Greener Methods: Ester Hydrogenation

Introduction

The reduction of esters to alcohols is typically accomplished using metal hydrides. While effective, this widely used method comes at the cost of stoichiometric waste and often complicated workup procedures that can be particularly time consuming on scale.

Sigma-Aldrich is proud to offer a number of metal complexes that catalyze the reduction of esters with hydrogen gas, increasing atom efficiency and eliminating the labor intensive workup that accompanies metal hydride reductions.

Representative Transformations

In 2006, Milstein and coworkers reported the catalytic hydrogenation of esters using versatile Ru-NNP complex 735809.1

Ester Hydrogenation Scheme 1

 

Concurrently, researchers at Firmenich AG discovered that a number of Ru-PNNP complexes (including 664979) catalyze this process with excellent efficiency. Notably, reduction of esters in the presence of alkenes was demonstrated chemoselectively.

Ester Hydrogenation Scheme 2

 

More recently, researchers at Takasago have disclosed another highly efficient Ru-PNP catalyst trademarked Ru-MACHO® (739103).3 This catalyst was demonstrated in the syntheses of two value-added products, (R)-1,2-propanediol and 2-(l-menthoxy)ethanol.

Ester Hydrogenation Scheme 3

 

In 2012 and 2013, Gusev and coworkers reported Ru-PNN and Ru-SNS complexes (746347 and 746339), new ruthenium catalysts that enable ester hydrogenation with unprecedented efficiency and activity at low temperature.4

Ester Hydrogenation Scheme 4

Materials

     
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