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Powerful Bis-facially Pyrazolate-Bridged Dinuclear Ruthenium Epoxidation Catalyst

† Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, 08193 Barcelona, Spain
‡ Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain
∥ Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain
⊥ Institut für Anorganische Chemie, Georg-August-Universität, Tammannstrasse 4, 37077 Göttingen,Germany
Inorg. Chem., Article ASAP
DOI: 10.1021/acs.inorgchem.5b00641
Publication Date (Web): June 29, 2015
Copyright © 2015 American Chemical Society
*Fax: + 34 93 581 24 77 E-mail: lluis.escriche@uab.cat. Homepage: www.seloxcat.wordpress.com., *Fax: + 34 93 581 24 77 E-mail: xavier.sala@uab.cat. Homepage: www.seloxcat.wordpress.com.

Synopsis


A novel Ru(II) dinuclear complex containing the bis-facial hexadentate bridging ligand Hbimp is described. This complex is an excellent catalyst for the epoxidation of a wide range of alkenes, yielding high turnover numbers and turnover frequencies. Furthermore, an outstanding stereospecificity for both cis and transolefins toward the formation of the corresponding epoxides is envisaged due to cooperative effects transferred by the Hbimp scaffold.

Abstract

Abstract Image
A new bis-facial dinuclear ruthenium complex, {[RuII(bpy)]2(μ-bimp)(μ-Cl)}2+, 22+, containing a hexadentate pyrazolate-bridging ligand (Hbimp) and bpy as auxiliary ligands has been synthesized and fully characterized in solution by spectrometric, spectroscopic, and electrochemical techniques. The new compound has been tested with regard to its capacity to oxidize water and alkenes. The in situ generated bis-aqua complex, {[RuII(bpy)(H2O)]2(μ-bimp)}3+, 33+, is an excellent catalyst for the epoxidation of a wide range of alkenes. High turnover numbers (TN), up to 1900, and turnover frequencies (TOF), up to 73 min–1, are achieved using PhIO as oxidant. Moreover, 33+ presents an outstanding stereospecificity for both cis and trans olefins toward the formation of their corresponding epoxides due to specific interactions transmitted by its ligand scaffold. A mechanistic analysis of the epoxidation process has been performed based on density functional theory (DFT) calculations in order to better understand the putative cooperative effects within this dinuclear catalyst.





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