N-Donor Ligand Supported ReO2+: A Pre-Catalyst for the Deoxydehydration of Diols and Polyols

A selected number of tetradentate N(2)Py(2)ligand-supported ReO(2)(+)complexes and a monodentate pyridine-supported ReO(2)(+)complex have been investigated as catalysts for the deoxydehydration (DODH) of diols and polyols. In situ(1)H NMR experiments showed that these N-donor ligand-supported ReO(2)(+)complexes are only the pre-catalyst of the DODH reaction. Treatment of (N2Py2) ReO(2)(+)with an excess amount of water generates an active species for DODH catalysis; use of the Re-product of this reaction shows a much shorter induction period compared to the pristine complex. No ligand is coordinated to the water-treated complex indicating that the real catalyst is formed after ligand dissociation. IR analysis suggested this catalyst to be a rhenium-oxide/hydroxide oligomer. The monodentate pyridine ligand is much easier to dissociate from the metal center than a tetradentate N(2)Py(2)ligand, which makes the Py4ReO2+-initiated DODH reaction more efficient. For the Py4ReO2+-initiated DODH of diols and biomass-based polyols, both PPh(3)and 3-pentanol could be used as a reductant. Excellent olefin yields are achieved.