Synthesis of tris(β-diketones) and study of their complexation with some transition metals

Article abstract of DOI:10.1007/s11172-006-0542-2

New chelating ligands consisting of three β-diketone fragments, viz., 1,3,5-tris[(acetylaceton-3-yl)methyl]benzene, 1,3,5-tris[(benzoylaceton-3-yl) methyl]benzene, and 1,3,5-tris[(dibenzoylmethan-1-yl)methyl]benzene, linked to each other through the mesit

Full text of DOI:10.1007/s11172-006-0542-2

2000
Russian Chemical Bulletin, International Edition, Vol. 55, No. 11, pp. 2000—2007, November, 2006
Synthesis of tris(βꢀdiketones) and study of their complexation
with some transition metals
а
a
b
a
S. N. Podyachev, S. N. Sudakova, A. K. Galiev, A. R. Mustafina,
a
a
c
a
V. V. Syakaev, R. R. Shagidullin, I. Bauer, and А. I. Konovalov
aA. E. Arbuzov Institute of Organic and Physical Chemistry,
Kazan Research Center of the Russian Academy of Sciences,
8
ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843) 273 2253. Eꢀmail: spodyachev@iopc.kcn.ru
b
Kazan State Technological University,
6
8 ul. K. Marksa, 420015 Kazan, Russian Federation.
c
Drezden University of Technology, Institute of Organic Chemistry,
Mommsenstrasse 13, Dꢀ01062 Drezden, Germany.
Fax: (0351) 463 34093
New chelating ligands consisting of three βꢀdiketone fragments, viz., 1,3,5ꢀtris[(acetylꢀ
acetonꢀ3ꢀyl)methyl]benzene, 1,3,5ꢀtris[(benzoylacetonꢀ3ꢀyl)methyl]benzene, and
,3,5ꢀtris[(dibenzoylmethanꢀ1ꢀyl)methyl]benzene, linked to each other through the mesitylene
1
spacer were synthesized by the reaction of 1,3,5ꢀtris(bromomethyl)benzene with the correꢀ
sponding βꢀdiketone sodium salt. The acidity of these compounds and their complexation
properties were studied by pHꢀpotentiometry in aqueousꢀethanol solutions. Tris(βꢀdiketones)
form mononuclear complexes with lanthanide ions, whose stability increases in the series
3
+
3+
3+
La < Gd < Lu . 1,3,5ꢀTris[(acetylacetonꢀ3ꢀyl)methyl]benzene forms both mononuclear
2
+
2+
and polynuclear complexes with the Ni and Cu ions. The stability constants and selectivity
of complex formation increase substantially with an increase in the degree of deprotonation of
the ligands, thus indicating that all deprotonated chelate groups are involved in coordination
with the metal ion. The replacement of the methyl groups by the phenyl substituents in the
βꢀdiketone fragments of the molecules affects substantially the composition and stability of the
complexes formed.
Key words: βꢀdiketones, pHꢀpotentiometry, complex formation, lanthanide complexes,
copper complexes, nickel complexes, stability constants, chelating agents.
βꢀDiketones are used for solving many tasks of orꢀ
concerns works on the synthesis of βꢀdiketone derivatives
in which one or both carbonyl oxygen atoms are substiꢀ
tuted for the S or Se atoms, imine or amine groups optiꢀ
mal for binding of specified metal ions.
ganic, coordination, and other divisions of chemistry. One
of the most practically important properties of these comꢀ
pounds is their ability to form chelate complexes of differꢀ
ent structure with ions of many metals.1,2 The develꢀ
opment of extraction methods provided wide use of
βꢀdiketones for separation of elements with similar propꢀ
erties, for instance, actinides and lanthanides, and conꢀ
Another, qualitatively distinctive approach to the
modification of the complexation properties of βꢀdiꢀ
1
0
ketones is the synthesis of polytopic ligands with threeꢀ
dimensional architecture. The presence of several funcꢀ
tional groups in a molecule can favor both an increase in
the efficiency and selectivity of complex formation due to
the "cooperative effect" and the creation of compounds
with a new architecture. However, only restricted number
of publications on polydentate compounds based on βꢀdiꢀ
ketones are available in literature. Interest in these comꢀ
pounds has especially increased during recent several years
due to the intensive development of supramolecular chemꢀ
istry. Among relevant studies we can distinguish the works
3
,4
centrating microadmixtures of elements.
