The catalytic function of a silica gel-immobilized Mn(II)-hydrazide complex for alkene epoxidation with H2O2

An efficient and highly selective heterogeneous catalyst was developed by immobilization of a manganese complex on an inorganic support to yield (silica gel)-O-2(EtO)Si-L-1-Mn(HL2) [(L-1)(-) = modified salicylaldiminato and H2L2=(E)-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide]. Mn(II) has been anchored on the surface of functionalized silica by means of N,O-coordination to the covalently Si-O bound modified salicylaldiminato Schiff base ligand. The prepared material (silica gel)-O-2(EtO)Si-L-1-Mn(HL2), was characterized by elemental and thermogravimetric analyses (TGA and DTA). UV-vis and FT-IR spectroscopy. This new material is demonstrated to be a very active catalyst in clean epoxidation reactions using a combined oxidant of aqueous hydrogen peroxide and actonitrile in the presence of aqueous sodium hydrogencarbonate. The effects of reaction parameters such as solvent, NaHCO3 and oxidant in the epoxidation of cis-cyclooctene were investigated. Cycloalkenes were oxidized efficiently to their corresponding epoxide with 87-100% selectivity in the presence of this catalyst. This catalytic system showed also good activities in the epoxidation of linear alkenes. The obtained results show that this catalyst is a robust and stable heterogeneous catalyst which can be recovered quantitatively by simple filtration and reused multiple times without loss of its activity. (C) 2011 Elsevier B.V. All rights reserved.