Synthesis and Characterization of Au Nanoparticles-Supported N-Heterocyclic Carbene Copper(I) Complex. The Catalytic Application on Huisgen Cycloaddition

• Main Authors: Yun-Ting Chuang, 莊雲婷
• Other Authors: Shu-chun Yu
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/53390868235711541261

碩士 === 國立中正大學 === 化學所 === 98 === Two types of Cu(I) catalysts mediated azide-alkyne cycloaddition reactions were discussed in this thesis. The first one is the molecular copper(I) N-heterocyclic carbene (NHC) complexes [CuI(hmim)] (2), where hmim = 1-hexly-3-methyl-imidazol-2-ylidene. The second one is the hybrid catalyst, Au NPs-S-(CH2)¬6-(NHC)CuCl (9), consisting of molecular Cu(I)-NHC complex immobilized on the surface of gold nanoparticles (Au NPs). 　　A series of cycloaddition reactions of azides (R-N3) and two kinds of alkynes (phenyl acetylene and nonyne) with a catalyst loading of 1 mol % of 2 were carried out under solventless conditions at ambient temperature to give the corresponding cycloaddition products with > 95% yields in 2 hours. It was found that the more acidic of the alkyne was, the more reactive the cycloaddition became. The complex 2 was found to be extreamly efficient that with a catalyst loading as little as 0.05 mole %, the catalysis was complete in 0.5 hour to give a product yield of > 99 % and a turnover frequency (TOF) of 4000 h-1. 　　We have also successfully immobilized the molecular catalyst 2 onto Au NPs to give Au NPs-S-(CH2)6-(NHC)-CuCl (9). Freshly prepared octanethiolate-protected Au NPs were dissolved in THF. To this solution was added spacer ligand, HS-(CH2)6-(NHC) (6), and the reaction mixture was stirred for 0.5 hours at 40 oC. The mixed thiolates-protected Au NPs, (RS)Au(S-hmim+)(PF6?) (8), thus obtained was further treated with CuCl in the presence of tBuONa to give our target hybrid catalyst 9. These Au colloids were dissolvable and perceptible. Therefore, their structures and solution chemistry were readily studied by solution phase 1H NMR, UV and IR spectrospcopies as well as TEM. Furthermore, the XPS analysis confirmed a Cu(I) oxidation state of 9. This hybrid catalyst 9 was also proved to be an efficient catalyst for phenyl acetylene and benzyl azide cycloaddition reaction. In addition, with a 1 mol % of Cu(I) on 9, the cycloaddition reaction was complete in 5 hours at 60 oC to give 93 % yield. However, it was found that the catalytic activity of 9 was not as efficient as it’s unbound free form 2. There are two possible reasons that could cause a reduction in reactivity when Cu(I) bound to Au NPs surface. One is competitive alkyne binding that may exist between Au surface atoms and Cu catalyst center. The other one is thiol ligands supported on the surface of Au NPs may leach into solution to oxidize Cu(I) catalyst center into the less reactive Cu(II). In the presence of excess amount of alkyne (phenyl acetylene), we found that the Au NPs-Cu(I) hybrid catalyst indeed offered higher yields under similar reaction conditions. These results implied that competitive alkyne binding between Au surface atoms and Cu catalyst center had influence on the overall product conversion. 　　The hybrid catalyst Au NPs-S-(CH2)6-(NHC)-CuCl (9) catalyzed azide-alkyne cycloaddition reactions can be further accelerated under microwave irradiation conditions (300 W) to give desired products in 72 % ~ 77 % yields with 2 drops (25 μL) of [bmim][PF6] in 2 minutes.