Diphosphines, sometimes called bisphosphanes, are organophosphorus compounds used as ligands in inorganic and organometallic chemistry. They are identified by the presence of two phosphino groups linked by a backbone, and are usually chelating.
The most widely used diphosphine ligands have the general formula Ph2P(CH2)nPPh2. These compounds can be prepared from the reaction of X(CH2)nX (X=halogen) and YPPh2 (Y=alkali metal):
- Cl(CH2)nCl + 2 NaPPh2 → Ph2P(CH2)nPPh2 + 2 NaCl
Diphosphine ligands can also be prepared by other methods, such as from dilithiated reagents and chlorophosphines or by the addition of secondary phosphines to vinylphosphines.
Chain length and coordinating properties 
The short-chain diphosphine dppm tends to promote metal-metal interactions as illustrated by A-frame complexes. When the two phosphine substituents are linked by two to four carbon centres, the resulting ligands often chelate rings with a single metal. The most common diphosphine ligand is 1,2-Bis(diphenylphosphino)ethane, which forms a five-membered chelate ring with most metals.
Some diphosphines, such as the extraordinary case of tBu2P(CH2)10PtBu2, give macrocyclic complexes with as many as 72 atoms in a ring.
To position phosphine donor groups trans on a coordination sphere, several atoms are required to link the donor centres and long-chain diphosphines are typically floppy and do not chelate well. This challenge has been resolved by the long but rigid diphosphine SPANphos.
Common ligands 
Particularly common diphosphine ligands are shown in the table below:
(from which abbreviation derived)
|IUPAC Name (rarely used)|
|DIPAMP||Dimer of phenylanisylmethylphosphine||Ethane-1,2-diylbis[(2-methoxyphenyl)phenylphosphane]|
- Wilkinson, G.; Gillard, R.; McCleverty, J. Comprehensive Coordination Chemistry: The synthesis, reactions, properties & applications of coordination compounds, vol.2.; Pergamon Press: Oxford, UK, 1987; p. 993. ISBN 0-08-035945-0
- Cotton, F.A.; Wilkinson, G. Advanced Inorganic Chemistry: A Comprehensive Text, 4th ed.; Wiley-Interscience Publications: New York, NY, 1980; p.246. ISBN 0-471-02775-8
- Z. Freixa, M. S. Beentjes, G. D. Batema, C. B. Dieleman, G. P. F. v. Strijdonck, J. N. H. Reek, P. C. J. Kamer, J. Fraanje, K. Goubitz and P. W. N. M. Van Leeuwen (2003). "SPANphos: A C2-Symmetric trans-Coordinating Diphosphane Ligand". Angewandte Chemie 42 (11): 1322–1325. doi:10.1002/anie.200390330. PMID 12645065.