Triphenylphosphine

Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C₆H₅)₃ and often abbreviated to PPh₃ or Ph₃P. It is versatile compound that is widely used as a reagent in organic synthesis and as a ligand for transition metal complexes, including ones that serve as catalysts in organometallic chemistry. PPh₃ exists as relatively air stable, colorless crystals at room temperature. It dissolves in non-polar organic solvents such as benzene and diethyl ether.

Triphenylphosphine

Names
Preferred IUPAC name Triphenylphosphane[1]
Identifiers
CAS Number	603-35-0 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:183318
ChemSpider	11283 Y
ECHA InfoCard	100.009.124
EC Number	210-036-0
PubChem CID	11776
RTECS number	SZ3500000
UNII	26D26OA393 Y
UN number	3077
CompTox Dashboard (EPA)	DTXSID5026251
InChI InChI=1S/C18H15P/c1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18/h1-15H Y Key: RIOQSEWOXXDEQQ-UHFFFAOYSA-N Y InChI=1/C18H15P/c1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18/h1-15H Key: RIOQSEWOXXDEQQ-UHFFFAOYAH
SMILES c1ccccc1P(c2ccccc2)c3ccccc3
Properties
Chemical formula	C18H15P
Molar mass	262.292 g·mol−1
Appearance	White Solid
Density	1.1 g cm−3, solid
Melting point	80 °C (176 °F; 353 K)
Boiling point	377 °C (711 °F; 650 K)
Solubility in water	Insoluble
Solubility	organic solvents
Acidity (pKa)	7.64[2] (pKa of conjugate acid in acetonitrile) 2.73[3] (pKa of conjugate acid, aqueous scale)
Magnetic susceptibility (χ)	-166.8·10−6 cm3/mol
Refractive index (nD)	1.59; εr, etc.
Structure
Molecular shape	Pyramidal
Dipole moment	1.4 - 1.44 D [4]
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H317, H350, H412
Precautionary statements	P201, P202, P261, P264, P270, P272, P273, P280, P281, P301+P312, P302+P352, P308+P313, P321, P330, P333+P313, P363, P405, P501
NFPA 704 (fire diamond)	2 1 2
Flash point	180 °C (356 °F; 453 K)
Safety data sheet (SDS)	Fisher Scientific
Related compounds
Related tertiary phosphines	Trimethylphosphine Phosphine
Related compounds	Triphenylamine Triphenylarsine Triphenylstibine Triphenylphosphine oxide Triphenylphosphine sulfide Triphenylphosphine dichloride Triphenylphosphine selenide Pd(PPh3)4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Preparation and structure

Triphenylphosphine can be prepared in the laboratory by treatment of phosphorus trichloride with phenylmagnesium bromide or phenyllithium. The industrial synthesis involves the reaction between phosphorus trichloride, chlorobenzene, and sodium:^[5]

PCl₃ + 3 PhCl + 6 Na → PPh₃ + 6 NaCl

Triphenylphosphine crystallizes in triclinic^[6] and monoclinic modification.^[7] In both cases, the molecule adopts a pyramidal structure with propeller-like arrangement of the three phenyl groups.

Principal reactions with chalcogens, halogens, and acids

Oxidation

Triphenylphosphine undergoes slow oxidation by air to give triphenylphosphine oxide, Ph₃PO:

2 PPh₃ + O₂ → 2 OPPh₃

This impurity can be removed by recrystallisation of PPh₃ from either hot ethanol or isopropanol.^[8] This method capitalizes on the fact that OPPh₃ is more polar and hence more soluble in polar solvents than PPh₃.

