Imine Metathesis Catalyzed by a Silica-Supported Hafnium Imido Complex

The well-defined single-site silica-supported hafniaaziridine complex [(≡Si–O−)Hf(η2,π-MeNCH2)(η1-NMe2)(η1-HNMe2)] was prepared using surface organometallic chemistry. Upon thermal treatment under high vacuum, the grafted species was converted into the unprecedented hafnium imido bis-amido complex [(≡Si–O−)Hf(═NMe)(η1-NMe2)]. The surface complexes were characterized by elemental analysis and the following spectroscopic techniques: infrared, solid-state single and multiple quantum NMR, advanced DNP-SENS, and extended X-ray absorption fine structure. [(≡Si–O−)Hf(═NMe)(η1-NMe2)] catalyzed imine metathesis under mild conditions, and characterization of the reactivity showed that the imido exchange with N-(4-phenylbenzylidene)benzylamine yielded [(≡Si–O−)Hf (═NCH2Ar)(η1-NMe2)], demonstrating a kind of 2 + 2 mechanism involving the imine and the imido groups; the proposed reaction mechanism is also supported by DFT calculations.