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Gas-Phase Rates of Alkane C-H Oxidative Addition to a Transient CpRh(CO) Complex
Science (New York, N.Y.)
|January 17, 1992
Summary
Researchers studied the reactivity of short-lived CpRh(CO) intermediates in gas-phase reactions. They found that these intermediates readily activate alkane C-H bonds upon collision, suggesting a new pathway for C-H activation.
Area of Science:
- Organometallic chemistry
- Photochemistry
- Reaction kinetics
Background:
- The study of 16-electron organometallic intermediates is crucial for understanding catalytic cycles.
- CpRh(CO)2 is a common precursor for generating reactive rhodium species.
- C-H bond activation by transition metals is a key transformation in organic synthesis.
Purpose of the Study:
- To investigate the gas-phase reactivity of "naked" CpRh(CO) generated by photolysis.
- To directly measure the rates of reaction between CpRh(CO) and alkane C-H bonds.
- To elucidate the mechanism of C-H oxidative addition involving these intermediates.
Main Methods:
- Gas-phase photolysis of cyclopentadienylrhodium dicarbonyl (CpRh(CO)2).
- Detection of transient "naked" CpRh(CO) using spectroscopic techniques.
- Kinetic measurements of the reaction between CpRh(CO) and various alkanes.
Main Results:
- "Naked" CpRh(CO) was successfully generated and detected in the gas phase.
- Direct rate measurements revealed extremely high reactivity towards alkane C-H bonds.
- C-H bond activation occurred with nearly every collision for medium-sized alkanes.
- Evidence for intermediates where alkanes bind to the metal without complete C-H bond cleavage was observed.
Conclusions:
- The "naked" CpRh(CO) intermediate is highly reactive towards C-H bond activation.
- The observed high reaction rates suggest a facile activation pathway.
- Transiently bound alkane species are likely intermediates in the C-H oxidative addition process.
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