Synthesis and structures of boron complexes of acyl hydroxy coumarins

Article abstract of DOI:10.1007/s11172-006-0553-z

New boron chelates were synthesized by the reactions of 3-acetyl-4-hydroxycoumarin and 8-acyl-7-hydroxy-4-methylcoumarins with boron trifluoride etherate and hydroxybenzodioxaborole. The structure of 3-acetyl-4-difluoroboryloxycoumarin containing an intramolecular C=O...B coordination bond was established by X-ray diffraction.

Full text of DOI:10.1007/s11172-006-0553-z

Russian Chemical Bulletin, International Edition, Vol. 55, No. 11, pp. 2091—2094, November, 2006
2091
Synthesis and structures of boron complexes of acyl hydroxy coumarins
a
a
b
b
aꢀ
A. V. Manaev, T. A. Chibisova, K. A. Lyssenko, M. Yu. Antipin, and V. F. Traven´
aD. I. Mendeleev Russian University of Chemical Technology,
3
pl. Miusskaya, 125047 Moscow, Russian Federation.
Fax: +7 (495) 609 2964. Eꢀmail: traven@muctr.edu.ru
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
8 ul. Vavilova, 119991 Moscow, Russian Federation
b
2
New boron chelates were synthesized by the reactions of 3ꢀacetylꢀ4ꢀhydroxycoumarin and
ꢀacylꢀ7ꢀhydroxyꢀ4ꢀmethylcoumarins with boron trifluoride etherate and hydroxybenzoꢀ
8
dioxaborole. The structure of 3ꢀacetylꢀ4ꢀdifluoroboryloxycoumarin containing an intramoꢀ
lecular C=O...B coordination bond was established by Xꢀray diffraction.
Key words: coumarins, boron complexes, chelates, Xꢀray diffraction analysis.
Complexes of βꢀhydroxyenones with boron comꢀ
pounds are characterized by high reactivity, in particular,
high mobility of the αꢀprotons of the acyl group. For
example, the methyl group in boron complexes of substiꢀ
tuted oꢀhydroxyacetophenones, benzoylacetone, and
acetylnaphthols is readily involved in condensation with
carbonyl compounds and their derivatives, in particular,
with acetals and anils. The reactions with DMF produce
Scheme 1
1
dimethylaminovinyl derivatives, whereas the reactions
2
with aldehydes afford substituted vinyl derivatives. The
aboveꢀmentioned boron complexes react also with trialkyl
orthoformates, 1,1,3,3ꢀtetraethoxypropane, and glutaconꢀ
aldehyde dianil to give symmetrical polymethine dyes
3
showing intense fluorescence. The reactions of boron
complexes of benzoylacetone and oꢀhydroxyacetopheꢀ
nones with phenylformamidine in acetic anhydride proꢀ
duce hemicyanine dyes. The latter readily react with meꢀ
thyleneꢀactive compounds to form unsymmetrical
polymethine dyes, which are also characterized by inꢀ
tense fluorescence.
4
Earlier, we have observed high reactivity of acyl hydrꢀ
oxy coumarin complexes with boron trifluoride in conꢀ
densation reactions. In the present study, the synthesis
conditions and the structural features of this type of boron
complexes were examined in detail.
Results and Discussion
The reactions of 3ꢀacetylꢀ4ꢀhydroxycoumarin (1),
ꢀacetylꢀ7ꢀhydroxyꢀ4ꢀmethylcoumarin (2), and 7ꢀhydrꢀ
oxyꢀ4ꢀmethylꢀ8ꢀpropionylcoumarin (3) with boron triꢀ
R = Me (2, 7a), Et (3, 7b)
Reagents and conditions: i. BF •OEt . ii. 1) Na CO , EtOH,
8
3
2
2
3
fluoride etherate or 2ꢀhydroxyꢀ1,3,2ꢀbenzodioxaborole
H O; 2) HCl.
