A unique reaction pathway of fluorine-substituted ethyl groups on Cu(111): successive alpha,alpha-fluoride elimination |
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Authors: | Chiang Chao-Ming Lu Deyi Huang Jia-Tze Hwang Chi-Chau Cho Chia-Chin Fan Liang-Jen Yang Yaw-Wen |
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Institution: | Department of Chemistry, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung, Taiwan 80424. cmc@mail.nsysu.edu.tw |
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Abstract: | Fluorine-substituted ethyl groups on Cu(111) were generated by thermal scission of the C-I bond in the adsorbed C2F5I. Temperature-programmed reaction spectrometry observed a novel pathway resulting in the evolution of C4F6 above 400 K. Among the various isomers, this product was identified as hexafluro-2-butyne. Although abstraction of two fluorine atoms from the starting Cu-CF2CF3 was required, Cu-CCF3 (trifluoroethylidyne) was favored over Cu-CF=CF2 (trifluorovinyl) as the intermediate because this ethyl-ethylidyne-butyne pathway was suppressed on a Cu(100) surface devoid of the key threefold hollow binding sites for ethylidyne. Once formed, perfluoroethylidyne readily coupled to afford a tightly surface-bound hexafluoro-2-butyne up to 400 K. Therefore, the C-F bonds adjacent to the metal were found to be more susceptible to the bond activation, leading the chemisorbed perfluoroethyl to eliminate two F atoms successively from the alpha-carbon. This preference for alpha-elimination rather than beta-elimination (the most favorable route in hydrocarbons) may be quite general for metal surface-mediated reactions involving fluorinated alkyl groups. |
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