Application of a Planar Chiralη5-Cyclopentadienylrhenium(I)tricarbonyl Complex in Asymmetric Catalysis: Highly Enantioselective Phenyl Transfer to Aldehydes

Abstract

A novel planar chiral cyrhetrene 1 has been identified as an efficient catalyst precursor for the asymmetric synthesis of diarylmethanol compounds 2 by phenylation of aldehydes. Compared to the corresponding ferrocene derivative, the performance of the cyrhetrene is superior or at least equally as good and gives excellent enantioselectivities even with catalyst loadings as low as 2 mol %.

Recent Development of Rhenium-Catalyzed Organic Synthesis

“…Bolm and co-workers reported the design and synthesis of the chiral η 5 -cyclopentadienylrhenium(I)tricarbonyl complex, and applied to catalyze the nucleophilic addition reaction of ZnPh 2 with a wide variety of aldehydes to synthesize the chiral secondary alcohols. The significant advantage of this rhenium(I)-catalyzed addition reaction is the higher enantioselectivity compared to other catalyst systems (Scheme 5) [11].…”

Synthesis of Cyclopentadienyl‐Based Tricarbonyl Rhenium Complexes and Some Unusual Reactivities of Cyclopentadienyl Substituents

“…[54,55] The formation of the rhenium(III) dihydride intermediate D correlates with the previously reported and well-characterized complex Cp*Re(CO) 2 (H) 2 and its conversion to Cp*Re(CO) 3 . [60] Aryl-appended cyclopentadiene ligands have long been known to afford robust metal complexes. [58,59] The planar chirality of 9a could be exploited for asymmetric catalytic transformations, such as the previously reported enantioselective phenyl transfer to aldehydes catalyzed by a planar chiral Cp′Re(CO) 3 complex.…”

“…[56,57] Furthermore, an understanding of the mechanism of this reaction would provide insights into the development of direct, target-oriented synthetic procedures for planar chiral Cp-based metal complexes. [60] They can be employed for the steric protection of a metal center owing to the ability of the aryl substituents to rotate out of the plane of the Cp ring and also provide tunable electronic environments for the metal center. [60] Aryl-appended cyclopentadiene ligands have long been known to afford robust metal complexes.…”

Synthesis of novel chiral phosphinocyrhetrenyloxazoline ligands and their application in asymmetric catalysis

“…1) was employed for this purpose, and indeed, an enantiomeric excess of up to 99% was obtained in the above mentioned reaction. 4 As compared with that of its ferrocenyl analogue the enantioselectivity was higher and, furthermore, the required catalyst loading was lower. This effect could be attributed to the existence of electron-withdrawing and bulky carbonyl groups.…”

“…1) have been applied to a variety of asymmetric catalytic reactions, such as Pd-catalyzed allylic alkylations and aminations, 7 Pdcatalyzed Heck reactions, 8 Ru-catalyzed transfer-hydrogenations, 9 and hydrosilylations. 10 Therefore, we decided to prepare its structurally analogous cyrhetrenyloxazolines 3, 11 4 and 5 (Schemes 1 and 2) and examine their efficiency in such asymmetric reactions.…”