Coordination-Accelerated Catalysis in the Heck Reaction Using N-H N-Heterocyclic Carbene Pd Complexes.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• The Heck reaction is a crucial carbon-carbon bond-forming reaction in organic synthesis.
• N-heterocyclic carbene (NHC) ligands have shown promise in enhancing transition metal catalysis.
• Controlling regioselectivity and conversion rates in Heck reactions remains an area of active research.

Purpose of the Study:

• To investigate the use of monosubstituted N-H NHC complexes in the Heck reaction.
• To explore the role of coordinating alcohol substrates in improving Heck reaction efficiency.
• To demonstrate the versatility of this catalytic system for synthesizing complex organic molecules.

Main Methods:

• Utilized monosubstituted N-H NHC ligands in palladium-catalyzed Heck coupling reactions.
• Employed substrates with coordinating alcohol groups and varying tether lengths.
• Investigated subsequent redox isomerization and tandem Heck coupling/hydroalkoxylation reactions.

Main Results:

• Monosubstituted NHC complexes engaging coordinating alcohol substrates significantly increased Heck reaction conversions and regioselectivity.
• The NHC ligand structure, substrate coordinating group, and tether length were identified as critical factors for catalytic improvement.
• A broad substrate scope was demonstrated for various aryl bromides and olefins, with successful synthesis of tetrahydrofuran products via tandem reactions.

Conclusions:

• Monosubstituted N-H NHC complexes offer a powerful strategy for enhancing the Heck reaction.
• The developed catalytic system provides efficient access to valuable aldehyde, amide, and tetrahydrofuran derivatives.
• This work expands the utility of NHC-based catalysis in complex organic synthesis.