Well-Defined Amidate-Functionalized N-Heterocyclic Carbene-Supported Rare-Earth Metal Complexes as Catalysts for Efficient Hydroboration of Unactivated Imines and Nitriles

Four amidate-functionalized N-heterocyclic carbene (NHC) rare-earth metal amido complexes [(kappa(2)-N,O-kappa L1-)(2)REN(SiMe3)(2)] (L = 1-(C6H5C=ONCH2CH2)-3-(CH3)(3)C6H2(N(CH)(2)NC)) [RE = Er (1), Y (2), Dy (3), Gd (4)] were synthesized by one-pot reactions of 2 equiv of (1-(C6H5C=ONHCH2CH2)-3-(CH3)(3)C6H2-(N(CH)(2)NCH))Br (H2LBr) with 5 equiv of KN(SiMe3)(3) followed by treatment with 1 equiv of RECl3 in tetrahydrofuran at -40 degrees C. These complexes were fully characterized, and their catalytic activities toward hydroboration of unactivated imines and nitriles were investigated, and it was found that these complexes displayed excellent activities as well as remarkable functional group compatibility for imine and nitrile substrates such as halo-, alkyl-, hydroxyl-, N,N-dimethylamino-, and nitro- substituents. Among those, the chemoselectivity for this reaction among the common unsaturated functional groups was achieved in the order C=O >> C=N > C N > CO2Et > C=C in the current catalytic system, which may facilitate their further application in synthetic chemistry.