It confuses me that many researches pointed out different results about phosphine ligands properties (σ-donor and π-acceptor). Since both phosphine $\ce{PH3}$ and phosphorus trifluoride $\ce{PF3}$ possess similar properties, which one is the better ligand in terms of forming a stronger bond with the center metal atom?

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    $\begingroup$ It may depend on the metal ion. PF3 would seem to be better wuth a soft metal ion that can donate pi electrons to it. (And won't blow up if you breath on it wrong.) $\endgroup$ Commented Aug 17, 2023 at 15:52
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    $\begingroup$ It would very much help your question if you provide references or better links to at least some of the papers you are referring to in the question. $\endgroup$
    – Ian Bush
    Commented Aug 18, 2023 at 12:36

1 Answer 1


What kind of metal center are you talking about? While all phosphines are good σ-donors and poor π-acceptors, $\ce{PF3}$ is more π-acidic than $\ce{PH3}$ because of the electron withdrawing effects of the $\ce{F-}$ substituents. The more electron-rich metal centers would then be more stabilized, theoretically, by $\ce{PF3}$ than $\ce{PH3}$ due to their ability to back-donate into the phosphine.

Hard-soft acid base theory would also suggest that the softer $\ce{PF3}$ ligand will coordinate to softer metal centers, while the $\ce{PH3}$ ligand would coordinate more easily to harder metal centers.

This is all to say, in reality, I would not want to work with either phosphine due to their dangers, but would rather work with alkyl and aryl phosphines instead. Tunability of these would be easier as well.


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