Stabilizing Effect of Bulky β-Diketones on Homogeneous Mo Catalysts for Deoxydehydration

Abstract

The deoxydehydration (DODH) of vicinal diols to alkenes is a promising reaction for the deoxygenation of biomass. While most reports so far concern Re-based catalysts, catalysts based on more abundant Mo and V have gained more interest in recent years. However, yields and activity are relatively low for these catalysts and, especially for Mo, little is known about the influence of ligands on the metal catalyst. Here, we study a series of β-diketones with different steric and electronic properties as ligand precursors for a Mo catalyst. We show that addition of the β-diketone 2,2,6,6-tetramethylheptanedione (TMHD) leads to a strong increase in yield for the desired product in DODH of a range of substrates using different reductants. The most likely explanation for this increased yield is that the sterically bulky ligand, that is, the conjugated β-diketonate, impedes oligomerization of the Mo catalyst and, hence, inhibits precipitation. This hypothesis was confirmed by electrospray mass spectrometry.