Formation of the cobalt hydrogenation catalysts at the action of lithium aluminum hydride and lithium tri(tert-butoxy)aluminohydride and their properties

Article abstract of DOI:10.1134/S1070363212080026

The interaction of Co(acac)2(3) with LiAlH4 or LiAlH(t-BuO)₃ was studied using NMR, UV, IR, ESR spectroscopy, electron microscopy, and volumometry. The basic stages of formation of cobalt catalysts for hydrogenation were suggested. The formation of the nanoparticles that are active in the hydrogenation process is shown to occur at a ratio of reagents 5 ≤ Red/Co ≤ 12. The nanoparticles are stabilized by an excess of LiAlH4 or LiAlH(t-BuO)₃, as well as by the products of their catalytic decomposition under the action of cobalt in the reduced state. At the ratio LiAlH4 / Co> 12 to obtain the particles active in catalysis their activation by a proton-donor compound is required.

Full text of DOI:10.1134/S1070363212080026

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 8, pp. 1334–1341. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © F.K. Schmidt, Yu.Yu. Titova, L.B. Belykh, V.A. Umanets, S.S. Khutsishvili, 2012, published in Zhurnal Obshchei Khimii, 2012,
Vol. 82, No. 8, pp. 1244–1251.
Formation of the Cobalt Hydrogenation Catalysts
at the Action of Lithium Aluminum Hydride and Lithium
Tri(tert-butoxy)aluminohydride and Their Properties
a
a
b
a
b
F. K. Schmidt , Yu. Yu. Titova , L. B. Belykh , V. A. Umanets , and S. S. Khutsishvili
a
Irkutsk State University, ul. Karla Marksa 1, Irkutsk, 664003 Russia
b
Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia
e-mail: fkschmidt@chem.isu.ru
Received June 16, 2011
4 3
Abstract—The interaction of Co(acac)2(3) with LiAlH or LiAlH(t-BuO) was studied using NMR, UV, IR,
ESR spectroscopy, electron microscopy, and volumometry. The basic stages of formation of cobalt catalysts for
hydrogenation were suggested. The formation of the nanoparticles that are active in the hydrogenation process
is shown to occur at a ratio of reagents 5 ≤ Red/Co ≤ 12. The nanoparticles are stabilized by an excess of
4 3
LiAlH or LiAlH(t-BuO) , as well as by the products of their catalytic decomposition under the action of cobalt
4
in the reduced state. At the ratio LiAlH / Co> 12 to obtain the particles active in catalysis their activation by a
proton-donor compound is required.
DOI: 10.1134/S1070363212080026
The study of the Ziegler systems based on the
transition metal complex compounds combined with
the organic hydride compounds of the metals from I–
III groups in the hydrogenation catalysis has been
carried out since the second half of XX century and is
continued now [1–4]. Despite such a long period of
study and industrial applications of these systems, in
particular, in the process of hydrogenation of polymers
metal compounds catalyzed by the transition metals
[8, 9].
We have previously shown [10] that in the forma-
tion of nickel-based hydrogenation catalysts using
lithium aluminum hydride LiAlH , the function of the
4
latter is not limited to the reduction of the nickel pre-
cursor. The tetrahydroaluminate anions adsorbed on
the surface act as a stabilizer of the nickel nano-
particles. Besides, the tetrahydroaluminate anions and
probably products of catalytic decomposition of
[5], some aspects of the formation and nature of the
catalytically active species require further research of
fundamental nature. This concerns, above all, establish-
ing all the functions of the I–III groups metal com-
pounds in the processes of formation and operation of
the Ziegler type catalyst.
LiAlH occupying the vacant positions on the surface
4
may act as catalyst poisons. Therefore, the resultant
nanoparticles are active in the hydrogenation only
when they are activated by a proton-donor compound.
In contrast to nickel, the palladium catalysts active in
the hydrogenation are formed under the action of
To date, experimentally has been shown that the co-
reagents in the Ziegler type systems are involved in the
formation of hydride or an organic derivative of the
transition metal, reduction of the transition metal com-
pound, most often to the metal in the zero oxidation
state, formation of adducts with the reduced form of
the transition metal of the type of acid–base
interaction, and stabilization of nanoparticles [6–8].
However, some aspects of this problem have not yet
been substantiated experimentally. These include the
role of the decomposition reactions of the I–III group
LiAlH without activation with alcohol or water at a
4
ratio of LiAlH /Pd < 10 [11].
