Main-chain organometallic polymers comprising redox-active iron(II) centers connected by ditopic N-heterocyclic carbenes

Main-chain organometallic polymers were synthesized from bimetallic iron(II)complexes containing a ditopic N-heterocyclic carbene (NHC) ligand [(cp)(CO)LFe(NHC~NHC)Fe (cp)(CO)L]X2 (where NHC~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 was depending 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 AgBF4-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.