HYDROGENATION OF UNSATURATED HYDROCARBONS CATALYZED
215
[
RhCl3 + Co(AcAc)2] : [Al(iꢀBu)3] : [allene] or [DMA] pounds on the support surface, the initial dark brown
was 1 : 2–6 : 4–6. A calculated amount of allene or solutions became colorless, and the support became
DMA was added to a dark pink suspension of RhCl3 in dark gray. The absence of palladium in the solution was
toluene. Then one half of triisobutylaluminum was confirmed by elemental analysis data.
added at vigorous stirring. Two hours later the second
The specific catalytic activity (A, mol/(mol h)) was
calculated as the number of moles of substrate conꢀ
verted per hour divided by the number of moles of the
portion of the organoaluminum component was
added. The solution gradually changed its color from
redꢀbrown to dark brown. The reaction was carried out
for 4 days. Since the reactant rhodium chloride is
insoluble in toluene, the end point of the complex forꢀ
mation was determined as that of the complete dissoꢀ
lution of the salt. The bimetallic Rh–Co complex was
obtained via the same procedure. According to eleꢀ
mental analysis data, the rhodium concentration in
the solution corresponded to the calculated value.
Below, these complexes will be denoted as
Rh(allene)ol, Rh(DMA)ol, and Rh–Co(DMA)ol.
Complexation was also carried out in anhydrous
ethanol, which completely dissolves rhodium chloꢀ
ride. A calculated amount of 1,1ꢀdimethylallene (1 : 6)
was added to a bright red solution of the salt with vigꢀ
orous stirring. The reaction was carried out for 4 h.
The reaction mixture gradually took a dark brown
color characteristic of hydrogenation catalysts. The
synthesized metalorganic compound was active in the
polymerization and oligomerization of allenes and
inactive in the hydrogenation of unsaturated subꢀ
strates. Neither the replacement of ethanol with an
aromatic solvent nor activation of the complex with an
organoaluminum compound was attempted.
metal, at 20 С and a hydrogen pressure of 0.1 MPa.
°
RESULTS AND DISCUSSION
It is known that the interaction of organoalumiꢀ
num compounds (triisobutylaluminum) with transiꢀ
tion metal (Pd, Ni, Co, Fe) salts in the presence of
1,2ꢀ or 1,3ꢀdienes (allene, 1,1ꢀdimethylallene, isoꢀ
prene) primarily occurs as an exchange reaction,
resulting in the formation of the alkyl derivatives of
transition metals. As a result of insertion of diene molꢀ
ecules at the formed metal–carbon or metal–hydroꢀ
gen bond, oligomer (linear or cyclic) fragments with
different chain lengths are formed [3]. In the case of
the synthesis of homogeneous metal complex comꢀ
pounds with oligomeric allene ligands, the determinꢀ
ing factor is the ratio of the reaction components. The
following molar ratio: [Rh] : [Al] : [DMA] = 1 : 6 : 6
are optimal for the production of oligodimethylallene
rhodium complexes. According to gas chromatograꢀ
phy–mass spectrometry data for the degradation
products of the synthesized complexes, the oligomeric
ligand corresponds to tetraꢀ, pentaꢀ, and mainly hexꢀ
americ forms of 1,1ꢀdimethylallene.
The substrates were hydrogenated by traditional
procedure in a thermostated batch shaking reactor
with a volume of the reaction mixture of 17 ml, using
toluene as a solvent, at a constant pressure of hydrogen
during the experiment (50 or 68 kPa). The temperaꢀ
Our investigations focused on the catalytic activity
of monoꢀ and bimetallic rhodium complexes with oliꢀ
godimethylallene ligands. The allene complexes
Rh(allene)ol exhibited a low catalytic activity in the
hydrogenation of hexeneꢀ1 (800 mol/(mol h)) and
were unstable: a black precipitate was formed during
the reaction and the solution became colorless.
ture varied from 20 to 35 С.
°
The materials used, namely, the solvents, the subꢀ
strates (isoprene, hexeneꢀ1, toluene), and the gases
(argon, hydrogen) were purified and dried according
to the conventional procedures accepted in operation
with metalorganic compounds.
The products of toluene hydrogenation were idenꢀ
tified by gas chromatography–mass spectrometry
(GC–MS) on a Kratos MSꢀRF spectrometer (a colꢀ
Figure 1 depicts isoprene hydrogenation rate
curves in the presence of rhodium and rhodium–
cobalt systems. The curves have two portions with difꢀ
ferent hydrogen uptake rates, indicating that both
double bonds are hydrogenated. The rate of hydrogen
uptake during isoprene hydrogenation on Rh–
Co(DMA)ol is 2.7 times that on Rh(DMA)ol. The speꢀ
cific catalytic activity in the hydrogenation of the first
double bond was 6130 and 2300 mol/(mol h) for these
two systems, respectively; the difference in activity in
the hydrogenation of the second double bond was
somewhat lower, 1380 vs. 820 mol/(mol h). In this
umn of 2 m
×
2 mm packed with PEGꢀ20M Carboꢀ
wax). The products of decomposition of the comꢀ
plexes with dilute sulfuric acid were characterized by
mass spectra recorded on the same instrument by the
direct injection of a sample into the ion source with
programming temperature up to 300 С.
°
The catalysts were heterogenized by contacting tolꢀ case, we also observed the synergistic effect of the
uene solutions of the homogeneous Pd(DMA)ol, Pd– bimetallic complexes which was earlier revealed in the
Ni(DMA)ol, Rh(DMA)ol, and RhꢀCo(DMA)ol comꢀ hydrogenation of dienes over bimetallic palladium sysꢀ
plexes with a mineral support (
The support was preliminary vacuumed at 300
3 h. During the absorption of metal complex comꢀ catalysts was described by Masters [3]: being active
γꢀAl2O3) under argon. tems containing a nonprecious transition metal [11,
°С
for 12]. The complete diene hydrogenation on rhodium
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010