An Ion‐Pair Immobilization Strategy in Rhodium‐Catalyzed Asymmetric Transfer Hydrogenation of Aromatic Ketones

Abstract

A chiral diamine-based homogeneous cationic rhodium catalyst was developed and two heterogeneous cationic rhodium catalysts were obtained via the encapsulation of the homogeneous cationic rhodium catalyst within Me-SBA-15 and Me-SBA-16. All these catalysts presented excellent catalytic activities and high enantioselectivities in ultrasoundpromoted asymmetric transfer hydrogenation of aromatic ketones and represent a successful use of the ion-pair immobilization strategy. More importantly, the encapsulation of the cationic rhodium functionality within Me-SBA-16 had an obvious high recyclability, in which the recycled catalyst could be reused nine times without significantly affecting its enantioselectivity, showing good potential in industrial application.

The Golden Age of Transfer Hydrogenation

“…The obtained composites exhibited heterogeneous nature, excellent catalytic activity, high enantioselectivities, and great substrate scope tolerance in ultrasoundpromoted ATH of aromatic ketones (Figure 1). 658 The catalytic activities of these two heterogeneous catalysts were comparatively even higher than those of the homogeneous counterpart. In addition, their good reusability and recyclability were observed, and in particular the cationic rhodium functionality within Me-SBA-16 was recycled at least 10 times with only slight loss of activity and retained the same enantioselectivity.…”

Multistep Organic Transformations over Base‐Rhodium/Diamine‐Bifunctionalized Mesostructured Silica Nanoparticles

“…The other group of broad F resonances between δ =−142 and −156 ppm are assigned to F signals in BF 4 − anions that interact with the Rh III centers of the (Cp*RhTsDPEN) + BF 4 − complex by the BF 4 − hydrogen bonding. This is proved by the homogeneous liquid‐state 19 F NMR spectrum (Figure S4) –…”

Selective Reduction of Carbonyl Compounds via (Asymmetric) Transfer Hydrogenation on Heterogeneous Catalysts

“…39 Chiral N-sulfonylated diamine-based η 5 -Cp*RhTsDPEN [Cp* = pentamethylcyclopentadiene; TsDPEN = 4-(methylphenylsulfonyl)-1,2-diphenylethylenediamine] was encapsulated into mesoporous siliceous Me-SBA-15 and Me-SBA-16 (ion-pair interactions as the mode of immobilization) (Scheme 3). 40 In the presence of the newly synthesized catalysts, excellent catalytic activity was achieved; for ultrasound-promoted ATH of aromatic ketones the heterogeneous catalysts showed higher initial rates then the neutral homogeneous counterpart (Cp*RhTsDPEN) (TOF values for 4-methylacetophenone: 475 vs 390 h -1 ; for 4-methoxyacetophenone: 300 vs 215 h -1 ). 40 Not only was high catalytic activity reported, but also high enantioselectivity, good reusability and recyclability.…”