[Nescafe]

Hello,

I read a paper today on pd catalyzed conjugate additions and they were talking about matched and mismatched examples, in the matched case the stereochemistry generated was the same face as the neighboring carbon and in the mismmatched case it was the opposite. Is this what these terms refer to or does it have to do with the face by which the ligand coordiantes to the ligand and how the C-C bond inserts?

thanks in advance,

Nescafe.

[discodermolide]

This refers to an observation by Masamune quite some time ago.
I have his publication. If you wish a copy pm me with an email.

[Nescafe]

Thanks, I did find that paper, but what are we really matching here? Does it have to do at all with the ligand used or the stereochemistry of the neighboring chiral centers on the end product?

[discodermolide]

The stereochemistry of the starting materials. You can't use the product, because you don't have it yet!

[Dan]

I read a paper today on pd catalyzed conjugate additions and they were talking about matched and mismatched examples

A link to the abstract on the publisher's website or citation information might be useful so that we can see the context.

[Nescafe]

Sorry this is the article, so it all has to do with he stereochemistry of the starting material and the ligand used.

ORGANIC LETTERS, 2009, Vol. 11, No. 12, 2491-2494

[Dan]

My interpretation is as follows:

If the reaction is carried with an achiral ligand, the S substrate gives predominantly the S,R product. This is sometimes called the inherent selectivity - it is the substrate-controlled selectivity.

Using a chiral ligand, the configuration of the new centre, if determined only by the ligand (ligand control), would be  independent of the configuration of pre-existing stereogenic centres. In reality, the dr is determined by a combination of substrate control and ligand control.

The matched ligand is the enantiomer of the ligand which has the same preference as the substrate control. In this case, the ligand that favours the formation of a new R centre.
The unmatched ligand is the enantiomer which has the opposite preference to the substrate control (favours formation of a new S centre)

In a matched combination, ligand and substrate control work in the same direction and dr should increase relative to the inherent selectivity.
In an unmatched combination, ligand and substrate control oppose. If ligand control dominates, the dr will reverse relative to the inherent selectivity (and will be lower than the matched combination since the two effects oppose - see table 1, entry 8 vs entry 10).
If substrate control dominates, the dr will drop but the major product will be the same as the inherent selectivity.

[Nescafe]

Makes a lot of sense to me, thanks Dan!