Three-coordinate copper(I) amido and aminyl radical complexes.
Neal P Mankad1, William E Antholine, Robert K Szilagyi
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Journal of the American Chemical Society
|March 4, 2009
Summary
A novel copper complex mimics blue copper proteins with rapid electron transfer. The oxidized form is a copper(I)-aminyl radical, not copper(II)-amido, showing unique reactivity.
Area of Science:
- Coordination chemistry
- Bioinorganic chemistry
- Organometallic chemistry
Background:
- Blue copper proteins are vital metalloenzymes with unique Type 1 active sites.
- Understanding their electronic structure is key to mimicking their function.
- Copper complexes with specific ligands can model these active sites.
Purpose of the Study:
- To synthesize and characterize a three-coordinate copper complex as a functional model for Type 1 blue copper proteins.
- To investigate the electronic structure of the oxidized copper complex.
- To explore the reactivity arising from its unique electronic configuration.
Main Methods:
- Isolation and structural characterization of copper complexes in Cu(I) and Cu(II) oxidation states.
- Measurement of self-exchange electron-transfer reaction rates.
- Multiedge X-ray absorption spectroscopy (XAS) and multifrequency electron paramagnetic resonance (EPR).
- Density functional theory (DFT) calculations.
Main Results:
- A three-coordinate Cu-NR(2) system was successfully synthesized and characterized.
- The system exhibits a high self-exchange electron-transfer rate constant (k(S) >= 10(7) M(-1) s(-1)).
- Spectroscopic and computational analyses reveal the oxidized form is a Cu(I)-aminyl radical, with ~70% unpaired electron on the NR(2) unit, rather than a Cu(II)-amido species.
Conclusions:
- The synthesized copper complex serves as a functional model for Type 1 blue copper protein active sites.
- The oxidized species possesses an unusual electronic structure, best described as a Cu(I)-aminyl radical.
- This unique electronic configuration enables novel reactivity, including hydrogen-atom transfer and C-C coupling reactions.
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