Practical significance of βꢀdiketones induced the deꢀ
velopment of studies directed to syntheses of new repreꢀ
sentatives of the series of βꢀdiketones,5—9 which can be
divided into two main groups. The first group includes
studies of the synthesis of βꢀdiketones with substituents of
more complicated structure, whereas the second group
*
Dedicated to Academician O. M. Nefedov on the occasion of
his 75th birthday.
2
+
aimed at synthesizing the binuclear Сu complexes,
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1926—1933, November, 2006.
066ꢀ5285/06/5511ꢀ2000 © 2006 Springer Science+Business Media, Inc.
1

Tris(βꢀdiketones) and their complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006 2001
where the βꢀdiketonate fragments in a molecule are linked
through the mꢀxylylene and 2,7ꢀnaphthalenediylꢀbisꢀ
methylene spacers, and at studying their metalꢀreceptor
oxide in boiling tertꢀbutyl alcohol, and then bis(bromoꢀ
methyl)benzene and KI were added. However, when
a considerable excess of βꢀdiketone over bis(bromoꢀ
properties.1
1—13
The binuclear V and V complexes
2+
3+
methyl)benzene was used, a problem of purification of
1
2
were also synthesized from the ligand with the mꢀxylylene
spacer, and they are promising catalysts of redox proꢀ
cesses.1
the target products from the initial βꢀdiketone appeared.
Therefore, we developed a modified procedure in which
the preliminarily prepared βꢀdiketone sodium salt and its
reaction with 1,3,5ꢀtris(bromomethyl)benzene (1) was
carried out in the absence of KI in a higherꢀboiling solꢀ
vent dioxane instead of tertꢀbutyl alcohol. This favored a
substantial shortening of the reaction duration (from 1 day
and more to 3 h) and obtaining more pure compounds.
4
The use of ligands with two spatially separated βꢀdiꢀ
ketonate groups made it possible to create the coordinaꢀ
tion "host" polymers with architecture of "molecular
shelves" of high strength and capacity.15 Bis(βꢀdiketones)
with rigid phenylene and naphthalenediyl spacers were
used to create metalꢀsupramolecular structures with triꢀ
2
+
2+
angular (complexes with Cu and Ni ) and tetrahedral
complexes with Ga3+ and Fe3+) geometry.16,17 Ligands
Scheme 1
(
with arylenedi(oxymethylene) and ethylenedioxide spacꢀ
ers were used for the synthesis of metallocryptands closed
into a macrocycle by two Cu2+ or Ni ions. An alkaline
metal ion is also involved in complex formation exerting
the template effect. This is indicated by its coordination
with the oxygen atoms of the bridging and βꢀdiketonate
fragments.18
2+
Intramolecular interactions between metal ions are
known to affect strongly the magnetic, redox, and specꢀ
tral properties of coordination compounds. This is conꢀ
firmed by the data on the binuclear lanthanide (in parꢀ
ticular, with Eu3+ ions) complexes of the series of
bis(βꢀdiketones) linked through arylene spacers, whose
luminescence is substantially higher than that of their
1
9,20
monoanalogs.
The works on the synthesis of trisꢀ21 and tetrakis(βꢀdiꢀ
ketones)22 and studies of their catalytic properties should
be mentioned. Publications on these poly(βꢀdiketones)
are virtually lacking, because, most likely, their syntheses
are difficult.
We have also reported earlier the synthesis of
1
,3ꢀbis(acetylacetonyloxy)ꢀ and 1,3ꢀbis(benzoylacetonylꢀ
oxy)benzenes and studies of the effect of their ditopic
structure on the complexation properties toward the lanꢀ
thanide ions.2 A substantial increase in the stability and
selectivity of complex formation with an increase in the
degree of deprotonation of the ligands was found. Conꢀ
tinuing this work, we synthesized new tris(βꢀdiketones)
and present the results of studies of their structures, acidic
properties, and ability to complex formation with the lanꢀ
1
R = Me (2, 3, 5, 6), Ph (4, 7)
2
R = Me (2, 5), Ph (3, 4, 6, 7)
3
Reagents and conditions: i. NBS, AlBN/HCO Me, 14 h, 20 °C.
2
ii. Dioxane, ∆, 3 h.
The compositions and structures of tris(βꢀdiketones)
5—7 were confirmed by the data of elemental analysis,
MALDIꢀTOF mass spectrometry, Н and C NMR specꢀ
troscopy, and IR spectroscopy.
thanide ions (La3+, Gd , Lu ), Ni , and Cu
3+
3+
2+
2+
.
