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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
Imparting catalyst control upon classical palladium-catalyzed alkenyl C-H bond functionalization reactions
Matthew S Sigman1, Erik W Werner
1Department of Chemistry, University of Utah, 315 S. 1400 E., Salt Lake City, Utah 84112, USA. sigman@chem.utah.edu
Accounts of Chemical Research
|November 25, 2011
Summary
Researchers developed catalyst-controlled Wacker and Heck reactions by understanding mechanistic similarities. This allows for predictable selectivity in complex organic synthesis, overcoming limitations of substrate control in these important palladium-catalyzed reactions.
Area of Science:
- Organic Chemistry
- Organometallic Chemistry
- Catalysis
Background:
- Palladium-catalyzed Wacker and Heck reactions are vital for alkenyl C-H bond functionalization in organic synthesis.
- Existing Wacker and Heck reactions suffer from substrate-controlled selectivity, limiting their synthetic potential.
- Mechanistic similarities in nucleopalladation and β-hydride elimination steps suggest potential for cross-application of insights.
Purpose of the Study:
- To develop catalyst-controlled variants of the Wacker oxidation and Heck reaction.
- To address limitations in selectivity and expand substrate scope for these reactions.
- To gain mechanistic insight into the organometallic processes governing selectivity.
Main Methods:
- Utilized electrophilic palladium catalysts with noncoordinating counterions and Lewis basic ligands for Wacker oxidation.
- Employed bidentate ligands to develop a mechanistically guided Wacker reaction.
- Investigated electrophilic Pd-σ-alkyl intermediates for selective C-H bond activation in Heck reactions using arylboronic acids and aryldiazonium salts.
Main Results:
- Developed a tert-butylhydroperoxide (TBHP)-mediated Wacker oxidation of styrenes using electrophilic palladium catalysts and Lewis basic ligands.
- Achieved catalyst-controlled Wacker oxidation for challenging substrates using a palladium complex with a bidentate ligand.
- Developed E-styrenyl selective oxidative Heck reactions for electronically nonbiased alkenes and a similarly selective classical Heck reaction.
Conclusions:
- Mechanistic insights from catalyst design enable predictable control over selectivity in Wacker and Heck reactions.
- Developed methods overcome limitations of substrate control, expanding the synthetic utility of these reactions.
- The findings pave the way for designing more complex organometallic reactions based on predictable selectivity.
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