Vapor-phase Beckmann rearrangement of cyclohexanone oxime over halide cluster catalysts

When a silica gel-supported tungsten halide cluster with an octahedral metal framework, (H3O)2[(W6Cl8)Cl6]·6H2O/SiO2, is treated in a helium stream in the temperature range 250–350 °C, catalytic activity for the Beckmann rearrangement of cyclohexanone oxime develops. Niobium and tantalum clusters with the same metal framework also catalyze the reaction. Cyclopentanone oxime and acetone oxime also undergo Beckmann rearrangements over the tungsten cluster. The weak Brønsted acidity (H0 ≈ +1.5) of the hydroxo ligand, which is developed on the activated cluster, is favorable for the rearrangement.