March 29, 2024, 02:47:46 AM
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Topic: DMSO as a ligand  (Read 4604 times)

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Ilaria

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DMSO as a ligand
« on: December 28, 2014, 07:18:21 AM »
I am studying the complex cis,fac-[RuCl2(DMSO)4], which has 3 DMSO molecules coordinated by the S atom and one by the O atom. Why is there π backdonation when DMSO is coordinated via S, while there isn't when the coordination is via O? In other words, why is DMSO-κS a π-acceptor ligand and why isn't DMSO-κO a π-acceptor ligand?

Offline kriggy

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Re: DMSO as a ligand
« Reply #1 on: December 28, 2014, 11:30:02 AM »
I suggest comparing electron configurations of oxygen and sulphur

Offline critzz

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Re: DMSO as a ligand
« Reply #2 on: December 28, 2014, 02:31:31 PM »
I think it can be explained in different ways, but here is one explanation involving electronegativity.
Since oxygen is more electronegative than sulfur, it likes to have a negative charge on oxygen rather than on the sulfur atom.
By π-back donation (or accepting electrons from the metal), the S-coordinated DMSO can delocalize electron density on the oxygen atom. (see picture)


Ilaria

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Re: DMSO as a ligand
« Reply #3 on: December 29, 2014, 02:28:31 AM »
Thank you for the explanation!
Now I have another question regarding the same complex: I've found in literature that the cis isomer is the facial one, but why couldn't it be the meridional?

Offline critzz

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Re: DMSO as a ligand
« Reply #4 on: December 29, 2014, 12:05:56 PM »
From what I've read, the meridional product does exist; however, the facial product is the thermodynamic stable one.
The -S-DMSO is more steric demanding than the O-DMSO, so probably it has to do with sterics.

Here is the synthesis from what i've found.



DOI: 10.1021/cr0307291

Ilaria

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Re: DMSO as a ligand
« Reply #5 on: December 30, 2014, 05:47:58 AM »
Thank you, particularly for the article. I didn't know about it, even if the author is my teacher! 

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