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Controlling Chemoselectivity in Ruthenium(II)-Induced Cyclization of Aniline-Functionalized Alkynes
Kai-Wa Io1, Hau-Lam Shek1, Tsun-Yin Li1
1Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|October 5, 2024
Summary
Researchers explored how ruthenium complexes activate alkynes, revealing that reaction conditions can control whether a vinylidene or non-vinylidene pathway is favored. This allows selective synthesis of different metalated indole complexes.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Synthetic Organic Chemistry
Background:
- D6-transition metal centers typically activate heteroatom-functionalized alkynes via a vinylidene pathway.
- Emerging evidence indicates d6-transition metal centers can also activate alkynes through non-vinylidene pathways.
- Understanding and controlling these pathways is crucial for developing new synthetic methodologies.
Purpose of the Study:
- To investigate the reaction mechanisms between a specific Ruthenium(II) complex and 2-alkynylanilines.
- To explore the factors influencing the selectivity between vinylidene and non-vinylidene pathways.
- To demonstrate practical control over the formation of specific metalated indole zwitterion complexes.
Main Methods:
- Comprehensive experimental studies using the Ru(II) complex [Ru([9]aneS3)(bpy)(OH2)]2+ and 2-alkynylanilines.
- Theoretical investigations to elucidate reaction mechanisms and intermediates.
- Systematic variation of reaction temperature, substrate structure, and solvent polarity.
Main Results:
- Demonstrated that reaction temperature, substrate, and solvent polarity can tune the selectivity between vinylidene and non-vinylidene pathways.
- Achieved preferential formation of either C2- or C3-metalated indole zwitterion complexes.
- Identified a novel decyclization pathway for converting C2-metalated indoles to C3-metalated indoles.
Conclusions:
- Provided practical strategies for controlling the vinylidene versus non-vinylidene pathway preference in alkyne cyclization reactions.
- Highlighted the importance of product stability in dictating reaction outcomes.
- The findings are significant for designing novel catalysts and metalated heterocyclic complexes.
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