.1 1271.1
1200 1300
1000
1100
1400
m/z
(c)
1037.1
890.2
3
2
1
0
1439.2
1280.2
919.1
989.1
770.5
800
900
1000
1100
1200
1300
1400
m/z
Fig. 3. ESI mass spectra of Eu(TTA)3 complexes with phosphine oxides (a) IIa, (b) IIb, and (c) IIc (propan-2-ol, c = 40 μg/mL).
located in the ortho position with respect to the phos-
phorus atom and methoxy group in IIb gave rise to
a doublet of doublets at δ 6.86 ppm with the coupling
constants 3JPH = 7.8 and 4JHH = 3.0 Hz.
As follows from Fig. 1, the sensitizing effect of
phosphine oxide ligands in acetonitrile solution in-
creases in going from monomethoxy- to dimethoxy-
phenyl-substituted derivatives. Surprisingly, the emis-
sion intensity of the trimethoxyphenyl-substituted
Eu(TTA)3 derivative was lower than that of its mono-
methoxy analog. A probable reason is partial rupture of
conjugation in the phosphine oxide antenna ligand due
to steric repulsion of the substituted benzene rings on
the phosphorus atom.
The complexation of Eu(TTA)3 with methoxy-
phenylphosphine oxides IIa–IIc was studied in aceto-
nitrile and isopropyl alcohol. These solvents were
selected with account taken of the solubility of the
initial components and resulting complexes. Addition
of phosphine oxides IIa–IIc to a solution of Eu(TTA)3
increased the luminescence intensity, indicating forma-
tion of the corresponding mixed-ligand complexes.
Figure 2 shows that the formation of mixed-ligand
complex with phosphine oxide IIb is accompanied by
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 4 2014

ZAIROV et al.
550
500
400
300
200
100
0
1439.1
1437.1
1457.9
1420
1430
1440
1450
1460
m/z
Fig. 4. Isotope distribution in the ESI mass spectrum of Eu(TTA)3 ·IIc (isopropyl alcohol, c = 40 μg/mL); m/z (Irel, %): 1439.05
(100), 1437.05 (75.3), 1440.05 (70.4), 1438.05 (47.2), 1441.04 (41.3), 1439.04 (34.3), 1442.05 (27.4), 1441.05 (27.3), 1443.05 (9.2),
1440.04 (7.0), 1443.04 (5.0), 1442.06 (3.4), 1442.04 (3.2), 1440.06 (2.9), 1444.04 (2.7), 1444.05 (2.5), 1438.04 (1.8), 1443.06 (1.2),
1441.06 (1.1), 1445.05 (1.0).
a downfield shift of proton signals of TTA coordinated
to Eu(III), whereas signals from the 1′-H–6′-H protons
of the free ligand do not change their position. Broad-
ening of signals of the aromatic protons of phosphine
oxide IIb reflects the effect of paramagnetic euro-
pium(III) ion, which may also be regarded as an evi-
dence of the formation of mixed-ligand complex.
trometer at 400 and 162.0 MHz, respectively, using
1
CDCl3 as solvent and reference (for H); the 31P
chemical shifts were determined relative to H3PO4 as
1
external reference. The H NMR spectra of the
Eu(TTA)3 complexes with phosphine oxides II were
measured at 303 K on a Bruker Avance-600 instrument
from solutions in CD3CN; the chemical shifts were
determined relative to the residual proton signal of the
solvent. The IR spectra were obtained on a Bruker
Vector-22 spectrometer from samples dispersed in
mineral oil or films placed between KBr plates. The
mass spectra (electrospray ionization, ESI) were
recorded on a Bruker Daltonics AmazonX mass spec-
trometer with positive and negative ion detection in the
a.m.u. range from 500 to 1500 (capillary voltage
±4500 V; nebulizer gas nitrogen, 220°C, flow rate
10 L/min); samples were introduced as solutions in
isopropyl alcohol at a concentration c of 40 μg/mL; the
data were processed using DataAnalysis 4.0 program
(Bruker).
The mass spectra of the complexes (Figs. 3, 4) are
in agreement with the luminescence spectroscopy and
1H NMR data. All the examined compounds displayed
[M – H]– ions (negative ion detection mode) with m/z
values of 1319.1, 1379.1, and 1439.1 for Eu(TTA)3·
IIa, Eu(TTA)3 ·IIb, and Eu(TTA)3 ·IIc, respectively.
The ion peak intensity grows in the series IIa < IIb <
IIc, which may be due to stabilization of the corre-
sponding complexes. In addition, the mass spectra of
all complexes contained a ion peak with m/z 1037.2,
which originates from the negative [Eu(TTA)4]– ion. In
all cases, the experimental isotope peak distribution
was identical to the theoretical one (hereinafter, peaks
with a relative intensity lower than 10% are omitted),
m/z (Irel, %): Eu(TTA)3 ·IIa: 1319.1 (100), 1317.1
(65.5), 1320.1 (54.6), 1318.1 (54.6), 1321.1 (51.0),
1322.1 (25.5); Eu(TTA)3 ·IIb: 1379.1 (100), 1377.2
(63), 1380.1 (61.9), 1381.1 (59.5), 1378.1 (40.2),
1382.1 (28.4), 1383.1 (12.6); Eu(TTA)3 ·IIb: 1439.2
(100), 1437.2 (67.6), 1441.1 (63.6), 1440.2 (59.4),
1438.2 (36.4), 1442.1 (31.8), 1443.1 (13.5). Europium
occurs as two abundant isotopes with atomic weights
of 152 and 154; therefore, europium-containing ion
peaks are easily interpretable.
Diaryl[2-(5-chloro-2-hydroxy-4-methylphenyl)-
2-phenylethenyl]phosphine oxides IIa–IIc were syn-
thesized according to a modified procedure [11, 12].
A solution of 3 mmol of 2,6-dichloro-7-methyl-4-
phenyl-2H-1,2λ5-benzoxaphosphinine 2-oxide (I) in
4 mL of benzene was added dropwise to the Grignard
reagent prepared from 0.192 g (8 mmol) of magnesium
turnings and 8 mmol of the corresponding halobenzene
in 10 mL of THF. The mixture was heated for 0.5 h
under reflux and evaporated under reduced pressure on
a rotary evaporator, and the residue was cooled to
room temperature, treated with water and 4 mL of
20% H2SO4, and extracted with methylene chloride.
The organic layer was separated and evaporated on
a rotary evaporator, the residue was washed with di-
EXPERIMENTAL
1
The H and 31P–{1H} NMR spectra of phosphine
oxides II were recorded on a Bruker Avance-400 spec-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 4 2014

POLYMETHOXYPHENYL-SUBSTITUTED [2-(5-CHLORO-2-HYDROXY-...
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3
6.45 s (1H, 8-H), 6.89 d (4H, 14-H, 18-H, JPH
=
=
2
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