Accelerating the insertion reactions of (NHC)Cu–H via remote ligand functionalization. Issue 34 (2nd August 2021)

• Record Type: Journal Article
• Authors: Speelman, Amy L.; Tran, Ba L.; Erickson, Jeremy D.; Vasiliu, Monica; Dixon, David A.; Bullock, R. Morris
• Is Part Of: Chemical science. Volume 12:Issue 34(2021)
• Page Start: 11495
• Page End: 11505
• Publication Date: 2021-08-02
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1sc01911b
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Remote modification of an N-heterocyclic carbene ligand with bulky or electron-rich groups in [(NHC)Cu(μ-H)]2 increases the rate of substrate insertion, which kinetics studies suggest arises from changes in the Cu–H monomer–dimer equilibrium. Abstract : 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.