| Summary: | 碩士 === 國立中正大學 === 化學所 === 96 === We have successfully synthesized the organotungsten Lewis acid, [N(CH2-2-py)3W(CO)(NO)2](BF4)2 (3) in quantitative yield by treating W(CH3CN)3(CO)3 with N(CH2-2-py)3 (tpa) in the presence of 2 equiv. of NOBF4 in CH3CN at 0 oC for 90 minutes. The complex 3 is very moisture- and air-stable. Its crystalline solid form can be stored in air for months and its solution can also stay unchanged for at least 48 hours without detectable decomposition. In addition, complex 3 has a relatively high water-solubility of 37 g/L and possesses strong Lewis acidity upon loss of the CO ligand. The Lewis acidity of [N(CH2-2-py)3W(CO)(NO)2]2+ measured by 1H NMR method falls between those found for AlCl3 and BF3. But the complex [N(CH2-2-py)3W(CO)(NO)2]2+ exhibits very different structures in solid state and in solution. The crystal structure of 3 shows the tpa ligand in its h4-coordination mode bound to the W center. While in solution state, tpa has various coordination possibilities (h3- or h4-interconversion) as suggested by its 1H NMR spectral data. Because the lability of CO ligand, the resulting 16-e species (the real active catalyst) could be further stabilized by the formation of the 4th W－N bonding via a fast h3-to-h4 interconversion.
The three-component Biginelli condensation reaction is one of the most widely applied method for the synthesis of 3,4-dihydropyridine-2(1H)-one (DHPMs). This one pot reaction involves the condensation of ethyl acetoacete, aldehyde and urea in the presence of a variety of acidic condensing agents. In this dissertation a series of Biginelli condensation reactions were catalyzed by a novel organotungten Lewis acid [N(CH2-2-py)3W(CO)(NO)2](BF4)2 (3). With the employment of as little as 0.6 mol% of catalyst 3, the condensation reactions were efficiently proceeded in molecular solvent systems such as DMF or in a thermally stable room temperature ionic liquid, BmimPF6 (1-butyl-3-methylimidazolium hexafluorophosphate). We have also investigated the congregating effect of this Lewis acid under microwave irradiation conditions. In all cases, a dramatic reaction rate-enhancement from hours to minutes was observed under microwave irradiation conditions as compared to those found by using thermal heating method. In addition, it has been demonstrated that catalyst 3 can be selective and as effective towards organic base functionality.
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