4
These results have generated the need to study the
cobalt-containing catalytic systems, formed by using
LiAlH and its alkoxy derivative LiAlH(t-BuO) as the
4
3
reducing agent, in the hydrogenation processes.
Among the catalytic systems of the Ziegler type based
on β-diketonates of the metals of first transition series,
the cobalt-containing catalysts are distinguished by
1
334

FORMATION OF THE COBALT HYDROGENATION CATALYSTS
Formation of hydrogen in the reaction of Co(acac)2(3) with LiAlH or LiAlH(t-BuO) : cCo= 8.3 mM, T = 30°C
1335
4
3
(
mol Н
2
)/(g-at Со)
Red:Co
Co(acac)
n
–LiAlH
4
, n = 2, 3
n 3
Co(acac) –LiAlH(tert-BuO)
а
b
b
а
а
Co(acac)
2
Co(acac)
2
Co(acac)
3
Co(acac)
2
Co(acac)
3
2
4
6
8
1.5
1.9
2.2
3.8
5.2
6.3
7
0.9
1.5
1.8
2.1
2.3
2.6
0.7
2.4
3.2
1.4
3.2
4.1
1.9
3.9
4.7
2.4
1
1
0
6
4.6
5.1
2.8
5.8
5.5
8
3.4
a
b
Mixed solvent: benzene–THF 10:2. Solvent THF.
two features: a high activity in the hydrogenation of
alkenes and arenes [3, 7] and a possibility of carrying
out the reactions of conjugated hydrogenation of
alkenes and arenes in the presence of the systems
modified with trialkylphosphines [12]. A research of
the cobalt-containing catalytic systems will allow
establishing general patterns and characteristics of the
The formation of hydrogen in the quantity above
equimolar points to the process of decomposition of AlH3
catalyzed by the transition metal clusters [10, 13]:
cat
2
AlH
3
→ 2Al + 3H
2
.
(3)
Since the total amount of the released hydrogen is
more than 4 mol of H per 1 mol of Co(acac) and
2
2
catalysts formed at the action of LiAlH and its
4
6
mol of H per 1 mol of Co(acac) (see the table),
2
3
alkoxyhydride derivatives on the cobalt compounds.
which could form at the quantitative decomposition of
The reaction between Co(acac) [or Co(acac) ] and
AlH and reduction of Co(acac)2(3), hence, along with
2
3
3
LiAlH in THF medium at room temperature proceeds
the decomposition of aluminum hydride AlH partial
4
3
with rapid change of the solution color from lilac [or
decomposition of LiAlH occurs.
4
green in the case of Co(acac) ] to brown, and with the
3
The hydrogen evolution in amount more than
equimolar was also observed in the reaction of cobalt
release of molecular hydrogen. The analysis of volu-
metric data suggests the existence of three periods on
the kinetic curves: the first period from 0 to 0.5 min,
the second from 0.5 to 5 min, and the third, the slowest
one, from 5 min to several hours. Given the fact that
the formation of cobalt catalysts did not exceed 5 min
and the principal amount of hydrogen is evolved in this
time interval, we analyze the results of gas release only
in the first and second periods.
acetylacetonates with LiAlH(t-BuO) (see the table),
3
but the amount and rate of hydrogen release is about
twice lower compared with LiAlH in the reaction with
4
Co(acac) and 3–5 times less with Co(acac) . Such a
2
3
result is quite expectable given the lower reactivity of
the aluminum alkoxyhydride derivatives.
According to the volumetric data, the partial order
As can be seen from the data listed in the table, the
hydrogen yield at various reactant ratios is much
higher than 1 mol of H per 1 mol of Co(acac) and
of the reaction with respect to LiAlH varies depending
4
on the LiAlH /Co(acac) ratio (Fig. 1). In the range
4
2(3)
2
2
of the ratio LiAlH /Co(acac) = 2–6 the order with
4
2
1
.5 mol of H per 1 mol of Co(acac) , as expected ac-
respect to LiAlH is unity, in the range 6–15, it
2
3
4
cording to the stoichiometric equations:
Co(acac) + 2LiAlH = Co + 2Li(acac) + 2AlH
Co(acac)
decreased to 0.3. Similar results were obtained for
Co(acac) : the first order on LiAlH in the range of
3
4
2
4
3
+ H
2
,
(1)
(2)
LiAlH /Co(acac) = 2–8, and n = 0.3 in the range of
4
3
2
3
+ 6LiAlH
4
the ratio of reagents 8–15. The reaction order in the
mixed solvent (benzene–THF) with both Co(acac)2,
=
2Co + 6Li(acac) + 6AlH
3
2
+ 3H .
