Universität zu Köln

Engler, Hauke, Lansing, Markus, Gordon, Christopher P., Neudoerfl, Joerg-M, Schaefer, Mathias, Schloerer, Nils E., Coperet, Christophe ORCID: 0000-0001-9660-3890 and Berkessel, Albrecht (2021). Olefin Epoxidation Catalyzed by Titanium-Salalen Complexes: Synergistic H2O2 Activation by Dinuclear Ti Sites, Ligand H-Bonding, and pi-Acidity. ACS Catal., 11 (6). S. 3206 - 3218. WASHINGTON: AMER CHEMICAL SOC. ISSN 2155-5435

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Abstract

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.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Engler, Hauke UNSPECIFIED UNSPECIFIED UNSPECIFIED Lansing, Markus UNSPECIFIED UNSPECIFIED UNSPECIFIED Gordon, Christopher P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Neudoerfl, Joerg-M UNSPECIFIED UNSPECIFIED UNSPECIFIED Schaefer, Mathias UNSPECIFIED UNSPECIFIED UNSPECIFIED Schloerer, Nils E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Coperet, Christophe UNSPECIFIED orcid.org/0000-0001-9660-3890 UNSPECIFIED Berkessel, Albrecht UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-572630
DOI:	10.1021/acscatal.0c05320
Journal or Publication Title:	ACS Catal.
Volume:	11
Number:	6
Page Range:	S. 3206 - 3218
Date:	2021
Publisher:	AMER CHEMICAL SOC
Place of Publication:	WASHINGTON
ISSN:	2155-5435
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language TERMINAL NONCONJUGATED OLEFINS; ASYMMETRIC EPOXIDATION; ENANTIOSELECTIVE EPOXIDATION; EFFICIENT EPOXIDATION; OXIDANTS Multiple languages Chemistry, Physical Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/57263