Bridges that drive me crazy

There is a staggering amount of oxidants out there and their use in synthesis is very context-dependent. The redox potential reachable with a given oxidizing agent is the differentiating factor – one that establishes a unique footprint on molecules that act as electron donors. We had a series of student talks here at U of T earlier today and I was very intrigued by the lecture on hypervalent iodine derivatives by Brendan Peters of the Lautens lab. I thought I knew a lot about oxidants, but when I saw sodium perborate (commonly drawn composition: NaBO3), I realized that there might be a gap in what I know about its exact structure. This reagent is well suited for turning aromatic iodine derivatives into their oxidized forms. I looked things up later in the day and, as it turns out, the structure of NaBO3 formally corresponds to the dimer of two “O=B-O-O” derived units. The peroxide bridge is where this salt holds its oxidizing “mojo”. I started digging a bit deeper and looked for any structures with a B-O-O-B bridge. It turns out that not much is known! However, this is where I am weaving my story all the way back to last week, when Professor Warren Piers of the University of Calgary visited us and gave a superb talk on some novel iridium chemistry. He will probably kill me if were to disclose the unpublished work carried out in his lab, but I will not do that. Let’s keep amphoteros a respectable establishment. Instead, here is a published account from Warren’s recent past and it comes full circle to what I was fascinated with this morning when I pondered over NaBO3. It turns out that Warren published an awesome reaction that features a boron-based peroxy bridge, although in a completely different context. Judge it by yourself below, but I think this is super cool. After I read Warren’s piece, I went back to Scopus and searched for more papers specifically dedicated to sodium perborate. After 10 seconds I realized that all 800+ of them come from dentistry-related journals (toothpaste…), which reminded me about the bridge I got earlier this week after breaking one of my molars. At this point I am done with searching and will get ready for the ChemClub Christmas party, wherein I plan to forget about my pains while sipping one of them tasty Leffe beverages (remember Samuel L. Jackson in Pulp Fiction?) at the Beergarden.

gg

http://onlinelibrary.wiley.com/doi/10.1002/anie.200901217/abstract

2 thoughts on “Bridges that drive me crazy

  1. Always enjoy your thoughts, but particularly liked this post! Thanks for the kind words. Another fascinating B-O-O-B compound was recently disclosed by Theo Agapie (Angew. Chem. Int. Ed. 2014, 53, 12893 –12896) that makes a nice connection with the NaBO3 case. Could be a very interesting and useful reagent.

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