In the mixed solvent THF–benzene the hydrogen
yield is lower compared to the reaction in THF. These
data evidence indirectly that benzene is directly
involved in the formation of reduced cobalt particles.
and Co(acac)
equal to 0.4 with respect to LiAlH
the reaction order from unity to 0.3 (or 0.4) isprobably
due to the heterophase character of the processes of the
3
in the range of LiAlH
4
/Co = 6–15 is
. The decrease in
4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 8 2012

1
336
SCHMIDT et al.
(
a)
(b)
Red:Co(acac)
2
Red:Co(acac)
3
Fig. 1. The dependence of the rate of hydrogen release at the reduction of (a) Co(acac)
2
and (b) Co(acac)
3
with lithium aluminum
(black
hydride (1, 2) and LiAlH(t-BuO)
circles). cCo = 8.3 mM, T = 30°C.
3
(3, 4) on the molar ratio of reagents, in THF (light circles) and mixed solvent THF–C H
6 6
AlH and LiAlH decomposition under the action of
quantitative analysis of UV spectra is not possible.
3
4
the reduced form of cobalt. For the system of Co(acac)
2(3)–LiAl(t-BuO) there is no clearly expressed areas
However, qualitative analysis of the UV spectra of
reaction mixtures of Co(acac) –nLiAlH in THF as
3
2
4
with a permanent order, the order varies from 1 to 0.5
in the investigated range of the ratio of LiAl(t-BuO)3
to Co(acac)2(3) (Fig. 1, curves 3, 4).
well as in benzene–THF showed that with the
increasing LiAlH /Co(acac) ratio and in the course of
4
2
time the intensity of the absorption band at 290 nm
decreases, in particular, for the Red/Co = 15 it was not
observed after 20 min of keeping (Fig. 2, curve 4). The
resulting spectral data indicate the destruction of the π-
system of acac ligand that may result from the
interaction of the resulting Li(acac) with lithium
aluminum hydride:
In parallel with volumometry, we carried out
studies of the reaction systems using IR, UV, and
NMR spectroscopy. The IR spectra of Co(acac)2–
nLiAlH (n = 2) recorded 10 min after the start of the
4
reaction indicated lower intensity of the absorption
–
1
bands at 1586 and 1520 cm of the mixed stretching
vibrations [ν(C=O)+ν(C = C)] of the acac ligands in
Li(acac) + LiAlH
4
O,O-chelate form of Co(acac) [7] and the appearance
2
→ LiO–C(CH )=CH–CH(CH )–OAlH Li.
3
3
3
of new poorly resolved absorption bands at 1607 and
–
1
Similar spectral pattern was obtained at the
1
515 cm , characteristic of stretching [ν(C=O) +
reduction of Co(acac) with lithium aluminum hydride.
3
ν(C=C)] vibrations of the acac ligand in Li(acac),
indicating the transfer of the acac ligands from cobalt
to lithium. For n = 4, in the IR spectrum in the region
At replacing the reducing agent by LiAlH(t-BuO) the
3
acac ligand also is transferred from cobalt to lithium,
but the destruction of π-acac ligand in Li(acac) is not
practically observed.
–
1
of 1500–1700 cm only the absorption bands of acac
ligand in Li(acac) were registered. The spectral analysis
of reaction mixtures revealed the following pattern: With
increasing molar ratio of LiAlH /Co(acac) the
The information on the nature of the products of
4
2
LiAlH and LiAlH(t-BuO) transformation was ob-
4
3
2
7
Li(acac) concentration in the reaction system
decreases. The IR spectroscopy data are consistent
with the results of UV spectroscopy. The spectral
characteristics of Co(acac) (λ = 288 nm, ε = 288 =
tained also from the analysis of Al NMR spectra of
the reaction systems. According to the Al NMR
2
7
spectroscopy, the resonance signal with the chemical
–
4
2
max
shift 98 ppm, characteristic of the AlH anion, was
–
1
–1
1
2
6 200 l mol cm ) and Li(acac) (λ = 292 nm, ε =
92 = 22 000 l mol cm ) are close, so the
registered in the system Co(acac) –nLiAlH at the ratio
max
2
4
–
1
–1
LiAlH /Co(acac) ≥ 4. Along with the resonance signal
4 2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 8 2012

FORMATION OF THE COBALT HYDROGENATION CATALYSTS
1337
D
λ, nm
Fig. 2. UV spectra of Co(acac)
of Co(acac) –nLiAlH for n = 2 (2), 6 (3), and 15 (4). cCo
.3 mM, benzene–THF (10:2), T = 30°C. Two-fold diluted
2
(1) and the reaction system
3
0 nm
2
4
=
8
2 4
Fig. 3. TEM image of the system of Co(acac) –10 LiAlH .
