Synthetic Applications of Bifunctional Knölker Type Iron Complexes as (De)hydrogenation Catalysts

Abstract

Knölker type iron complexes, used directly or generated in situ, are suitable catalysts for (de)hydrogenation reactions enabling the synthesis of carbonyl derivatives, amines and alcohols of industrial and academic interest. Enantioselective hydrogenation of prochiral C=X double bonds (X: O, N) was achieved with up to 94% e.e. using iron-complexes bearing chiral ligands or Knölker’ complex in combination with a chiral additive. Knölker type complexes were also competent catalysts for sequential reactions based on temporary dehydrogenative alcohol activation including dynamic kinetic resolution of racemic secondary alcohols (99% e.e.) and borrowing hydrogen methodology. The latter method was applied to synthesize N-alkyl substituted amines, α-alkylated ketones and oxygen- or nitrogen-heterocycles.

Keywords: Alcohol, Amine, Asymmetric hydrogenation, Bifunctional catalyst, Borrowing hydrogen, Carbonyl compound, Dehydrogenation, Direct hydrogenation, Dynamic kinetic resolution, Heterocycle, Iron, Knölker’s complex, Metal-ligand cooperation, Transfer hydrogenation, Water-gas-shift reaction.