Radical Frustrated Lewis Pairs

While a growing body of literature describes FLP adducts of diamagnetic unsaturated substrates such as alkenes, alkynes and heterocumulenes such as carbon dioxide, capture of the diatomic radical nitric oxide (NO) by intramolecular phosphane/borane FLPs gives a new family of radical frustrated Lewis pair adducts. Capture of NO results in heterocycles with new P-N and B-N bonds featuring a spin density Umpolung of NO to give FLP-NO species that possess significant O-centered radical reactivity. Use of these radical FLP-NO species in C-H functionalization chemistry via H-atom abstraction/radical recombination sequences as well as deployment in nitroxide mediated polymerization of alkenes indicates a rich and diverse chemistry for FLP-NO species. An alternative, complementary strategy to generate radical FLPs involves the use of transition metal centers with unpaired electrons as the Lewis acid component of an FLP in conjunction with a tethered but hindered Lewis base.