Transfer Hydrogenation from 2-propanol to Acetophenone Catalyzed by [RuCl2(η6-arene)P] (P = monophosphine) and [Rh(PP)2]X (PP = diphosphine, X = Cl−, BF4−) Complexes

Alberto Mannu,Arnald Grabulosa,Salvatore Baldino

doi:10.3390/catal10020162

Abstract

The reduction of ketones through homogeneous transfer hydrogenation catalyzed by transition metals is one of the most important routes for obtaining alcohols from carbonyl compounds. The interest of this method increases when opportune catalytic precursors are able to perform the transformation in an asymmetric fashion, generating enantiomerically enriched chiral alcohols. This reaction has been extensively studied in terms of catalysts and variety of substrates. A large amount of information about the possible mechanisms is available nowadays, which has been of high importance for the development of systems with excellent outcomes in terms of conversion, enantioselectivity and Turn Over Frequency. On the other side, many mechanistic aspects are still unclear, especially for those catalytic precursors which have shown only moderate performances in transfer hydeogenation. This is the case of neutral [RuCl2(η6-arene)(P)] and cationic [Rh(PP)2]X (X = anion; P and PP = mono- and bidentate phosphine, respectively) complexes. Herein, a summary of the known information about the Transfer Hydrogenation catalyzed by these complexes is provided with a continuous focus on the more relevant mechanistic features.

Highlights

The possibility to reduce ketones to alcohols in an enantioselective way through ATH represents a milestone in the asymmetric catalysis, as chiral alcohols are employed as intermediates, as well as end-products in many industries, including fragrancies and pharmaceutics [2]
The protocol can be extended to a general C=X polar substrate (X = O, N), allowing the synthesis of chiral alcohols [2], amines, and many corresponding derivatives [3]
A milestone was reached in 1995, when Noyori reported the enantioselective reduction of prochiral ketones by employing as catalytic precursors [RuCl2(diphosphane)(diamine)] complexes in the presence of a base

Summary

Introduction

The possibility to reduce ketones to alcohols in an enantioselective way through ATH represents a milestone in the asymmetric catalysis, as chiral alcohols are employed as intermediates, as well as end-products in many industries, including fragrancies and pharmaceutics [2]. A milestone was reached in 1995, when Noyori reported the enantioselective reduction of prochiral ketones by employing as catalytic precursors [RuCl2(diphosphane)(diamine)] complexes in the presence of a base. The impact of these new catalytic systems for achieving alcohols with high optical purity has been very impressive, and since an intensive and systematic research work has allowed the extension of the protocol to many substrates and catalysts [6].

Results

Conclusion