RareEarth
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Are the non-binding groups of coordination complexes reactive?
Forgive me if this is a dumb question, I've done a lot of reading into coordination complexes and they're typically pretty stable due to the strong
binding effects, but I never see any mentions of the reactivity of the non-binding groups of these complexes, such as the aryl groups on something
like triphenylphosphine.
If I had a pre-formed coordination complex, would it be possible to add substituents to the groups to functionalize them even further? I'm assuming
yes, I've just never read anything about doing this.
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blogfast25
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There really are no 'non-binding' groups in complexes. By definition, a complex binds groups (ligands), usually to a central transition metal atom, by
coordination bonds.
Reacting (bound) ligands with 'stuff' is possible 'on paper', I think. But why would you want to do that?
Thinking about it, they might do such things with so-called metallocene complexes, not quite sure though...
[Edited on 27-5-2015 by blogfast25]
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RareEarth
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I was just curious if it were possible. There's a number of different applications, such as changing the reactivity and other properties of the
complex by changing ligand substituents.
With a ligand like triphenylphoshine, the phosphine would be the only thing bound to the metal while the phenyl groups are free. I can't think of any
reason why I couldn't do something like halogenate the phenyl groups and then engage them in other reactions.
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blogfast25
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Quote: Originally posted by RareEarth  |
With a ligand like triphenylphoshine, the phosphine would be the only thing bound to the metal while the phenyl groups are free. I can't think of any
reason why I couldn't do something like halogenate the phenyl groups and then engage them in other reactions. |
Per se there's no reason why it wouldn't work, at least in some cases. But expect steric hindrance to rear its head. Because bound ligands are... erm,
well... bound, they will be less 'accessible'.
[Edited on 28-5-2015 by blogfast25]
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mnick12
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In almost every case I can think of, trying to modify a ligand such a PPh3 when it is bound to a metal is not going to work. If you were to add
chlorine to some phosphine complex you would most likely oxidize the metal center.
If you want to do some modifications, you should do it before you form your complex.
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smaerd
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This question is really weird.
Here's why, ligation is often used for catalysis. Durring catalytic processes IE (check a palladacycle reaction) there is ligand
exchange/insertion/etc with one(or more) substrates. Then the ligands react. So yea, ligands can be reacted, sometimes in an incredibly
favorable(chemical potential) way while bound to a metal, leaving the metal untouched.
However, I think you're question is different...
As in, say you have a ligand bound to a metal center via dative bonds or whatever, can you react the organic component selectively? The answer is yes,
but it really depends. I ran a decarboxylation reaction based on this principle years and years ago.
However... if you want to create a phosphine ligand with aryl substituents, or modify it, to my understanding the ligand modifications are typically
made prior to the introduction of a metal. There's definitely reasons for that aside from purification difficulties. like others have said, the metal
itself is liable, and modifications of aromatics isn't the kindest of conditions.
Anyways, yes metallic bonding really can open up advantages and huge differences in electron density in the ligand(s) making them more or less
reactive. Ligand synthesis is not easy, some inorganic chemists do as much carbon based synthesis as organic chemists. Ex, see scorpionate ligands. It
really all depends...
[Edited on 28-5-2015 by smaerd]
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