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.
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:
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.
^Clark, R. J.; Busch, M. A. (1973). "Stereochemical Studies of Metal Carbonyl-Phosphorus Trifluoride Complexes". Accounts of Chemical Research. 6 (7): 246–252. doi:10.1021/ar50067a005.