2
5
(
4) produced boron complexes 5—7 (Scheme 1).
Difluoroboryl derivatives 5 and 7a,b were synthesized
boron trifluoride etherate. Catecholborane derivative 6
was synthesized by the reaction of compounds 1 and 4.
by refluxing benzene solutions of compounds 1—3 with
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2012—2015, November, 2006.
066ꢀ5285/06/5511ꢀ2091 © 2006 Springer Science+Business Media, Inc.
1

2092
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006
Manaev et al.
Compound 4 was prepared in situ by refluxing pyroꢀ
catechol with boric acid in benzene with azeotropic disꢀ
tillation of water and then used without additional purifiꢀ
cation.
pound can be used in different condensation reactions
and for the synthesis of new 3ꢀsubstituted 4ꢀhydroxyꢀ
coumarins.
It was of interest to study the electronic and threeꢀ
dimensional structure of compound 5 and compare its
structure with the data obtained earlier for 3ꢀacetylꢀ4ꢀ
The structures of the boron complexes were estabꢀ
1
11
1
lished by H and B NMR spectroscopy. In the H NMR
spectra of the chelates, the signals for the protons of the
methyl group of the acetyl fragment are shifted downfield
compared to the signals of the starting acetylhydroxyꢀ
coumarins due to a lower electron density on the carbonyl
7
,8
hydroxycoumarin (1).
Xꢀray diffraction study demonstrated that complexꢀ
ation of compound 1 with BF leads to a pronounced
3
change in the molecular geometry and the bond lengths
in the O—C=C—C(O)Me fragment (Fig. 1). Earlier, it
1
oxygen atom. The H NMR spectrum of compound 6
7
,8
shows a singlet for four protons at δ 6.84 corresponding to
the pyrocatechol moiety.
The 11B NMR spectra of compounds 5 and 6 show
signals at δ 0.228 and 14.488, respectively, belonging to
the fourꢀcoordinate boron atom.
has been demonstrated that molecule 1 in the crystal is
planar, and the acetyl group С(11)С(10)O(3) is rotated
relative to the 4ꢀhydroxycoumarin fragment by 6.2°. In
compound 5, the corresponding angle is 9.7°. Unlike the
planar Hꢀbonded ring in coumarin 1, the sixꢀmembered
boronꢀcontaining ring in complex 5 adopts a sofa conforꢀ
mation with the boron atom deviating from the plane
through the O(3), O(4), С(10), С(8), and С(7) atoms
by 0.375 Å. The bond lengths in the sixꢀmembered boꢀ
ronꢀcontaining heterocycle are indicative of the presence
of conjugation in the O—C=C—C=O fragment (Table 1).
The observed equalization of the С—С and С—O bonds
is due to formation of the donorꢀacceptor B...O bond and
a high extent of π delocalization. The С(10)—O(3),
C(7)—O(4) and С(10)—С(8), С(7)—С(8) bonds in molꢀ
ecule 5 (1.287(2), 1.297(2) and 1.412(2), 1.395(2) Å, reꢀ
spectively) are more equalized compared to the analogous
The mass spectra of all the compounds under study
have molecular ions with an intensity of 100%.
The IR spectrum of compound 5 shows an intense
stretching band of the carbonyl group of lactone at
1
740 cm–1. This band remains virtually unchanged upon
–
1
complexation. The band at 1600 cm becomes less inꢀ
tense compared to the analogous band in the spectrum of
the starting 3ꢀacetylꢀ4ꢀhydroxycoumarin (1), in which
this band is more intense and broader than the band of the
lactone carbonyl fragment and is a superposition of two
bands of the conjugated C=C and C=O bonds. The change
in the intensity is associated with the fact that the stretchꢀ
ing band of the carbonyl group in the spectrum of comꢀ
plex 5 is shifted to lower frequencies and is observed at
F(2)
F(1)
1
560 cm–1. A decrease in the frequency of the C=O
B(1)
stretching band of the acetyl group is attributed to its
donorꢀacceptor interaction with the boron atom (cf. lit.
