Acceptorless dehydrogenative coupling reactions with alcohols over heterogeneous catalysts

We developed the first acceptorless dehydrogenation of aliphatic secondary alcohols to ketones under visible light irradiation at room temperature by devising a ternary hybrid catalyst system comprising a photoredox catalyst, a thiophosphate organocatalyst, and a nickel catalyst. The reaction proceeded through three main steps: hydrogen atom transfer from the α-C-H bond of an alcohol substrate to the thiyl radical of the photo-oxidized organocatalyst, interception of the generated carbon-centered radical with a nickel catalyst, and β-hydride elimination. The reaction proceeded in high yield under mild conditions without producing side products (except H2 gas) from various alcohols, including sterically hindered alcohols, a steroid, and a pharmaceutical derivative. This catalyst system also promoted acceptorless cross-dehydrogenative esterification from aldehydes and alcohols through hemiacetal intermediates.

Catalytic Acceptorless Dehydrogenation of Aliphatic Alcohols

Cooperative iridium complex-catalyzed synthesis of quinoxalines, benzimidazoles and quinazolines in water

Methylation of Amines and Ketones with Methanol Catalyzed by an Iridium Complex Bearing a 2-Hydroxypyridylmethylene Fragment

We introduce iridium-based conditions for the conversion of primary alcohols to potassium carboxylates (or carboxylic acids) in the presence of potassium hydroxide and either [Ir(2-PyCH2(C4H5N2))(COD)]OTf (1) or [Ir(2-PyCH2PBu2t)(COD)]OTf (2). The method provides both aliphatic and benzylic carboxylates in high yield and with outstanding functional group tolerance. We illustrate the application of this method to a diverse variety of primary alcohols, including those involving heterocycles and even free amines. Complex 2 reacts with alcohols to form the crystallographically characterized catalytic intermediates [IrH(η1,η3-C8H12)(2-PyCH2PtBu2)] (2a) and [Ir2H3(CO)(2-PyCH2PtBu2){μ-(C5H3N)CH2PtBu2}] (2c). The unexpected similarities in reactivities of 1 and 2 in this reaction, along with synthetic studies on several of our iridium intermediates, enable us to form a general proposal of the mechanisms of catalyst activation that govern the disparate reactivities of 1 and 2, respectively, in glycerol and formic ...

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Iridium Catalysts for Acceptorless Dehydrogenation of Alcohols to Carboxylic Acids: Scope and Mechanism

A dicationic iridium complex bearing a bidentate ligand that comprises N-heterocyclic carbene and α-hydroxypyridine moieties has been designed and synthesized. The complex exhibited high catalytic performance in aqueous media for the dehydrogenative oxidation of secondary alcohols to ketones accompanying the evolution of hydrogen. Furthermore, dehydrogenative transformation of primary alcohols to the carboxylic acids in aqueous media was also catalyzed by the complex without using base.

Dehydrogenative Oxidation of Alcohols in Aqueous Media Catalyzed by a Water-Soluble Dicationic Iridium Complex Bearing a Functional N-Heterocyclic Carbene Ligand without Using Base

Ryuichi Tamura

Papers

Dehydrogenative Oxidation of Alcohols in Aqueous Media Catalyzed by a Water-Soluble Dicationic Iridium Complex Bearing a Functional N-Heterocyclic Carbene Ligand without Using Base