Lanthanide complexes based on ethyl 2-hydroxymethylidene-3-oxobutanoate

Article abstract of DOI:10.1016/j.mencom.2016.01.021

The reaction of europium(iii) or terbium(iii) chlorides with ethyl 2-hydroxymethylidene-3-oxobutanoate in the presence of 2,2'-bipyridine (2,2'-bipy) resulted in the luminescent complexes [LnL₃]·2,2'-bipy (L = ethyl 2-hydroxymethylidene-3-oxobutanoate, Ln = Tbⁱⁱⁱ or Euⁱⁱⁱ), whose molecular structure has been determined by X-ray analysis.

Full text of DOI:10.1016/j.mencom.2016.01.021

Mendeleev
Communications
Mendeleev Commun., 2016, 26, 54–56
Lanthanide complexes based on ethyl 2-hydroxymethylidene-3-oxobutanoate
Yulia S. Kudyakova,* Denis N. Bazhin, Yanina V. Burgart and Victor I. Saloutin
I. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences,
6
20990 Ekaterinburg, Russian Federation. Fax: +7 343 374 5954; e-mail: kud@ios.uran.ru
DOI: 10.1016/j.mencom.2016.01.021
The reaction of europium(iii) or terbium(iii) chlorides with ethyl 2-hydroxymethylidene-3-oxobutanoate in the presence of
,2'-bipyridine (2,2'-bipy) resulted in the luminescent complexes [LnL ]·2,2'-bipy (L = ethyl 2-hydroxymethylidene-3-oxobutanoate,
2
3
iii
iii
Ln = Tb or Eu ), whose molecular structure has been determined by X-ray analysis.
The synthesis of new trivalent rare earth complexes is of great
interest due to their wide applications in medicine and materials
H
O
OEt
OEt i or ii
O
O
H
O
H
O
1
–3
Me
OEt
science. The substituents of ligands influence the properties
O
4
–7
of metal complexes. The use of b-diketones in complexation
O
Me
O
Me OEt
with rare earth metal ions is an efficient approach to metal com-
8,9
1
E-2
Z-2
plexes possessing very bright luminescence. However, organic
ligands based on 2-substituted 1,3-dicarbonyl compounds are
less examined.
Scheme 1 Reagents and conditions: i, H O, room temperature; ii, 1% aqueous
NaOH, room temperature.
2
Here we studied ethyl 2-(hydroxymethylidene)-3-oxobutanoate
with different substituents in carbonyl fragments as a ligand for
the preparation of the luminescent complexes of europium(iii)
and terbium(iii).
without catalysts. Desired product 2 was isolated by vacuum
distillation in 68% yield. The use of a 1% aqueous solution of
NaOH in this process decreased the yield of compound 2 to 54%
because of formation of ethyl acetoacetate as a by-product.
Tricarbonyl-substituted derivatives can be synthesized from
b-dicarbonyl compounds by (i) acylation with acyl halides under
Published data on the structure of compound 2 are contra-
1
0–12
15–17
basic conditions
or (ii) condensation with triethyl ortho-
dictory.
For example, the product of hydrolysis of methyl
formate with the subsequent hydrolysis.13 To obtain target non-
2-methoxymethylidene-3-oxobutanoate was described as an
aldehyde. Hydroxy tautomer 2 was reported to exist as a mix-
16
1
5
symmetric tricarbonyl compound 2, 2-ethoxymethylidene-3-oxo-
1
4
butanoate 1 was initially synthesized by a known procedure
ture of two tautomers, whereas only one hydroxy derivative was
1
7
in 83–87% yield via the condensation of ethyl acetoacetate with
triethyl orthoformate in the presence of acetic anhydride. The
following hydrolysis of an ethoxy substituent in ester 1 afforded
described more recently. Based on spectral data, the enol form
†
of product 2 was confirmed. Thus, there is one high-frequency
–
1
absorption band of the ethoxycarbonyl group (1719 cm ) in the IR
†
ethyl 2-hydroxymethylidene-3-oxobutanoate 2 (Scheme 1). Pre-
spectrum of ester 2 and a low-field OH group signal (17.09 ppm)
