Synthesis of a Water-Soluble Ruthenium Complex and Its Catalytic Activity for Acceptorless Alcohol Dehydrogenation in Aqueous Medium

Abstract

The synthesis of a ruthenium complex bearing a PN-chelating ligand is described. The complex, in the presence of KOH, enabled the synthesis of ketones from secondary alcohols in the absence of a hydrogen acceptor in aqueous medium. This synthetic protocol, which uses water as the medium, is green and has a high atom economy as it avoids the use of an acceptor and produces hydrogen as the sole ­byproduct. Mechanistic investigations revealed that the catalytic cycle involves a phosphine dissociative pathway.

Key words

alcohols - ketones - ruthenium catalysis - ligands - dehydrogenation

• References and Notes

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• 16 Dehydrogenation of Alcohols; General Procedure A Schlenk tube was charged with Ru complex 2 (5 mol%), base (15 mol%), the appropriate alcohol (5 mmol), and H₂O (1.0 mL), and the mixture was stirred under reflux for 48 h. When the reaction was complete, the product was extracted with CH₂Cl₂. All the CH₂Cl₂ was evaporated under vacuo, and the product ketone or aldehyde was isolated from the crude mixture by column chromatography (silica gel, hexane–EtOAc). The formation and purity of all the products were confirmed by comparing their ¹H NMR spectra with the report values.
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