Five new alkyl zinc complexes supported by different formylfluorenimide ligands were prepared and characterized. Complex 1 was obtained by the reaction of 9-[N(CH3)2-Cy-NCH]Fl (Cy = 2-cyclohexyl) (Fl = fluorenyl) (L1) with diethylzinc (ZnEt2) in tetrahydrofuran. Reacting 9-[2-pyridyl-CH-NCH]Fl (L2) with ZnEt2 in tetrahydrofuran yielded complex 2. Under analogous conditions, complexes 3 and 4 were obtained through the reaction of 9-[2-pyridyl-CH(CH3)-NCH]Fl (L3) and 9-[8-quinoline-CH-NCH]Fl (L4) with ZnEt2 in tetrahydrofuran, respectively. The above ligands formed a tridentate four-coordinate structure with the introduction of a THF molecule along with the elimination of one ethyl group during its coordination with zinc. Notably, the formylfluorenimide ligand 9-[2-phenoxy-Ph-NCH]Fl (Ph = phenyl) (L5) bearing a phenoxy group exhibited unique reactivity compared to the other ligands and formed a bidentate three-coordinated structure when reacting with ZnEt2 in THF. All complexes were characterized via1H NMR, 13C NMR spectroscopy, and elemental analysis, with structural determination confirmed through single-crystal X-ray diffraction. Furthermore, the catalytic properties of these complexes were investigated. All these complexes exhibited excellent catalytic activities for the hydroboration of benzaldehyde, among which complex 5 demonstrated excellent catalytic performance (up to 99% yield) with a versatile substrate scope and high tolerance to functional groups (27 substrates) at a low catalyst loading (0.8 mol%) under mild reaction conditions.
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