Frustrated Lewis Pairs

A couple of years’ ago I noted a paper by G Erker et al (JCS Chem Commun, 2008, 45) with the term ‘frustrated Lewis Pair’ in the title and intrigued by this I read further as it described the use of these materials to activate hydrogen, promising the option of catalytic reductions without the use of transition metals catalysis.  Since that time I have noted a few other papers, and indeed a simple search on Scifinder using the term ‘frustrated Lewis pair’ gave over 100 hits.

A review by D Stephan in Angew Chemie In ed, 2010, 49 (1), 46 gives a nice overview of the area with specific sections on the activation of hydrogen, metal-free hydrogenation and activation of small molecules.  As example, see the schemes below.

In addition, enamines are reduced as are enol ethers

In this review, Stephan concludes ‘while any commercial impact of catalytic hydrogenation derived from frustrated Lewis pairs developed to date remains to be seen, the potential for metal-free hydrogenation catalysis is an attractive notion given the reductions in both cost of production and of environmental impact of these main-group catalysts.’  

I am excited by this proposition and look forward to further reports in this area, especially if applications start to broaden to other small molecules enabling access to hitherto undiscovered chemistries and strategies in synthesis.