Synthesis of some 1-fluoroaryl-1,3-diketones, bis(1,3-diketonato)copper(II), bis(1,3-diketonato)dioxouranium(VI), and their electrophilic substitution reactions

Article abstract of DOI:10.1081/SIM-120013154

Some 1-fluoroaryl-1,3-diketones were prepared by treatment of methyl 1-fluoroaryl ketone with ethyl acetate, ethyl fluoroacetate or ethyl pentafluoropropionate in the presence of sodamide which were characterized in the form of their copper chelates. 1-Su

Full text of DOI:10.1081/SIM-120013154

SYNTH. REACT. INORG. MET.-ORG. CHEM., 32(1), 155–170 (2002)
SYNTHESIS OF SOME
1-FLUOROARYL-1,3-DIKETONES,
BIS(1,3-DIKETONATO)COPPER(II),
BIS(1,3-DIKETONATO)DIOXOURANIUM(VI),
AND THEIR ELECTROPHILIC
SUBSTITUTION REACTIONS
Vijai N. Pathak,1,* Chandra K. Oza,1 Ragini Gupta,2
Ranjana Tiwari,1 and Sarita Chaudhary1
1Department of Chemistry, University of Rajasthan,
Jaipur-302004, India
E-mail: pathakvn@yahoo.com
2Department of Chemistry, Malaviya Regional
Engineering College, Jaipur-302017, India
E-mail: guptaragini@yahoo.com
ABSTRACT
Some 1-fluoroaryl-1,3-diketones were prepared by treatment
of methyl 1-fluoroaryl ketone with ethyl acetate, ethyl fluor-
oacetate or ethyl pentafluoropropionate in the presence of
sodamide which were characterized in the form of their cop-
per chelates. 1-Substituted-aryl-1,3-diketones (1a-h) in turn
on treatment with uranyl acetate afforded corresponding
*Corresponding author.
155
Copyright # 2002 by Marcel Dekker, Inc.
www.dekker.com

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PATHAK ET AL.
bis(1,3-diketonato) dioxouranium(VI) (3a-f). Bis(1,3-diketo-
nato)dioxouranium(VI) (3a-f) when subjected to electrophilic
bromination or nitration reactions yielded bis(2-bromo-
1,3-diketonato)dioxouranium(VI) (4a-e) and bis(2-nitro-1,3-
diketonato)dioxouranium(VI) (5a-e), respectively. The
bonding mode of the ligands to the uranium ion has also been
1
determined from IR and H NMR spectral studies.
INTRODUCTION
The chemistry of 1,3-diketones has attracted the attention of scientists
for almost a century1. Diverse applications of 1,3-diketones as intermediates
for the synthesis of various biologically active heterocyclic compounds276
,
herbicides7, photoprotectant against skin damage8, etc. have been reported
in the literature from time to time during the last three decades. Sulfur-
containing 1,3-diketones have also been used for the treatment of liver
diseases9. Metal 1,3-diketonates have found application in the production of
laser devices10, as NMR shift reagents11 and in analytical chemistry12.
Neodymium 1,3-diketonates have found applications as shielding agents for
plastics13 and europium complexes have been used as UV-sensitive lumi-
nescent compounds for ink and resins14.
A comprehensive account of the chemistry of metal 1,3-diketonates
has been given by Mehrotra et al.15 Joshi and Pathak16 have reviewed
the overall characteristics of 1,3-diketonates with emphasis on fluorinated
1,3-diketonates. Bala-Subramanian et al.17 have reviewed the substitu-
tion reactions of coordinated 1,3-diketones, 1,3-diketoamines and thio-1,3-
diketones.
Metal 1,3-diketonate systems behave as reactive heterocycles posses-
sing at least some aromatic character (Fig. 1). The quasi-aromatic nature of
fluorinated 1,3-diketonatochromium(III)18 and fluorinated tris(1,3-diketo-
nato)europium(III)19 systems have been reported from our laboratories.
However, a perusal of the literature revealed that there is only one report
on the electrochemical synthesis and quasi-aromatic nature of uranyl
1,3-diketonates20. Therefore, as a part of our comprehensive program,
the synthesis of some new 1-fluoroaryl-1,3-diketones (1f-h), bis(1,3-di-
ketonato)copper(II) complexes (2a-h) and bis(1,3-diketonato)dioxour-
anium(VI) complexes (3a-f) and their electrophilic substitution reactions i.e.,
bromination (4a-e) and nitration (5a-e) are reported in the present
communication.

