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

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)]AgBr(2)}(2) revealed an unusual tetranuclear silver core with a Ag-Ag bond distance of 3.0241(8) A with 1 as a trans-chelating ligand (C-Ag-C = 171 degrees). A preliminary X-ray structure of pseudo-square planar [PdCl(2)(1)] showed a similar binding mode of 1 (C-Pd-C = 177 degrees). High yields were obtained in Suzuki-Miyaura coupling reactions utilizing [PdCl(2)(1)] as the procatalyst and the results were compared with analogous complexes of trans-spanning diphosphine (2) and diphosphinite (3) complexes. The diphosphinite complex, [PdCl(2)(3)], decomposes to [mu-ClPd(PPh(2)OH)(PPh(2)O)](2) at room temperature.