alfred wernerfritz habermax planck

Tripodal N-Heterocyclic Carbene Ligands for High-Valent Reactive Metal Complexes



Transition metal coordination compounds in high oxidation states are active intermediates in many biocatalytic cycles.  In this context, the study of high valent transition metal complexes featuring the terminal, multiple bonded oxido (O2–) and nitrido (N3–) ligands is of significant and current interest due to their proposed intermediacy in biological systems and industrial processes. Examples include O- and N-atom transfer chemistry, epoxidation and aziridination catalysis, water-splitting catalysis with Co-oxo species and biological ammonia synthesis performed by iron nitride intermediates stabilized by the nitrogenase enzyme.  Spectroscopic evidence for these inter­mediates is often based on studies of well-defined inorganic coordination complexes modeling the natural analogues.  The synthesis and characterization of high-valent metal oxo and nitrido model compounds is therefore often key to delineating the nature and reactivity of these unusually reactive species and assigning their role e.g. in water splitting catalysis and ammonia synthesis.  Insight into the molecular and electronic structure of complexes that stabilize the intermediate [FeºN] entity appears to be valuable in unveiling the key steps of both biological (nitrogenase) and industrial (Haber-Bosch process) NH3 synthesis.

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The Meyer group’s approach to high-valent complexes is based on our signature tripodal NHC ligands, which provide a powerful platform for small molecule activation chemistry. This is due to the ligand field resulting from the trigonal carbene environment enabling the stabilization of the desired and highly unusual metal to ligand multiple bonds.

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Chelating tris(carbene) ligands employed by the Meyer Group



We have discovered that employing tripodal N-heterocyclic carbene chelates developed by us, allows for the synthesis, isolation as well as the structural and spectroscopic characterization of discrete mid- and high valent imido, nitride, and peroxo complexes.

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With these ligands we successfully prepared and fully characterized a series of high- and mid-valent manganese, cobalt and iron nitrido complexes. The X-ray structure of the iron(IV) nitrido complex is the first structural verification of the [FeN] synthon that has been recognized as the reactive intermediate in the industrial Haber–Bosch process.  Reactivity studies of the Fe(V) species include the reaction of an FeVºN with water to yield ammonia in near quantitative yields.  

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For details, check this out:

An Iron Nitride Complex

Angew. Chem. Int. Ed. 2008, 47, 2681–2684. get it here, get science editor's choice here, get the "german chemical news" here

Synthesis, Structure, and Reactivity of an Iron(V) Nitride

Science 2011, 331, 1049–1052. get it here, get RCS highlight here, get C&E News highlight here, get GDCh highlight here, NatChem news & views

Manganese Nitride Complexes in Oxidation States III, IV, and V: Synthesis and Electronic Structure
J. Am. Chem. Soc. 2012, 134, 15538–15544. get it here

An Intermediate Cobalt(IV) Nitrido Complex and its N-Migratory Insertion Product

J. Am. Chem. Soc. 2014, 136, 15072–15078.
get it here






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