Accelerating the insertion reactions of (NHC)Cu-H via remote ligand functionalization

Area of Science:

• Organometallic Chemistry
• Catalysis
• Ligand Design

Background:

• Traditional N-heterocyclic carbene (NHC) ligand design for copper hydride (Cu-H) catalysis focuses on steric bulk near the copper center.
• The impact of remote modifications on NHC ligands for Cu-H catalysis remains less explored.

Purpose of the Study:

• To investigate the effect of remote functionalization on the N-aryl groups of NHC ligands in [(NHC)CuH]₂ complexes.
• To determine how these remote modifications influence the catalytic activity and kinetics of Cu-H mediated reactions.

Main Methods:

• Synthesis and characterization of a series of [(NHC)CuH]₂ complexes with varying para-substituents (R) on the N-aryl groups.
• Spectroscopic analysis to observe differences in complex signatures.
• Kinetics studies of substrate insertion reactions (ketones, aldimines, alkynes, α-olefins) using these complexes.

Main Results:

• Remote substituents, even six bonds away from the copper center, influence the spectroscopic properties of the complexes.
• Complexes with bulky or electron-rich para-substituents (R groups) exhibit accelerated rates of substrate insertion.
• This acceleration is attributed to the destabilization of the dimeric [(NHC)CuH]₂ species, favoring the formation of the active (NHC)Cu-H monomer.

Conclusions:

• Remote functionalization of NHC ligands is an effective strategy to tune the reactivity of Cu-H species.
• This approach offers a novel pathway for enhancing the catalytic performance of copper hydride complexes in various organic transformations.