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

• Published in: Chemical science (Cambridge) Vol. 12; no. 34; pp. 11495 - 11505
• Main Authors: Speelman, Amy L., Tran, Ba L., Erickson, Jeremy D., Vasiliu, Monica, Dixon, David A., Bullock, R. Morris
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 01.09.2021; Royal Society of Chemistry (RSC); The Royal Society of Chemistry
• Subjects: Alkynes; Chemical reactions; Chemistry; Crystallography; Destabilization; Dimers; Insertion; Kinetics; Ligands; Monomers; Spectroscopic analysis; Substrates
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/D1SC01911B

Most ligand designs for reactions catalyzed by (NHC)Cu–H (NHC = N-heterocyclic carbene ligand) have focused on introducing steric bulk near the Cu center. Here, we evaluate the effect of remote ligand modification in a series of [(NHC)CuH] 2 in which the para substituent (R) on the N -aryl groups of the NHC is Me, Et, t Bu, OMe or Cl. Although the R group is distant (6 bonds away) from the reactive Cu center, the complexes have different spectroscopic signatures. Kinetics studies of the insertion of ketone, aldimine, alkyne, and unactivated α-olefin substrates reveal that Cu–H complexes with bulky or electron-rich R groups undergo faster substrate insertion. The predominant cause of this phenomenon is destabilization of the [(NHC)CuH] 2 dimer relative to the (NHC)Cu–H monomer, resulting in faster formation of Cu–H monomer. These findings indicate that remote functionalization of NHCs is a compelling strategy for accelerating the rate of substrate insertion with Cu–H species.