6
–1
data ). In the 1000—1100 cm range, there is an intense
absorption band consisting of two maxima at 1040 and
1
O(4)
C(7)
O(3)
065 cm–1, which can be assigned to C—O—B stretching
vibrations. The stretching band of the B—O=C donorꢀ
acceptor bond is pronounced and observed at 720 cm
C(1)
C(11)
–
1
C(6)
C(10)
C(8)
.
The resulting boron complexes differ in hydrolytic staꢀ
bility. For example, storage of boron complex 6 in air is
accompanied by its gradual decomposition. On the conꢀ
trary, boron complex 5 is not only stable during proꢀ
longed storage but also does not undergo hydrolysis even
on refluxing in water in neutral and acidic media. Hydroꢀ
lysis was successfully performed only in an aqueous alcoꢀ
holic solution of sodium carbonate, and compound 1 was
recovered in quantitative yield. In turn, complexes 7a,b
containing the functional groups in other positions are
unstable to hydrolysis and prolonged storage. Unlike boꢀ
ron complexes of 3ꢀacetylꢀ4ꢀhydroxycoumarin 5 and 6,
complexes of 7ꢀhydroxyꢀ8ꢀacylcoumarins 7a,b are colored
and show fluorescence both in solution and in the solid
state.
C(2)
C(9)
C(5)
C(4)
O(2)
C(3)
O(1)
F(1)
B(1)
F(2)
C(11)
Due to high stability of complex 5 to hydrolysis
and high proton acidity of its methyl group, this comꢀ
Fig. 1. Overall view of compound 5a in two projections.

Coumarinoid boron chelates
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006 2093
Table 1. Selected bond lengths (d) and bond angles (ω) in boron
complex 5 determined by Xꢀray diffraction
Experimental
1
The H NMR spectra were recorded on a Bruker WPꢀ200ꢀSY
Bond
d/Å
Bond
d/Å
instrument in CDCl with Me Si as the internal standard. The
3
4
1
1
B NMR spectra were measured on a Bruker WMꢀ250 instruꢀ
F(1)—B(1)
F(2)—B(1)
B(1)—O(3))
B(1)—O(4)
O(1)—C(5)
O(1)—C(9)
O(2)—C(9)
1.355(2) O(3)—C(10)
1.359(2) O(4)—C(7)
1.503(2) C(6)—C(7)
1.483(2) C(7)—C(8)
1.372(2) C(8)—C(10)
1.376(2) C(8)—C(9)
1.204(2) C(11)—C(10)
1.287(2)
1.297(2)
1.439(2)
1.395(2)
1.412(2)
1.453(2)
1.476(2)
ment in DMSOꢀd with boron trifluoride etherate as the exterꢀ
6
nal standard. The electronic absorption spectra were recorded
on a Specord UVꢀVIS spectrometer in chloroform. The IR specꢀ
tra were measured on a Specord IRꢀ71 instrument in Nujol
mulls and in KBr pellets. The mass spectra were obtained on a
MATꢀ112 mass spectrometer; the ionizing electron energy was
8
0 eV, the ion source temperature was 250 °С, and the inlet
temperature was 240 °С.
ꢀAcetylꢀ4ꢀdifluoroboryloxycoumarin (5). Boron trifluoride
etherate (9.8 g, 0.18 mol) was added dropwise to a boiling soluꢀ
Angle
ω/deg
Angle
ω/deg
3
C(5)—O(1)—C(9) 122.2(1) C(8)—C(7)—C(6)
C(10)—O(3)—B(1) 122.9(1) C(7)—C(8)—C(10) 118.4(1)
C(7)—O(4)—B(1) 120.5(1) C(7)—C(8)—C(9) 120.3(1)
119.8(1)
1
1
tion of 3ꢀacetylꢀ4ꢀhydroxycoumarin (1) (14 g, 0.17 mol) in
dry benzene (50 mL). After 10 min, crystallization started. The
reaction mixture was then refluxed for 1 h. The precipitate that
formed was filtered off, washed with benzene, and dried in air.
