Diphosphines

Skeletal formula of a generic diphosphine ligand. R represents a side chain.

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.[1]

Synthesis

Many widely used diphosphine ligands have the general formula Ar2P(CH2)nPAr2. These compounds can be prepared from the reaction of X(CH2)nX (X=halogen) and MPPh2 (M = alkali metal):[2]

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:[3]

XLi2 + 2 ClPAr2 → X(PAr2)2 + 2 LiCl (X = hydrocarbon backbone)

Another popular method involves the addition of secondary phosphines to vinylphosphines:

Ph2PH + 2 CH2=CHPAr2 → Ph2PCH2-CH2PAr2

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. A common diphosphine ligand is dppe, 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.[4]

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.[5] The bite angle of the diphosphine influences the reactivity of the metal center.[6]

Some examples of non-chelating diphosphine also exist. Due to steric effect, these phosphorus atoms can not react with anything except a proton. [7]

Common ligands

Particularly common diphosphine ligands are shown in the table below:[8]

Abbreviation Common name
(from which abbreviation derived)		 IUPAC Name (rarely used)
dppm 1,1-Bis(diphenylphosphino)methane Methylene bis(diphenylphosphane)
dmpe 1,2-Bis(dimethylphosphino)ethane Ethane-1,2-diylbis(dimethylphosphane)
dippe 1,2-Bis(diisopropylphosphino)ethane Ethane-1,2-diylbis(di(propan-2-yl)phosphane)
dppe 1,2-Bis(diphenylphosphino)ethane Ethane-1,2-diylbis(diphenylphosphane)
DIPAMP derivative of phenylanisylmethylphosphine Ethane-1,2-diylbis[(2-methoxyphenyl)phenylphosphane]
dppp 1,3-Bis(diphenylphosphino)propane Propane-1,3-diylbis(diphenylphosphane)
dppb 1,4-Bis(diphenylphosphino)butane Butane-1,4-diylbis(diphenylphosphane)
Chiraphos 2,3-Bis(diphenylphosphino)butane Butane-2,3-diylbis(diphenylphosphane)
BINAP 2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl 1,1'-Binaphthalene-2,2'-diylbis(diphenylphosphane)
Xantphos 4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene 9,9-Dimethyl-9H-xanthene-4,5-diylbis(diphenylphosphane)
SPANphos 4,4,4',4',6,6'-Hexamethyl-2,2'-spirobichromane-8,8'-diylbis(diphenylphosphane)
SEGPHOS 4,4'-Bi-1,3-benzodioxole-5,5'-diylbis(diphenylphosphane)
dppf 1,1'-Bis(diphenylphosphino)ferrocene
Me-DuPhos 1,2-Bis(2,5-dimethylphospholano)benzene 1,2-Phenylenebis(2,5-dimethylphospholane)
Josiphos (Diphenylphosphino)ferrocenyl-ethyldicyclohexylphosphine

References

  1. ↑ Hartwig, J. F. Organotransition Metal Chemistry, from Bonding to Catalysis; University Science Books: New York, 2010. ISBN 189138953X
  2. ↑ 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
  3. ↑ Gareth J. Rowlands "Planar Chiral Phosphines Derived from [2.2]Paracyclophane" Israel Journal of Chemistry 2012, Volume 52, Issue 1-2, pages 60–75.doi:10.1002/ijch.201100098
  4. ↑ 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
  5. ↑ 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.
  6. ↑ Birkholz, M.-N., Freixa, Z., van Leeuwen, P. W. N. M., "Bite angle effects of diphosphines in C-C and C-X bond forming cross coupling reactions", Chem. Soc. Rev. 2009, vol. 38, 1099.
  7. ↑ Zong, J., J. T. Mague, C. M. Kraml, and R. A. Pascal, Jr., A Congested in,in-Diphosphine, Org. Lett. 2013, 15, 2179-2181.
  8. ↑ http://old.iupac.org/reports/provisional/abstract04/RB-prs310804/TableVII-3.04.pdf
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