Frustrated Lewis Pairs Beyond the Main Group

Frustrated Lewis Pairs
FLP 2
FLP 3

Solution phase combinations of sterically hindered Lewis acid-Lewis base pairs, so-called Frustrated Lewis Pairs (FLPs – for example tBu3P and B(C6F5)3), have been the subject of recent interest, particularly because of the high latent reactivity of such species in the activation of small molecules.

We have been extending this concept to transition metal systems, such as cationic group 4 metallocene-phosphinoaryloxide complexes, where the Lewis acidic borane component is replaced with an electrophilic transition metal centre. Our results have established the analogy with main group frustrated pairs but also demonstrated additional reactivity, for example the catalytic dehydrogenation of amine-boranes, a reaction only known in a stoichiometric sense with main group FLP systems. We have also demonstrated new activation chemistry; for example, the cleavage of C-O bonds in non-cyclic ethers, aliphatic C-Cl and C-F cleavage, and the stepwise reduction of CO or CO2.