| Summary: | 碩士 === 國立中山大學 === 化學研究所 === 86 === The insertion of methylene (CH2) into the metal-alkyl bonds has been studied on Ag(111) surface under ultrahigh vacuum (UHV) conditions. The methyl (CH3) groups formed on Ag(111) by thermal dissociation of the C-Ibond in adsorbed methyl iodide (CH3I) below 200 K were coupled to produceethane (C2H6) around 250 K in temperature-programmed reaction (TPR) experiments. Similar low temperature C-I bond scissions in adsorbed methylene iodide (CH2I2) forming CH2(ad) was implicated based on the evolution of ethylene (C2H4) at 260 K in TPR. By studying the interaction of CH3(ad) and CH2(ad) coadsorbed on Ag(111), propane (C3H8) and butane (C4H10) were detected. It suggests that methylene was inserted into the Ag-CH3 bond to produce an ethyl (CH2CH3) group on Ag(111). In the presenceof methyl and ethyl groups, the fo;;owing self and cross coupling reactionsresulted in those longer-chain hydrocarbon compounds. In order to demonstratethe methylene insertion mechanism again, we used CF3 to substitute CH3 as thetarget for the methylene insertion. Trifluoromethyl iodide (CF3I) was used asa molecular precursor to generate adsorbed trifluoromethyl (CF3) fragments on Ag(111) surface. TPR studies of the CF3(ad) + CD2(ad) showed that CD2 was also inserted into the Ag-CF3 bond, however, followed by a simple termination step ,B-fluoride elimination, to produced 1,1-difluoroethylene-d2(CF2=CD2) in the gas phase. Two sequential methylene insertions were also implicated as evidencedby the production of 1,1,1-trifluoropropyl iodide - 2,3-d4 (CF3CD2CD2I) as aresult of the rcombination of CF3CD2CD2 with iodine. To our knowledge, this is the firat example of explicitly demonstrate the methylene insertion onAg(111) surface under ultrahigh vacuum conditions.
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