{{redirect|Diphosphines|compounds of the type P<sub>2</sub>R<sub>4</sub>|Diphosphine#Organic diphosphanes}} [[File:Generic-diphoshine-ligand-2D-skeletal.png|thumb|right|Skeletal formula of a generic diphosphine ligand. R represents a side chain. The phosphine donors are connected by a backbone linker.]] '''Diphosphines''', sometimes called '''bisphosphanes''', are organophosphorus compounds most commonly used as bidentate phosphine ligands in inorganic and organometallic chemistry. They are identified by the presence of two phosphino groups linked by a backbone, and are usually chelating.<ref>Hartwig, J. F. Organotransition Metal Chemistry, from Bonding to Catalysis; University Science Books: New York, 2010. {{ISBN|189138953X}}</ref> A wide variety of diphosphines have been synthesized with different linkers and R-groups. Alteration of the linker and R-groups alters the electronic and steric properties of the ligands which can result in different coordination geometries and catalytic behavior in homogeneous catalysts.<ref>{{cite journal |doi=10.1021/acs.chemrev.9b00682 |title=Trends in the Usage of Bidentate Phosphines as Ligands in Nickel Catalysis |date=2020 |last1=Clevenger |first1=Andrew L. |last2=Stolley |first2=Ryan M. |last3=Aderibigbe |first3=Justis |last4=Louie |first4=Janis |journal=Chemical Reviews |volume=120 |issue=13 |pages=6124–6196 |pmid=32491839 }}</ref>
==Synthesis== [[image:IPr2PCl.png|thumb|220px|right|Chlorodiisopropylphosphine is a popular building block for the preparation of diphosphines.]]
===From phosphide building blocks=== thumb|right|144px|(2-Bromophenyl)diphenylphosphine is a precursor to unsymmetrical diphosphines. Many widely used diphosphine ligands have the general formula Ar<sub>2</sub>P(CH<sub>2</sub>)<sub>n</sub>PAr<sub>2</sub>. These compounds can be prepared from the reaction of X(CH<sub>2</sub>)<sub>n</sub>X (X=halogen) and MPPh<sub>2</sub> (M = alkali metal):<ref>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}} <!--ref is too vague, need chapter--></ref> :Cl(CH<sub>2</sub>)<sub>n</sub>Cl + 2 NaPPh<sub>2</sub> → Ph<sub>2</sub>P(CH<sub>2</sub>)<sub>n</sub>PPh<sub>2</sub> + 2 NaCl Diphosphine ligands can also be prepared from dilithiated reagents and chlorophosphines:<ref>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}}</ref> :XLi<sub>2</sub> + 2 ClPAr<sub>2</sub> → X(PAr<sub>2</sub>)<sub>2</sub> + 2 LiCl (X = hydrocarbon backbone) This approach is suitable for installing two dialkylphosphino groups, using reagents such as chlorodiisopropylphosphine.
Another popular method, suitable for preparing unsymmetrical diphosphines, involves the addition of secondary phosphines to vinylphosphines: :Ph<sub>2</sub>PH + 2 CH<sub>2</sub>=CHPAr<sub>2</sub> → Ph<sub>2</sub>PCH<sub>2</sub>-CH<sub>2</sub>PAr<sub>2</sub> (2-Lithiophenyl)diphenylphosphine can be used also to give unsymmetrical diphosphines. The lithiated reagent is available from (2-bromophenyl)diphenylphosphine: :Ph<sub>2</sub>P(C<sub>6</sub>H<sub>4</sub>Br) + BuLi → Ph<sub>2</sub>P(C<sub>6</sub>H<sub>4</sub>Li) + BuBr :Ph<sub>2</sub>P(C<sub>6</sub>H<sub>4</sub>Li) + R<sub>2</sub>PCli → Ph<sub>2</sub>P(C<sub>6</sub>H<sub>4</sub>PR<sub>2</sub>) + LiCl
===From bis(dichlorophosphine) precursors=== Many diphosphines are prepared from compounds of the type X(PCl<sub>2</sub>)<sub>2</sub> where X = (CH<sub>2</sub>)<sub>n</sub> or C<sub>6</sub>H<sub>4</sub>. The key reagents are 1,2-bis(dichlorophosphino)ethane and 1,2-bis(dichlorophosphino)benzene.