2
Co(acac) solution (1).
2
7
at 98 ppm, in the Al NMR spectra the resonance
signal of weak intensity with chemical shift 34 ppm,
and a broad signal with chemical shift about 70 ppm
were observed. The resonance signal at δ 34 ppm,
which, according to the scale of chemical shifts,
corresponds to pentacoordinted Al, presumably can be
will be favored at the decomposition of AlH to the
elements catalyzed by the reduced forms of cobalt. The
set of reactions (3–6) allows us to understand and
3
explain not only the formation of LiAl(t-BuO) in the
4
reaction system, but also the release of hydrogen in the
amount more than equimolar (see the table). The
assigned to AlH(acac) . The large width of the
resonance signal from the free LiAlH(t-BuO) was
detected in the Al NMR spectrum at a molar ratio of
2
3
2
7
resonance signal at δ 70 ppm (~5000 Hz) indicates the
presence of aluminum in the form with a high
nuclearity, and its position, according to the scale of
Red/Co(acac) ≥ 8.
2
Study of the system Co(acac) –LiAlH(t-BuO) by
2
7
2
3
Al chemical shifts, corresponds to the aluminum in a
ESR spectroscopy revealed theappearance of a broad
signal of the ferromagnetic resonance in the range of
molar ratios Red/Co = 2–16 [3] with the g-factor from
tetrahedral oxygen environment [14]. Most likely, it
should be attributed to an associate of the interaction
products of Li(acac)with lithium aluminum hydride.
2
.22 to 2.47 (ΔH = 860–1520 Gs). This signal is
When LiAlH(t-BuO) was used as a reducing agent,
3
characteristic of associated nanosized cobalt particles
in a reduced state like Co(0). In the systems of
Co(acac) –LiAlH in the range of molar ratios LiAlH /
the resonance signals with chemical. shifts of 53, 59
2
7
and 70 ppm were found in the Al NMR spectra. The
2
4
4
signals with δ 53 and 59 ppm correspond to LiAl(t-
Co = 2–16 in the ESR spectrum a low-intensity ESR
signal was observed, which so far cannot be attributed
to a specific compound. It should be noted that in the
BuO) [15] and [Al(t-BuO) ] , respectively. The [Al(t-
4
3 2
BuO) ] is formed in the redox process between Co
3
2
(
acac)2 and LiAlH(t-BuO) . The formation of tetra-
(3) 3
systems based on LiAlH , in contrast to the systems
4
substituted derivative LiAl(t-BuO) may be the a result
4
based on LiAlH(t-BuO) , the ferromagnetic resonance
3
of several reactions.
signal was not observed.
2
LiAlH(tert-BuO)
[AlH(tert-BuO) + 2Li(tert-BuO),
Al(tert-BuO) + 2Li(tert-BuO)
3
The nanoparticles formed in these systems are likely
to be the associates of the heterometallic (Al–Co) com-
pounds appearing at the catalytic decomposition of
aluminum hydrides (AlH and LiAlH ) at the action of
→
←
]
2 2
(4)
[
3 2
]
→
2LiAl(tert-BuO)
4
,
(5)
(6)
3
4
→
3
AlH(tert-BuO)2 ← AlH
3
+ 2Al(tert-BuO)
3
.
the complexes containing cobalt in the reduced state
[Co(0), Co(I)].
Despite the relative stability of LiAl(t-BuO) and
4
AlH(t-BuO) to disproportionation, these processes
The diameter of the basic particles formed in the
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 8 2012

1
338
SCHMIDT et al.
