Rhenium oxo compounds containing η2-pyrazolate ligands

Abstract

Reaction of potassium salts of sterically demanding pyrazolates (pz = bis-3,5-tert-butylpyrazolate, pz′ = bis-3,5-tert-butyl-4-methylpyrazolate) with Re₂O₇ affords soluble η²-pyrazolate complexes of the type [(η²-pz)ReO₃(THF)_n] (1: pz, n = 1 and 2: pz′, n = 0). They were characterized by spectroscopic methods and by X-ray crystallography confirming the η²-coordinate ligands. Complex 1 employing the ligand with a proton in the 4-position retains one molecule of THF, whereas the additional methyl group in 2 leads to the base-free compound 2. Compound 1 reacts with pyridine and 3,5-dimethylpyridine to form Lewis base adducts of the type [(η²-pz)ReO₃(L)] (3: L = py; 4: L = 3,5-Me₂py). The pronounced sensitivity towards water of these complexes is demonstrated by the reaction of 1 with one equivalent of water forming the corresponding pyrazolium perrhenate [ReO₄][pzH₂] (5). Its solid state structure shows a hydrogen bonded dimeric assembly. Catalytic activity of 1 is established in oxygen atom transfer-reactions (OAT) from dimethylsulfoxide to triphenylphosphine, and in epoxidations of cyclooctene employing bis(trimethylsilyl) peroxide (BTSP).