Asymmetrische Nanokatalyse: N‐heterocyclische Carbene als chirale Modifikatoren von Fe₃O₄/Pd‐Nanopartikeln

Stereoselective Hydrosilylation of Enals and Enones Catalysed by Palladium Nanoparticles

“…[8,12] Promising results were obtained with Pd-A C H T U N G T R E N N U N G (OAc) 2 and tricyclohexylphosphine (PCy 3 ); a catalyst combination described by Oshima et al for the stereoselective 1,4-hydrosilylation of a,b-unsaturated ketones, [13] allowing us to isolate the desired enolsilane as a single Z isomer with a conversion of 63 % (Table 1, entry 1). Superior yields and faster conversions were obtained with the PdCl 2 /PCy 3 catalyst system (Table 1, entry 3).…”

“…[1] However, stereoselective reactions catalysed by nanoparticles are still quite rare, [2] the substrate scopes of the reactions are often very limited [3] and, in many cases, these reactions have turned out to be catalysed by leached catalyst species in the solution phase. [4] Herein, we report that palladium nanoparticles (PdNPs) can be used in a highly stereoselective hydrosilylation of unsaturated enals and enones catalysed by PdNPs with a wide substrate scope.…”

Enantioselective α‐Arylation of Cyclic Ketones Catalyzed by a Combination of an Unmodified Cinchona Alkaloid and a Palladium Complex

“…After completion of the reaction (monitored by GC-MS), the reaction mixture was poured into saturated aqueous NH 4 Cl (5 mL). The aqueous phase was extracted with CH 2 Cl 2 (3 10 mL), the combined organic phases were dried over MgSO 4 and concentrated under vacuum. Purification of the residue by flash column chromatography provided the respective title compounds.…”

“…However, surprisingly, no heterogeneous system resulted, as mercury poisoning and filtration test indicated a homogeneous nature of the catalytically active species. [4,18] In conclusion, we have developed a Pd/Cinchonacatalyzed a-arylation reaction of cyclic ketones and aryl bromides and iodides under phosphine-free conditions. An unmodified Cinchona alkaloid results in high levels of activity and selectivity with up to 93% ee.…”

“…[3] In addition, a chiral heterogeneous catalyst, Pd/Fe 3 O 4 nanoparticles modified by a chiral N-heterocyclic carbene (NHC), has been successfully employed in the asymmetric a-arylation. [4] In the past 30 years, the naturally occurring Cinchona alkaloids have been widely applied by themselves or as versatile precursors for organocatalysts in asymmetric synthesis, chromatographic selectors and NMR discriminating agents. [5] Many attractive properties like ready availability, high levels of rigidity, robustness and multifunctional nature render Cinchona alkaloids especially valuable.…”