1
viously, the hydrolysis of ethoxymethylidene group proceeding
through the copper(ii) salt formation was reported.1 In this work,
the direct hydrolysis was performed in water at room temperature
in the H NMR spectrum. Regardless of the solvent used, enol 2
5
mainly exists in E-form (90%).
Although ethyl 2-hydroxymethylidene-3-oxobutanoate 2 is an
O,O,O-tridentate ligand, there was no data on its metal com-
plexes so far. We showed that the reaction of compound 2 with
†
All commercially available reagents and solvents were used without
‡
additional purification.
lanthanide chlorides (TbCl and EuCl ) gave complexes 3a,b
3
3
The H and 13C NMR spectra were recorded on a Bruker DRX-400
1
(Scheme 2). To fulfill the coordination number of a lanthanide
spectrometer (400 MHz) in CDCl . The IR spectra were obtained on
3
–1
a Perkin-Elmer Spectrum One spectrometer (FT-IR) (400–4000 cm ).
Elemental analysis was performed using a Perkin-Elmer PE 2400 (series II
CHNS-O EA 1108) analyzer. Melting points were measured on a Stuart
Yield of 2, 5.38 g (68%) (A), 4.27 g (54%) (B), bp 75–76°C (10 Torr).
–1
IR (KBr, n/cm ): 2985, 2938 (C–H), 1719 (br., C=O), 1636 (C=C), 1265,
1
1
078 (C–O). H NMR, d: 9.19 (d, 1H, CH, J 6.1 Hz), 17.09 (d, 1H,
SMP3 apparatus in open capillaries. The luminescence spectra were recorde
d
OH, J 6.1 Hz); E (90%): 1.33 (t, 3H, OCH Me, J 7.1 Hz), 2.56 (s, 3H,
2
on a Varian Cary Eclipse spectrofluorimeter within 286–800 nm
wavelength range with selective luminescence excitation at lexc = 281 (for
Me), 4.26 (q, 2H, OCH Me, J 7.1 Hz); Z (10%): 1.39 (t, 3H, OCH Me,
2
2
13
J 7.1 Hz), 2.53 (s, 3H, Me), 4.39 (q, 2H, OCH Me, J 7.1 Hz). C NMR,
2
3
a) and 276 nm (for 3b). Reactions were monitored by TLC with 0.20
d: E: 14.23 (CH ), 26.28 (MeCH ), 60.30 (MeCO), 107.92 (C=COH),
2
2
mm Alugram Sil G/UV254 pre-coated silica gel plates (60 F254).
Synthesis of ethyl 2-hydroxymethylidene-3-oxobutanoate 2.
Method A. A solution of compound 1 (9.31 g, 0.05 mol) in water (100 ml)
was stirred at room temperature for 1 h. Then, the mixture was extracted
165.03 (CO Et), 187.32 (CHOH), 199.49 (MeCO). Found (%): C, 52.98;
2
H, 6.37. Calc. for C H O (%): C, 53.16; H, 6.28.
7
10
4
‡
Lanthanide complexes 3 (general procedure). Compound 2 (1.58 g,
0 mmol) and 2,2'-bipyridine (0.47 g, 3 mmol) were added to a solution
1
with Et O (2×30 ml). The organic layer was washed with water (3×20 ml)
of NaOH (0.40 g, 10 mmol) in ethanol (50 ml). The resulting mixture was
stirred at room temperature for 15 min. Then, the previously prepared
solution of TbCl or EuCl (3 mmol) in water (5 ml) was added dropwise
2
and dried over MgSO for 4 h. The distillation of a crude residue in vacuo
4
gave target compound 2 as colorless oil.
3
3
Method B. A solution of ethyl 2-ethoxymethylidene-3-oxobutanoate 1
and the reaction mixture was stirred at room temperature. After 5 h,
(
9.31 g, 0.05 mol) in 1% aqueous NaOH (200 ml) was stirred at room
a precipitate was filtered. After filtrate evaporation, Et O (10 ml) was
2
temperature for 1 h. Then, the reaction mixture was treated with a 10%
added to the crude residue with the formation of a solid. The precipitate
aqueous solution of HCl to reach pH 6 and extracted with Et O (2×30 ml).
was filtered and crystallized from hexane–Et O (3:1) mixture to give
2
2
The product was isolated as described in method A.
complexes 3a,b as white solids.
©
2016 Mendeleev Communications. Published by ELSEVIER B.V.
–
54 –
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.