(
a)
(b)
4 2
LiAlH :Co(acac)
3 3
LiAlH(tert-BuO) :Co(acac)
Fig. 4. Dependence of the activity of cobalt catalysts in the hydrogenation of styrene on the Red/Co molar ratio: (a) without adding
n-BuOH (1), after the activation with n-BuOH (2), cCo = 8.3 mM, (b) at various concentrations of Co(acac) : cCo = 4.2 mM (3),
Co = 12.5 mM (4), T = 30°C, P(H ) = 2 atm.
3
c
2
system Co(acac) –10 LiAlH , according to TEM
position of these two reducing agents under the action
of cobalt in the reduced state.
2
4
(
transmission electron microscopy), is 2–3 nm, they
are partially aggregated to form particles with a
diameter up to 7–9 nm (Fig. 3). The size of the
particles formed at the reduction of Co(II) with LiAlH
Testing the above cobalt-containing systems in the
process of hydrogenation of styrene showed that the
activity of the nanoparticles formed depends on the
nature of the reducing agent, the Red/Co(acac)2(3) ratio,
and the sequence of mixing the components. In
particular, the Co(acac) –LiAlH system is almost
(
t-BuO) (Red/Co = 10) varies from 1.9 to 5.7 nm.
3
Thus, at the reduction of cobalt acetylacetonates
with LiAlH or LiAlH(t-BuO) the nanoparticles are
4
3
2
4
formed stabilized by the excess of LiAlH or LiAlH(t-
4
inactive in the hydrogenation at the ratio Red/Co < 5.
BuO) and also by the products of catalytic decom-
3
In the range of 5 ≤ Red/Co ≤ 12 the activity increases,
–
1
reaching 30 min (Fig. 4). With increasing ratio of
LiAlH /Co > 12 a decrease in the catalytic activity
4
occurs and at the Red/Co ≥ 20 the activity almost
reaches zero. An extreme form of the dependence was
previously found for the Pd(acac) –nLiAlH system
2
4
[11]. The introduction of n-butanol to the system of
Co(acac) –LiAlH after the formation of the catalyst
2
4
(
n-BuOH/LiAlH = 1) leads to the appearance and (or)
4
increase in the hydrogenating activity of the system
Fig. 4, curve 2). Obviously, like the case of nickel
(
catalysts [10], LiAlH and its catalytic decomposition
4
products adsorbed on the surface of cobalt nano-
particles poison the catalytically active sites, and intro-
duction of a proton-donor compound can eliminate or
diminish their inhibitory effect. In contrast to lithium
aluminum hydride, LiAlH(t-BuO) shows no inhibitory
effect on the catalytic properties of the cobalt
hydrogenation catalysts (Fig. 5).
3
3 2
LiAlH(t-BuO) :Co(acac)
Fig. 5. Dependence of initial rate of anthracene hydro-
genation on the Red/Co molar ratio in the presence of a
catalytic system Co(acac)
absence of substrate by method a (1) and in the presence of
the substrate by method b (2, 3): cCo = 21 mM (1), cCo
.3 mM (2, 3), T = 30°C, P(H ) = 2 atm, solvent THF.
2 3
–LiAlH(t-BuO) formed in the
By changing the order of mixing the components,
=
that is, by adding the Co(acac) in the LiAlH –styrene
2 4
8
2
solution in THF (or mixed solvent), is possible to
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 8 2012

FORMATION OF THE COBALT HYDROGENATION CATALYSTS
1339
increase the activity of the catalytic system by about
0% compared to the catalyst obtained by adding a
solution of LiAlH to a solution of Co(acac) . The
substance regardless of the catalyst system composi-
3
tion [10], whereas for Co(acac) the composition in the
2
range 5 ≤ LiAlH /Co ≤ 12 not requires an additional
4
2
4
catalyst performance is better at the Red/Co = 10
without activation with a proton-donor compound, and
an improvement of the catalyst in time is observed. At
the consecutive hydrogenation of several portions of
styrene, the maximum activity was observed at
introducing 2nd and 3rd 1-ml portions of styrene. With
proton-donor compound for the formation of a
hydrogenation catalyst. At increasing the molar ratio
over twelve it becomes necessary to add alcohol for
the catalyst activation. It follows from these observa-
tions that the decomposition products of lithium
aluminum hydride appearing under the influence of
cobalt do no block the entire surface of the Co(0)
nanoclusters, due may be to a lower degree of
increasing concentration of Co and LiAlH there is a
4
tendency to shift the maximum toward larger amounts
of styrene.
decomposition of LiAlH
. The comparison of the yield
4
of hydrogen in the reaction of LiAlH with Co(acac)
4
2
Effect of the order of mixing components on the
catalyst system can also be seen in the hydrogenation
and Ni(acac) shows that the yield of hydrogen per one
2
mole of the metal is about 1.5–2 smaller for the former.
