Isomerization of Allylic Alcohols to Ketones Catalyzed by Well-Defined Iron PNP Pincer Catalysts

[Fe(PNP)(CO)HCl] (PNP=di-(2-diisopropylphosphanyl-ethyl)amine), activated in situ with KOtBu, is a highly active catalyst for the isomerization of allylic alcohols to ketones without an external hydrogen supply. High reaction rates were obtained at 80 degrees C, but the catalyst is also sufficiently active at room temperature with most substrates. The reaction follows a self-hydrogen-borrowing mechanism, as verified by DFT calculations. An alternative isomerization through alkene insertion and beta-hydride elimination could be excluded on the basis of a much higher barrier. In alcoholic solvents, the ketone product is further reduced to the saturated alcohol.