Mild synthetic methods for the generation of carboxylic acids are highly desirable for organic synthesis applications. Current synthetic methods depend on stoichiometric oxidants such as permanganate, dichromate, hydrogen peroxide, or oxygen gas. A milder alternative is the dehydrogenative oxidation of aldehydes; in which water serves as the terminal oxidant. This reaction bears strong resemblance to the well-known water-gas shift reaction, and as a result, has been coined the 'aldehyde-water shift.' We have screened a variety of iridium, rhodium, and ruthenium complexes for activity in catalyzing this desirable transformation. In many cases a competing reaction pathway of aldehyde disproportionation is found to dominate reactivity. However, with select catalysts, high selectivity for the aldehyde-water shift reaction can be achieved. Utilizing [(p-cymene)Ru(bpy)OH2][OTf]2as precatalyst, we have demonstrated, for the first time, a perfectly selective aldehyde-water shift under neutral conditions in the absence of an external hydrogen acceptor.

Catalyzing the "aldehyde-water shift" reaction: Oxidation of aldehydes utilizing water as the terminal oxidant

248th National Meeting (2014)

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