An Unusual Lewis Acid Hydrocarbon.

I would like to highlight the definition of hydrocarbon, a very basic concept in organic chemistry but of relevance for this post. According to the IUPAC, hydrocarbons are compounds consisting of carbon and hydrogen only. It doesn’t seem obvious to imagine an organic compound composed only by carbon and hydrogen with Lewis acidity not being a charged species such as a carbocation. Back in 2010 the group of Manuel Alcarazo at Max Planck Institute of Coal Research published a  very creative paper describing the properties of a bisfuorenylallene as a Lewis acid. The natural tendency of the fluorene moites to accept a pair of electrons to gain aromatization gives the central carbon of the allene a carbocationic character and thus the ability to behave as a Lewis acid.

Unsual hydrocarbon lewis acid

A clear experimental evidence of the behaviour of the bisfluorenylallene as a Lewis acid is the formation of classical Lewis acid-Lewis base adducts in the presence of small Lewis bases. In another stroke of genius, Acarazo and co-workers apply the Lewis acid ability of the fluorenyl based allene to the field of Frustrated Lewis Pairs (a field dominated by borane-based Lewis acids) towards the activation of sufur-sulfur bonds.

Do you want to know more? Check this paper out.

Blanca Ins, Sigrid Holle, Richard Goddard, and Manuel Alcarazo. Heterolytic S-S Bond Cleavage by a Purely Carbogenic Frustrated Lewis Pair. Angew. Chem. Int. Ed. 2010, 49, 8389 –8391.


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