Synthesis and properties of homogeneous models of the Re2O7/Al2O3 metathesis catalyst

The aim of this work was to synthesize and to study homogeneous models of the rhenium oxide on alumina metathesis catalyst. A series of aluminium complexes, (ArO) 2 Al–Y, has been synthesized, where ArO is a 4-substituted-2,6-di- tert -butylphenoxy ligand, or (ArO) 2 is a –CH 2 – or – S - ortho bridged-4,4′-di- tert -butyldiphenoxy ligand, and Y is an alkyl or chloride ligand. The reaction of (ArO) 2 Al–Cl with AgReO 4 led to new complexes (ArO) 2 Al–OReO 3 ( A ). These complexes exhibit a low activity in the metathesis of 2-pentene. Complexes (ArO) 2 Al–R (R=iBu, Et) react with Re 2 O 7 in THF or dioxane, giving type B complexes including oligomeric linkages like O 3 Re–[Al(OAr)–O] 2 –ReO 3 . They show a fairly high activity in the metathesis of 2-pentene, with TOF values as high as 100 min −1 . Complexes of type A may be converted into complexes of type B upon reaction with (ArO) 2 Al–R in an ether solvent. The high activity of B complexes is tentatively related to the presence of Al–O–Al linkages that are known to induce a powerful bidentate Lewis acidity.