[[image:C2H4(PCl2)2.svg|thumb|164px|right|1,2-Bis(dichlorophosphino)ethane is a key intermediate in the synthesis of 1,2-bis(dimethylphosphino)ethane.<ref name=":0">{{cite journal|doi=10.1016/S0022-328X(00)94383-3|title=A convenient synthesis of 1,2-bis(dichlorophosphino)ethane, 1,2-bis(dimethylphosphino)ethane and 1,2-bis(diethylphosphino)ethane|journal=Journal of Organometallic Chemistry|volume=182|pages=203–206|year=1979|last1=Burt|first1=Roger J.|last2=Chatt|first2=Joseph|last3=Hussain|first3=Wasif|last4=Leigh|first4=G.Jeffery|issue=2 }}</ref><ref name=":1">{{cite journal|doi=10.1021/ja00134a014|title=N-Pyrrolyl Phosphines: An Unexploited Class of Phosphine Ligands with Exceptional .pi.-Acceptor Character|journal=Journal of the American Chemical Society|volume=117|pages=7696–7710|year=1995|last1=Moloy|first1=Kenneth G.|last2=Petersen|first2=Jeffrey L.|issue=29|bibcode=1995JAChS.117.7696M }}</ref>]]
==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 <sup>''t''</sup>Bu<sub>2</sub>P(CH<sub>2</sub>)<sub>10</sub>P<sup>''t''</sup>Bu<sub>2</sub>, give macrocyclic complexes with as many as 72 atoms in a ring.<ref name="Cotton1">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}}</ref><!--pretty esoteric-->
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.<ref>{{cite journal | author = 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 | title = SPANphos: A ''C''<SUB>2</SUB>-Symmetric ''trans''-Coordinating Diphosphane Ligand | journal = Angewandte Chemie | year = 2003 | volume = 42 | issue = 11 | pages = 1322–1325 |doi = 10.1002/anie.200390330 | pmid = 12645065}}</ref> The bite angle of the diphosphine influences the reactivity of the metal center.<ref>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</ref>
Some examples of non-chelating diphosphine also exist. Due to steric effect, these phosphorus atoms can not react with anything except a proton. <ref>Zong, J., J. T. Mague, C. M. Kraml, and R. A. Pascal, Jr., A Congested in,in-Diphosphine, Org. Lett. 2013, 15, 2179-2181.</ref> It can be changed from non-chelating to chelating diphosphine by tuning the length of the linking arm.<ref>Zong, J., J. T. Mague, and R. A. Pascal, Jr., "Encapsulation of non-hydrogen atoms by in, in-bis (triarylelement)-containing cyclophanes." Tetrahedron, 2017, 73, 455-460.</ref>
==Representative ligands== Particularly common diphosphine ligands are shown in the table below:<ref>{{Cite web |date=April 2, 2004 |title=Ligand abbreviations |url=https://old.iupac.org/reports/provisional/abstract04/RB-prs310804/TableVII-3.04.pdf |url-status=live |publisher=IUPAC}}</ref> {| class="sortable wikitable" style="background-color:#ffffff;" !Abbreviation !Common name<br />(from which abbreviation derived) !Structure !Bite angle <!--natural, from van Leeuwen Chem. Soc. Rev 2009, unless otherwise noted--> |- |dppm |1,1-Bis(diphenylphosphino)methane |200px|Dppm-2D-skeletal |73 |- |dmpe |1,2-Bis(dimethylphosphino)ethane |200px|Dmpe-2D-skeletal-B | |- |dippe |1,2-Bis(diisopropylphosphino)ethane |200px|1,2-Bis(diisopropylphosphino)ethane-2D-by-AHRLS-2012 | |- |dppbz |1,2-Bis(diphenylphosphino)benzene |File:Dppbz.svg | |- |dppe |1,2-Bis(diphenylphosphino)ethane |200px|DPPE structure |86 |- |DIPAMP |derivative of phenylanisylmethylphosphine |200px|DIPAMP|alt=DIPAMP.png | |- |dcpe |Bis(dicyclohexylphosphino)ethane |200px|Dcpe|alt=Dcpe.svg | |- |dppp |1,3-Bis(diphenylphosphino)propane |200px|Dppp|alt=Dppp.png |91 |- |dppb |1,4-Bis(diphenylphosphino)butane |200px|The diphoshine ligand diphenylphosphinobutane AKA dppb |94 |- |DIOP |(S,S)-DIOP (O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane) |200px|(S,S)-DIOP|alt=(S,S)-DIOP.svg | |- |Chiraphos |2,3-Bis(diphenylphosphino)butane |200px|Chiraphos|alt=Chiraphos | |- |BINAP |2,2'-Bis(diphenylphosphino)-1,1'-binaphthyl |200px|BINAP Enantiomers Structural Formulae V.1|alt=BINAP Enantiomers Structural Formulae V.1.svg |93 |- |Xantphos |4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene |200px|Xantphos|alt=Xantphos.svg |108 |- |DPEphos |Bis[(2-diphenylphosphino)phenyl] ether |200px|DPEphos |104 |- |SPANphos |4,4,4',4',6,6'-Hexamethyl-2,2'-spirobichromane-8,8'-diylbis(diphenylphosphane) |200px|SPANphos|alt=SPANphos.svg | |- |SEGPHOS |4,4'-Bi-1,3-benzodioxole-5,5'-diylbis(diphenylphosphane) |100px | |- |dppf |1,1'-Bis(diphenylphosphino)ferrocene |100px |99 |- |Me-DuPhos |1,2-Bis(2,5-dimethylphospholano)benzene |200px|DuPhos ligands | |- |Josiphos |(Diphenylphosphino)ferrocenyl-ethyldicyclohexylphosphine1,5-Diaza-3,7-diphosphacyclooctanes |[[File:Josiphos.png|200px|General Josiphos ligand[3]]] | |- |P2N2 |1,5-Diaza-3,7-diphosphacyclooctanes |100px | |}
==See also== Dialkylbiaryl phosphine ligands
==References== <references/>
Category:Diphosphines