Sciencemadness Discussion Board

How do I go about separating a metal - phosphine complex from amines in the organic phase?

Zensate - 23-4-2014 at 05:06

I've never worked with metal-phosphine complexes before, NiCl2-PPH3, RhCl2-BINAP, etc.

The end reaction mixture would contain amine and the metal complex. I had thought I could just add the acid to salt the amine into the aqueuous phase, but I am not sure if the phosphine will follow. Phosphines can behave as acidic-lewis-bases, yet I read HERE that BINAP compounds, for instance, can be washed out with NaOH or Sodium Bicarbonate solution. Phosphines like BINAP and PPH3 bind fairly tightly to the metal centers so I'm not sure they would be effected at all by any added acids.

BINAP being deprotonated by bases could be problematic seeing as bases are commonly used to catalyze reactions with metal-phosphine catalysts. Above all I need to find a way to recover these catalysts seeing as they can be very expensive, and chormatography and distillation are not options.

Would these soluble complexes not react with acids at all seeing as they in somewhat neutral states due to binding with the metal core?

[Edited on 23-4-2014 by Zensate]

DraconicAcid - 23-4-2014 at 08:19

Phosphines are far weaker Bronsted-Lowry bases than amines; I'm not sure that they act as bases at all in aqueous solution. They also bond fairly strongly with metals, so I doubt they'd be affected by dilute acids.

Zensate - 23-4-2014 at 10:51

That was my inclination. I guess it also makes sense to reason that added bases such as NaOH/Bicarbonate which can be needed to catalyzed some of these reactions won't effect the complex after it is pre-formed in its own solution. That link I have above seems to be referring to isolating a phosphine not in a complex.

ProChem - 23-4-2014 at 12:16

can you distill the amine?

forgottenpassword - 23-4-2014 at 14:12

Quote: Originally posted by Zensate  
chormatography and distillation are not options.
They should be!

mnick12 - 23-4-2014 at 15:38

Are you trying to recover the catalyst from a reaction, or the actual synthesis of the complex? If it is the latter we usually just pump our reaction mixture to dryness then wash away the soluble organics with ether or pentane depending upon the ligand. If you are trying to recover the catalyst from a reaction I would suggest something similar, but I don't what you are making so its hard to suggest a good way to separate your stuff. If its that expensive, chromatography may be your best option to recover your cat.

madscientist - 14-5-2014 at 08:16

Separations like these usually, yes, require chromatography. Phosphines (and phosphine oxides in particular - ligands tend to get oxidized) are difficult to separate with extractions. You won't be able to pull them into the aqueous layer with acid. You can extract many phosphonium salts from aqueous solutions with ether, for example.