N-heterocyclic carbene ligands with a bicyclic framework fused with either naphthalene or anthracene

Abstract

N-heterocyclic carbene (NHC) ligands equipped with a bicyclic framework fused with either naphthalene or anthracene (NCPSI and ACPSI, respectively) were synthesized, and their silver and iridium complexes were obtained. Tolman's electronic parameter (TEP) values for these NHC ligands were calculated by using the Ir complexes, which indicated that the electron-donating ability of these NHCs was almost identical to that of the structurally related NHCs, DHASI and BCPSI, that we had previously reported. The structures of [(NHC)AgCl] and [Ir(COD)Cl(NHC)] were analyzed via XRD study, which showed structural changes that depended on the bound metals. Although the NHCs analyzed in this study involve the same bicyclo[2.2.1]heptene core, three aromatic rings, benzene, naphthalene, and anthracene, caused different interplanar angles between the aromatic rings and the NHC's five-membered rings. The regio-selectivities during copper-catalyzed allylic arylation were found to be related to the interplanar angles of the [(NHC)AgCl] complexes, indicating that the interplanar angles would be a useful factor in tuning the steric properties of these NHC ligands.