1
13
Results and Discussion
Spectral and structural features of compounds 5—7.
Diketones can exist as ketoꢀenol tautometers (I and II),
whereas enols can have cisꢀ or transꢀconfiguration
(Scheme 2). Enols of βꢀdiketones that exist in the cisꢀform
(IIa) can additionally be stabilized due to the formation
of a strong intramolecular form (IIc). IR and NMR
spectroscopic methods are very informative for determinꢀ
ing structural features of these compounds.
Synthesis of ligands. To synthesize tris(βꢀdiketones),
we used the modified method of nucleophilic substitution
described for 1,4ꢀbis[(acetylacetonꢀ3ꢀyl)methyl]benꢀ
zene2 and applied later for the synthesis of similar
metaꢀisomers. According to a previously described proꢀ
cedure,12 βꢀdiketone was added to potassium tertꢀbutꢀ
4
25
1
2

2002
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006
Podyachev et al.
for 5, 1716 and 1674 cm–1 for 6, and 1695 and 1668 cm–1
for 7. The frequencies of these vibrations decrease with
an increase in the number of aromatic substituents in
the βꢀdiketone fragments due to conjugation with the
πꢀsystems of these substituents, which agrees with
Scheme 2
2
6
published data. The doublet character of the ketoꢀcarꢀ
bonyl bands, which are almost the same in intensity, is
caused, most likely, by synꢀ and antiphase stretching viꢀ
brations of the carbonyl groups in the βꢀdiketone fragꢀ
2
7
ments.
At the same time, in the IR spectrum of compound 5,
unlike those of compounds 6 and 7, the absorption band
–
1
at ∼ 1600 cm , which exhibits stretching vibrations of
multiple bands of the aromatic rings and enol structures
2
6,27
ν(С=О) and ν(С=С),
is broadened and the whole
spectrum is diffuse (the peaks are less distinct). This indiꢀ
cates the presence of considerable amounts of enol forms
along with ketone forms. The stretching vibrations ν(ОH)
are detected as a broad diffuse base of the ν(СH) lines in
–
1
the interval 2400—3300 cm with an uncertain maxiꢀ
2
6,27
mum, which is characteristic of enol structures.
The
presence of some amounts of enol forms cannot be exꢀ
cluded for compounds 6 and 7, because the properties
described for them can be disguised by strong stretching
vibrations ν(С=О) and ν(Ph) that are observed at the
corresponding frequencies and characteristic of keto strucꢀ
tures.
The IR spectra (Fig. 1) of compounds 5—7 are charꢀ
–
1
acterized by absorption bands at 3000—3100 cm
It is known that an increased content of the enol form
is observed in inert solvents due to the formation of an
–
1
(
ν(=СН)); 3000—2800 cm ((ν(CН), ν(СН ), and
2
–
1
25
ν(Me)); 1750—1650 cm (ν(С=О)); at ∼ 1450, 1500, and
600 cm–1 (ν(Ph)); 1100—1400 cm–1 (ν (ССС)) and
intramolecular hydrogen bond. Indeed, the chemical
1
1
shifts of protons of the OH groups (∼ 16—17 ppm, Table 1)
as
1
050—900 (ν (CCC)). In addition, the spectra of comꢀ
observed in the H NMR spectra of solutions of comꢀ
s
pounds 6 and 7 exhibit intense absorption bands in
pounds 5—7 in CDCl indicate that their molecules conꢀ
3
–
1
an interval of 800—650 cm assigned to the absorpꢀ
tion of the monosubstituted phenyl fragments: γ(=СН)
and δ(Ph).2
tain a strong intramolecular hydrogen bond. At the same
1
time, according to the H NMR spectral data, tris(βꢀdiꢀ
6
ketones) 5—7 exist predominantly in the keto form in
solutions. For instance, for compound 5 the fraction of
the enol form is ∼ 35%, whereas the replacement of one
of the methyl groups by the phenyl group in the βꢀdiꢀ
ketone fragments decreases the content of the enol form
to 5% in compound 6, while it is virtually absent (<0.3%)
in the case of hexaphenyl derivative 7. An inverse depenꢀ
dence could be expected, because in βꢀdiketones with
aromatic substituents the fraction of the enol form usually
increases due to an additional stabilization caused by the
formation of a single πꢀelectron system of conjugation
between the phenyl substituent and sixꢀmembered ring of
For all the three βꢀdiketones, the bands assigned to
–
1
the ν(C=O) vibrations are doublet: 1727 and 1699 cm
5
6
2
5
the enol tautomer. This did not occur, most likely, due
to steric hindrance induced by the adjacent βꢀdiketone
fragments in these compounds that prevent this stabiliꢀ
zation.