However, we cannot exclude also other possible causes
of the observed results. For example, cobalt aluminides
are richer in aluminum compared with nickel deriva-
tives at the identical conditions of their production, and
probably this decreases the effect of poisoning of the
cobalt catalyst compared to nickel one.
of anthracene. The activity of a Co(acac) –LiAlH(t-
2
BuO) system formed in the presence of anthracene in
3
the hydrogenation reaction at 30ºC and hydrogen
pressure 2 bar is very low (Fig. 5, curve 3). The rate of
hydrogenation of anthracene increases dramatically
(
by ~2 orders of magnitude) when anthracene is added
to a solution of catalyst 2–5 min after the components
have been mixed and the release of the main part of
hydrogen has ceased, that is, after the formation of the
cobalt nanoclusters. Anthracene is converted into 9,10-
dihydro- and 1,2,3,4-tetrahydroanthracene quantita-
tively. The rate of hydrogenation of anthracene in the
presence of the cobalt catalyst prepared in this way
EXPERIMENTAL
Solvents [benzene, tetrahydrofuran (THF)], sub-
strates (styrene, anthracene), reagent (t-butanol) were
purified by the techniques used commonly in the work
with organometallic materials [16]. For deeper re-
moving water, benzene was subjected to further
(
method a) depends on the Red/Co molar ratio (Fig. 5,
distillation over LiAlH on a distillation column and
4
curve 1) and the concentration of Co(acac) (Fig. 5,
2
stored under argon in sealed ampules over molecular
sieves 4A. THF after the removal of peroxides was
curves 1, 2.) The increase in the Red/Co ratio leads not
only to increase in the initial rate, but also to the
improvement in the catalyst performance. A formal
order with respect to cobalt is equal to 2.2–2.4, which
indicates a microheterogeneous (nanoscale) nature of
the catalysis.
distilled successively over sodium, LiAlH , and
4
benzophenone ketyl, and then stored under argon in
sealed ampules. Water concentration determined by
the method of Fischer [11], was in benzene 1.1×
–3
–3
1
0 M, in THF 1.6×10 M.
The study of the system using electron microscopy
showed that the average particle size is 3.7 nm prior to
the anthracene hydrogenation and 10.9 nm after it. The
cobalt nanoclusters aggregation may be one of the
causes of deactivation of the examined catalysts.
Anthracene was additionally purified by sublime-
tion (T = 160–170ºC, 1 mm Hg).
Synthesis of cobalt bis-acetylacetonate and tris-
acetylacetonate was carried out in accordance with the
procedures described in [17] and [18], respectively.
The results obtained show the occurrence of rather
complex processes at the formation of cobalt catalysts
under the action of lithium aluminum hydride and its t-
butoxyhydride derivative, as seen from the catalytic
properties of the catalyst. Comparison of the catalytic
properties of systems based on Co(acac) and Ni(acac)
Lithium aluminum hydride (commercial) was used
without prior recrystallization. Weighed portion of
LiAlH
in an inert atmosphere through a glass frit. The LiAlH
was dissolved in THF, the solution was filtered
4
4
concentration determined by the volume of hydrogen
released at the hydrolysis was about 95–98% of
2
2
obtained at the action of lithium aluminum hydride
shows their fundamental difference. Nickel catalyst is
formed only after the activation with a proton-donor
2
7
theoretical. Al NMR spectrum (THF): δAl 98 ppm,
1
quintet, JAlH = 173 Hz.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 8 2012

1
340
SCHMIDT et al.
Synthesis of LiAlH(t-BuO) was carried out by
Experiments on the hydrogenation of styrene were
carried out in a hydrogenation vessel of common form
with temperature control, at 30°C, hydrogen pressure
2 atm (0.20265 MPa), at vigorous stirring, which
ensures that the reaction in the diffusion region occurs
in kinetic region. In the pre-filled with hydrogen and
evacuated reactor was charged successively under
3
alcoholysis of LiAlH with t-butanol in THF at 30°C
4
over 48 h in accordance with [19], the molar ratio
[
t-BuOH]/[LiAlH ] = 3. Monitoring was carried out by
4
2
7
27
Al NMR spectroscopy. The Al NMR spectrum
(
THF): δ 78 ppm (singlet).