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157
Figure 1. 1,3-Diketones and their metal chelates.
RESULTS AND DISCUSSION
Synthesis of 1-Substituted-aryl-1,3-diketones and 1-Fluoroaryl-
1,3-diketones (1a-h)
The condensation of appropriately substituted methyl ketone with an
appropriate ester in the presence of sodamide afforded the desired 1-sub-
stituted-aryl-1,3-diketones and l-fluoroaryl-1,3-diketone (Fig. 2; (1a-h)). The
1-fluoroaryl-1,3-diketones (1f-h) are new while tie 1-chlorophenyl-l,3-dike-
tone (1b) has been reported earlier but by a different procedure22. The IR
spectra of b-diketones showed a very strong band in the 164071538 cmꢀ1
region. This band was assigned to the C¼O (enol) vibration. In all the
fluorinated b-diketones, very strong absorption bands were observed in the
134571110 cmꢀ1 region and were assigned due to C-F vibrations. No band
was observed in the usual conjugated ketone region 169571672 cmꢀ1 for
Figure 2. Synthesis of 1-substituted-aryl-1,3-diketones.

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PATHAK ET AL.
either compound. These analytical and spectroscopic data of 1-fluoroaryl-
1,3-diketones are in agreement with the data reported from our laboratory
and=or elsewhere3,16,18,19,21723,25
All compounds synthesized (1a-h) along with their physical char-
acteristics, analytical analyses are recorded in Table I.
.
Synthesis of Bis(1,3-diketonato)copper(II) Complexes (2a-h)
The bis(1,3-diketonato)copper(II) complexes (Fig. 3; (2a-h)) have been
prepared by adding a hot filtered solution of cupric acetate to a methanolic
solution of appropriately substituted-aryl-1,3-diketones.
The IR spectra of these complexes (2a-h) show two very strong ab-
sorption bands between 1617 and 1542 cmꢀ1 which are assigned mainly to
the > C¼O stretching mode. The third strong bands between 1538 and
1492 cmꢀ1 are the > C¼C < stretching modes coupled slightly with the C-H
in-plane bending mode. The absorption bands around 146071425 cmꢀ1 are
assigned to the degenerate symmetric deformation of the methyl group. The
bands between 1280 and 1156 cmꢀ1 are >C¼C< stretchings slightly cou-
pled with the C-CH3 stretching mode and C-H in-plane bending mode. The
bands between 1020 and 1080 cmꢀ1 are assigned to the C-F stretching mode.
The bands between 748 and 677 cmꢀ1 are assigned to a ring deformation
coupled with both the Cu-O stretching and C-CH3 stretching modes and the
Cu-O stretching coupled slightly with the C-CH3 bending mode. The bands
between 5007400 cmꢀ1 may be assigned to the pure Cu-O stretching mode.
All compounds synthesized (2a-h), along with their physical char-
acteristics and analyses are recorded in Table II.
Synthesis of Bis(1,3-diketonato)dioxouranium(VI) Complexes (3a-f)
The bis(1,3-diketonato)dioxouranium(VI) complexes (Fig. 4; (3a-f))
have been prepared by heating the solution of the substituted-aryl-1,3-di-
ketone and uranyl acetate dihydrate in ethanol.
The IR spectra of these complexes (3a-f) show prominent absorption
bands at 160071552 cmꢀ1 which are attributed to >C¼O and >C¼C<
stretching modes, respectively. The absorption bands between 12647
1100 cmꢀ1 are assigned to the C-H in-plane bending mode. The absorption
bands in the region of 9207964 cmꢀ1 and 8507790 cmꢀ1 are attributed to
O¼U¼O (asym) and O¼U¼O (sym), respectively.
All compounds synthesized (3a-f), along with their physical char-
acteristics and analyses are recorded in Table III.