7
Acidic and complexation properties of tris(βꢀdiketones).
The constants of stepped deprotonation pKi for
compounds 5—7 described by equilibria (1) and (2)
and pK of acetylacetone (8), benzoylacetone (9),
3
500
3000
2500
2000
1500
1000
ν/cm–1
Fig. 1. IR spectra of compounds 5—7.

Tris(βꢀdiketones) and their complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006 2003
Table 1. Parameters of the H and 13С NMR spectra (CDCl3,
1
gen atom in the methylene group of βꢀdiketone for any
substituent R usually also results in a sharp decrease in the
acidity, which is caused by both steric hindrance and
a decrease in the mobility of the second proton of the
δ, J/Hz) for the keto form* of compounds 5—7
Atom
5
6
7
1H
13C
1H
13C
1H
13C
methylene group and, hence, an insignificant degree of
enolization of βꢀdiketone. However, the deprotonation
constants of tris(βꢀdiketones) 5—7 and their monoanalogs
2
5
a
b
1
2
3
4
6.5—6.8 124—129 6.8—6.9
6.77)
128.2
(127.2)
138.8
6.98
128.1
139.9
(
8—10 by the first step have the same order. In the case of
139.0
compound 5, even a slight increase in acidity compared
to that of compound 8 is observed. Further two protons
are abstracted. For compounds 5 and 6, the acidity conꢀ
stant increases, on the average, by one order of magniꢀ
tude. At the same time, for compound 7 this constant
almost coincides with the average value of the second and
third acidity constants (pK1 ≈ pK2,3/2), indicating the
absence of a mutual effect on the acidꢀbase properties of
the βꢀdiketone fragments in this compound. As a whole,
this can indicate the stabilization of the monoanion
formed in compounds 5 and 6 due to the formation of an
(
140.9)
(141.0)
28.3
(25.3)
202.5
2.1—2.2 30.0
2.0—2.1) (23.2)
203.2
2.0—2.1
(1.99)
(
(
195.3
58.7
(
191.8)
(183.3)
3.9—4.0 69.9 4.58—4.68 64.0
108.1) (96.7) J = 7.1)
3.0—3.2 34.0 3.10—3.20 34.0 3.27 (d, 34.9
3.5—3.7) (32.9) (3.53—3.57) (33.5) J = 7.1)
3.85)
5.28 (t,
(
(
5
195.3
193.3)
138.8
(
intramolecular hydrogen bond decreasing pK , whereas
6
7
135.9
1
the bulky substituents in compound 7 prevent, most likely,
its formation.
7.8—7.9
128.8 7.78 (d, 128.9
J = 7.8)
8
9
7.35—7.48 128.6 7.34 (t, 128.6
The addition of the lanthanide ions in the lanthanide
ion to ligand mole ratios equal to 0.5 : 1, 1 : 1, and 2 : 1
considerably shifts the equilibrium of tris(βꢀdiketones)
to the deprotonated forms. The curves of pHꢀmetric titraꢀ
tion of ligands 5—7 in the presence of the lanthanide
ions are much lower (Fig. 2) and indicate complex forꢀ
mation in solutions. The stability constants (logβ) of
the complexes of βꢀdiketones 5—7 calculated from the
J = 8.2)
7.5—7.6
133.3 7.47 (t, 133.5
J = 7.0)
1
*
0
(16.7—16.8)
(17.0; 16.1)
(17.1; 16.8)
The values for the enol forms if any are given in parentheses.
and dibenzoylmethane (10) determined under simiꢀ
lar conditions by pHꢀmetric titration are presented in
Table 2.W
pH
11
–
+
H L
H L + H ,
(1)
(2)
3
2
–
L2– + 2 H+.
