Formation of Highly Strained N-Heterocycles via Decomposition of Iron N-Heterocyclic Carbene Complexes: The Value of Labile Fe-C Bonds.
An unusual, highly-strained annulated 2,2'-biimdazole was isolated as decomposition product of the outer-sphere one-electron oxidation of an iron(II) N-heterocyclic carbene (NHC) complex bearing a tetradentate bis(NHC)-bis- (pyridine) ligand (NCCN). Reductive elimination leading to the 2,2'-biimdazole is a consequence of the lability of the FeC bonds in the transient species and also extends to complexes with modified ligands but the same coordination geometry. Closely related by a two-electron redox step to a family of less-strained tetraazafulvalenes, the obtained 2,2'-biimidazolium salts were studied electrochemically. Introduction of methyl substituents at the methylene tether significantly increased the reversibility of the electrochemical reduction. Furthermore, the reactivity of the 2,2'-biimidazolium salt was examined by oxidative addition of [Ni(cod)2 ] to the central CC bond, providing a previously unknown way for the formation of NHC transition metal complexes.
Chair of Inorganic Chemistry/Molecular Catalysis, Technische Universität München (TUM), Ernst-Otto-Fischer-Straße 1, 85747 Garching b. München (Germany).
Stefan
S
Haslinger
Chair of Inorganic Chemistry/Molecular Catalysis, Technische Universität München (TUM), Ernst-Otto-Fischer-Straße 1, 85747 Garching b. München (Germany).
Jens W
JW
Kück
Chair of Inorganic Chemistry/Molecular Catalysis, Technische Universität München (TUM), Ernst-Otto-Fischer-Straße 1, 85747 Garching b. München (Germany).
Markus R
MR
Anneser
Chair of Inorganic and Organometallic Chemistry, Technische Universität München (TUM), Ernst-Otto-Fischer-Straße 1, 85747 Garching b. München (Germany).
Mirza
M
Cokoja
Catalysis Research Center, Technische Universität München (TUM), Ernst-Otto-Fischer-Straße 1, 85747 Garching b. München (Germany).
Alexander
A
Pöthig
Chair of Inorganic Chemistry/Molecular Catalysis, Technische Universität München (TUM), Ernst-Otto-Fischer-Straße 1, 85747 Garching b. München (Germany). fritz.kuehn@ch.tum.de.
Fritz E
FE
Kühn
biimidazolium; iron; nitrogen heterocycles; oxidation; reductive elimination