Chloride‐Bridged Dinuclear Rhodium(III) Complexes Bearing Chiral Diphosphine Ligands: Catalyst Precursors for Asymmetric Hydrogenation of Simple Olefins

Abstract

Efficient rhodium(III) catalysts were developed for asymmetric hydrogenation of simple olefins. A new series of chloride-bridged dinuclear rhodium(III) complexes 1 were synthesized from the rhodium(I) precursor [RhCl(cod)]2 , chiral diphosphine ligands, and hydrochloric acid. Complexes from the series acted as efficient catalysts for asymmetric hydrogenation of (E)-prop-1-ene-1,2-diyldibenzene and its derivatives without any directing groups, in sharp contrast to widely used rhodium(I) catalytic systems that require a directing group for high enantioselectivity. The catalytic system was applied to asymmetric hydrogenation of allylic alcohols, alkenylboranes, and unsaturated cyclic sulfones. Control experiments support the superiority of dinuclear rhodium(III) complexes 1 over typical rhodium(I) catalytic systems.

Iridium‐Catalyzed Asymmetric Hydrogenation of Unfunctionalized Exocyclic C=C Bonds

“…In 1997, Pfaltz discovered that using ap hosphine-oxazolinel igand (PHOX) [3] as ac hiral mimic of Crabtree'sc atalyst [4] could enantioselectively reduce unfunctionalized olefins,w hicha re challengings ubstrates for ruthenium-a nd rhodium-based catalyst systems because of the absence of ac helating group. [5,6] Iridium complexes bearing P, N-ligands [7] have attracted much attention as ar esult of their high activity and good enantioselectivec ontrol. Prompted by these groundbreaking discoveries, hundreds of chirali ridium-based catalysts were developeda nd applied to the reductiono fn umerous unfunctionalized alkenes.…”

“…With the optimized reactionc onditions in hand, the asymmetric hydrogenation of substituted (E)-1-benzylidene-2,3-dihydro-1H-indenew as conducted at room temperature using the complex iridium-L4 ((aS)-Ir/In-BiphPHOX, 1mol %) in o-xylene (2 mL), under 60 bar of H 2 for 24 h( Ta ble 2). Various substrates 1 bearing unfunctionalized exocyclic doubleb onds could be easily converted into chiral substituted 1-benzyl-2,3-dihydro-1H-indenes 2.T he R 1 electron-withdrawing and electron-donating groups had no effect on the conversion (Table 2, entries [1][2][3][4][5][6][7][8][9][10][11][12]. Reductiono fs ubstrates bearing4 -Cl or 6-CH 3 groups pro- , AcOH (10 mL; 5 mLmL À1 ); [e] the absolute configuration of 2k was determined by X-ray crystallographic analysis.…”

“…Reductiono fs ubstrates bearing4 -Cl or 6-CH 3 groups pro- , AcOH (10 mL; 5 mLmL À1 ); [e] the absolute configuration of 2k was determined by X-ray crystallographic analysis. [12] vided as lightly lower enantioselectivity with 91 and 90 % ee, respectively (entries 2a nd 9), whereas substrates bearing aryl groups with 5-substituted electron-withdrawingF ,C l, or Br substituents were all reduced with higher ee values (entries [4][5][6][7]. Notably,a tasubstrate/catalyst ratio of 1000, the reaction also proceeded smoothly within 48 hw ith no loss of enantioselectivity (entry 6).…”

Asymmetric Hydrogenation of Aryl Perfluoroalkyl Ketones Catalyzed by Rhodium(III) Monohydride Complexes Bearing Josiphos Ligands

“…Recently, the synthesis and application of triply chloride‐bridged dinuclear rhodium(III) complexes bearing chiral C 2 symmetric diphosphine ligands such as BINAP and SEGPHOS were reported by Mashima . In analogy to previously developed dinuclear iridium(III) derivatives, these systems display high catalytic activity and enantioselectivity in diverse asymmetric hydrogenation reactions, including that of simple unfunctionalized alkenes …”

“…[16] Recently,t he synthesis and application of triply chloridebridged dinuclear rhodium(III) complexes bearing chiral C 2 symmetric diphosphine ligands such as BINAP and SEGPHOS were reported by Mashima. [24] In analogy to previously developed dinucleari ridium(III) derivatives, these systems display high catalytic activity and enantioselectivity in diversea symmetric hydrogenation reactions, including that of simple unfunctionalized alkenes. [25][26][27] Inspired by the hydrogenationo fp olar C=Nd ouble bonds using Ir III monohydride catalysts by Verdaguer and co-workers, we decided to investigate the asymmetric C=Oh ydrogenation of trifluoroacetophenones using rhodium(III) monohydride systems.…”