Ruthenium Catalysts for Asymmetric Transfer Hydrogenation
COMMUNICATIONS
Catalysis with Organometallic Compounds, Wiley-
VCH, Weinheim, 1996.
Experimental Section
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General Remarks
All manipulations were performed under an argon atmos-
phere using standard Schlenk techniques. Isopropyl alcohol
was used without further purification (purchased from
Fluka, dried over molecular sieves). Sodium isopropoxide
was prepared by reacting sodium with isopropyl alcohol
under an argon atmosphere (stock solution). All ketones
were dried over CaH2, distilled in vacuum and stored under
argon, except 4’-methoxyacetophenone and phenacyl chlo-
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ride, which were used without further purification.
[19]
BuP(Ad)2
and N-phenyl-2-(di-tert-butylphosphino)-pyr-
role[20] were synthesized according to literature protocols.
General Procedure for the Transfer Hydrogenation of
Ketones
In a 10-mL Schlenk tube, the in situ catalyst was prepared
by stirring a solution of [RuCl2
(C6H5)]2 (1.910À6 mmol),
G
ligand 3a (3.810À6 mmol) and PPh3 (3.810À6 mmol) in
1.0 mL isopropyl alcohol for 16 h at 658C. To this mixture
sodium isopropoxide (1.910À5 mmol in 0.5 mL isopropyl al-
cohol (stock solution)) was added and the solution stirred at
1008C for 10 min. After addition of the corresponding
ketone (0.38 mmol in 0.5 mL isopropyl alcohol (stock solu-
tion)) the reaction mixture was stirred for 1 h at 1008C. The
solution was cooled to room temperature and filtered over a
plug of silica. The conversion and ee were measured by GC
without further manipulations.
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Acknowledgements
This work has been supported by the State of Mecklenburg-
Western Pomerania and the “Bundesministerium für Bildung
und Forschung (BMBF)”. Additional support came from the
BMBF excellence center “CELISCA” and the “Graduierten-
kolleg 1213 - Neue Methoden für Nachhaltigkeit in Katalyse
und Technik” and Leibniz price of the DFG. We thank Mrs.
M. Heyken, Mrs. C. Voss, Dr. C. Fischer, Mrs. S. Buchholz
(all Leibniz-Institut für Katalyse e.V. an der Universität Ro-
stock) and J. Schumacher (Universität Rostock) for their ex-
cellent technical and analytical support.
[8] No product was obtained when [RuHCl
A
performed without addition of base.
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