4 research outputs found
Active Catalytic Centers in Silica-Supported Cu(II) and Mn(II) Biomimetic Complexes : Correlation Between Catalytic and EPR Data.
Two polydentate ligands represented as LA and LB have been synthesized and subsequently grafted on a silica surface via covalent bonds. The
organic ligands LA and LB as well as the heterogenized ligands LA路SiO2 and LB路SiO2 reacted with manganese(II) and copper(II) ions leading
to the formation of the corresponding metal complexes. Catalytic epoxidations of simple olefins with hydrogen peroxide were studied using the
above manganese complexes in the presence of a cocatalyst. The major products of the oxidations were the epoxides and the studied manganese
complexes showed significant catalytic activities. The copper(II) complexes have been evaluated for the catalytic oxidation of 3,5-di-t-butylcatechol
(DTBC) by dioxygen. Based on a combination of structural information, obtained form EPR spectroscopy, and the catalytic activity we suggest
that the catalysis of DTBC oxidation by copper complexes is critically determined by two factors (a) for dinuclear complexes, it is enhanced
when the Cu路路路Cu distance approaches the OC路路路CO distance in the catechol molecule (2.7A掳 ), and (b) immobilization on silica support results in
enhancement of the catalytic activity in cases where even monomeric complexes are located at relative distances approaching the critical OC路路路CO
distance (2.7A掳 ). This provides a practical rule for design and synthesis of more efficient copper-catalysts for the catechol oxidation