Synthesis and polymerization in unsaturated Co β-diketonates

Article abstract of DOI:10.1023/B:RUCO.0000043895.61512.77

Polymerization of some unsaturated β-diketonates of cobalt containing double bonds both unconjugated and conjugated with a metal cycle. Unlike monomeric complexes, cobalt in metal-containing polymers was shown to have tetrahedral structure of the coordination polyhedron. The kinetic parameters of polymerization depend on electronic and steric properties of β-diketonates.

Full text of DOI:10.1023/B:RUCO.0000043895.61512.77

Russian Journal of Coordination Chemistry, Vol. 30, No. 10, 2004, pp. 709–712. Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 10, 2004, pp. 753–757.
Original Russian Text Copyright © 2004 by Zub, Berezhnitskaya, Savchenko, Voloshanovskii, Gudich, Mazurenko, Shevchenko.
Synthesis and Polymerization in Unsaturated Co b-Diketonates
V. Ya. Zub*, A. S. Berezhnitskaya**, I. S. Savchenko*, I. S. Voloshanovskii***,
I. N. Gudich*, E. A. Mazurenko**, and O. V. Shevchenko***
*Kiev National University, ul. Glushkova 6, Kiev, 252127 Ukraine
**Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine,
pr. Akademika Palladina 32/34, Kiev, 252680 Ukraine
***Mechnikov National University, Dvoryanskaya ul. 2, Odessa, Ukraine
Received August 4, 2003
Abstract—Polymerization of some unsaturated β-diketonates of cobalt containing double bonds both uncon-
jugated and conjugated with a metal cycle. Unlike monomeric complexes, cobalt in metal-containing polymers
was shown to have tetrahedral structure of the coordination polyhedron. The kinetic parameters of polymeriza-
tion depend on electronic and steric properties of β-diketonates.
Recently, researchers show great interest in the are of unquestionable interest. One of the requirements
metal-containing polymers, since they are the promis-
ing catalysts and materials with valuable functional
properties [1, 2]. One of the most suitable methods for
synthesizing metal-containing polymers consists in
polymerization of metal-containing unsaturated com-
pounds, in particular, coordination compounds with
unsaturated ligands. This method is interesting in that it
allows one to produce polymers where all functional
groups are bound to the metal ions, i.e., to produce
materials with homogeneous chemical composition.
However, polymerization of coordination compounds
for the metal complexes as monomers is that they have
the high solubility and thermodynamic stability in
organic solvents used in the polymerization reactions.
With this fact in view, the metal β-diketonates are con-
sidered to be suitable models for studying polymeriza-
tion of coordination compounds.
Previously, we described polymerization of some β-
diketonates of Ni(II) [6]. The aim of this work was to
synthesize and study polymerization of unsaturated β-
diketonates of Co(II) containing both α- and γ-unsatur-
is poorly studied [3–5], although the studies in this field ated substituents.
R2
R1
R2
R1
CH3
O
O
5-Methyl-5-hexene-2,4-dione (Mhd)
7-Octene-2,4-dione (Od)
3-Allylpentane-2,4-dione (Apd)
1,1,1-Trifluoro-3-allylpentane-2,4-dione (Fapd)
–C(CH3)=CH2
–CH2–CH2–CH=CH2
–CH3
H
H
–CH2–CH=CH2
–CH2–CH=CH2
–CF3
EXPERIMENTAL
The structure and composition of the synthesized
compounds were determined from the data of elemen-
tal analysis, electronic and IR spectroscopies. The elec-
tronic absorption and diffuse reflection spectra were
recorded on a Specord M40 spectrophotometer in the
range of 25000–11000 cm–1; IR spectra were measured
on a Specord M80 spectrophotometer in the range of
4000–400 cm–1 (with KBr pellets).
The β-diketonates used in the synthesis were pre-
pared according to the procedures described in [7, 8].
The cobalt β-diketonate complexes were obtained by
reacting an aqueous solution of cobalt acetate (1 mmol)
with an alcoholic solution of the corresponding β-dike-
tone (2 mmol). The complexes obtained were filtered
off and recrystallized from the alcoholic solutions at
room temperature. Since the metal diketonates with
The kinetics of a free-radical polymerization was
unsaturated substituents can polymerize on heating, studied by dilatometric method at 80°ë in DMF solu-
their purification by vacuum sublimation is undesir- tion at the monomer concentration 0.15 mol/l and at the
able.
concentration of initiator (2,2'-azo-bis(isobutyronitrile)
1070-3284/04/3010-0709 © 2004 åÄIä “Nauka /Interperiodica”