Al
Study of the reaction of Co(II) and Co(III) bis
–4
hydrogen weighed sample of Co(acac) (2×10 mol)
2
(
acetylacetonates) with LiAlH [or LiAlH(t-BuO) ] at
4
3
and benzene (10 ml), and the mixture was stirred till
dissolving. To the resulting lilac solution of Co(acac)2
the different ratios of the initial components was
carried out in an atmosphere of dry oxygen-free argon
in a thermally controlled reactor providing a possibility
of preliminary evacuation and filling with argon.
was added substrate (styrene, 1 ml) and LiAlH or
4
LiAlH(t-BuO) solution in THF. The reactor was
3
closed by a Teflon stopper with a rubber gasket (for
sampling), hydrogen was added at a pressure of 1 atm,
and the stirring was switched on. The course of the
hydrogenation reaction was monitored by a decrease of
the hydrogen pressure and by GLC on a Chrom-5
chromatograph with a flame ionization detector (FID),
carrier gas nitrogen, column length 3.6 m, diameter
3 mm; phase carbowax 20M. Similarly the experi-
To quantify the amount of the molecular hydrogen
produced in the reaction of components of a catalytic
system a special vessel was used under temperature
control, with an additional section inside where to
place the second component. Into the reactor, pre-
evacuated, filled with argon, and connected to a
volumetric system was placed a solution of 0.0257 g
–
4
–4
(
1×10 mol) of Co(acac) or 0.0356 g (1×10 mol) of
ments with Co(acac) were carried out.
2
3
Co(acac) in 10 ml of benzene. To the internal section
3
Hydrogenation of anthracene. a. In the pre-filled
with hydrogen and evacuated hydrogenation vessel of
common form under the hydrogen flow were charged
was placed an aliquot of LiAlH [or LiAlH(t-BuO) }
4
3
solution in THF. The vessel was closed with a Teflon
stopper, and at vigorous stirring the reducing agent and
the Co(acac)2(3) solutions were mixed. The resulting
hydrogen was determined volumetrically. The solutions
were analyzed using UV, IR, and NMR spectroscopy.
successively a solution of LiAlH(t-BuO) in THF (1 ml)
3
–
4
–4
and a solution of Co(acac) (1×10 to 5×10 mol) in
2
2
3 ml of THF. To the resulting dark brown solution of
the catalyst was added anthracene under the hydrogen
flow. After closing with Teflon stopper with a rubber
gasket (for sampling), the hydrogen pressure was
raised to 1 at and the stirring was switched on. The
course of the hydrogenation was monitored by the drop
in hydrogen pressure. Analysis of the products of
anthracene hydrogenation was carried out using gas
chromatography–mass spectrometry. Cobalt catalyst
formed in this way had the maximum catalytic activity.
UV spectra were recorded on a SF 2000
spectrometer in the range of 250–430 nm in a fused
quartz cell with absorbing layer thickness 0.01 cm. The
IR spectra of solutions were taken on a Specord 75 IR
spectrometer using a KRS cell of 0.2 mm thickness
flushed with argon (solvent benzene–THF). NMR
spectra were recorded on a VXR-500S Varian pulse
2
7
spectrometer. The Al chemical shifts were measured
relative to external reference: 0.1 M solution of
2
7
b. Differs from the method a that in the hydro-
genation vessel under a hydrogen flow were suc-
Al(NO ) . To prevent hydrolysis at recording the Al
3
3
NMR spectra, the liquid sample was placed in a quartz
ampule 5 mm in diameter previously evacuated and
filled with argon, and sealed. The ESR spectra were
recorded on ELEXSYS E580 Bruker spectrometer at
room temperature.
cessively charged a solution of LiAlH(t-BuO) in 1 ml
3
of THF, dry anthracene, and 13 ml of THF at stirring.
