Rhenium oxo compounds containing eta(2)-pyrazolate ligands

Reaction of potassium salts of sterically demanding pyrazolates (pz = bis- 3,5-tert-butylpyrazolate, pz' = bis- 3,5-tertbutyl-4- methylpyrazolate) with Re2O7 affords soluble eta(2)-pyrazolate complexes of the type [(eta(2)- 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 eta(2)- 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 [(eta(2)-pz) ReO3( L)] ( 3: L = py; 4: L = 3,5- Me(2)py). 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][pzH(2)] ( 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).