Owens Gregory S, Durazo Armando, Abu-Omar Mahdi M
Department of Chemistry and Biochemistry, 607 Charles E. Young Drive, East University of California, Los Angeles, CA 90095-1569, USA.
Chemistry. 2002 Jul 2;8(13):3053-9. doi: 10.1002/1521-3765(20020703)8:13<3053::AID-CHEM3053>3.0.CO;2-G.
The kinetics of oxygen-atom transfer from the peroxo complexes of methyltrioxorhenium (MTO) to alkenes in ionic liquids have been investigated. Noncatalytic conversions of alkenes to epoxide were monitored by UV/Vis at 360 nm, where the monoperoxorhenium (mpRe) and diperoxorhenium (dpRe) complexes absorb. Water- and peroxide-free dpRe was prepared in situ by the reaction of MTO and urea hydrogen peroxide (UHP) in dry THF. The observed biexponential time profiles in conjunction with kinetic modeling allow the assignment of the fast step to the reaction of olefin with dpRe (k4) and the slow step to the analogous reaction with mpRe (k3). In most of the tudied ionic liquids, k4 approximately 5 x k3. 2H NMR experiments conducted with [D3]dpRe under non-steady-state conditions confirm the speciation of the catalytic system in ionic liquids and assert the validity of the UV/Vis kinetics. Deuteriated alkenes were used to study the catalytic epoxidation and dihydroxylation of alkenes by 2H NMR spectroscopy. The values of k4 for alpha-methylstyrene in several ionic liquids exceed what is observed in acetonitrile by an order of magnitude. While the rate of olefin epoxidation is unaffected by the nature of the ionic liquid cation, a discernible kinetic effect is observed with coordinating anions such as nitrate.
研究了甲基三氧化铼（MTO）的过氧配合物中氧原子向离子液体中烯烃转移的动力学。通过紫外/可见光谱在360 nm处监测烯烃向环氧化物的非催化转化，单过氧铼（mpRe）和双过氧铼（dpRe）配合物在此波长处有吸收。在干燥的四氢呋喃中，通过MTO与尿素过氧化氢（UHP）反应原位制备无水无过氧化物的dpRe。结合动力学模型观察到的双指数时间曲线，可将快速步骤归为烯烃与dpRe的反应（k4），慢速步骤归为与mpRe的类似反应（k3）。在大多数研究的离子液体中，k4约为k3的5倍。在非稳态条件下用[D3]dpRe进行的2H NMR实验证实了离子液体中催化体系的形态，并证实了紫外/可见光谱动力学的有效性。用氘代烯烃通过2H NMR光谱研究烯烃的催化环氧化和二羟基化反应。在几种离子液体中，α-甲基苯乙烯的k4值比在乙腈中观察到的值高出一个数量级。虽然烯烃环氧化速率不受离子液体阳离子性质的影响，但对于配位阴离子如硝酸盐，可观察到明显的动力学效应。
