A New Approach To Studying the Mechanism of Catalytic Reactions: An Investigation into the Photocatalytic Hydrogenation of Norbornadiene and Dimethylfumarate Using Polyethylene Matrices at Low Tempera
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- 作者：Gavin I. Childs ; Andrew I. Cooper ; Trevor F. Nolan ; Michael J. Carrott ; Michael W. George ; and Martyn Poliakoff
- 刊名：Journal of the American Chemical Society
- 出版年：2001
- 出版时间：July 18, 2001
- 年：2001
- 卷：123
- 期：28
- 页码：6857 - 6866
- 全文大小：154K
- 年卷期：v.123,no.28(July 18, 2001)
- ISSN：1520-5126
文摘
This paper presents a new method for investigating the mechanisms of homogeneously catalyzedreactions involving gases, particularly H2. We show how the combination of polyethylene (PE) matrices andhigh pressure-low temperature (HPLT) experiments can be used to provide new mechanistic information onhydrogenation processes. In particular, we show how we are able to generate reaction intermediates at lowtemperature, and then to extract the contents of the PE film at room temperature to characterize the organicproducts using GC-MS. We have used our new technique to probe both the hydrogenation of dimethyl fumarate(DF), using Fe(CO)4(
2-DF) as the catalytic species, and the hydrogenation of norbornadiene (NBD), using(NBD)M(CO)4 (M = Cr or Mo) as the catalytic species. Irradiation of Fe(CO)4(2-DF) in a PE matrix at 150K resulted in the formation of an intermediate complex tentatively assigned Fe(CO)3(4-DF). Warming thiscomplex to 260 K under H2 leads to the formation of Fe(CO)3(2-DF)(2-H2). Further warming of the reactionsystem results in the hydrogenation of the coordinated DF, to generate dimethyl succinate (DS). Characterizationof the intermediate species was obtained using FTIR spectroscopy. Formation of DS was confirmed usingboth FTIR spectroscopy and GC-MS analysis. UV photolysis of (NBD)M(CO)4 in PE under H2 in the presenceof excess NBD results in the formation of the hydrogenated products norbornene (NBN) and nortricyclene(NTC), with trace amounts of norbornane (NBA) being observed. These products were in similar ratios tothose observed in fluid solution. However, for (NBD)Mo(CO)4, the relative amounts of the organic productschange considerably when the reaction is repeated in PE under H2 in the absence of free NBD, with NBAbeing the major product. The use of our HPLT cell allows us to vent and exchange high pressures of gaseswith ease, and as such we have performed gas exchange reactions with H2 and D2. Analysis of the reactionproducts from these exchange reactions with GC-MS provides evidence for the mechanism of formation ofNBA, in both the presence and absence of excess NBD, a reaction which has been largely ignored in previousstudies.
2-DF) as the catalytic species, and the hydrogenation of norbornadiene (NBD), using(NBD)M(CO)4 (M = Cr or Mo) as the catalytic species. Irradiation of Fe(CO)4(2-DF) in a PE matrix at 150K resulted in the formation of an intermediate complex tentatively assigned Fe(CO)3(4-DF). Warming thiscomplex to 260 K under H2 leads to the formation of Fe(CO)3(2-DF)(2-H2). Further warming of the reactionsystem results in the hydrogenation of the coordinated DF, to generate dimethyl succinate (DS). Characterizationof the intermediate species was obtained using FTIR spectroscopy. Formation of DS was confirmed usingboth FTIR spectroscopy and GC-MS analysis. UV photolysis of (NBD)M(CO)4 in PE under H2 in the presenceof excess NBD results in the formation of the hydrogenated products norbornene (NBN) and nortricyclene(NTC), with trace amounts of norbornane (NBA) being observed. These products were in similar ratios tothose observed in fluid solution. However, for (NBD)Mo(CO)4, the relative amounts of the organic productschange considerably when the reaction is repeated in PE under H2 in the absence of free NBD, with NBAbeing the major product. The use of our HPLT cell allows us to vent and exchange high pressures of gaseswith ease, and as such we have performed gas exchange reactions with H2 and D2. Analysis of the reactionproducts from these exchange reactions with GC-MS provides evidence for the mechanism of formation ofNBA, in both the presence and absence of excess NBD, a reaction which has been largely ignored in previousstudies.