| Summary: | 碩士 === 國立中正大學 === 化學所 === 94 === The complex {[O=P(2-py)3]Mo(CO)(NO)2}(BF4)2 (1) can be easily synthesized in two steps within 60 minutes from the commercially available Mo(CO)6. The precursor [O=P(2-py)3]Mo(CO)3 obtained in the first step can be prepared either through the conventional heating or under microwave irradiation conditions. The former method took 18 hours to give 80% yield of product after multi-step work-up procedures, and the later case gave greater than 90% yield of high purity product in just 5 minutes without further purifications. The direct reaction of [O=P(2-py)3]Mo(CO)3 with 2 equiv. of NOBF4 afforded complex 1 which can be stored as a crystalline solid in air for months without significant decomposition. In addition, complex 1 has high water-solubility of 116 g/L and possesses strong Lewis acidity upon loss of the CO ligand. The relative Lewis acid strength of complex 1 is found to be comparable to the acidity of AlEtCl2.
The Pechmann condensation reaction is the most widely applied method for the synthesis of coumarins since it involves the condensation of phenols with β-ketonic esters in the presence of a variety of acidic condensing agents and gives good yields of 4-substituted coumarins. In this dissertation the catalyses of a novel organomolybdenum Lewis acid catalyst [O=P(2-py)3W(CO)(NO)2](BF4)2 (1) in a series of Pechmann condensation reactions of ethyl acetoacetate with various phenols were investigated. We have also emphasized on the congregating effect of this Lewis acid under microwave irradiation conditions. With the employment of as little as 1 mol% of catalyst 1, the condensation reactions were efficiently performed either in a solvent-less system or in a thermally stable ionic liquid BmimPF6 (1-butyl-3-methylimidazolium hexafluorophosphate). In all cases, a dramatic reaction rate-enhancement from hours to minutes was observed under microwave irradiation conditions as compared to those found in the thermal heating method. In addition, it has been demonstrated that catalyst 1 can be selective and as effective towards organic base functionality such as 3-aminophenol.
Finally, on account of its extreme stability, the catalytic systems containing Lewis acid 1 in BmimPF6 can be recycled up to the 6th run with the conversion maintained at >80%.
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