Frustrated Lewis Pair-Type Reactivity of Intermolecular Rare-Earth Aryloxide and N-Heterocyclic Carbene/Olefin Combinations

This work reports the cooperative reactivity of rare-earth aryloxide complexes with N-heterocyclic carbene (NHC) or N-heterocyclic olefin (NHO), showcasing their synergistic effect on the activation of H-2 and diverse organic substrates. Reactions of RE(OAr)(3) (RE=La, Sm, and Y; Ar=2,6-Bu-t(2)-C6H3) with unsaturated NHC (IBu)-Bu-t (:C[N(R)CH](2), R=Bu-t) isolated abnormally bound RE metal NHC complexes RE/aNHC. In contrast, no metal-NHO adducts were formed when RE(OAr)(3) were treated with NHO (R2C=C[N(R)C(R)](2), R=CH3). Both RE/aNHC and RE/NHO Lewis pairs enabled cooperative H-2 activation. Furthermore, RE(OAr)(3) were found to catalyze the hydrogenation of the exocyclic C=C double bond of NHO under mild conditions. Moreover, treatment of the La/aNHC complex with benzaldehyde produced a La/C4 1,2-addition product. The La/NHO Lewis pair could react with (trimethylsilyl)diazomethane and alpha, beta-conjugated imine, affording an isocyanotrimethylsilyl lanthanum amide complex and a La/C 1,4-addition product, respectively.