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Figure 3. Synthesis of bis(1,3.diketonate)copper(II).
Bromination of Bis(1,3-diketonato)dioxouranium(VI)
Complexes (4a-e)
Bromination of the complexes is effected by refluxing a mixture of
bis(1,3-diketonato)dioxouranium(VI) (Fig. 5; (3a-e)) and N-bromosuccini-
mide in chloroform without any catalyst.
The disappearance of C-H in-plane bending vibrations seen in the
diketonate uranium complexes (3a-e) from the region of 126471100 cmꢀ1
provides strong evidence for bromine attaching to the central carbon of the
chelating ring of the diketone moiety. Besides this, the appearance of an
additional band in the 5507500 cmꢀ1 region due to C-Br also gives strong
evidence for bromination of the uranyl complexes.
All compounds synthesized (4a-e) along with their physical char-
acteristics, analytical analyses are recorded in Table V.
Nitration of Bis(1,3-diketonato)dioxouranium(VI) Complexes (5a-e)
The nitration of bis(1,3-diketonato)dioxouranium(VI) (Fig. 6; (3a-e))
is accomplished by treating bis(1,3-diketonato)dioxouranium(VI) (3a-e)
with cupric nitrate trihydrate and acetic anhydride.
The active electrophile, nitronium ion, for this reaction is generated
from acetyl nitrate as shown below:
CuðNO3Þ2 Á3H2O þ Ac2Oꢀ!AcONO2
ꢀ
þ
*
AcONO2)AcO þ NO2
The disappearance of the C-H in-plane bending vibrations from the
region 126471100 cmꢀ1 provides strong evidence for nitration of both chelate

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PATHAK ET AL.
Figure 4. Synthesis of bis(1,3-diketonato)dioxouranium(VI).
rings. The appearance of three additional absorption bands in the 158071550,
136571350 and 8257800 cmꢀ1 regions are attributed to asymmetric and
symmetric NO2 stretching modes and C-N or N-O vibration mode.
All synthesized compounds (5a-e) along with their physical char-
acteristics and analytical data are recorded in Table VI.
Similarly, the disappearance of the resonance signal due to methine C-H
from the region of 6.2 ppm of bis(1,3-diketonato)dioxouranium(VI) (3a-e) is
also in agreement with the effected bromination and nitration at the central
carbon atom of the chelate ring. Substitution in the phenyl ring is unlikely
because of electron release and the resonance effect of the coplanar phenyl ring.
EXPERIMENTAL
IR spectra were recorded using a Perkin-Elmer model 557 and a Ni-
kolet Magna model-750 spectrophotometer in KBr pellets at the Central
Drug Research Institute, Lucknow and Department of Chemistry,
1
University of Rajasthan, Jaipur. H NMR spectra were recorded on a Jeol
FX-90 Q at 89.55 Hz in CDCl3 solution with TMS as an internal standard.
Melting points are uncorrected.
Preparation of 1-Substituted-aryl-1,3-butanedione (1a-h)
The title compounds (Table I; (1a-h)) were prepared by the method of
Joshi et al.25 To a stirred solution of sodamide (1.95 g, 50 mmol) in dry ether
(50 mL) was added a solution of aryl methyl ketone (25 mmol) in dry ether
(50 mL) and after 2 hours the calculated amount of the appropriate ester
(25 mmol) (i.e., ethyl acetate (2.2 g), or ethyl fluoroacetate (2.65 g), or ethyl
pentafluoropropionate (4.8 g)) in dry ether (25 mL) was added. The resulting

