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Eight [CNN] pincer nickel NHC chlorides, [RCcarbeneNamidoR′2Namine–Ni–Cl] (R/R′2 = quinolinyl/nBu (3a), quinolinyl/Me (3b), quinolinyl/PhCH2 (3c), (CH2)4/nBu (5a), (CH2)4/iPr (5b), Me2/nBu (5c), Me2/iPr (5d), and Me2/PhCH2 (5e)), were prepared by the reactions of related asymmetric [CNN] NHC preligands with Ni(DME)Cl2via N–H bond activation. The molecular structures of complexes 3a, 3b and 5a were investigated using single crystal XRD. The catalytic experiments showed that the nickel complexes could catalyze the hydrosilylation of unsaturated compounds like aldehydes and ketones, and complex 3b was found to exhibit the best catalytic activity at 30 °C. Using NaBHEt3 as an additive, the catalytic activity of 3b was greatly improved. Furthermore, it was found that good to complete conversion of aldehydes could be achieved within 1.5 h at 30 °C after pre-reacting 3b and NaBHEt3 with silane for 0.5 h. The substrate ketones could be converted to alcohols in good yields by prolonging the reaction time to 2.5 h at 30 °C. It is worth mentioning that all eight [CNN] pincer nickel NHC chlorides are stable in air, and this is rare in nickel catalysts for hydrosilylation of aldehydes and ketones. Moreover, the substrate universality of the catalytic system is also very good, with good functional group tolerance. The molecular structures of complexes 3a, 3b and 5a were investigated using single crystal XRD and a possible reaction mechanism was proposed. [ABSTRACT FROM AUTHOR]

Four NHC [CNN] pincer nickel (II) complexes, [iPrCNN (CH2)4‐Ni‐Br] (5a), [nBuCNN (CH2)4‐Ni‐Br] (5b), [iPrCNN (Me)2‐Ni‐Br] (6a) and [nBuCNN (Me)2‐Ni‐Br] (6b), bearing unsymmetrical [C (carbene)N (amino)N (amine)] ligands were synthesized by the reactions of [CNN] pincer ligand precursors 4 with Ni (DME)Cl2 in the presence of Et3N. Complexes 5a and 5b are new and were completely characterized. The transfer hydrogenation of ketones catalyzed by the four pincer nickel complexes were explored. Complexes 5a and 6a have better catalytic activity than 5b and 6b. With a combination of NaOtBu/iPrOH/80 °C and 2% catalyst loading of 5a, 77–98% yields of aromatic alcohols could be obtained. [ABSTRACT FROM AUTHOR]