Check out the following review, in Chemical Reviews:

http://pubs.acs.org/doi/abs/10.1021/cr010289i

Also, look for other review articles by Prof. Shu Kobayashi, University of Tokyo.

best, James

Thank you so much sir. I appreciate it.

Dear Dr. Amgad Rabie,

Thank you so much for the information you have given. I still have many questions, if you don't mind. My first concern is about the preparation of the microencapsulated Sc(OTf)3. Is cross-linked poly(4-vinylpyridine/styrene) co-polymer more excellent in terms of catalytic activity or can I just use polystyrene? Is the preparation of the former polymer easily done? I had a hard time understanding the preparation of P/S. Another thing is the reusability of the catalyst, how will you know that the recovered catalyst cannot be reused anymore and what to do with the P/S-Sc(OTf)3 if it cannot be reused anymore?

And my last question would be the mechanism or interaction of the polymer with the metal triflate. Thank you so much Dr. for the time you've spared.

I'm sorry, but I'm going to have to call you out on this. I don't think cutting and pasting from the abstract of a journal article:

http://is.gd/byMHo

qualifies as a very useful answer.

I'm not an expert, but I can tell you that the polystyrene itself doesn't participate in the reaction, it only serves as a matrix for the active catalyst. Cross-linking is used to trap the catalyst during preparation, which prevents leaching of the active metal into the solution. The polystyrene is mechanically robust, hence its use - check out "solid phase organic chemistry" for more examples.

See http://pubs.acs.org/doi/abs/10.1021/ja029146j and http://pubs.acs.org/doi/full/10.1021/ja053176f