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Olefin Coupling Catalyzed by (Pybox)Os Complexes via Osmacyclopentane Intermediates: Comparison with Isoelectronic
Ashish Parihar1, Santanu Malakar2, Soham Chakraborty1
1Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, United States.
JACS Au
|December 26, 2025
Summary
The (Pybox)Os complex catalyzes alkene hydrovinylation, unlike its (Phebox)-Ir counterpart which favors dehydrogenative coupling. This difference arises from a lower C-H reductive elimination barrier in the Os system, enabling distinct catalytic pathways.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Homogeneous Catalysis
Background:
- The catalytic activity of late transition metals is crucial in organic synthesis.
- Iridium and Osmium complexes with pincer ligands exhibit diverse reactivity.
- Understanding reaction mechanisms is key to designing efficient catalysts.
Purpose of the Study:
- To investigate the catalytic activity of (Pybox)Os in alkene hydrovinylation.
- To compare the reactivity of (Pybox)Os with the isoelectronic (Phebox)-Ir catalyst.
- To elucidate the mechanistic differences between Os- and Ir-catalyzed reactions.
Main Methods:
- Experimental studies of alkene hydrovinylation using (Pybox)Os.
- Computational investigations of reaction mechanisms.
- Comparison of kinetic and thermodynamic parameters for Os and Ir systems.
Main Results:
- (Pybox)Os efficiently catalyzes alkene hydrovinylation, including ethylene dimerization and cross-coupling.
- (Phebox)-Ir catalyzes dehydrogenative coupling of ethylene.
- Both reactions proceed via a metallacyclopentane intermediate followed by beta-H elimination.
- Os-catalyzed C-H reductive elimination is kinetically favored over Ir, despite less thermodynamic driving force.
Conclusions:
- The distinct chemoselectivity of (Pybox)Os and (Phebox)-Ir stems from differences in C-H reductive elimination barriers.
- Lower kinetic barriers for C-H elimination in Os complexes can lead to unique catalytic outcomes.
- The findings provide insights into the general behavior of d6 vs. d8 metal complexes in C-H activation/elimination.
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