Leadbeater (2003)

Biaryl compounds have a wide range of applications in chemistry, from pharmaceuticals to materials science. Ever since its introduction in 1979 the Suzuki reaction has been a go-to method for generating asymmetric biaryl compounds (among other things). While certainly Nobel Prize material, this synthetic method has its drawbacks, namely the use of a Palladium catalyst. Through careful experimentation and solvent manipulation, our intrepid authors demonstrate that a Suzuki-like cross coupling can be achieved in the absence of Palladium catalyst. All it takes is liberal use of a quaternary ammonium salt, a bit of the old English what-for, and a microwave…

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12 Responses to “Leadbeater (2003)”

  1. Adam Settimo Says:

    First of all, when discussing the advantages to using water one of them is that it has a clear advantage… Pun?….

    I guess the meat of my question has to do with the overall reason for getting rid of the metal catalysts in the first place. This was briefly addressed in the last paragraph, but not in great detail. I would like to know the other side what makes this a favored way of doing these reactions? Cost of material/ difference and so forth.

    Secondly, in the section discussing actions taken to determine whether their is metals still present, the method they used was ICP-AA? I can’t say I have any experience with this instrument, and with detection limits that are laughable when compared to either ICP-MS or GFAAS, why use this? Perhaps I’m just confused with the amount of metal catalyst needed for this reaction.

    • Antony Says:

      Palladium is ~$700/oz. way more than, say, silver ~$16/oz (Gold is ~$1000/oz) so finding a cheap substitute or not using it at all would be great.

      You are really on to something by questioning whether they really determined palladium is still present or not. This will be the topic of Friday’s class. 😉

  2. Hunter Burgin Says:

    In regards to table two which shows the Suzuki-type coupling of various aryl halides and aryl boronic acids in water, I was interested as to why certain halogen substituents were more easily added (Boron with high yield, iodine with modest yields) and why some were not added at all to the complex (chlorine substituents were not added at all). Leadbeater and Marco mention this in their paper but they do not offer any justification as to why this occurs. Is it due to the lack of a metal catalyst, or something simpler that I may just be overlooking?

  3. Kevin Greenwood Says:

    I suppose the most obvious question is “but how?” Suzuki-Miyaura reactions are characterized by transmetalation from alkyl or aryl boronic acids to organic palladium complexes. The result is a palladium II metal center between two alkyl/aryl groups. With the final step being reductive elimination, how do the products as outlined in this paper form with just the alkylboronic acid and the tetraalkylammonium cation?

  4. Antony Says:

    I think its ballsy to publish a paper discrediting a widely accepted mechanism without proposing a substitute. How exactly is the mechanism suppose to work? Josh, do you propose anything for a palladium free Suzuki?

  5. Daniel Begay Says:

    After reading this short article, I’m curious to how this has affected the synthesis of C–C bonds in future works. And after looking through different examples of the Suzuki-Type Coupling reaction, I came across a topic of the Palladium metal catalysis and switching it out with other transition metals such as Nickel. When switching it out, the Nickel catalyst was able to readily synthesize compounds that Palladium could not. Which compounds can the Transition-Metal-Free reaction synthesize more readily and which are more difficult?

  6. Porter Marsh Says:

    The paper says that aryl bromides cane be coupled with phenylboronic acid to yield biaryl compounds in good yields but the reaction does not complete with aryl iodides. There’s no nearby citation to look into and the paper doesn’t offer an explanation why reactions with aryl iodides do not reach completion.
    So my question is why don’t aryl iodides work when they’re so similar to aryl bromides?

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