Canopied trans-chelating bis(N-heterocyclic carbene) ligand: synthesis, structure and catalysis

Abstract

The terphspan scaffold was employed to support a bis(N-heterocyclic carbene) ligand (1) that provides a m-terphenyl canopy over one side of its metal complexes. Single-crystal X-ray diffraction studies on a silver complex of {[Ag(1)]AgBr₂}₂ revealed an unusual tetranuclear silver core with a Ag–Ag bond distance of 3.0241(8) Å with 1 as a trans-chelating ligand (C–Ag–C = 171°). A preliminary X-ray structure of pseudo-square planar [PdCl₂(1)] showed a similar binding mode of 1 (C–Pd–C = 177°). High yields were obtained in Suzuki–Miyaura coupling reactions utilizing [PdCl₂(1)] as the procatalyst and the results were compared with analogous complexes of trans-spanning diphosphine (2) and diphosphinite (3) complexes. The diphosphinite complex, [PdCl₂(3)], decomposes to [μ-ClPd(PPh₂OH)(PPh₂O)]₂ at room temperature.