Triphenylphosphine abstracts sulfur from polysulfide compounds, episulfides, and elemental sulfur. Simple organosulfur compounds such as thiols and thioethers are unreactive, however. The phosphorus-containing product is triphenylphosphine sulfide, Ph₃PS. This reaction can be employed to assay the "labile" S⁰ content of a sample, say vulcanized rubber. Triphenylphosphine selenide, Ph₃PSe, may be easily prepared via treatment of PPh₃ with red (alpha-monoclinic) Se. Salts of selenocyanate, SeCN⁻, are used as the Se⁰ source. PPh₃ can also form an adduct with Te, although this adduct primarily exists as (Ph₃P)₂Te rather than PPh₃Te.^[9]

Aryl azides react with PPh₃ to give phosphanimines, analogues of OPPh₃, via the Staudinger reaction. Illustrative is the preparation of triphenylphosphine phenylimide:

PPh₃ + PhN₃ → PhNPPh₃ + N₂

The phosphanimine can be hydrolyzed to the amine. Typically the intermediate phosphanimine is not isolated.

PPh₃ + RN₃ + H₂O → OPPh₃ + N₂ + RNH₂

Chlorination

Cl₂ adds to PPh₃ to give triphenylphosphine dichloride ([PPh₃Cl]Cl), which exists as the moisture-sensitive phosphonium halide. This reagent is used to convert alcohols to alkyl chlorides in organic synthesis. Bis(triphenylphosphine)iminium chloride (PPN⁺Cl⁻, formula [(C₆H₅)₃P)₂N]Cl is prepared from triphenylphosphine dichloride:^[10]

2 Ph₃PCl₂ + NH₂OH·HCl + Ph₃P → {[Ph₃P]₂N}Cl + 4HCl + Ph₃PO

Protonation

PPh₃ is a weak base (aqueous pK_aH = 2.73, determined electrochemically), although it is a considerably stronger base than NPh₃ (estimated aqueous pK_aH < –3).^[11] It forms isolable triphenylphosphonium salts with strong acids such as HBr:^[12]

P(C₆H₅)₃ + HBr → [HP(C₆H₅)₃]⁺Br⁻

Organic reactions

PPh₃ is widely used in organic synthesis. The properties that guide its usage are its nucleophilicity and its reducing character.^[13] The nucleophilicity of PPh₃ is indicated by its reactivity toward electrophilic alkenes, such as Michael-acceptors, and alkyl halides. It is also used in the synthesis of biaryl compounds, such as the Suzuki reaction.

Quaternization

PPh₃ combines with alkyl halides to give phosphonium salts. This quaternization reaction is particularly fast for benzylic and allylic halides:

PPh₃ + CH₃I → [CH₃PPh₃]⁺I⁻

These salts, which can often be isolated as crystalline solids, react with strong bases to form ylides, which are reagents in the Wittig reactions.

Aryl halides will quaternize PPh₃ to give tetraphenylphosphonium salts:

PPh₃ + PhBr → [PPh₄]Br

The reaction however requires elevated temperatures and metal catalysts.

Mitsunobu reaction

In the Mitsunobu reaction, a mixture of triphenylphosphine and diisopropyl azodicarboxylate ("DIAD", or its diethyl analogue, DEAD) converts an alcohol and a carboxylic acid to an ester. DIAD is reduced as it serves as the hydrogen acceptor, and the PPh₃ is oxidized to OPPh₃.

Appel reaction

In the Appel reaction, a mixture of PPh₃ and CX₄ (X = Cl, Br) is used to convert alcohols to alkyl halides. Triphenylphosphine oxide (OPPh₃) is a byproduct.

PPh₃ + CBr₄ + RCH₂OH → OPPh₃ + RCH₂Br + HCBr₃

This reaction commences with nucleophilic attack of PPh₃ on CBr₄, an extension of the quaternization reaction listed above.

