有機金屬化學中配位基含不飽和鍵的碳氫化合物是最被廣泛研究的，尤其是C3H3-M系列。C3H3擁有propargyl (HC≡CCH2-M)、allenyl (H2C=C=CH-M)，以及acetylide (H3C-C≡C-M)等三種不同的同分異構物。為探討這些物種在金屬表面上的化學問題，於超高真空環境，以propargyl bromide (HC≡C-CH2-Br)為前驅物，在Ag(111)的表面上產生C3H3(ad)，又利用程溫脫附(Temperature Programmed Desorption，TPD) 以及反射吸收紅外光譜(Reflection-Absorption Infrared Spectroscopy，RAIRS)偵測熱反應路徑，另外配合密度泛函理論(Density Functional Theory，DFT)計算，除了解表面吸附物種的位向，計算所得的IR光譜也方便指認實際振動模式。TPD結果顯示310 K與475 K皆有氫化產物，然而310 K脫附峰寬，可能包含不只一個物種。除了氫化產物，475 K亦發現有C6H6偶合產物(2,4-hexadiyne)脫附。由於可能的氫化產物(propyne和allene)質譜碎裂模式近似而無法區別，因此利用與propargyl bromide具有相同反應行為但氫化產物質譜卻可以分辨的二甲基取代propargyl chloride以鑑別氫化產物種類。結果發現310 K的寬峰包含allene (較低溫)以及propyne (較高溫)，而475 K的氫化產物則是propyne。RAIRS資料顯示200 K時，C-Br鍵斷裂後表面C3H3(ad)隨即以allenyl型式存在，這說明310 K allene是由表面allenyl的α碳加氫產生。加熱到250 K光譜發現明顯變化，與使用propynyl iodide (H3C-C≡C-I)在Ag(111)上直接產生H3C-C≡C-Ag所觀測到的振動光譜幾乎相同。因而合理解釋propyne和2,4-hexadiyne的生成機制。

In organometallic chemistry, metal complexes bearing unsaturated hydrocarbon ligands are of extensive interest, especially the C3H3-M system which includes propargyl (HC≡CCH2-M), allenyl (H2C=C=CH-M), and acetylide (H3CC≡C-M) forms. To study the chemistry of these species on metal surfaces, we used proprargyl bromide (HC≡CCH2-Br) as precursor to produce C3H3(ad) on Ag(111) under ultrahigh vacuum (UHV) conditions. The thermal reactions pathway was investigated by Temperature-Programmed Desorption (TPD), and Reflection-Absorption Infrared Spectroscopy (RAIRS). In addition, density functional theory (DFT) calculations were conducted to obtain the optimized geometry for the adsorbates, and the computed IR spectra facilitated the vibrational mode assignments. TPD spectra showed that hydrogenation products C3H4 evolved at 310 K and 475 K. However, the desorption peak at 310 K was broad, indicating that more than one species were encompassed. Besides the hydrogenation product, a coupling product C6H6 (2,4-hexadiyne) was also unveiled as part of the desorption feature at 475 K. The identity of the possible C3H4 hydrogenation products (propyne and/or allene) was not discriminable by the mass spectrometry. The problem was circumvented by using α,α-dimethyl-substituted propargyl chloride because this dimethyl-substituted species also resulted in hydrogenatioin products around 310 K and 475 K, respectively; and the corresponding allenic and acetylenic end-products are distinguishable by the mass spectrometry. The results indicated that the broad feature at 310 K, in fact, contained both allene (lower temperature) and propyne (higher temperature), whereas the hydrogenation product at 475 K was propyne. The RAIR spectrum at 200 K showed that all C3H3(ad) on Ag(111) readily took on the allenyl form after the C-Br bond scission. It is thus obvious that allene at 310 K was generated by adding one hydrogen to the α-carbon of the surface allenyl. RAIR spectroscopy revealed a drastic change after annealing the surface to 250 K, where the spectrum was almost identical to that obtained from using propynyl iodide (H3C-C≡C-I) as a direct source for methylacetylide (H3C-C≡C-Ag). Consequently, the products of propyne and 2,4-hexadiyne could be reasoned out.

Chapter 1 Introduction…………………………………………………….. 1

Chapter 2 Experiments…………………………………………………... 4

Chapter 3 Results

3.1 Thermal Reactions of Propargyl Bromide on Ag(111) from TPD and IR spectra.………………………………………………………………
8
3.2 Chemistry below 250 K: Isomerization and Hydrogenation……………
3.2.1 IR spectra of Propargyl Bromide………………………………… 15
3.2.2 DFT Calculations for the Adsorption Structure and IR Spectral Assignments……………………………………………………...
17
3.2.3 Identification of the Hydrogenation Products by α,α-Dimethyl-substituted Propargyl Chloride (3-Chloro-3-Methyl-1-Butyne)


3.2.3.1 IR spectra of 3-Chloro-3-Methyl-1-Butyne…………….…… 20
3.2.3.2 DFT Calculations and IR Assignments……………………… 22
3.2.3.3 TPD spectra of 3-chloro-3-Methyl-1-Butyne………………... 26
3.3 Chemistry from 300 K to 500 K: Isomerization, Coupling, and Hydrogenation
3.3.1 IR spectra and DFT calculations of Propynyl Iodide on Ag(111)... 33
3.3.2 TPD spectra of Propynyl Iodide on Ag(111)……………………... 38
3.3.3 TPD spectra of Propargyl Chloride on Ag(111)………………….. 43
3.4 Other Methyl–Substituted Propargyl Halides on Ag(111)
3.4.1 The Surface Chemistry of

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