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ing Information). For the continuous C4 hydroformylation,
slight deactivation was observed over a prolonged reaction
time. The extent of this deactivation behavior is comparable to
that observed for Rh-2/silica100 with a pure 1-butene feed. A
temperature variation to 110 and 1208C resulted in slightly
lower n/iso selectivities and more pronounced catalyst deacti-
vation. Even though the extraordinary long-term stability of
Experimental Section
Chemicals
Rh(CO) (acac) (acac=acetylacetonate), methanol, and dichlorome-
2
thane (HPLC grade) were purchased from Sigma–Aldrich and used
without further purification. The sulfoxantphos ligand 1 was syn-
thesized by sulfonation of 9,9-dimethyl-4,5-bis(di-tert-butylphosphi-
[14]
[
10]
no)xanthene (Sigma–Aldrich) according to a literature procedure.
a comparable SILP system was not achieved, the observed
behavior is quite remarkable for an initially purely physisorbed
catalyst complex with a labile diphosphite ligand such as 2.
One possible explanation for deactivation might be the forma-
tion of water as a side-product of the aldol reaction. During
the long-term test, considerable amounts of water are formed
in the pores, which possibly lead to the gradual hydrolysis of 2
over time.
The benzopinacol ligand 2,2’-[(3,3’-di-tert-butyl-5,5’-dimethoxybi-
phenyl-2,2’-diyl)bis(oxy)]bis-(4,4,5,5-tetraphenyl-1,3,2-dioxaphos-
pholane) (2) was supplied by Evonik Industries AG, Marl, Germany.
Silica gel 100 (63–200 mm) was purchased from Merck, and Triso-
por 423 (100–200 mm) from VitroBio GmbH. For the long-term sta-
bility experiment silica gel 100 (200–500 mm) was used. The SiO
2
materials were pretreated at 6008C for 18 h before use in catalyst
preparation. 1-Butene (99.5%), ethylene (99.95%), CO (99.97%),
and H (99.999%) were purchased from Linde AG. The industrial C
2
4
In addition, inductively coupled plasma (ICP) measurements
of spent catalyst materials often revealed a decreased Rh con-
tent, which was of the same order of magnitude as the loss of
catalytic activity observed during the catalytic runs. This loss of
Rh is probably caused by liquid entrainment of the condensed
aldol phase from the support over the duration of a continuous
experiment.
feedstock was provided by Evonik Industries AG and contained
2
8% 1-butene, 44% 2-butenes, ꢂ 0.1% iso-butene, and 28% inert
butanes. 2-Methyl-2-pentenal (97%) was purchased from Sigma–
Aldrich.
Catalyst preparation
All syntheses were carried out using standard Schlenk techniques
under Ar (99.999%). Rh(CO) (acac) was dissolved in methanol or di-
2
chloromethane, for the reaction with 1 or 2, respectively, and
stirred for 5 min. Ligand 1 or 2 was added in a fivefold molar
excess (ligand/Rh=5) dissolved in methanol or dichloromethane,
respectively, and the resulting solution was stirred for 5 min. In the
long-term stability experiment, a tenfold molar excess of 2 (ligand/
Rh=10) was used. After addition of the appropriate amount of cal-
cined silica 100 or Trisopor 423 (see Supporting Information), the
suspension was stirred for another 10 min. The organic solvent was
removed by using a rotatory evaporator, and the dry powder was
Conclusions
Catalytic materials comprising Rh complexes with sulfoxant-
phos (1) and benzopinacol-based ligands (2), Rh-1 and Rh-2,
respectively, dispersed on the internal surface of porous SiO2
materials have been prepared and successfully tested in the
continuous gas-phase hydroformylation of short-chain alkenes.
The observed regioselectivities to the linear aldehyde were 97
and 99.5%, respectively, which are comparable to those typi-
cally obtained in classical liquid-phase and supported ionic-
liquid-phase (SILP) catalysis. A significant mass increase of up
to 30% was revealed by weighing the catalytic materials after
the reaction in the case of Rh-2/silica100. By using headspace-
GC–MS analysis, this increase in catalyst mass could be attrib-
uted to high-boiling compounds that were generated during
the hydroformylation process itself. Herein, the aldol condensa-
tion products were clearly assigned as the main components.
Dissolved in a condensed phase of high-boiling compounds
inside the pores of the supporting material, the catalytically
active species operate in a homogeneous fashion. A model
that explains the process of pore filling during the catalytic re-
action and possible differences in the start-up behavior of the
tested catalyst materials has been presented. The amount of
condensed high-boiling compounds was found to depend on
ꢀ4
further dried under vacuum (1ꢃ10 bar) overnight. In the case of
aldol addition prior to catalysis, 2-methyl-2-pentenal was mixed
with the Rh-1 and Rh-2 solution, respectively, before addition of
the solid support. No drying under high vacuum was performed
for these catalytic materials (for details see Supporting Informa-
tion).
Catalytic experiments
The reaction setup applied in our laboratories for continuous gas-
phase hydroformylation comprised a fixed-bed reactor, upstream
feed dosing, evaporation and mixing, downstream pressure regula-
tion, and online GC. The entire rig was heated by using electric
heating devices. The catalyst material was filled into a tubular reac-
tor and purged three times with He at room temperature. The rig
was pressurized with He and left under pressure for 15 min while
monitoring the pressure. If no pressure drop was observed, the re-
actor was heated to the reaction temperature under He pressure.
After adjustment of the molar flows, the feed gas (alkene and
syngas) was allowed to enter the reactor. The alkene substrate was
fed into the rig by using an HPLC pump, and syngas was dosed by
using mass-flow controllers. Evaporated alkene was combined with
the preheated reaction gases in a mixing unit, which was filled
with glass beads to ensure proper mixing and isothermal condi-
tions. The gas mixture could then either enter the reactor or exit
the system through a bypass. The reactor consisted of a stainless-
steel tube (12 mm diameter, 500 mm length) equipped with
the catalyst activity and porosity of the applied SiO support.
2
The catalysts were remarkably stable under the optimized con-
ditions, but long-term experiments (up to 1000 h) still revealed
some decay in the system activity. This finding distinguishes
these product-supported systems from classical SILP catalysts,
in which the presence of an ionic liquid film provides a more
robust stabilizing liquid phase for the active Rh complex.
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 2955 – 2963 2962