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Mechanistic considerations for C-C bond reductive coupling at a cobalt(III) center
Hongwei Xu1, Wesley H Bernskoetter
1Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States.
Journal of the American Chemical Society
|September 8, 2011
Summary
This study reveals how a cobalt complex selectively forms carbon-carbon bonds, producing ethane. The mechanism involves phosphine dissociation and a concerted C-C bond formation, confirmed by kinetic and isotopic experiments.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Reaction Mechanisms
Background:
- Cobalt complexes are investigated for catalytic applications.
- Understanding reductive elimination is crucial for C-C bond formation.
Purpose of the Study:
- To elucidate the mechanism of reductive elimination in a specific cobalt(III) dimethyl complex.
- To investigate the factors influencing C-C bond formation.
Main Methods:
- Kinetic studies
- Isotopic labeling experiments
- Exchange spectroscopy (EXSY) Nuclear Magnetic Resonance (NMR)
- Radical trapping and crossover experiments
Main Results:
- The complex cis,mer-(PMe(3))(3)Co(CH(3))(2)I selectively forms ethane via reductive elimination.
- Ethane formation rate: 3.1(5) × 10(-5) s(-1) at 50 °C.
- Reversible phosphine dissociation precedes C-C bond formation, with phosphine loss rate of 9(2) s(-1).
- A mechanism involving a five-coordinate intermediate and concerted C-C bond formation is proposed.
- Unusual intermolecular exchange of cobalt-methyl ligands was observed.
Conclusions:
- The study clarifies the reductive elimination pathway for ethane formation from a cobalt(III) complex.
- Reversible ligand dissociation plays a key role in the catalytic cycle.
- The findings contribute to the understanding of C-C bond formation mechanisms in organometallic chemistry.
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