Iridium pentahydride complex catalyzed dehydrogenation of alcohols in the absence of a hydrogen acceptor

Acceptorless Dehydrogenation of Aliphatics, Amines, and Alcohols with Homogeneous Catalytic Systems

The dehydrogenation of saturated substrates is fundamentally essential for producing value-added unsaturated organic molecules both in academia and industry. In recent years, homogeneously catalyzed acceptorless C–C, C–N, and C–O bond desaturations have attracted increasing attention due to high atom economy, environmentally benign nature, and wide availability of the starting materials. This short review discusses the acceptorless dehydrogenation of aliphatics, alcohols, and amines by homogeneous catalytic systems based on two categories of reaction mechanisms: thermal transition-metal-catalyzed two-electron pathway and photoredox catalyzed or electrochemically driven one-electron pathway.

1 Introduction

2 Catalytic Acceptorless Dehydrogenation of Aliphatics

3 Catalytic Acceptorless Dehydrogenation of Amines

4 Catalytic Acceptorless Dehydrogenation of Alcohols

5 Conclusion

Dehydrogenation of alcohols and polyols from a hydrogen production perspective

The production of hydrogen from renewable resources is still a major challenge in our way to reach a foreseen hydrogen economy. Abstracting the hydrogen contained in alcohols by means of acceptorless dehydrogenation reactions has emerged as a viable method with high potential. This is particularly true when applied to bio-based alcohols such as ethanol, glycerol or sugars, whose hydrogen extrusion is covered in this contribution. A general overview of the development of aceptorless alcohol dehydrogenation reactions and its potential implementation into future biorefineries are discussed.

Effective dehydrogenation of 2-pyridylmethanol derivatives catalyzed by an iron complex

Effective dehydrogenation of 2-pyridylmethanol derivatives was achieved using an iron catalyst (TON = 67 000) without a hydrogen acceptor.

Electron-rich, bulky PNN-type ruthenium complexes: synthesis, characterization and catalysis of alcohol dehydrogenation

Reaction of the electron-rich, bulky tridentate PNN ligand (PNN=2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) with Ru(PPh3)3Cl2 at 65 degrees C resulted in formation of the mononuclear dinitrogen complex (PNN)Ru(Cl)2N2 (minor) and the N2 bridged Ru(II) dinuclear complex [(PNN)Ru(Cl)2]2(micro-N2) (major). These complexes can be interconverted; passing argon through a solution of the mixture resulted in formation of pure . The cationic square-pyramidal [(PNN)Ru(PPh3)Cl]OTf was obtained by the reaction of complex with silver triflate followed by PPh3. Reaction of complex with CO yielded (PNN)Ru(CO)Cl2, which upon reaction with one equiv. of AgBF4 gave the cationic [(PNN)Ru(CO)Cl]BF4. The dicationic [(PNN)Ru(CO)(H2O)(acetone)](BF4)2 was obtained from with 2 equiv. of AgBF4 in acetone solution. Complexes , and were structurally characterized by X-ray crystallography. Complexes and upon addition of an equivalent of base, catalyzed the dehydrogenation of secondary alcohols to the corresponding ketones and primary alcohols to esters in good yields and high selectivity accompanied with the evolution of hydrogen gas.

Facile conversion of alcohols into esters and dihydrogen catalyzed by new ruthenium complexes

An efficient, environmentally benign method for the preparation of esters from alcohols under mild, neutral conditions without the need for carboxylic acid derivatives and condensing agents was developed. Catalyst design, based on new Ru(II) hydrido carbonyl complexes incorporating electron-rich PNP and PNN ligands has resulted in the novel complex (I) which is an outstanding catalyst for the dehydrogenation of primary alcohols to esters and H(2) under neutral conditions.

Hydrogen evolution from organic “hydrides”

Benzimidazolines (dihydrobenzimidazoles) are shown for the first time to eliminate hydrogen (H2) by catalyzed reaction with protic compounds.