School of Engineering and Science - Jacobs University

“quasi-homogeneous” cinchonidine stabilized Pt nanoclusters are discussed below.
Further, the experimental conditions selected for these experiments were chosen to be
mild: room temperature and low hydrogen pressure (2-10 bar) since these are likely to
be the most relevant conditions for hydrogenation of α-ketoesters on an industrial scale.
4.2 Experimental
Materials
Unless otherwise mentioned the following materials: Pt on alumina (Aldrich 5% Pt),
cinchonidine (> 98%, Fluka), acetic acid (99.8% Fluka), ethyl pyruvate (98%, Aldrich),
THF (Applichem, 99.8%), formic acid (Aldrich, 99%), bis-dibenzylidene acetone
(Fluka, ≥96.0%), K 2 PtCl 4 (Acros Organics) and ethanol (Applichem, 99.9%) were used
as received in all chapters.
The 5 % Pt on alumina (E4759) catalyst was kindly provided by Engelhard company by
request.
Sample preparation
In order to activate the conventional Pt/Al 2 O 3, it was heated at 300 °C under vacuum
(10 -3 mbar) for 1 hour, then kept for 3 hours under flowing hydrogen (100 ml/min) and
cooled to room temperature. Then the required amount was weighed and transferred
into a glass reactor with acetic acid, ethyl pyruvate and cinchonidine.
Chiral modification of conventional Pt/Al 2 O 3 . 40 mg of conventional Pt/Al 2 O 3 was
heated to 400 ºC under vacuum (10 -3 mbar) for 1 hour, then the mixture of N 2 (93%)
and H 2 (7%) gases were passed (100 ml min -1 ) over the sample for 3 hours. Then, under
flowing gases (H 2 and N 2 ), the support was cooled to room temperature and the solution
of cinchonidine in CHCl 3 (6.0 ml, 3 mM) was added by syringe through a stopper. The
system was kept at 10-15 ºC for 24 hours, then washed 3 times with CHCl 3 and finally
dried under vacuum at room temperature.
Preparation of 10.11-dihydrocinchonidine (DHCIN) has been done according to the
protocol from work of Morawsky [171]. 10 g cinchonidine (33 mmol) was dissolved in
100 ml 0.5 M H 2 SO 4 and placed in a metal reactor. 0.5 g Pd/C (5 % wt, Degussa
E101/0/W) was added to the solution. The H 2 pressure was set to 6 bars, reaction
started by stirring. After 1.5 h reaction was finished. The catalyst was removed via a G4
filter, 50 ml 2 M NaOH was added to precipitate the hydrated alkaloid. The white
precipitate was washed with 500 ml H 2 O and recrystallized in ethanol. It has to be
noted that resulted product had some amount of cinchonidine, as was detected as
presence of attenuated peak at 1636 cm -1 in IR spectrum of the product, which
corresponds to the stretching of C=C bond.
The preparation of Pt 2 (DBA) 3 organometallic complex has been done according to the
literary protocol [172, 173]. Typically, to a solution of 2.8 g sodium acetate
and 2.36 g of bis-dibenzylidene acetone (dba) in 60 mL of ethanol at 50 °C was added a
solution of 1.40 g K 2 PtCl 4 in 12 mL of freshly distilled water. The initial pale yellow
suspension redissolved while the mixture was heated to the refluxing temperature (90
°C). After refluxing for 1 h a dark violet precipitate formed. The mixture was allowed
to settle overnight. The solution was eliminated by filtration and the solid washed three
times with 200 mL of water, dried overnight under vacuum, further washed three times
with 200 mL of pentane and finally dried under vacuum overnight.
A water soluble Pt nanoclusters modified with DHCIN was prepared based on the
protocol published by Bönnemann [114]. Typically, 0.208 g (0.6 mmol) PtCl 4 in 160 ml
distilled water was reduced with 0.1 M aqueous formic acid (15 ml) with dissolved
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