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Figure 5. Bromination of bis(1,3-diketonato)dioxouranium(VI).
Table IV. IR Data of Bis(1,3-diketonato)dioxouranium(VI) (nmax Values in cmꢀ1
)
Compd.
No.
C¼O
C¼C
C-H In-plane
bending
UO2
(Asym)
UO2(Sym)
Stretching
Stretching
(3a)
(3b)
(3c)
(3d)
(3e)
(3f)
1586 vs
1588 vs
1604 vs
1596 vs
1600 vs
1600 vs
1532 vs
1534 vs
1532 vs
1530 vs
1500 vs
1500 vs
1178 m
1212 m
1234 m
1264 m
1190 m
1200 m
962 m
962 m
964 m
964 m
920 m
940 m
844 s
846 s
854 s
832 s
790 s
800 s
solution was stirred and refluxed for 4 hours and then poured into hydro-
chloric acid (10%, 200 mL) and allowed to settle for 30 minutes. The re-
sulting 1-substituted-aryl-1,3-butanedione (1a-h) was extracted with
chloroform, washed with water (3650 mL) and dried over sodium sulphate.
Chloroform was distilled off and the 1-substituted-aryl-1,3-butanedione (1a-
h) was recrystallized from petroleum ether (b. p. 60780 ꢁC).
Preparation of Bis(1,3-diketonato)copper(II) (2a-h)
To a methanolic solution of substituted-aryl- 1,3-diketone (25 mmol)
was added a hot filtered solution of cupric acetate (40 g, in 250 mL water) and
the mixture was allowed to cool to room temperature. The resulting bis(1,3-
diketonato) copper(II) (Table II; (2a-h)) was filtered, dried, washed with
petroleum ether (100 mL, b. p. 60780 ꢁC) and recrystallized from chloroform.
Preparation of Bis(1,3-diketonato)dioxouranium(VI) (3a-f)
These compounds (Table III; (3a-f)) were prepared by the method of
Das24. A hot filtered solution of uranyl acetate dihydrate (1.50 g, 3.53 mmol in

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Figure 6. Nitration of bis(1,3-diketonate)dioxouraniun(VI).
25 mL water) was added dropwise with constant stirring to a solution of
substituted-aryl-1,3-diketone (7.06 mmol in 25 mL ethanol). The reaction
mixture was digested for 10 minutes and then cooled in an ice bath. The
resulting orange products were filtered and washed with aqueous ethanol
(50%, 3620 mL). Recrystallization of the product was carried out with
chloroform.
Electrophilic Substitution Reactions
Substitution reactions of bis(1,3-diketonato)dioxouranium(VI) (3a-e)
were carried out by the method of Joshi et al.25 The methine proton of the
central carbon atom of the chelate ring was subjected to bromination and
nitration.
Bromination of Bis(1,3-diketonato)dioxouranium(VI) (4a-e)
To a solution of bis(1,3-diketonato)dioxouranium(VI) (3a-e) (1 mmol)
in chloroform (25 mL) was added N-bromosuccinimde (0.534 g, 3 mmol)
and the solution was refluxed for 477 hours. The solvent was removed and
the solid thus obtained was collected. Subsequently, it was washed several
times with a solution of sodium hydroxide (2%, 3620 mL), dried and col-
lected (Table V; (4a-e)).
Nitration of Bis(1,3-diketonate)dioxouranium(VI) (5a-e)
The nitration of bis(1,3-diketonato)dioxouranium(VI) (3a-e) was car-
ried out under mild conditions. A cooled solution of bis(1,3-diketonato)-
dioxouranium(VI) (3a-e) (1 mmol) in acetic anhydride (5 mL) was added
dropwise with constant stirring to cupric nitrate trihydrate (0.7248 g,
3 mmol) in acetic anhydride (5 mL) and kept at 0 to ꢀ5 ꢁC for 5 to 15 hours.

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The reaction mixture was then treated with an ice-cold aqueous solution of
sodium acetate (8.2 g, 100 mmol in 25 mL of water). The precipitate thus
obtained was extracted with chloroform, washed with water (3650 mL) and
dried. The residue after evaporation of chloroform was recrystallized from
ethyl acetate and dried under vacuum (Table VI; (5a-e)).
ACKNOWLEDGMENTS
Authors are thankful to Dr. V. J. Ram, Scientist-E-II, Medicinal
Chemistry Division, Central Drug Research Institute, Lucknow for valuable
suggestions. Financial support from the Council of Scientific and Industrial
Research is also acknowledged.
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Received March 21, 2001
Accepted October 25, 2001
Referee I: P. Ilankumaran
Referee II: J. E. Hutchison

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