trans-Spanning ferrocene amidodiphosphine ligand: Synthesis, palladium complexes and catalytic use in Suzuki–Miyaura cross-coupling

Amide coupling between [2-(diphenylphosphino)phenyl]methylamine and 1′-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) afforded a novel diphosphine-amide, 1-{N-[(2-(diphenylphosphino)phenyl)methyl]carbamoyl}-1′-(diphenylphosphino)ferrocene (1), which was subsequently studied as a ligand for palladium(II) complexes. Depending on the metal precursor, the following complexes were isolated: [PdCl2(1-κ2P,P′)] (2), [PdCl(Me)(1-κ2P,P′)] (3), [(μ-1){PdCl2(PBu3)}2] (4) and [(μ-1){PdCl(LNC)}2] (LNC = 2-[(dimethylamino-κN)methyl]phenyl-κC1), featuring this ligand either as a trans-chelating or as a P,P′-bridging donor. The crystal structure of 2·1.25CH2Cl2 was established by X-ray crystallography, corroborating that 1 coordinates as a trans-spanning diphosphine without any significant distortion to the coordination sphere. Complex 2 together with a catalyst prepared in situ from 1 and palladium(II) acetate were tested in Suzuki–Miyaura reaction of aryl bromides with phenylboronic acid in dioxane.

A novel diphosphine-amide, viz 1-{N-[(2-(diphenylphosphino)phenyl)methyl]carbamoyl}-1′-(diphenylphosphino)ferrocene (1) was prepared by amide coupling between 2-Ph2PC6H4CH2NH2 and 1′-(diphenylphosphino)ferrocene-1-carboxylic acid. Depending on the metal source, this ligand forms trans-chelate complexes [PdCl(X)(1-κ2P,P′)] (X = Cl or Me) or P,P′-bridged dipalladium(II) complexes [(μ-1){Pd(Cl)L}2] (L = (Cl)PBu3 or 2-[(dimethylamino-κN)methyl]phenyl-κC1).Figure optionsDownload as PowerPoint slide