A Cp^tt-Based Trioxo-Rhenium Catalyst for the Deoxydehydration of Diols and Polyols

Trioxo-rhenium complexes are well known catalysts for the deoxydehydration (DODH) of vicinal diols (glycols). In this work, we report on the DODH of diols and biomass-derived polyols using Cp^ttReO₃ as a new catalyst (Cp^tt=1,3-di-tert-butylcyclopentadienyl). The DODH reaction was optimized using 2 mol % of Cp^ttReO₃ and 3-octanol as both reductant and solvent. The Cp^ttReO₃ catalyst exhibits an excellent activity for biomass-derived polyols. Specifically, glycerol is almost quantitatively converted to allyl alcohol and mucic acid gives 75 % of muconates at 91 % conversion. In addition, the loading of Cp^ttReO₃ can be reduced to 0.1 mol % to achieve a turn-over number as high as 900 per Re when using glycerol as substrate. Examination of DODH reaction profiles by NMR spectroscopy indicates that catalysis is related to Cp-ligand release, which raises questions on the nature of the actual catalyst.