Hello,
I am searching differnt ways to exchange a phosphine in a metal complex, with another, a former phosphine metathesis. Any suggestion, or article?
Thank you
Phosphine ligand bond works in two different ways: by a sigma lone pair donation of the phosphine to an empty metal orbital and a back-donation from a filled metal orbital to an empty orbital on the phosphine. If the phosphorous atom brings an electron-withdrawing groups, the sigma-donating capacity of the phosphine ligand tends to decrease but the pi-acceptor on phosphorous increase his back-bonding capacity. Phosphines, therefore, show a range of sigma donor and pi-acceptor. Empirically the sigma donor ability, for isosteric phosphines, decrease in this order:
PCH3, PPh3, P(OCH3)3, P(OPh)3, P(NCH3)3, P(NPh)3, PCl3
For example P(OCH3)3 can replace the P(Ph)3.
In the same order increase their back-bonding ability. In this way you can try to figure out which phosphine can move the tied one but, if you use a different type of phosphine, you also have to take into account the steric effect.
I hope I've helped. Good luck
you need to give more information.. it all depends on what type of phosphines and what metal or metal complex you are using...
When ever we want to make neutral or ionic complexes, we follow at least two methods and the easiest one is substitution reaction. While doing substitution reaction we simply follow ligand field strengths and ligands have been classified that way. M-Cl bond can be readily replaced by water which inturn can be replaced by NH3. Two NH3 ligands can be readily replaced by ethylene diamine or any other bidentate sigma-donor ligands. To replace one phosphine by another one we have to know the nature of the metal atom/ion, its oxidation state, other ligands present on it. For example, From Mo(CO)3(PPh3)3, you can take out two PPh3 with Ph2PCH2PPh2 (dppm) or dppe or any similar biphosphines. Trisphosphine can replace all three PPh3s. If if the metal is a good pi-acid, good pi-acceptor bidentate ligands can easily replace them. Relative sigma-donor and pi-acceptor properties have to be analysed before we perform any substitution reaction.
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