710
ZUB et al.
Table 1. Results of elemental analysis of Co β-diketonates
The electronic absorption and diffuse reflection
spectra of the Co complexes are almost identical, which
suggests that the complexes in solution and in polycrys-
talline state have similar structures. The electronic
absorption spectra of monomeric complexes contain a
broad absorption band at 515 nm that was assigned to
Content (found/calcd), %
Complex
M
C
H
the 4T1g(F)
4T1g(P) transition of Co(II) with pseu-
Co(Mhd)2 · 2H2O 16.93/16.87 48.46/48.38 6.92/6.84
Co(Od)2 · 2H2O 15.66/15.55 51.24/51.17 7.47/7.38
Co(Apd)2 · 2H2O 15.66/15.57 51.24/51.15 7.47/7.39
Co(Fapd)2 · 2H2O 12.16/12.07 39.78/39.7 4.56/4.47
dooctahedral ligand surrounding (Fig. 1, 1). The coor-
dination sphere of Co is completed to octahedron as the
result of coordination of two water molecules. The dif-
fuse reflection spectra of anhydrous complexes indicate
the tetrahedral structure of the Co coordination sur-
rounding (the absorption band of Co(II) appears that is
characteristic of this symmetry type and corresponds to
the 4A2
4T1(P) transition at 630 nm).
The radical polymerization of Co β-diketonates can
be considered as three parallel reactions (initiation,
growth and termination of a chain) that occur at con-
stant rate only at the initial stage of the process:
0.0015 mol/l for all complexes. The obtained metal-
containing polymers were precipitated from solutions
with isopropanol.
CH3
RESULTS AND DISCUSSION
Me
R
.
CH2
The results of elemental analysis of the synthesized
β-diketonates of Co indicate the formation of ëÓ(β-Dik)2 ·
2H2O complexes (β-Dik is β-diketone) that are colored
red (Table 1). However, these compounds can readily
transform into anhydrous blue-colored complexes
ëÓ(β-Dik)2 or can form as a mixture of two phases.
IR spectra of unsaturated β-diketonates of cobalt are
similar to those of metal β-diketonates with bidentately
coordinated unsaturated ligand and a delocalized sys-
tem of π-bonds in a chelate ring (Table 2) [9]. However,
these spectra are peculiar in that they contain a band in
the region of 1630–1650 cm–1 due to the stretching
vibration of a double bond ν(ë=ë) of unsaturated sub-
stituents. The bands due to the stretching vibrations
ν(ëÓ–O) are slightly shifted toward long-wave region
as compared to cobalt acetylacetonate and are close in
their parameters to the bands observed for cobalt triflu-
oroacetylacetonate ëo(Tfa)2.
O
O
O
Co
H2O
OH2
O
Me
Me
O
O
O
.
+R
Co
H2O
OH2
CH3
O
Me
R
.
CH2
Me
O
O
O
Co
H2O
OH2
O
CH2
.
R
Me
CH3
CH2 CH
(
CH2 CH
)
m
(
)
n
A
Co(Od)2
0.9
0.6
0.3
Me
Me
2
O
O
O
O
O
O
Co
Co
O
O
Me
Me
(
1
H2C
CH2 CH
)
k
400
500
600
700
λ, nm
Shown in Fig. 2 are the kinetic curves of polymer-
ization of 0.15 M solutions of cobalt β-diketonates in
DMF. One can see that the polymerization reaction pro-
ceeds with a short induction period. The rate of poly-
Fig. 1. Electronic absorption spectra of 0.02 M solution of
(1) monomer and (2) 0.002 M solution of polymer of
ëÓ(Mhd) in DMF.
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 10 2004