Mendeleev Commun., 2016, 26, 54–56
5
7
D
4
® F
5
1
00
OH
OEt
EtO
O
O
O
N
N
LnCl3·3H2O
,2'-bipy
2
Ln
80
60
Me
NaOH, EtOH,
room temperature
Me
O
O
3
2
5
7
3
a,b (88–92%)
4 6
D ® F
4
0
a Ln = Tb
b Ln = Eu
5
7
D
4
® F
4
20
5
7
4 3
D ® F
0
4
Scheme 2
00 450 500 550 600 650 700
l/nm
ion, 2,2'-bipyridine (2,2'-bipy) was used as a co-ligand.
iii
iii
Coordination compounds of Tb and Eu exhibit strong ionic
fluorescence due to efficient energy transfer from a triplet state
Figure 2 Photoluminescence spectrum of terbium(iii) complex 3a in
ethanol.
1
8
of the organic ligand to the resonance level of a lanthanide ion.
For this reason, the luminescence spectrum of a substance is
mostly determined by the complexing ion.
5
7
0 2
D ® F
2
40
The structure of complex 3a was refined by XRD analysis
§
200
160
(
Figure 1). The complex formation occurs through the coor-
iii
dination of a Tb ion with three ligands and one 2,2'-bipy mole-
iii
cule. The central Tb cation is bonded with the oxygen atoms of
1
20
80
hydroxyl and acyl groups and its coordination sphere is saturated
through coordination with the nitrogen atoms of 2,2'-bipy. The
complex has a trigonal prismatic geometry.
5
7
0 1
D ® F
4
0 5
5
7
7
5
7
0 4
D ® F
D
0
® F
0
0 3
D ® F
C(24)
0
5
50
600
650
l/nm
700
750
C(31)
C(23)
C(30)
O(7)
O(8)
O(12)
O(11)
C(25)
Figure 3 Photoluminescence spectrum of europium(iii) complex 3b in
ethanol.
C(19)
C(20)
C(26)
C(28)
C(18)
C(22)
C(27)
O(5)
O(3)
C(29)
C(21)
C(17)
C(16)
Under photoexcitation, complexes 3a,b have luminescence
characteristic of terbium and europium (green and red, respec-
tively). The luminescence spectrum of 3a (Figure 2) contained
O(6)
O(2)
O(4)
C(10)
O(9)
C(12)
Tb(1)
C(13)
C(9)
C(6)
C(8)
N(2)
N(1)
O(1)
C(11)
O(1)
C(14)
C(15)
5
7
C(1)
C(5)
C(2)
characteristic luminescence bands corresponding to the D ® F
4 j
C(7)
C(4)
iii
(j = 6, 5, 4, 3) electron transitions of Tb at 490, 546, 583 and
21 nm, respectively; the D ® F transition of Tb at 546 nm
C(3)
5
7
iii
6
4 5
was the strongest. In the fluorescence emission spectrum of
Figure 1 ORTEP view of complex 3a (thermal ellipsoids at a 50% probability
at 295 K).
europium complex 3b (Figure 3), five emission peaks were
5
7
observed, which were attributed to the D ® F (j = 0, 1, 2, 3, 4)
0
j
Terbium(iii) (2,2'-bipyridine)-tris(ethyl-2-hydroxymethylidene-3-oxo-
transitions at 580, 592, 612, 654 and 705 nm, respectively; the
–
1
butanoate) 3a. Yield, 2.08 g (88%), mp 135–136°C. IR (DRA, n/cm ):
060, 2984 (C–H), 1700 (br.), 1639 (C=O), 1604 (C=C). Found (%):
C, 47.34; H, 4.45; N, 3.50. Calc. for C H N O Tb (%): C, 47.34;
iii
5
7
strongest transition of Eu was the D ® F at 612 nm.
0
2
3
In summary, we synthesized luminescent europium(iii) and
terbium(iii) complexes based on an O,O,O-tridentate ligand, ethyl
31
35
2
12
H, 4.49; N, 3.56.
Europium(iii) (2,2'-bipyridine)-tris(ethyl-2-hydroxymethylidene-3-oxo-
2
-hydroxymethylidene-3-oxobutanoate. The regiospecific coor-
–1
dination of the lanthanide ion to the oxygen atoms of a 1,3-di-
carbonyl moiety was demonstrated.
butanoate) 3b. Yield, 2.15 g (92%), mp 106–107°C. IR (NPVO, n/cm ):
061, 2984 (C–H), 1699, 1635 (C=O), 1608 (C=C). Found (%): C, 47.85;
3
H, 4.48; N, 3.60. Calc. for C H N O Eu (%): C, 47.76; H, 4.53; N, 3.59.
3
1
35
2
12
§
Crystallographic data for 3a. The single crystal (colorless prism,
.20×0.14×0.07 mm) of complex 3a (C H N O Tb) was used for
This work was supported by the Presidium of the Ural Branch
of the Russian Academy of Sciences (project no. 15-21-3-7) and
the State Program for Supporting of Leading Scientific Schools
of the Russian Federation (grant no. NSh-8922.2016.3).
0
31
35
2
12
X-ray analysis at 295(2) K on an Xcalibur 3 diffractometer using graphite
monochromated MoKa radiation (l = 0.71073 Å) and a CCD detector.
–
Crystal is triclinic, space group P1 with a = 11.5924(7), b = 11.7977(5)
and c = 13.1915(9) Å, a = 93.542(5)°, b = 102.551(6)°, g = 106.352(5)°,
3
V = 1675.15(17) Å , Z = 2. On the angles 2.84 < q < 30.51° 19043 reflec-
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