To the resulting white suspension a solution of
–
4
–4
Co(acac) (2×10 to 5×10 mol) in THF (10 ml) was
2
poured. In this case, the catalyst has less activity than
The study of samples with transmission electron
microscopy was performed on a Philips EM-410
microscope. A drop of the catalyst solution formed in
situ was applied to the bearing mesh coated with
carbon film and dried under argon. The conditions of
registering preclude melting and decomposition of the
samples under electron beam.
the catalyst obtained by the method a.
–
4
When to the solution of Co(acac) (1×10 –5×
2
–4
10 mol) in THF (20 ml) was added dropwise a
solution of LiAlH(t-BuO) in the presence of dissolved
3
anthracene, the formed catalytic system is not active in
the hydrogenation under the above conditions.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 8 2012

FORMATION OF THE COBALT HYDROGENATION CATALYSTS
1341
ACKNOWLEDGMENTS
nets, V.A., and Shmidt, F.K., Kinetika i Kataliz, 2006,
vol. 47, no. 3, p. 373.
. Ganem, B. and Osby, J., Chem. Rev., 1988, vol. 86,
p. 763.
0. Belykh, L.B., Titova, Yu.Yu., Rokhin, A.V., and
Shmidt, F.K., Zh. Prikl. Khim., 2010, vol. 83, no. 11,
p. 1778.
1. Belykh, L.B., Titova, Yu.Yu., Umanets, V.A., and
Shmidt, F.K., Zh. Prikl. Khim., 2006, vol. 79, no. 8,
p. 1285.
This work was performed under the Federal Target
Program “Research and scientific-pedagogical staff of
innovation in Russia” (State contract no. P1344).
9
1
1
REFERENCES
1
2
3
. Sloan, M.F. and Matlack, A.S., and Breslow, D.S.,
J. Am. Chem. Soc., 1963, vol. 85, p. 4014.
. Kalechits, I.V. and Shmidt, F.K., Kinetika i Kataliz,
966, vol. 7, no. 4, p. 614.
. Shmidt, F.K., Kataliz kompleksami metallov pervogo
perekhodnogo ryada reaktsii gidrirovaniya
1
12. Shmidt, F.K., Levkovskii, Yu.S., Ryutina, H.M., and
Bakunina, T.I., Kinetika i Kataliz, 1982, vol. 23, no. 10,
p. 360.
i
dimerizatsii (Catalysis of Hydrogenation and Dimeriza-
tion Reactions by the Complexses of the Metals of First
Transition Row), Irkutsk: Irkutsk. Gos. Univ., 1986.
. Alley, W.M., Hamdemir, I.K., Johnson, K.A., and
Finke, R.G., J. Mol. Catal. (A), 2010, vol. 315, no. 1,
p. 1.
. McManus, N.T. and Rempel, G.L., J. Macromol. Sci.
Rev. Macromol. Chem. Phys. C, 1995, vol. 35, no. 2,
p. 239.
. Bonnemann, H., Braun, G., Brijoux, W., Brinkmann, R.,
Tilling, A.S., Seevogel, K., and Siepen, K., J. Organo-
met. Chem., 1996, vol. 520, p. 143.
13. Soloveichik, G.L. and Bulychev, B.M., Usp. Khim.,
1983, vol. 52, no. 1, p. 72.
14. Fedotov, M.A., Molchanov, V.V., Zotov, R.N., and
Tuzikov, F.V., Zh. Neorg. Khim., 2008, vol. 53, no. 10,
p. 1735.
15. Horne, D.A., J. Am. Chem. Soc., 1980, vol. 102, no. 19,
p. 6011.
16. Gordon, A.J. and Ford, R.A., The Chemist’s Com-
panion. A Handbook of Practical Data, Techniques and
References, New York: Wiley, 1972.
4
5
6
7
8
17. Ellern, J.B. and Ragsdale, R., Inorg. Syntheses., 1968,
vol. 11, p. 82.
1
8. Shalhoub, G.M., J. Chem. Education., 1980, vol. 57,
. Shmidt, F.K., Nindakova, L.O., Shainyan, B.A., Sara-
ev, V.V., Chipanina, N.N., and Umanetz, V.A., J. Mol.
Catal. (A), 2005, vol. 235, nos. 1–2, p. 161.
no. 7, p. 525.
19. Schuldt, B., Heller, D., Storz, F., and Madeja, K.,
J. Mol. Catal., 1993, vol. 81, no. 2, p. 195.
. Belykh, L.B., Goremyka, T.V., Skripov, N.I., Uma-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 8 2012