ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 8, pp. 1271!1277. + Pleiades Publishing, Inc., 2006.
Original Russian Text + L.B. Belykh, Yu.Yu. Titova, V.A. Umanets, F.K. Shmidt, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79,
No. 8, pp. 1285!1291.
Palladium Hydrogenation Catalysts Modified
with Aluminum- and Phosphorus-containing
Compounds and with Alcohols:
Effect of Modifiers
L. B. Belykh, Yu. Yu. Titova, V. A. Umanets, and F. K. Shmidt
Irkutsk State University, Irkutsk, Russia
Received March 14, 2006
Abstract-The catalytic properties of nanosize catalysts derived from Pd(acac)
and triethylaluminum in
hydrogenation of organic substrates were studied, and the optimal conditions for the catalyst preparation
were found. The maximum observed on the plot of the catalyst specific activity vs. Al/Pd ratio was explained
Transition metals and their complexes catalyze
hydrogenation of unsaturated organic compounds with
gaseous hydrogen; the process has numerous industri-
al applications [1, 2]. A particular place is occupied
by palladium catalysts, whose properties significantly
differ from those of catalysts containing Rh, Pt, Ru,
Ni, or Cu . Palladium is one of the most active
metals in the hydrogenation of double bonds conju-
fated with an aromatic ring, such as Ar3C=C, Ar3C=O,
or Ar3C=NR. Furthermore, Pd is one of the most
selective metal catalysts in the hydrogenation of triple
and conjugated double bonds and the most active
metal in hydrogenolysis, i.e., reductive cleavage of
C3X bonds. However, at low temperatures Pd is vir-
tually inactive in the hydrogenation of the majority
of aromatic rings and shows low activity in the hy-
drogenation of aliphatic ketones and aldehydes .
These characteristics determine the applications of
palladium-based catalysts in chemo- and stereo-selec-
tive hydrogenation, hydrogenolysis, and dehydrogena-
tion of various organic compounds.
Along with heterogeneous catalysts, hydrogenation
catalysts based on transition metal complexes has at-
tracted growing researchers’ attention since the second
half of the XXth century with the development of co-
ordination catalysis. A particular place among such
catalysts is occupied by Ziegler-type catalytic systems
. The majority of studies in this field concerned the
nature and properties of hydrogenation catalysts based
on b-diketonate, carboxylate, and cyclopentadienyl
complexes of transition metals of the first row ,
and also the synthesis of metal nanoparticles by treat-
ment with organoaluminum compounds .
The problems of the formation mechanism, phase
state, and nature of hydrogenation-active species in
Ziegler-type catalytic systems based on Pd(II) com-
plexes and the properties of these systems have been
studied to a lesser extent [17, 18] and are the subject
of this paper.
Solvents (toluene, benzene, hexane) were purified
by standard procedures required for manipulations
with organometallic compounds . For more ex-
haustive drying, the solvents were additionally dis-
tilled from LiAlH
on a distillation column and were
stored under Ar in sealed ampules over 4 A molecular
Palladium bis(acetylacetonate) Pd(acac)
pared according to .
H NMR, d, ppm: 5.04 s (2H,
CH), 1.76 s (12H, CH
Commercial-grade triethylaluminum AlEt
distilled in a vacuum; the fraction boiling at 48349oC
(1 mm Hg) was collected.
H NMR, d, ppm: 1.22 t
J = 8.24 Hz), 0.45 q (6H,
J = 8.24 Hz).
The samples were stored in a glass ampule under Ar.
Solutions of triethylaluminum in hexane were pre-
pared in a Schlenk vessel under Ar.