Synthesis, Characterization, and Catalytic Reactivities of Novel Dinuclear Cu(II) Complexes: Efficient Ring Opening Reaction of Epoxide

Novel tridentate N₂O-type ligands L1–L4 (((((X-benzyl)pyridine-2-yl)methylamino)methyl)phenol); L1 for X=4-CH₃, L2 for X=H, L3 for X=2-F, L4 for X=4-CF₃) and their dinuclear copper(II) complexes C1–C4 (C1 for [(L1)₂Cu₂(NO₃)₂], C2 for [(L2)₂Cu₂(NO₃)₂], C3 for [(L3)₂Cu₂(NO₃)₂] and C4 for [(L4)₂Cu₂(NO₃)₂]) was synthesized and verified by ¹H NMR, IR, and ESI-Mass. The structural forms of the copper complexes were determined by X-ray crystallography. The dinuclear copper complexes C1–C4 showed efficient ring-opening properties of epoxides with methanol under mild conditions. In particular, the copper complex C1 having electron-donating group in the ligand showed the most efficient reactivity in the ring opening of epoxides. The sole attack at the benzylic carbon of styrene oxide and the less steric preference in 1,2-epoxyhexane demonstrated that the regiochemistry of the ring opening catalyzed by dinuclear copper complexes might be dependent on the electronic feature of epoxide.