A new post for the series I am crazy about Frustrated Lewis Pairs (FLPs). If you are new to this exciting field I recommend you to read first one of my previous posts: “Frustration to a Good End”.The extraordinary reactivity of FLPs allows the stoichiometric and catalytic activation of small molecules being the most important application the heterolytic cleavage of hydrogen. The spectrum of Lewis bases used in FLP chemistry is wider compared to the Lewis acid partners. Phosphines, amines, N-heterocyclic carbenes or carbodiphosphoranes have been used, with a few exceptions, combined with boranes such as B(C6F5)3 and derivatives.
The activation of the strong H-H bond has been commonly achieved using a type of the Lewis bases mentioned above in the presence of strong Lewis acidic boranes. Krempner and co-workers have recently showed that the use of strong Lewis acids is not strictly necessary for the activation of hydrogen. In this new approach denominated as “Inverse” Frustrated Lewis Pairs, organic superbases combined with rather moderate and weak Lewis acids are capable to reversibly cleavage hydrogen. Organic superbases have an enormous proton affinity and are very strong due to the great stability of their conjugated acids once they are protonated. In their recent work Krempner and co-workers activate hydrogen using phosphazene based superbases with BPh3, HBMes2 or 9-BBN and extend the concept of Inverse Frustrated Lewis Pairs to the catalytic hydrogenation of organic molecules using N-Benzylidenaniline as model substrate.Do you want to know more? Read the original paper
Suresh Mummadi, Daniel K. Unruh Jiyang Zhao, Shuhua Li and Clemens Krempner. “Inverse” Frustrated Lewis Pairs – Activation of Dihydrogen with Organosuperbases and Moderate to Weak Lewis Acids. J. Am. Chem. Soc., 2016, 138 (10), pp 3286–3289.
Are you a newcomer to the topic? Take a look to this papers
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.