Compound 5 was obtained in a yield of 12 g (72%) as colorless
needleꢀlike crystals with m.p. 198—199 °С. In condensation
reactions, this compound was used without additional purificaꢀ
tion. An analytically pure sample was obtained by recrystallizaꢀ
tion from benzene, m.p. 199—200 °С. Found (%): C, 52.45;
F(1)—B(1)—F(2) 113.2(1) C(10)—C(8)—C(9) 121.0(1)
F(1)—B(1)—O(4) 109.6(1) O(2)—C(9)—O(1) 115.9(1)
F(2)—B(1)—O(4) 108.9(1) O(2)—C(9)—C(8) 126.6(1)
F(1)—B(1)—O(3) 107.9(1) O(1)—C(9)—C(8) 117.4(1)
F(2)—B(1)—O(3) 107.8(1) O(3)—C(10)—C(8) 119.5(1)
O(4)—B(1)—O(3) 109.3(1) O(3)—C(10)—C(11) 115.7(1)
O(4)—C(7)—C(8) 122.4(1) C(8)—C(10)—C(11) 124.8(1)
O(4)—C(7)—C(6) 117.8(1)
H, 2.76; B, 4.32; F, 15.10. C11H BF O . Calculated (%):
7
2
4
1
C, 52.43; H, 2.80; B, 4.29; F, 15.08. H NMR (CDCl ), δ: 3.00
3
(
s, 3 H, Me); 7.30 (d, 1 H, C(8)H, J = 9.0 Hz); 7.44 (t, 1 H,
bonds in the Hꢀbonded fragment A (1.254(2), 1.303(2),
C(7)H); 7.87 (t, 1 H, C(6)H); 8.23 (d, 1 H, C(5)H, J = 9.0 Hz).
11
7
,8
1
.454(2), and 1.392(2) Å). The B—O bonds in comꢀ
B NMR (DMSOꢀd ), δ: –0.228. MS, m/z (%): 252 (93).
6
plex 5a are similar in length (1.503(2) and 1.483(2) Å),
the B(1)—O(3) bond being slightly elongated. The pseudoꢀ
equatorial and pseudoaxial B—F bonds are virtually
equal.W
3ꢀAcetylꢀ4ꢀ(1,3,2ꢀbenzodioxaborolꢀ2ꢀyloxy)coumarin (6).
3ꢀAcetylꢀ4ꢀhydroxycoumarin (1) (2.04 g, 10 mmol) and dry
benzene (10 mL) were placed in a flask equipped with a
Dean—Stark trap. The reaction mixture was heated to reflux.
After complete dissolution of compound 1, 2ꢀhydroxyꢀ1,3,2ꢀ
benzodioxaborole (4)5 (1.35 g, 10 mmol) was added. The reacꢀ
tion mixture was refluxed for 3 h with distillation of a waꢀ
ter—benzene azeotrope, dry benzene being gradually added to
maintain the volume of the mixture of ∼ 15 mL. After ~3 h, an
orange solid precipitated. The reaction mixture was cooled, and
the precipitate was filtered off and dried in air. The compound
with m.p. 243—244 °C was obtained in a yield of 2.77 g (86%).
After recrystallization from benzene, orange crystals had m.p. of
To estimate whether a distortion of the boronꢀconꢀ
taining ring in complex 5 is a characteristic feature of
this compound or it is caused by the crystal packing efꢀ
fects, we performed quantum chemical calculations
(
B3LYP/6ꢀ311G*) with the use of the G98W program.9
According to the calculations, the boronꢀcontaining ring
in the isolated molecule, like that in the crystal, is
nonplanar. The rotation angle of the acetyl group is 4.3°.
