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

Frustrate Lewis pair-type reactivity of rare-earth (RE) metal abnormal NHC complexes and RE/NHO Lewis pairs was investigated, including synergistic H₂ activation and catalytic hydrogenation of the exocyclic C=C double bond of NHO. These combinations also exhibited cooperative reactivity toward benzaldehyde, (trimethylsilyl)diazomethane and N-phenylcinnamaldimine, affording a series of intriguing rare-earth metal complexes.

Abstract

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 H₂ and diverse organic substrates. Reactions of RE(OAr)₃ (RE=La, Sm, and Y; Ar=2,6- ^t Bu₂−C₆H₃) with unsaturated NHC I ^t Bu (:C[N(R)CH]₂, R= ^t Bu) 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 H₂ 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 α, β-conjugated imine, affording an isocyanotrimethylsilyl lanthanum amide complex and a La/C 1,4-addition product, respectively.

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