H L
2
1
0
9
8
7
6
5
4
H L
3
The replacement of the methyl substituent by the pheꢀ
nyl group in the βꢀdiketone fragments in the series of
compounds 5—7 decreases the acidity of the first proton,
which agrees with the indicated above decrease in the
fraction of the enol form. The substitution of one hydroꢀ
2
3
1´
1″
1
Table 2. Values of pK for compounds 5—10
2´
3´
i
2″
3″
Comꢀ
pound
pK1
pK2,3
5
6
7
8
9
9.37±0.04
9.97±0.05
10.34±0.07
9.47±0.03*
9.56±0.03*
9.68±0.08
21.02±0.04
22.63±0.1
20.58±0.1
1
2
3 V/mL
Fig. 2. Curves of pHꢀmetric titration of compound 5 in
the absence (H L) and presence of Ln3+: La3+ (1, 1´, 1″),
3
1
0
Gd3+ (2, 2´, 2″), and Lu3+ (3, 3´, 3″) at the Ln3+ to ligand mole
*
Data in Ref. 23.
ratios 0.5 : 1, 1 : 1, and 2 : 1, respectively.

2004
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006
Podyachev et al.
Table 3. Stability constants (logβ, β/L mol–1) of the complexes of βꢀdiketones 5—7 {([H3–k/mL]k/m–)m(Mep+) }
pn–k
formed
n
p+
in the H L – Me system
3
Mep+
La3+
m
n
k
logβ
∆logβLn/La
5
6
7
5
6
7
1
1
1
2
2
2
1
1
2
2
1
1
2
2
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
3
1
2
3
3
4
5
2
3
3
5
1
3
3
5
1
2
3
1
2
6
6.3±0.07
—
14.1±0.12
17.9±0.2
—
6.9±0.07
—
15.9±0.09
18.7±0.2
—
6.54±0.07
10.0±0.13
13.12±0.06
17.54±0.12
20.1±0.3
20.1±0.3
12.2±0.12
16.22±0.06
—
20.4±0.4
—
17.78±0.04
—
—
—
—
—
Gd3+
2.2
3.1
15.7±0.16
17.7±0.2
—
6.8±0.06
17.3±0.16
19.6±0.25
—
5.5±0.04
8.24±0.05
14.63±0.05
8.76±0.04
13.63±0.1
44.8±0.16
18.6±0.12
20.44±0.16
—
7.5±0.04
19.6±0.16
20.3±0.24
—
5.1±0.2
8.7±0.2
15.8±0.1
*
1.6
–0.2
1.7
–0.2
0.3
Lu3+
0.5
3.2
1.7
0.6
3.7
1.6
4.66
2.8
22.9±0.5
—
9.7±0.1
—
Ni2+
Cu2+
*
*
The constants were not determined because of precipitation in the system.
above data and described by equilibrium (3) are given in
Table 3.
For a twofold excess of the ligand, the predominant
neutral complex has the composition m = 2, n = 1, k = 3.
The stability of the complex of this type with ligand 6 also
exceeds the stability of similar complexes with ligands 5
and 7 by ∼ 1—2 orders of magnitude. However, the
logβ values of the 1 : 2 complexes increases less considerꢀ
ably with an increase in the degree of deprotonation. For
instance, for compound 7, on going from the La comꢀ
plexes with the composition m = 2, n = 1, k = 3 to the
complex with m = 2, n = 1, k = 4, the stability increases
only by 2.5 logarithmic units. The further deprotonation
of the ligands on going to the complex with m = 2, n = 1,
k = 5 exerts no effect on the logβ value. This indicates that
the deprotonation of the βꢀdiketone fragment does not
result, in this case, in the formation of an additional coorꢀ
dination bond with the lanthanide ion.
mH L + nLn3
+
3
([H3–k/mL]k/m–)m (Mep+)n}pn–k + kH+,
{
(3)
p+
where H L is ligand 3—5, and Me is the metal ion.
3
3
+
According to Eq. (3), stoichiometry of the
p+
pn–k
{
([H3–k/mL]k/m–)m(Me ) }
complexes that formed
n
was designated by indices m, n, k, where m is the number
k–
of reacting [H3–kL] anions of the ligand, n is the numꢀ
ber of cations, p is the cation charge, and k is the number
of abstracting protons.