The deviation of the boron atom is 0.235 Å. The bond
lengths in the boronꢀcontaining ring in the isolated molꢀ
ecule (calculated data), like those in the crystal, are subꢀ
stantially equalized (the С(10)—O(3), C(7)—O(4) and
С(10)—С(8), С(7)—С(8) bond lengths are 1.286, 1.277
and 1.413, 1.421 Å, respectively). The observed differꢀ
ences in the geometry of isolated molecule 5 (calculated
data) and the molecule in the crystal (experimental data)
are apparently attributed to both the difference in the
degree of distortion of the boronꢀcontaining ring and an
elongation of the B—O bonds (1.532 and 1.515 Å), which
is a general characteristic of donorꢀacceptor bonds inꢀ
volving the boron atoms.1 Therefore, it can be concluded
that complexation with the boron atom is accompanied
by equalization of the С—С and С=O bonds due to deloꢀ
calization of π bonds.
2
44—245 °C. Found (%): C, 63.42; H, 3.47; B, 3.32. C17H BO6.
11
1
Calculated (%): C, 63.40; H, 3.44; B, 3.36. H NMR (CDCl ),
3
δ: 2.99 (s, 3 H, —СH ); 6.84 (m, 4 H, pyrocatechol); 7.35
3
(
m, 2 H, C(7)H, C(8)H); 7.83 (t, 1 H, C(6)H); 8.25 (d, 1 H,
11
C(5)H). B NMR (DMSOꢀd ), δ: 14.488. MS, m/z (%):
6
3
22 (100).
8ꢀAcetylꢀ7ꢀdifluoroboryloxyꢀ4ꢀmethylcoumarin (7a) was synꢀ
thesized according to an analogous procedure. 8ꢀAcetylꢀ7ꢀhydrꢀ
1
2
oxyꢀ4ꢀmethylcoumarin (2) (0.413 g, 2 mmol) was dissolved in
benzene (10 mL) and then boron trifluoride etherate (0.3 g,
.05 mmol) was added. A yellowꢀgreen luminescent compound
was obtained in a yield of 0.39 g (73%) with m.p. 228—229 °C.
2
Found (%): C, 54.21; H, 3.42; B, 4.02; F, 14.31. C12H BF O .
9
2
4
1
Calculated (%): C, 54.18; H, 3.41; B, 4.06; F, 14.28. H NMR
CDCl ), δ: 2.46 (d, 3 H, C(4)Me, J = 1.1 Hz); 3.22 (s, 3 H,
0
(
3
С(O)Me); 6.25 (d, 1 H, C(3)H, J = 1.1 Hz); 7.05 (d, 1 H,
C(6)H, J = 9.1 Hz); 7.96 (d, 1 H, C(5)H, J = 9.1 Hz). MS,
m/z (%): 266 (85).

2094
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006
Manaev et al.
7
ꢀDifluoroboryloxyꢀ4ꢀmethylꢀ8ꢀpropionylcoumarin (7b) was
4. V. F. Traven, A. V. Manaev, and T. A. Chibisova, Dyes and
Pigments, 2003, 58, 41.
5. M. J. S. Dewar and R. Dietr, J. Chem. Soc., 1959, 2728.
6. L. J. Bellamy, The Infrared Spectra of Complex Molecules,
Methlen and Co. Ltd., New York, John Wiley and Sons,
Inc., 1957.
7. V. F. Traven´, A. V. Manaev, O. B. Safronova, T. A.
Chibisova, K. A. Lyssenko, and M. Yu. Antipin, Zh. Obshch.
Khim., 2000, 70, 853 [Russ. J. Gen. Chem., 2000, 70 (Engl.
