Chapter

Iridium Catalysis

Volume 34 of the series Topics in Organometallic Chemistry pp 77-106

Date:

Iridium-Catalyzed Hydrogen Transfer Reactions

  • Ourida SaidiAffiliated withDepartment of Chemistry, University of Bath
  • , Jonathan M. J. WilliamsAffiliated withDepartment of Chemistry, University of Bath Email author 

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Abstract

This chapter describes the application of iridium complexes to catalytic hydrogen transfer reactions. Transfer hydrogenation reactions provide an alternative to direct hydrogenation for the reduction of a range of substrates. A hydrogen donor, typically an alcohol or formic acid, can be used as the source of hydrogen for the reduction of carbonyl compounds, imines, and alkenes. Heteroaromatic compounds and even carbon dioxide have also been reduced by transfer hydrogenation reactions. In the reverse process, the oxidation of alcohols to carbonyl compounds can be achieved by iridium-catalyzed hydrogen transfer reactions, where a ketone or alkene is used as a suitable hydrogen acceptor. The reversible nature of many hydrogen transfer processes has been exploited for the racemization of alcohols, where temporary removal of hydrogen generates an achiral ketone intermediate. In addition, there is a growing body of work where temporary removal of hydrogen provides an opportunity for using alcohols as alkylating agents. In this chemistry, an iridium catalyst “borrows” hydrogen from an alcohol to give an aldehyde or ketone intermediate, which can be transformed into either an imine or alkene under the reaction conditions. Return of the hydrogen from the catalyst provides methodology for the formation of amines or C–C bonds where the only by-product is typically water.

Keywords

Alcohols Alkenes Asymmetric transfer hydrogenation C-alkylation Imines Ketones N-alkylation Oxidation Reduction Transfer hydrogenation