Under the concentration conditions studied, ligands
5
—7 are characterized by the formation of neutral comꢀ
3
+
3+
3+
plexes with the lanthanide ions (La , Gd , Lu ) with
stoichiometry m = 1, n = 1, k = 3. In the case of the
complex with ligand 6, the stability constant is maximum,
exceeding the stability constants of similar complexes with
ligands 5 and 7 by 2—3 orders of magnitude. This increase
in stability correlates with the decrease in the dissociation
constant of compound 6 (pK1—3 = 32.6±0.15) as comꢀ
pared to those for compounds 5 (pK1–3 = 30.39±0.08)
and 7 (pK1—3 = 30.92±0.17) (see Table 3). The remarkꢀ
able increase in the stability of the complex with m = 1,
n = 1, k = 3 as compared to that with m = 1, n = 1,
k = 1—2 suggests that all the three diketonate fragments
act as donor groups toward the lanthanide ions.
The formation of a neutral complex particle with three
ligands (m = 3, n = 1, k = 3), which is typical of the
2
5
lanthanide ion complexes with monoꢀβꢀdiketones, could
be expected. However, the results of processing the data
of pHꢀmetric titration obtained even in a threefold excess
of ligand 5 did not confirm the formation of complexes
with this composition.
The stability constants of the complexes β increase in
3
+
3+
3+
the series La < Gd < Lu (see Table 3). The selectivꢀ
ity of complex formation (∆logβLn/La = logβLn – logβLa
)
increases noticeably on going from compounds 5 and 6 to
compound 7. An increase in the degree of deprotonaꢀ

Tris(βꢀdiketones) and their complexes
α (%)
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006 2005
only one metal ion was observed for the lanthanide ions
in the whole pH range studied. The increase in the volume
of substituents on going from ligands 5 and 6 to comꢀ
pound 7 prevents the formation of a binuclear complex.
3
1
8
6
4
2
0
0
0
0
2
+
The study of complex formation with the Cu ion in
an aqueous solution found only three complex particles,
two of which are neutral (see Table 3). The plots of the
degree of their accumulation vs. pH are shown in Fig. 3.
Their stability is much higher than that in the case of
3
+
similar in composition complexes with the Ln and
2
+
Ni ions. The accumulation of the complexes also inꢀ
creases with an increase in ligand deprotonation in the
complex (m = 1, n = 1), indicating coordination of the
both βꢀdiketonate fragments to the metal ion.
2
4
5
6
pH
When the metal ion concentration and pH increase, a
neutral complex particle containing three metal ions
Fig. 3. Plots of the degree of accumulation of the complex forms
vs. pH for a system of ligand 5 and Cu2 taken in the 1 : 2 ratio.
Complex forms: m = 1, n = 1, k = 1 (1); m = 1, n = 1, k = 2 (2);
m = 2, n = 3, k = 6 (3).
+
(
m = 2, n = 3, k = 6) is accumulated instead of the
2
+
binuclear particle (m = 1, n = 2, k = 3) found for Ni
.
The shape of the calculated model of the structure of this
complex is a cylindrical capsule 8.6 Å in diameter (nonꢀ
bonding distance 7.7 Å) and ∼ 8.1 Å in height (Fig. 4).
The addition of three equivalents of KOH (рН = 6.1)
with respect to tris(βꢀdiketone) at the metal to ligand
ratio 2 : 1 resulted in the precipitation of a neutral comꢀ
plex. The elemental analysis data correspond to the comꢀ
position of a trinuclear complex similar to that existing in
solution. Nevertheless, the low solubility of the complex
indicates its polymeric character. Probably, the increase
in the degree of accumulation of this complex and the
complete deprotonation of ligand 5 in solution upon the
addition of about three equivalents of KOH induce the
disproportionation of the trinuclear complexes leading to
the precipitation of polymeric complexes.
tion (k) of the complexes also enhances the selectivity.
Among all the tris(βꢀdiketones) studied, the maximum
selectivity is observed for the formation of neutral comꢀ
plexes with m = 1, n = 1, k = 3, in particular, for the
complex of βꢀdiketone 7 with Lu3 , whose ∆logβLn/La
is 4.66.
+
The composition and stability constants were deterꢀ
mined by pHꢀmetric titration for the Ni2 complexes with
all the tris(βꢀdiketones) synthesized. In the case of the
+
2
+
Cu ion, the complex was synthesized only with ligand 5,
whereas precipitates were formed in the presence of
ligands 6 or 7. The stability constants of the complexes
2
+
with Ni (m = 1, n = 1, k = 1 and m = 1, n = 1, k = 2) are
by approximately 1—2 orders of magnitude lower than the
corresponding constants for the complexes with the lanꢀ
thanides. It is of interest that binuclear complexes (m = 1,
n = 2, k = 3) were formed with an increase in the degree
of deprotonation of the ligands, whereas coordination of
Thus, synthesized tris(βꢀdiketones) 5—7 in the solid
state and in solutions exist predominantly in the keto
form. They form with the lanthanide ions the monoꢀ and
bisꢀβꢀdiketonate complexes, whose stability increases
with an increase in the number of lanthanide
Cu2+
Cu2+
Cu2+
8.1 Å
8
.6 Å
Fig. 4. Model of the structure of the neutral trinuclear Cu2+ complex with two tris(βꢀdiketonates) 5 optimized by the semiempirical
method (PM3).