Transl.)].
synthesized according to an analogous procedure. 8ꢀPropionylꢀ
1
2
7
ꢀhydroxyꢀ4ꢀmethylcoumarin (3) (0.47 g, 2 mmol) was disꢀ
solved in benzene (10 mL) and then boron trifluoride etherate
0.3 g, 2.05 mmol) was added. A yellowꢀgreen luminescent comꢀ
pound was obtained in a yield of 0.4 g (72%) with m.p.
06—207 °C. Found (%): C, 55.72; H, 3.96; B, 3.90; F, 13.54.
C13H11BF O . Calculated (%): C, 55.76; H, 3.96; B, 3.86;
(
2
2
4
1
F, 13.57. H NMR (CDCl ), δ: 1.43 (t, 3 H, СH Me); 2.46 (d,
H, С(4)Me, J = 1.1 Hz); 3.78 (q, 2 H, СH ); 6.25 (d, 1 H,
2
3
2
3
C(3)H, J = 1.1 Hz); 7.04 (d, 1 H, C(6)H, J = 9.1 Hz); 7.95 (d,
8. K. A. Lyssenko and M. Yu. Antipin, Izv. Akad. Nauk, Ser.
Khim., 2001, 400 [Russ. Chem. Bull., Int. Ed., 2001, 50, 418].
9. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A.
Montgomery, Jr., R. E. Stratmann, J. C. Burant,
S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin,
M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi,
R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford,
J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui,
K. Morokuma, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz,
A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J.
Fox, T. Keith, M. A. AlꢀLaham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, J. L. Andres, C. Gonzalez, M. HeadꢀGordon,
E. S. Replogle, and J. A. Pople, Gaussian 98, Revision A.9,
Gaussian, Inc., Pittsburgh PA, 1998.
1
H, C(5)H, J = 9.1 Hz). MS, m/z (%): 280 (89).
Xꢀray diffraction study of compound 5 (C11H BF O ) was
7
2
4
carried out on an automated fourꢀcircle EnrafꢀNonius СADꢀ4
diffractometer. At 298 K, crystals of 5 are monoclinic, space
group P2 /c, a = 10.194(2) Å, b = 5.390(1) Å, c = 18.815(4) Å,
1
3
β = 91.54(3)°, V = 1033.4(4) Å , Z = 4 (Z´ = 1), d
=
calc
–
3
–1
1
.620 g cm , µ(MoꢀKα) = 1.43 cm , F(000) = 512. The intenꢀ
sities of 2011 reflections were measured at 298 K (MoꢀKα
λ = 0.71073 Å), graphite monochromator, θ/2θꢀscanning
technique, 2θ < 50°), and 1834 independent reflections
Rint = 0.0131) were used in the refinement. The structure was
(
(
solved by direct methods and with the use of successive electron
density maps. All hydrogen atoms were located in differꢀ
ence electron density maps. The refinement was performed
against F 2
with anisotropic displacement parameters for
hkl
nonhydrogen atoms and isotropic displacement parameters for
hydrogen atoms. The final R factors were as follows: R = 0.0373
based on 1430 reflections with I > 2σ(I ), wR2 = 0.1132,
GOOF = 1.048 based on all measured reflections. All calculaꢀ
tions were carried out with the use of the SHELXTL 5.10 proꢀ
gram package.13
10. (a) A. A. Korlyukov, K. A. Lyssenko, M. Yu. Antipin, V. N.
Kirin, E. A. Chernyshev, and S. P. Knyazev, Inorg. Chem.,
2002, 41, 5043; (b) K. A. Lyssenko, V. A. Ponomarev, M. E.
Gurskii, M. Yu. Antipin, and Yu. N. Bubnov, Mendeleev
Commun., 2004, 189.
1
1. E. R. Eisenhauer and K. P. Link, J. Am. Chem. Soc., 1953,
5, 2044.
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7
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Received November 11, 2005;
[
Mendeleev. Chem. J., 1984, 29 (Engl. Transl.)].
in revised form September 6, 2006