期刊
ACS CATALYSIS
卷 11, 期 6, 页码 3206-3217出版社
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.0c05320
关键词
epoxidation; titanium; salalen ligands; hydrogen peroxide; mechanism; kinetics; spectroscopy; DFT calculations
资金
- Fonds der Chemischen Industrie
- Scholarship Fund of the Swiss Chemical Industry (SSCI)
- Deutsche Forschungsgemeinschaft (DFG) [SPP 1807, BE 998/14-1, BE 998/14-2]
Titanium-salalen complexes have solved the long-standing problem in homogeneous epoxidation catalysis by enabling the selective catalytic epoxidation of terminal, nonconjugated olefins with hydrogen peroxide. The mechanism involves a slow pre-equilibrium and rearrangement of the coordination sphere of the dinuclear complex to allow efficient activation of H2O2. This efficient activation of H2O2 parallels recent findings on the active sites of the industrial heterogeneous titanium silicalite TS-1 catalyst.
Titanium-salalen complexes have recently solved a long-standing problem in homogeneous epoxidation catalysis by enabling the selective catalytic epoxidation of terminal, nonconjugated olefins with hydrogen peroxide. In this work, we disclose the mechanism of this intriguing catalyst system, based on XRD analyses, kinetic studies, and NMR elucidation of intermediate structures, complemented by DFT computations. Titanium-salalen catalysts are typically prepared/stored as bis-mu-oxo or mu-oxo-mu-peroxo dimers. Under reaction conditions, while the mu-oxo bridged catalyst dimers remain intact, the epoxidation occurs through an octahedral, yet altered, coordination geometry of the homochiral monomeric subunits. This catalytically active coordination mode is accessed by a slow pre-equilibrium, involving uptake of hydrogen peroxide, and subsequent rearrangement of the coordination sphere of the dinuclear complex. This configuration allows a three-pronged electrophilic activation of hydrogen peroxide, which enables oxygen transfer by the joint action of (i) the Lewis acidic titanium center, (ii) H-bond donation by the ligand's NH, and (iii) mu-chalcogen interaction with the ligand's pentafluorophenyl moieties. This efficient activation of H2O2 by a dinuclear site parallels recent findings on the active sites of the industrial heterogeneous titanium silicalite TS-1 catalyst.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据