SYNTHESIS AND CATALYTIC PROPERTIES OF FUNCTIONAL DENDRITIC TIN COMPLEXES FOR BAEYER-VILLIGER OXIDATION OF KETONES

Different generations of polyamidoamine dendrimers were successfully incorporated to chloromethyl polystyrene through solid phase synthesis methodology. The peripheral amino groups on these dendrimers have been modified by 2,4-dihydroxybenzaldehyde and salicylaldehyde, respectively. Then the ligands reacted with SnCl2 center dot 2H(2)O to obtained chloromethyl polystyrene supported dendritic Sn complexes. The ligands and complexes were well characterized by IR, ICP and XPS. The complexes as heterogeneous catalysts show promising catalytic activities for the Baeyer-Villiger oxidation of cyclic and acyclic ketones with 30% hydrogen peroxide. 2-Adamantanone, cyclopentanone, 4-methylcyclohexanone, 4-tert-butylcyclohexanone, 3-methyl-2-pentanone and 4-methyl-2-pentanone have all been oxidized in a reaction catalyzed by these complexes at 70 similar to 90 degrees C in different organic solvents, affording the corresponding lactones or esters with high conversion (>87%) and selectivity ( >99%). Compared to the Baeyer-Villiger oxidation of ketones using complexes with different ligands (4-hydroxybenzaldehyde, 2, 4-dihydroxybenzaldehyde and salicylaldehyde), it was discovered that ligands played a vital role in metal loadings and the catalytic activity of the complexes. Among them, salicylaldehyde modified complexes were found to be the optimum catalysts as they had the highest tin content. The catalysts could be obtained in a simple and efficient manner using environmentally friendly oxidant under mild reaction condition. Moreover, the catalysts can be recycled for several times without losing significantly the catalytic activity.