Journal
INORGANIC CHEMISTRY
Volume 57, Issue 21, Pages 13494-13504Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.inorgchem.8b02109
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Funding
- NSERC Vanier Canada Graduate scholarship
- NSERC CGS-D scholarship
- NSERC Canada
- Memorial University
- Research Development Corporation-NL
- Canada Foundation for Innovation
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A series of iron(III) chloride and iron(III) mu-oxo compounds supported by tetradentate amino-bis(phenolate) ligands containing a homopiperazinyl backbone were prepared and characterized by electronic absorption spectroscopy, magnetic moment measurement, and MALDI-TOF mass spectrometry. The solid-state structures of three iron(III) mu-oxo compounds were determined by single crystal X-ray diffraction and revealed oxo-bridged bimetallic species with Fe-O-Fe angles between 171.7 and 180 degrees, with the iron centers in distorted square pyramidal environments. Variable temperature magnetic measurements show the oxo complexes exhibit strong antiferromagnetic coupling between two high spin S = 5/2 iron(III) centers. The oxo complexes exhibit poor activity for the reaction of carbon dioxide and epoxides in the presence of a cocatalyst, under solvent free conditions to yield cyclic carbonates. The least active iron oxo compound bears tert-butyl groups on the phenolate donors, and we propose that steric congestion around the iron center reduces catalytic. activity in this case. We provide evidence that an epoxide deoxygenation step occurs when employing monometallic iron(III) chlorido species as catalysts. This affords the corresponding mu-oxo compounds which can then enter their own catalytic cycle. Deoxygenation of epoxides during their catalytic reactions with carbon dioxide is frequently overlooked and should be considered as an additional mechanistic pathway when investigating catalysts.
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