2006
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006
Podyachev et al.
ity of 4 cm–1 and accumulation of 16 scans. The geometry of
the model of the Cu2 complex structure was optimized by
(
La3+ < Gd3+ < Lu3+). The replacement of the both meꢀ
+
thyl substituents by the phenyl groups in the βꢀdiketonate
ligands decreases the stability of the complexes and inꢀ
creases the selectivity in the series La3+, Gd , and Lu
which is probably caused by steric hindrance for the forꢀ
mation of a coordination site. The Ni2+ and Cu2+ ions
3
0
the semiempirical method (PM3) incorporated into the
HyperChem7.03 program package.3
1
3+
3+
,
pHꢀMetric titration. Titration was carried out with a soluꢀ
tion of KOH (1.36•10–2 mol L ) in an H O—EtOH (80 vol.%.)
–1
2
mixture on an Iꢀ130 instrument with the measurement accuꢀ
form, in addition to mononuclear complexes, biꢀ and
trinuclear complexes involving one and two ligands, reꢀ
spectively. The increase in the degree of deprotonation of
tris(βꢀdiketones) substantially increases the stability conꢀ
stants of the complexes and selectivity of complex forꢀ
mation.
racy to 0.05 pH unit at 40±1 °C. To determine acidity in
the H O—EtOH (80 wt.%) mixture, a known procedure32,33
2
was used, according to which the ionomer was tuned by stanꢀ
dard buffer solutions in water and the electrode was preliminarꢀ
ily kept for 1 day in the H O—EtOH (80 vol.%) mixture for
2
measurements of pH of aqueousꢀorganic solutions. The pH valꢀ
ues of aqueousꢀorganic solvents were determined from the equaꢀ
tion
Experimental
рН = рНexp – ∆рН,
Bidistilled water was used, and EtOH was additionally puriꢀ
2
8
fied according to a standard procedure. 1,4ꢀDioxane and toluꢀ
ene were purified by distillation over metallic sodium, and
acetylacetone was distilled. Commercial reagents (KOH, lanꢀ
where рНexp is the value measured in a mixed solvent, and ∆рН
reflects the difference in activity of protons in aqueous and
aqueousꢀorganic solutions.
thanide chlorides, CuCl , mesitylene, Nꢀbromosuccinimide,
azoisobutyronitrile, methyl formate, benzoyl acetone, diꢀ
benzoylmethane, and metallic sodium) were used as received.
The ∆рН values were determined by measuring pH of soluꢀ
tions with different HCl concentrations in a mixed solvent
(рНw+s) and in water (рНw) using the following equation:
2
1
,3,5ꢀTris(bromomethyl)benzene (1) was synthesized by a deꢀ
2
9
∆рН = рНw+s – рНw.
scribed procedure. Sodium salts of βꢀdiketones 2—4 were synꢀ
thesized by the addition of equimolar amounts of the correꢀ
sponding βꢀdiketone to a suspension of metallic sodium, and
after stirring at 40 °C for 3 h the precipitate formed was deꢀ
canted from residues of unreacted sodium, washed with diethyl
ether, and dried in vacuo.
General procedure of synthesis of tris(βꢀdiketones) (5—7).
A mixture of sodium salt of βꢀdiketone (18.6 mmol) and
1
dioxane (100 mL) was refluxed with stirring for 3 h under argon.
The reaction mixture was filtered, and the solvent was distilled
off from the filtrate in vacuo. The residue was dissolved in CH Cl2
and washed several times with water. The organic layer was
separated, dried with MgSO , and concentrated. Solvent resiꢀ
Solutions were titrated at the lanthanide ion to ligand mole
ratios 1 : 1 and 1 : 2 in the range of pH = 2.5—8, and for the free
ligand this range was extended to pH 12 at the ligand concentraꢀ
tions 2•10–3 and 4•10 mol L . The choice of the composiꢀ
tion of the mixed solvent, concentrations used, and temperature
of the medium during titration was caused by necessity to proꢀ
vide satisfactory solubility of the initial components and reacꢀ
tion products.
