3d Transition Metal Catalyzed Dehydrogenation of Alcohols

Alcohols are a good energy source from biomass and can be converted to functional groups, such as amides, amines, carboxylic acids, esters, and imines. One of the key transformations is the dehydrogenation of alcohols. The common method is to use traditional oxidants, or use catalysts based on precious metals. However, these two methods are either not “green” or sustainable. The 3d transition metals are cheap and relatively nontoxic, and they have a high abundance and a large annual production. Catalysts based on these metals could have a good performance on the dehydrogenation.

The acceptorless dehydrogenation of alcohols means that alcohol, catalyzed by metal complexes, undergoes formal oxidation to the corresponding carbonyl compound accompanied by the removal of H₂ gas. The advantage of these dehydrogenative transformations is that alcohol oxidation occurs in the absence of an oxidizing agent, which leads to less waste and more environmentally friendly reaction conversions.

Two catalysts based on Earth-abundant transition metals for acceptorless alcohol dehydrogenation are described in this Ph.D. thesis. Both catalysts mediate the dehydrogenative coupling of primary alcohols and amines to form imines.

The first developed catalyst is chromium(III) tetraphenylporphyrin chloride (Cr(TPP)Cl). This is the first time for Cr(TPP)Cl to be applied for acceptorless alcohol dehydrogenation. The catalyst has a good performance on the dehydrogenation of alcohols with amines to form imines. The reaction mechanism has been investigated by various practical experiments, and a metal-ligand cooperative pathway has been proposed.

The second developed catalyst is vanadium(IV) salen chloride. The catalyst indeed has a good performance on the dehydrogenation of alcohols, and the mechanism is believed to involve a metal-ligand cooperation pathway.

The thesis begins with four short chapters regarding the aim of the project, introduction to alcohols, imines, and acceptorless alcohol dehydrogenation. Subsequently, the development of the two novel catalysts is described and discussed in two chapters, followed by a conclusion on the entire project.