Deoxygenation

The easy oxygenation of PPh₃ is exploited in its use to deoxygenate organic peroxides, which generally occurs with retention of configuration:

PPh₃ + RO₂H → OPPh₃ + ROH (R = alkyl)

It is also used for the decomposition of organic ozonides to ketones and aldehydes, although dimethyl sulfide is more popular for the reaction as the side product, dimethyl sulfoxide is more readily separated from the reaction mixture than triphenylphosphine oxide. Aromatic N-oxides are reduced to the corresponding amine in high yield at room temperature with irradiation:^[14]

Sulfonation

Sulfonation of PPh₃ gives tris(3-sulfophenyl)phosphine, P(C₆H₄-3-SO₃⁻)₃ (TPPTS), usually isolated as the trisodium salt. In contrast to PPh₃, TPPTS is water-soluble, as are its metal derivatives. Rhodium complexes of TPPTS are used in certain industrial hydroformylation reactions.^[15]

3,3′,3″-Phosphanetriyltris(benzenesulfonic acid) trisodium salt is a water-soluble derivative of triphenylphosphine.

Reduction to diphenylphosphide

Lithium in THF as well as Na or K react with PPh₃ to give Ph₂PM (M = Li, Na, K). These salts are versatile precursors to tertiary phosphines.^[16][17] For example, 1,2-dibromoethane and Ph₂PM react to give Ph₂PCH₂CH₂PPh₂. Weak acids such ammonium chloride, convert Ph₂PM (M = Li, Na, K) into diphenylphosphine:^[17]

(C₆H₅)₂PM + H₂O → (C₆H₅)₂PH + MOH

Transition metal complexes

Triphenylphosphine binds well to most transition metals, especially those in the middle and late transition metals of groups 7–10.^[18] In terms of steric bulk, PPh₃ has a Tolman cone angle of 145°,^[19] which is intermediate between those of P(C₆H₁₁)₃ (170°) and P(CH₃)₃ (115°). In an early application in homogeneous catalysis, NiBr₂(PPh₃)₂ was used by Walter Reppe for the synthesis of acrylate esters from alkynes, carbon monoxide, and alcohols.^[20] The use of PPh₃ was popularized by its use in the hydroformylation catalyst RhH(PPh₃)₃(CO).

Polymer-anchored PPh3 derivatives

Polymeric analogues of PPh₃ are known whereby polystyrene is modified with PPh₂ groups at the para position. Such polymers can be employed in many of the applications used for PPh₃ with the advantage that the polymer, being insoluble, can be separated from products by simple filtration of reaction slurries. Such polymers are prepared via treatment of 4-lithiophenyl-substituted polystyrene with chlorodiphenylphosphine (PPh₂Cl).

See also

• Tris(o-tolyl)phosphine
• Decyl(triphenyl)phosphonium
• Vaska's complex
• Wilkinson's catalyst
• Bis(triphenylphosphine)nickel(II) dichloride
• Bis(triphenylphosphine)palladium(II) dichloride
• Stryker's reagent