–3
–1
,3,5ꢀtris(bromomethyl)benzene (2.12 g, 6 mmol) in anhydrous
Experimental data were processed using the CPESSP proꢀ
gram.34 The mathematical model represented a set of
Eqs (1), (2), and (3). The dissociation and complexation conꢀ
stants (βi...q) corresponding to the minimum of the Fischer funcꢀ
tional (Eq. (4)) were determined by the iteration procedure
using the CPESSP program. Reliability of the model was estiꢀ
mated from the Fischer criterion (Eq. (5))
2
4
dues were removed at 80 °C in vacuo.
1
,3,5ꢀTris(2ꢀacetylꢀ3ꢀoxobutꢀ1ꢀyl)benzene (5) was syntheꢀ
sized in a yield of 1.84 g (74%) as a viscous oil. Found (%):
C, 69.89; H, 7.45. C H O . Calculated (%): C, 69.54; H, 7.30.
MALDIꢀTOF mass spectrum, m/z: 416 [M + H] , 438
2
4
30
6
+
,
(4)
(5)
+
+
[
M + Na] , 455 [M + K] .
,3,5ꢀTris(2ꢀacetylꢀ2ꢀbenzoylethyl)benzene (6) was isolated
2
1
Fmin < Fσ (N – 2k),
in a yield of 3.10 g (86%) as a viscous oil. Found (%): C, 77.84;
H, 6.43. C39H36O . Calculated (%): C, 77.98; H, 6.04.
where n~ and n~
culated values of the Bjerrum function, N is the number of
experimental points, k is the number of approached equilibria,
are the experimental and theoretically calꢀ
calc
6
exp
+
MALDIꢀTOF mass spectrum, m/z: 624 [M
40 [M + K] .
,3,5ꢀTris(2,2ꢀdibenzoylethyl)benzene (7) was isolated in
+
Na] ,
+
6
1
w is the rootꢀmeanꢀsquare error for the mth experimental point,
m
2
a yield of 3.82 g (81%) as a solid, m.p. 65 °C. Found (%):
and σ is the rootꢀmeanꢀsquare deviation.
C, 81.95; H, 6.36. C H O . Calculated (%): C, 82.42; H, 5.38.
The model that adequately describes experimental data unꢀ
der certain concentration conditions (ligand concentration
5
4
42
6
+
MALDIꢀTOF mass spectrum, m/z: 810 [M
+ Na] ,
+
–3
–1
8
26 [M + K] .
Investigation methods. H NMR spectra were recorded on a
Bruker Avance 600 instrument with a working frequency of
00 MHz, and chemical shifts in the δ scale were measured
2•10 mol L , metal to ligand concentration ratio 1 : 1 and
1 : 2) was checked under different concentration conditions
(ligand concentration 4•10–3 mol L , metal to ligand concenꢀ
tration ratios 1 : 1 and 1 : 2). This verification made it possible to
refine stoichiometry of the formed complexes, in particular, to
choose between the complexes with m = 1, n = 1 and m = 2,
n = 2 or those with m = 1, n = 1 and m = 2, n = 1.
1
–1
6
using Me Si as internal standard. IR spectra (see Fig. 1) were
4
obtained for compounds in thin layer between KBr plates on a
FTꢀIR Vectorꢀ22 spectrometer (Bruker) with a resolution abilꢀ

Tris(βꢀdiketones) and their complexes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 11, November, 2006 2007
H. von Schnering, Angew. Chem., Int. Ed. Engl., 1995,
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 04ꢀ03ꢀ32992
and 05ꢀ03ꢀ08086ofi_a).
3
4, 993.
1
1
2
8. R. W. Saalfrank, H. Maid, N. Mooren, and F. Hampel,
Angew. Chem., 2002, 114, 323.
9. J. Yuan, S. Sueda, R. Somazawa, K. Matsumoto, and
K. Matsumoto, Chem. Lett., 2003, 32, 492.
0. A. P. Bassett, S. W. Magennis, P. B. Glover, D. J. Lewis,
N. Spencer, S. Parsons, R. M. Williams, L. De Cola, and
Z. Pikramenou, J. Am. Chem. Soc., 2004, 126, 9413.
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Received July18, 2006