SYNTHESIS AND POLYMERIZATION
711
Table 2. Selected frequencies (cm–1) in IR spectra of monomeric and polymeric Co β-diketonates
Compound
Co(Acac)2
ν(MO)
ν(CO)
ν(CC)
ν(C=C)
450
427
1598
1621
1545
1550
1560
1555
1550
1550
1598
1639
1590
1580
1580
1575
1590
1590
Co(Tfa)2
Co(Mhd)2
[Co(Mhd)2]n
Co(Od)2
435
1630
1645
<400
435
[Co(Od)2]n
Co(Apd)2
[Co(Apd)2]n
<400
435
1630
<400
1630resid
merization reaction (Vp), the reduced polymerization
The values of polymerization rate constants suggest
rate (Vred), and the overall rate constant of polymeriza- that, as in the case with Ni complexes, the reactivity of
tion (KΣ) were calculated from the initial sections of β-diketonates of Co depends on the nature of β-dike-
polymerizatiaon curves:
tone. The highest polymerization rate at concentration
0.15 mol/l is observed for the Co complex with meth-
acrylacetone ëÓ(Mhd)2. This can be explained by the
fact that the given double bond is conjugated with the
metal cycle plane. In the case with the fluorinated β-
diketonate complex ëÓ(Fapd)2, the polymerization rate
and the yield of the metal-containing polymer are sub-
stantially lower than in the case of non-fluorinated
β-diketonates, which is likely to occur due to delocal-
ization of the electron density on the trifluoromethyl
substituent.
10Ugm
MmV t
1
–d[M]
---------------- --
Vp = ---------------- =
,
dt
where [M] is the initial monomer concentration, U is
conversion over time t (%), gm is the weighed portion of
a monomer (g), Mm is the molar mass of a monomer, V
is the dilatometer volume (ml), t is the polymerization
time (s);
Vp
Vred = ---------
[M]
It is worth noting that for ëÓ(Mhd)2, the polymer-
ization of complexes in DMF proceeds at the higher
rate than in ethanol. The values of Vp for ëÓ(Mhd)2 in
DMF are almost one order of magnitude as high as the
rates of polymerization of this complex in alcohol (Vp =
0.87 × 10–3 mol/l s) [3]. The authors of [3] failed to
obtain metal complexes with the other β-diketones in
and
Vp
[M][I]1/2
----------------------
KΣ =
,
where [I] is the starting concentration of initiator. The alcohol solutions. This can be due to the fact that the
results obtained are listed in Table 3.
reaction of polymerization in the alcohol solutions
U, %
1
2
(a)
(b)
60
1
80
60
40
20
2
3
50
40
30
20
10
3
4
20 40 60 80 100 120
20
40
60
80
100
0
0
t, min
Fig. 2. Kinetic curves of polymerization in DMF of 0.15 M solutions of (a) (1) ëÓ(Mhd) , (2) ëÓ(Od) , (3) ëÓ(Apd) , and (4)
2
2
2
Co(Fapd) ; (b) (1) Ni(Mhd) , (2) Ni(Od) , and (3) Ni(Apd) [6].
2
2
2
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 10 2004

