Herbert Brown (1980) - Organoboranes - The Modern Miracle

Herbert Brown (1980)

Organoboranes - The Modern Miracle

Herbert Brown (1980)

Organoboranes - The Modern Miracle

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This is the first Lindau lecture given by Herbert C. Brown after he shared the 1979 Nobel Prize in Chemistry with Georg Wittig. In 2000, twenty years and six chemistry meetings later, he should give his last Lindau lecture at the 50th Lindau Nobel Laureate Meeting. Through all this time, Browns topic remained unchanged: the chemistry of the chemical element boron, with a particular focus on its applications in synthetic organic chemistry. Indeed, organoboron chemistry has been a hot topic throughout all this time. In the realm of the Nobel Prizes, its latest fruit was the 2010 Nobel Prize in Chemistry. One of the Laureates, Akira Suzuki, had invented the “Suzuki coupling”, a method for carbon-carbon bond formation, which is based on organoboron reagents. Not surprisingly, Suzuki had been a PostDoc in Browns laboratory from 1963 to 1965.In the present lecture, Brown gives a review of organoboron chemistry, starting in 1936. He closely links his chemical endeavours to his personal history and presents the latter with a degree of openness, which is exceptional and refreshing. He points out, for example, that the reason for him going into boron research had been a book on this topic given to him as a gift by his girlfriend (and later wife) Sarah. Apparently, however, the book was chosen only due to the fact that it was, at $2, the cheapest chemistry book available. In view of the ensuing scientific output and the $100.000 Nobel Prize award, an excellent value for money!On the basis of this (in)valuable gift, Brown began to develop organoboron chemistry, which was just in its infancy. A first major hurdle was the large-scale synthesis of one of the simplest boron compounds: borane, a molecule made from one boron atom and three hydrogen atoms. Borane (BH3) resembles methane (CH4), however, contrary to methane, individual borane molecules spontaneously pair up to yield diborane (B2H6). Brown eventually succeeded in making large quantities of this compound via a straightforward method. Until today, diborane is industrially synthesized in the same way.The synthesis of diborane was an essential prerequisite for the further development of organoboron chemistry. Organoboranes can be imagined as BH3, in which one or more hydrogen atoms have been replaced by an organic residue, for example a hydrocarbon chain. Further on in the lecture, Brown discusses the reactivity of organoboranes and their use in synthetic organic chemistry in quite some detail.Besides these purely chemical aspects, the description of the impact of war on chemical research is another intriguing feature of Brown’s lecture. He explains, for example, how, during the Second World War, the supply of lithium in the US was running low. A situation, which complicated his research significantly. The reason for the lack of lithium was that each military airplane carried two one-pound canisters of lithium hydride. If mixed with water, lithium hydride spontaneously and vigorously generates hydrogen gas. If the plane had to make a forced landing, this reaction could be used by the crew to fill a balloon carrying an antenna, allowing them to contact their home base.It might be mentioned here, that carrying lithium hydride in an airplane is not without risk: once the substance catches fire, it may not be extinguished with water, water-containing solids or carbon dioxide due to its high reactivity with these substances. However, Brown also worked on a solution of this problem and eventually suggested sodium borohydride (NaBH4) as a safer alternative to lithium hydride. Due to its military relevance, this research was classified until 1953 and could not be published. A rather annoying situation, as Brown points out.Still, he did not let these problems get the best of him. In closing his talk, Brown encourages the young researchers in the audience to relentlessly apply intelligence, enthusiasm and optimism – according to him, the basic ingredients of Nobel Prize worthy research.David Siegel

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