Phosphorus trifluoride

Phosphorus trifluoride (formula PF₃), is a colorless and odorless gas. It is highly toxic and reacts slowly with water. Its main use is as a ligand in metal complexes. As a ligand, it parallels carbon monoxide in metal carbonyls,^[1] and indeed its toxicity is due to its binding with the iron in blood hemoglobin in a similar way to carbon monoxide.

Phosphorus trifluoride has an F−P−F bond angle of approximately 96.3°. Gaseous PF₃ has a standard enthalpy of formation of −945 kJ/mol (−226 kcal/mol). The phosphorus atom has a nuclear magnetic resonance chemical shift of 97 ppm (downfield of H₃PO₄).

Phosphorus trifluoride hydrolyzes especially at high pH, but it is less hydrolytically sensitive than phosphorus trichloride. It does not attack glass except at high temperatures, and anhydrous potassium hydroxide may be used to dry it with little loss. With hot metals, phosphides and fluorides are formed. With Lewis bases such as ammonia addition products (adducts) are formed, and PF₃ is oxidized by oxidizing agents such as bromine or potassium permanganate.

As a ligand for transition metals, PF₃ is a strong π-acceptor.^[2] It forms a variety of metal complexes with metals in low oxidation states. PF₃ forms several complexes for which the corresponding CO derivatives (see metal carbonyl) are unstable or nonexistent. Thus, Pd(PF₃)₄ is known, but Pd(CO)₄ is not.^[3][4][5] Such complexes are usually prepared directly from the related metal carbonyl compound, with loss of CO. However, nickelmetal reacts directly with PF₃ at 100 °C under 35 MPa pressure to form Ni(PF₃)₄, which is analogous to Ni(CO)₄. Cr(PF₃)₆, the analogue of Cr(CO)₆, may be prepared from dibenzenechromium:

Cr(C₆H₆)₂ + 6 PF₃ → Cr(PF₃)₆ + 2 C₆H₆

Phosphorus trifluoride is usually prepared from phosphorus trichloride via halogen exchange using various fluorides such as hydrogen fluoride, calcium fluoride, arsenic trifluoride, antimony trifluoride, or zinc fluoride:^[6][7][8]

2 PCl₃ + 3 ZnF₂ → 2 PF₃ + 3 ZnCl₂

Phosphorus trifluoride is similar to carbon monoxide in that it is a gas which strongly binds to iron in hemoglobin, preventing the blood from absorbing oxygen.

PF₃ is highly toxic, comparable to phosgene.^[9]

• Toy, A. D. F. (1973). The Chemistry of Phosphorus. Oxford, UK: Pergamon Press.
• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
• Lide, D. R., ed. (1990). Handbook of Chemistry and Physics (71st ed.). Ann Arbor, MI: CRC Press. ISBN 978-0-8493-0471-2.
• March, J. (1992). Advanced Organic Chemistry (4th ed.). New York: Wiley. p. 723. ISBN 978-0-471-60180-7.
• Stecher, P. G., ed. (1960). The Merck Index (7th ed.). Rahway, NJ, USA: Merck & Co.
• Holmes, R. R. (1960). "An Examination of the Basic Nature of the Trihalides of Phosphorus, Arsenic and Antimony". Journal of Inorganic and Nuclear Chemistry. 12 (3–4): 266–275. doi:10.1016/0022-1902(60)80372-7.

• National Pollutant Inventory - Fluoride and compounds fact sheet
• WebBook page for PF3