712
ZUB et al.
Table 3. Kinetic parameters of polymerization of 0.15 M
solutions of Co β-diketonates in DMF
form tetrahedral structures that considerably reduce
steric hindrances for the formation of the polymer
chains.
Vp × 105,
Vred × 105,
KΣ × 104,
Complex
s–1
l1/2/(mol1/2 s)
It is interesting that in the case with the nickel com-
plexes Ni(β-Dik)2(H2O)2, the highest polymerization
rate was observed for Ni(Od)2 with a flexible α-substit-
uent n-ë4ç7. Obviously, this is due to the fact that in the
formation of metal-containing polymers with pseu-
dooctahedral configuration of the chelate unit, the most
important role is played by the steric factors rather than
the electronic structure: in the given complex, the dou-
ble bond is located at a significant distance from the
metal cycle plane and therefore, the complex polymer-
ization occurs with the least spatial hindrances.
mol/(l s)
Co(Mhd)2
Co(Apd)2
10.33
7.45
10.14
2.93
4.28
3.86
4.88
36.21
31.72
34.78
9.58
13.12
10.48
12.60
3.41
Co(Od)2
Co(Fapd)2
Ni(Mhd)2 [6]
Ni(Apd)2 [6]
Ni(Od)2 [6]
14.34
12.96
15.67
7.52
6.09
7.78
Thus, the results of the above study showed that the
reactivity of the metal-containing monomers based on
β-diketonates in the polymerization reaction depends
on the nature of a metal and β-diketone and is deter-
mined both by the electronic and steric factors.
occurs with significant chain transfer to the solvent.
Moreover, the system homogeneity can be violated as
the result of insolubility of the polymer formed in eth-
anol.
The isolated metal-containing polymers are finely
dispersed powders of blue color. The results of elemen-
tal analysis correspond to the calculated composition
[ëÓ(β-Dik)2]n, i.e., all the functional groups of a mac-
roligand are bound to the metal ion. IR spectra of poly-
mers exhibit some broadening of the bands due to
vibrations ν(ëé) and ν(ëë) and substantial reduction
in the intensity of the bands due to the stretching vibra-
tions of double bonds C=C. The bands corresponding to
ν(ëÓé) are shifted to the region below 400 cm–1, which
indicates that this bond becomes weaker after polymer-
ization (Table 2).
The electronic absorption spectra of solutions of
poly-β-diketonates of Co in DMF have the shape typi-
cal of the Co2+ ions with tetrahedral configuration
(Fig. 1, 2). Thus, the composition of the Co2+ coordina-
tion polyhedron changes during polymerization. It is
obvious that the tetrahedral structure of the coordina-
tion core is most favorable for macromolecules.
REFERENCES
1. Pomogailo, A.D. and Sevast’yanov, V.S., Metallo-
soderzhashchie monomery i polimery na ikh osnove
(Metal-Containing Monomers and Polymers on Their
Base), Moscow: Khimiya, 1988
2. Pomogailo, A.D. and Uflyand, I.E., Makromoleku-
lyarnye metallokhelaty (Macromolecular Metal Che-
lates), Moscow: Khimiya, 1991.
3. Movchan, T.I., Voloshanovskii, I.S., and Pomogailo,A.D.,
Izv. Ross. Akad. Nauk, Ser. Khim., 1993, no. 12, p. 2060.
4. Zagnii, V.V., Syromyatnikov, V.G., and Sinyavskii, V.G.,
Vestnik Kievskogo Universiteta. Khimiya, 1987, no. 28,
p. 37.
5. Pomogailo, A.D. and Uflyand, I.E., Ross. Khim. Zh.,
1996, vol. 40, nos. 4–5, p. 55.
6. Zub, V.Ya., Berezhnitskaya, A.S., Oliinyk, N.F, and
Savchenko, I.A., Ukr. Khim. Zh., 2001, vol. 67, no. 12,
p. 69.
7. Voloshanovskii, I.S., Butova, T.D., and Shevchenko, O.V.,
The comparison of the above results with the data
that we previously obtained for analogous Ni com-
plexes [6] shows that polymerization of Co2+ β-diketo-
nates takes place at the higher rate and with the higher
yield (Fig. 2, Table 2) than in the case with Ni2+. This
can be explained by the tendency of the Co2+ ions to
Zh. Obshch. Khim., 1999, vol. 69, no. 9, p. 1504.
8. Voloshanovskii, I.S., Manaeva, T.I., Shevchenko, O.V.,
and Mamontov, V.P., Zh. Prikl. Khim. (S.-Peterburg),
2000, vol. 73, no. 2, p. 283.
9. Thornton, A.D., Coord. Chem. Rev., 1990, vol. 104,
p. 173.
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