bisphosphines

Bisphosphines are organophosphorus compounds that contain two phosphino (PR2) groups connected by a covalent linker. They are most commonly used as bidentate ligands in coordination chemistry, where both phosphorus atoms bind to a single metal center to form chelate complexes. The general formula is R2P–(linker)–PR2, and the linker can range from a single atom (e.g., methylene) to rigid frameworks such as ferrocene or biaryl backbones.

Key properties of bisphosphines include their donor strength, steric bulk, and bite angle (the P–M–P angle when coordinated). These parameters are tunable through the choice of R substituents and the nature of the backbone, allowing control over electronic and geometric effects at the metal. Well-known examples include dppm (bis(diphenylphosphino)methane), dppe (1,2-bis(diphenylphosphino)ethane), dppf (1,1'-bis(diphenylphosphino)ferrocene) and chiral ligands such as BINAP and DuPhos.

Bisphosphines play a central role in homogeneous catalysis, including hydrogenation, hydroformylation, and cross-coupling reactions, where bidentate coordination can enhance activity, selectivity, and stability of metal catalysts. Chiral bisphosphines are especially important in asymmetric syntheses.

Synthesis typically proceeds by formation of P–C or P–P bonds using halophosphines and nucleophiles or by functionalizing preformed phosphine precursors. Many phosphine ligands are air-sensitive and oxidize to phosphine oxides; they can also be malodorous and toxic, so handling under inert atmosphere and appropriate safety measures are common.