COBALT-CATALYZED ACCEPTORLESS DEHYDROGENATIVE HOMOCOUPLING OF SECONDARY ALCOHOLS TO KETONES

Abstract

The replacement of rare and expensive transition metals such as Ru, Rh, Pt, Pd, and Ir with earth abundant transition metals is an appealing target in the field of catalysis. A cobalt complex bearing a novel tetradentate tripodal ligand has been synthesized and utilized for the homo-coupling of secondary alcohols to form ketones. Along with the cobalt complex, a strong base is introduced into the coupling reaction in order to activate the catalyst. A wide variety of both aliphatic and aromatic secondary alcohol substrates have been investigated to determine the effects of different substituents on reactivity. All reactions were performed under an inert atmosphere using either argon flow or nitrogen filled pressure vessels. Coupled products are assessed using NMR with an internal standard to determine yield as well as GCMS to confirm structure. These reactions provide high yields of coupled ketone products using cobalt-catalyst loadings as low as 3.5 mol%. Acceptorless dehydrogenative coupling is an eco-friendly method for ketone production, generating only H2 gas and water as byproducts.