Frustration: “The feeling of being upset or annoyed as a result of being unable to change or achieve something”. It sounds like a very negative feeling that every researcher has felt at some point at their careers. It is not the case for the topic of Frustrated Lewis Pairs, where frustration is actually a good thing. But, what is a Frustrated Lewis Pair (usually abbreviated as FLP)?, well not that fast, let’s start for the beginning.
One of the basics of chemistry reactivity is that the combination of a Lewis acid and a Lewis base leads to the formation of a classical Lewis adduct as exemplified by the combination of borane with ammonia to form the ammonia-borane adduct NH3.BH3. But, what happens if we introduce steric impediments in both the Lewis acid and the Lewis base? Then, it comes “the frustration” of the adduct. Do not mistake this with the actual frustration of a chemist attempting a reaction that does not work. In this situation, the steric demands preclude formation of simple Lewis acid-base adducts and then is when we have a Frustrated Lewis Pair.
In this very particular scenario where both acidity and basicity remain unquenched, FLPs have an extraordinary reactivity towards the cleavage and activation of small molecules such as hydrogen, alkenes, alkynes or CO2 among others. Unarguably the most important and more developed applications are within the fields of activation of hydrogen and catalytic hydrogenations. The number of publications and citations in Frustrated Lewis Pairs chemistry has been increasing since the first publication in 2006 by Douglas Stephan, one of the “fathers” and most active researchers of the topic.
In my opinion there is still a long way to walk and we’ll see in the next years new developments in catalytic asymmetric hydrogenation along with applications in areas such as hydrogen storage, CO2 capture and fuel cells.
If you want to know more there are many good articles and reviews on the topic, these could be a starting point:
Seminal work by Douglas Stephan’s group
Gregory C. Welch, Ronan R. San Juan, Jason D. Masuda, Douglas W. Stephan. Reversible, Metal-Free Hydrogen Activation. Science, 2006, 314, 1124-1126.
A couple of reviews for newcomers to the topic
Stephan, Douglas W. “Frustrated Lewis pairs”: a concept for new reactivity and catalysis Organic & Biomolecular Chemistry (2008), 6(9), 1535-1539.
Stephan, Douglas W.; Erker, Gerhard. Frustrated Lewis Pairs: Metal-free Hydrogen Activation and More. Angewandte Chemie, International Edition (2010), 49(1), 46-76.