| Abstract: | Since Tomalia and Dovornic discussed the promising outlook of surface-functionalized dendrimer catalysts in 1994, 1] dendritic catalysts have been proposed to many kinds of catalysis.These well-defined macromolecular structures enable the construction of precisely controlled catalyst structures. The large number of the peripheral functionalities enhanced their activity in many processes. 2,3] We report herein a new method of using the dendritic catalysts in the oxidation of cyclohexene. The reactions give some interesting results.In short, the synthesis of the dendritic catalysts was initiated from the well-known PAMAM dendrimers by using their peripheral ammonia groups. The condensation reactions of these ammonia groups and salicyaldehyde (SA) offer the ligands PAMAMSA with different generation (G) numbers.dendrimer-bond PAMAMSA-Ni(Ⅱ) complexes.In the presence of the dendritic PAMAMSA-Ni(Ⅱ) catalysts, cyclohexene was fully oxidized under 1 atm of molecular oxygen at 70℃. All the oxidations give 7-oxabicyclo4.1.0]heptane 1,2-cyclohexen-l-ol 2, 2-cyclohexen-1-one 3 and 7-oxabicyclo 4.1.0]heptan-2-one 4 as the major products. The results of the oxidation are shown in the table below (table 1):Table 1 Oxidation of cvclohexene bv PAMAMSA-Ni2+ catalysts** Reaction condition: cat. 2mg, cyclohexene 5mL, 1atm O2, 6hat 70℃.**Oxygen absorption (mL) per mol catalyst.It can be seen from table that the oxidations give a new product 7-oxabicyclo4.1.0]heptan-2-one 4, which is the first reported product in this oxidation. Meanwhile, product 4possesses relatively high selectivity in the six oxidation processes. It will arise much more emphasison the optimizing of these reactions. |
