The scope, mechanism and kinetics of the aerobic epoxidation of alkenes with an aldehyde and substituted β-diketonateâtransition metal complexes as catalysts were studied. β-Diketonate complexes of nickel(II) proved to be among the best catalysts for this reaction. The epoxidation is not dependent on substrate concentration and is first order in aldehyde, catalyst concentration and oxygen partial pressure. It was shown by reactivity studies and EPR experiments that the reaction is radical in nature. Additional evidence for this was obtained from stereochemical investigations. The metal catalyst is not only an efficient initiator of the reaction, but is also believed to enhance the reactivity of intermediate species in the oxidation process by allowing these to co-ordinate to the metal center. A mechanism is proposed for the catalytic reaction.
研究了以醛和取代
β-二酮配合物作为催化剂的烯烃好氧环氧化反应的范围、机制和动力学。
镍(II)
β-二酮配合物被证明是该反应的最佳催化剂之一。环氧化反应不依赖于底物浓度,而是对醛、催化剂浓度和
氧气分压呈一级反应。通过活性研究和电子顺磁共振实验表明,该反应具有自由基性质。此外,立体
化学研究也提供了支持这一结论的证据。
金属催化剂不仅是反应的有效
引发剂,还被认为通过使中间体与
金属中心配位来提高氧化过程中中间体的反应活性。提出了一个催化反应机理。