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An intermediate cobalt(IV) nitrido complex and its N-migratory insertion product
Eva M Zolnhofer1, Martina Käß, Marat M Khusniyarov
1Department of Chemistry and Pharmacy, Inorganic Chemistry, Friedrich-Alexander University Erlangen - Nürnberg (FAU) , Egerlandstr. 1, 91058 Erlangen, Germany.
Journal of the American Chemical Society
|September 23, 2014
Summary
Low-temperature experiments reveal a highly reactive cobalt(IV) nitride species formed from an azido complex. This transient nitride undergoes N-migratory insertion, yielding a rare, chiral, trigonal pyramidal cobalt(II) complex.
Area of Science:
- Inorganic Chemistry
- Organometallic Chemistry
- Spectroscopy
Background:
- Investigating the reactivity of low-coordinate, high-valent metal nitride species is crucial for understanding nitrogen transfer mechanisms.
- Azido complexes serve as precursors for generating reactive nitrido intermediates.
- The electronic configuration and spin state of metal centers dictate their reactivity and stability.
Purpose of the Study:
- To synthesize and characterize a high-valent cobalt nitride species.
- To elucidate the reaction pathway of the cobalt nitride intermediate.
- To characterize the resulting N-migratory insertion product and its unique structural features.
Main Methods:
- Low-temperature (10 K) photolysis of an azido cobalt complex.
- Electron Paramagnetic Resonance (EPR) spectroscopy for intermediate monitoring.
- Density Functional Theory (DFT) calculations for electronic structure and reaction pathways.
- Comprehensive characterization of the product using CHN elemental analysis, NMR, IR, UV-vis, SQUID magnetometry, and X-ray crystallography.
Main Results:
- Formation of a highly reactive, high-valent cobalt(IV) nitride species (2) from the azido precursor (1) at low temperatures.
- DFT calculations support a low-spin d(5), S=1/2 configuration for the cobalt(IV) nitride.
- Isolation and characterization of the N-migratory insertion product, a trigonal pyramidal cobalt(II) complex (3).
- The reaction pathway from nitride (2) to product (3) proceeds via facile N-migratory insertion with a low activation barrier (2.2 kcal mol(-1)).
Conclusions:
- The study demonstrates the generation and characterization of a transient, high-valent cobalt(IV) nitride species.
- The cobalt(IV) nitride undergoes facile N-migratory insertion into a Co-C bond.
- The resulting cobalt(II) complex (3) is a rare example of a chiral, trigonal pyramidal complex with diverse donor ligands, highlighting unusual coordination chemistry.
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