Mechanism of Alcohol Oxidation by FeV(O) at Room Temperature
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- 作者：Munmun Ghosh ; Y. L. K. Nikhil ; Basab B. Dhar ; Sayam Sen Gupta
- 刊名：Inorganic Chemistry
- 出版年：2015
- 出版时间：December 21, 2015
- 年：2015
- 卷：54
- 期：24
- 页码：11792-11798
- 全文大小：435K
- ISSN：1520-510X
文摘
Selective oxidation of alcohol to its corresponding carbonyl compound is an important chemical process in biological as well as industrial reactions. The heme containing enzyme CytP450 has been known to selectively oxidize alcohols to their corresponding carbonyl compounds. The mechanism of this reaction, which involves high-valent FeIV(O)鈭抪orphyrin鈥? intermediate with alcohol, has been well-studied extensively both with the native enzyme and with model complexes. In this paper, we report for the first time the mechanistic insight of alcohol oxidation with FeV(O) complex of biuret TAML (bTAML), which is isoelectronic with FeIV(O)鈭抪orphyrin鈥? intermediate form in CytP450. The oxidations displayed saturation kinetics, which allowed us to determine both the binding constants and first-order rate constants for the reaction. The K and k values observed for the oxidation of benzyl alcohol by FeV(O) at room temperature (K = 300 M鈥?, k = 0.35 s鈥?) is very similar to that obtained by CytP450 compound I at 鈭?0 掳C (K = 214 M鈥?, k = 0.48 s鈥?). Thermodynamic parameters determined from van鈥檛 Hoff鈥檚 plot (螖H鈭?鈭? kcal/mol) suggest hydrogen bonding interaction between substrate and bTAML ligand framework of the FeV(O) complex. Analysis of H/D KIE (kH/kD 鈭?19 at 303 K), Hammett correlation and linearity in Bell-Evans-Polyanski plot points to the C鈥揌 abstraction as the rate determination step. Finally, experiments using FeV(O18) for benzyl alcohol oxidation and use of the 鈥渞adical clock鈥?cyclobutanol as a substrate shows the absence of a rebound mechanism as is observed for CytP450. Instead, an ET/PT process is proposed after C鈥揌 abstraction leading to formation of the aldehyde, similar to what has been proposed for the heme and nonheme model compounds.