Effect of hydrogen bonding on catalytic activity of some manganese porphyrins in epoxidation reactions
Abstract
Mn(III)-tetra phenyl porphyrin-acetate (MnTPPOAc) and some kinds of meso-phenyl substituted porphyrins by hydroxyl groups and their Mn(III) complexes were synthesized. These Mn-porphyrins were used as catalyst in the epoxidation of various alkenes with tetra-n-butylammonium hydrogen monopersulfate (n-Bu4NHSO5) as oxidant and tetra-n-butylammonium acetate (n-Bu4NOAc) as the axial ligand. The following order of catalytic activity was observed for cyclooctene: T(2,3-OHP)PMnOAc ≫ T(2,4,6-OHP)PMnOAc ≥ T(4-OHP)PMnOAc ≥ T(2,6-OHP)PMnOAc ≥ TPPMnOAc and T(2,3-OHP)PMnOAc ≫ TPPMnOAc > T(4-OHP)PMnOAc > T(2,4,6-OHP)PMnOAc > T(2,6-OHP)PMnOAc for other alkenes. Different activity and stability of the catalysts were interpreted based on the hydrogen bonding between hydroxyl groups with appropriate orientation on the meso-position of the phenyl groups and axial bases or oxidant. T(2,3-OHP)PMnOAc catalyst has shown optimal condition for effective hydrogen bonding. In the case of other catalysts, electronic and steric factors overcome the hydrogen bonding effect.

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