Hans Günter Nedden

The Development of Phosphine-Free "Tethered" Ruthenium(II) Catalysts for the Asymmetric Reduction of Ketones and Imines.

In this account, we describe the design, synthesis and applications of tethered versions of the Ru(II)/N-tosyl-1,2-diphenylethylene-1,2-diamine (TsDPEN) class of catalyst that are commonly used for asymmetric transfer hydrogenation and asymmetric hydrogenation of ketones and imines. The review covers key aspects of the reaction mechanisms and examples of applications, including industrial applications to pharmaceutically important target molecules. In addition, closely related catalysts based on Rh(III) and Ir(III) are also described.

Transfer Hydrogenation and Hydrogenation of Commercial‐Grade Aldehydes to Primary Alcohols Catalyzed by 2‐(Aminomethyl)pyridine and Pincer Benzo[h]quinoline Ruthenium Complexes

The chemoselective reduction of commercial‐grade aldehydes (97–99 %) to primary alcohols is achieved with cis‐[RuCl2(ampy)(PP)] [ampy=2‐(aminomethyl)pyridine; PP=1,4‐bis(diphenylphosphino)butane, 1,1′‐ferrocenediyl‐bis(diphenylphosphine)] and pincer [RuCl(CNNR)(PP)] [PP=1,3‐bis(diphenylphosphino)propane, 1,4‐bis(diphenylphosphino)butane, 1,1′‐ferrocenediyl‐bis(diphenylphosphine); HCNNR=4‐substituted‐2‐aminomethyl‐benzo[h]quinoline; R=Me, Ph] complexes by transfer hydrogenation and hydrogenation reactions. Aromatic, conjugated, and aliphatic aldehydes are converted quantitatively to the corresponding alcohols using 2‐propanol with potassium carbonate at substrate/catalyst ratios up to 100 000 by transfer hydrogenation, whereas aldehyde hydrogenation (5–20 atm of H2) is achieved efficiently in MeOH in the presence of KOtBu at substrate/catalyst ratios up to 40 000.

Chemoselective Transfer Hydrogenation of Aldehydes with HCOONH4 Catalyzed by RuCl(CNNPh)(PP) Pincer Complexes

Aldehydes were chemoselectively reduced to primary alcohols by using HCOONH4 as the hydrogen donor through transfer hydrogenation catalyzed by benzo[h]quinoline pincer complexes RuCl(CNNPh)(PP) at substrate to catalyst molar ratios of 2000 to 20 000. This practical reaction performed with aldehydes of commercial‐grade purity in a water/toluene biphasic system afforded alcohols without the formation of condensation or amination side products.