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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Main-chain organometallic polymers comprising redox-active iron(II) centers connected by ditopic N-heterocyclic
Laszlo Mercs1, Antonia Neels, Helen Stoeckli-Evans
1Department of Chemistry, University of Fribourg, Chemin du Musee 9, CH-1700 Fribourg, Switzerland.
Abstract:
Main-chain organometallic polymers were synthesized from bimetallic iron(ii) complexes containing a ditopic N-heterocyclic carbene (NHC) ligand [(cp)(CO)LFe(NHC approximately NHC)Fe(cp)(CO)L]X(2) (where NHC approximately NHC represents a bridging dicarbene ligand, L = I(-) or CO). Addition of a diimine ligand such as pyrazine or 4,4'-bipyridine, interconnected these bimetallic complexes and gave the corresponding co-polymers containing iron centers that are alternately linked by a dicarbene and a diimine ligand. Diimine coordination depended on the wingtip groups at the carbene ligands and was accomplished either by photolytic activation of a carbonyl ligand from the cationic [Fe(cp)(NHC)(CO)(2)](+) precursor (alkyl wingtips) or by AgBF(4)-mediated halide abstraction from the neutral complex [FeI(cp)(NHC)(CO)] (mesityl wingtips). Remarkably, the polymeric materials were substantially more stable than the related bimetallic model complexes. Electrochemical analyses indicated metal-metal interactions in the pyrazine-containing polymers, whereas in 4,4'-bipyridine-linked systems the metal centers were electronically decoupled.
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