Selective Oxidation of an Active Intramolecular Amine/Borane Frustrated Lewis Pair with Dioxygen

Oxidation
reactions are rarely encountered in frustrated Lewis pair (FLP) chemistry.
We describe the selective reaction of an amine/borane FLP with molecular
oxygen. The trimethylene-bridged amine/borane frustrated Lewis pair
was prepared by hydroboration of N-allyl-tetramethylpiperidine
with Piers’ borane [HB­(C6F5)2]. The intramolecular N/B system undergoes a variety of typical FLP
reactions. It is a very active hydrogen splitting reagent at ambient
conditions. Its reaction with dioxygen takes place rapidly at ambient
conditions to give a tetrahydroisoxazolium/borate salt. A possible
pathway of its formation is proposed and supported by DFT calculations.