References

1. International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 431. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
2. Haav, Kristjan; Saame, Jaan; Kütt, Agnes; Leito, Ivo (2012). "Basicity of Phosphanes and Diphosphanes in Acetonitrile". European Journal of Organic Chemistry. 2012 (11): 2167–2172. doi:10.1002/ejoc.201200009. ISSN 1434-193X.
3. Allman, Tim; Goel, Ram G. (1982). "The Basicity of Phosphines". Canadian Journal of Chemistry. 60 (6): 716–722. doi:10.1139/v82-106.
4. Warchol, M.; Dicarlo, E. N.; Maryanoff, C. A.; Mislow, K. (1975). "Evidence for the Contribution of the Lone Pair to the Molecular Dipole Moment of Triarylphosphines". Tetrahedron Letters. 16 (11): 917–920. doi:10.1016/S0040-4039(00)72019-3.
5. Corbridge, D. E. C. (1995). Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology (5th ed.). Amsterdam: Elsevier. ISBN 0-444-89307-5.
6. Kooijman, H.; Spek, A. L.; van Bommel, K. J. C.; Verboom, W.; Reinhoudt, D. N. (1998). "A Triclinic Modification of Triphenylphosphine" (PDF). Acta Crystallographica. C54 (11): 1695–1698. Bibcode:1998AcCrC..54.1695K. doi:10.1107/S0108270198009305.
7. Dunne, B. J.; Orpen, A. G. (1991). "Triphenylphosphine: a Redetermination" (PDF). Acta Crystallographica. C47 (2): 345–347. Bibcode:1991AcCrC..47..345D. doi:10.1107/S010827019000508X.
8. Armarego, W. L. F.; Perrin, D. D.; Perrin, D. R. (1980). Purification of Laboratory Chemicals (2nd ed.). New York: Pergamon. p. 455. ISBN 978-0-08-022961-4.
9. Jones, C. H. W.; Sharma, R. D. (1987). "¹²⁵Te NMR and Mössbauer Spectroscopy of Tellurium-Phosphine Complexes and the Tellurocyanates". Organometallics. 6 (7): 1419–1423. doi:10.1021/om00150a009.
10. Ruff, J.K.; Schlientz, W.J. (1974). "μ-Nitridobis(triphenylphosphorus)(l+) ("PPN") Salts with Metal Carbonyl Anions". Inorganic Syntheses. Vol. 15. pp. 84–90. doi:10.1002/9780470132463.ch19. ISBN 978-0-470-13246-3. {{cite book}}: |journal= ignored (help)
11. Allman, Tim; Goel, Ram G. (1982-03-15). "The basicity of phosphines". Canadian Journal of Chemistry. 60 (6): 716–722. doi:10.1139/v82-106. ISSN 0008-4042.
12. Hercouet, A.; LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157–158
13. Cobb, J. E.; Cribbs, C. M.; Henke, B. R.; Uehling, D. E.; Hernan, A. G.; Martin, C.; Rayner, C. M. (2004). "Triphenylphosphine". In L. Paquette (ed.). Encyclopedia of Reagents for Organic Synthesis. New York: J. Wiley & Sons. doi:10.1002/047084289X.rt366.pub2. ISBN 0-471-93623-5.
14. Burke, S. D.; Danheiser, R. L. (1999). "Triphenylphosphine". Handbook of Reagents for Organic Synthesis, Oxidizing and Reducing Agents. Wiley. p. 495. ISBN 978-0-471-97926-5.
15. Herrmann, W. A.; Kohlpaintner, C. W. (2007). "Syntheses of Water-Soluble Phosphines and their Transition Metal Complexes". Inorganic Syntheses. Vol. 32. pp. 8–25. doi:10.1002/9780470132630.ch2. ISBN 978-0-470-13263-0. {{cite book}}: |journal= ignored (help)
16. George W. Luther III; Gordon Beyerle (1977). "Lithium Diphenylphosphide and Diphenyl(Trimethylsilyl)Phosphine". Inorganic Syntheses. Vol. 17. pp. 186–188. doi:10.1002/9780470132487.ch51. ISBN 978-0-470-13248-7.
17. V. D. Bianco S. Doronzo (1976). "Diphenylphosphine". Inorganic Syntheses. Vol. 16. pp. 161–188. doi:10.1002/9780470132470.ch43. ISBN 978-0-470-13247-0.
18. Elschenbroich, C.; Salzer, A. (1992). Organometallics: A Concise Introduction (2nd ed.). Weinheim: Wiley-VCH. ISBN 3-527-28165-7.
19. Immirzi, A.; Musco, A. (1977). "A method to measure the size of phosphorus ligands in coordination complexes". Inorganica Chimica Acta. 25: L41–L42. doi:10.1016/S0020-1693(00)95635-4.
20. • Reppe, W.; Schweckendiek, W. J. (1948). "Cyclisierende Polymerisation von Acetylen. III Benzol, Benzolderivate und hydroaromatische Verbindungen". Justus Liebigs Annalen der Chemie. 560 (1): 104–116. doi:10.1002/jlac.19485600104.

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