Secondary Ferrocenyl Phosphines: Versatile Precursors for the Synthesis of Bi- and Tridentate Ligands

The high-yield preparation of the new ferrocenyl ligands 1–6 is reported. These compounds contain a tertiary phosphino group combined with a secondary stereogenic phosphine and were thus obtained as an inseparable mixture of isomers in a ratio that depends on the nature of the substituents at phosphorus. These secondary phosphines are highly versatile and can be used as ligands for Pd(II) and Rh(I) complexes as well as precursors for the synthesis of tertiary phosphines or secondary phosphine oxides (SPOs). Diphosphine 2 forms a stable complex with [PdCl2(COD)] but undergoes an intramolecular allylation upon reaction with [Pd2(μ-Cl)2(η3-C3H5)2] and generates a bidentate ligand with two tertiary phosphino groups coordinated to a dichloropalladium unit (9). The ferrocenyl diphosphine 5, bearing a P(CF3)2 group, could be oxidized to the corresponding SPO derivative. Tridentate phosphine ligands of the Pigiphos type were synthesized using ferrocenyl secondary phosphines 4 and 5 as the main precursors. Additionally, palladium(II) and nickel(II) complexes containing these ligands were prepared and characterized by NMR spectroscopy and X-ray crystallography.