Four N,O‐Bidentate‐Chelated Ligand‐Tunable Copper(II) Complexes: Synthesis, Structural Characterization and Exceptional Catalytic Properties for Chan–Lam Coupling Reactions

Abstract

AbstractFour N,O‐bidentate chelating ligands [L1=N‐(4‐thiazolylmethyl)morpholine‐N‐oxide, L2=N‐(2‐pyridylmethyl)pyrrolidine‐N‐oxide, L3=N‐(4‐thiazolylmethyl)pyrrolidine‐N‐oxide, and L4=N‐(2‐pyridylmethyl)morpholine‐N‐oxide] were designed and synthesized. The treatment of N,O‐bidentate ligands with CuCl2 in ethanol at room temperature afforded four new copper complexes—[Cu(L1)2]Cl2 (I), [Cu(L2)2][CuCl4] (II), [Cu(L3)2Cl]2[CuCl2(H2O)2]Cl2⋅10 H2O (III) and [Cu(L4)2][Cu(L4)2(CH3OH)2][CuCl4]2 (IV)—which were fully characterized by single‐crystal X‐ray diffraction, IR spectroscopy and elemental analyses. Most interestingly, the single‐crystal X‐ray diffraction analyses revealed that the N,O‐bidentate ligands L1–L4 can tune the corresponding geometry configuration of copper atoms in complexes I–IV. The copper atoms in I and II showed four‐coordinated distorted square planar geometry, whereas the central copper atom in III adopted a distorted square pyramidal geometry. It should be noted that complex IV was constructed by a distorted square planar CuN2O2 unit, one octahedral CuN2O4 unit and two [CuCl4]2− anions. Importantly, these copper(II) complexes, especially complex IV, showed high catalytic activity in Chan–Lam coupling reactions of primary or secondary amines with arylboronic acid under mild conditions. Substrates with many functional groups were tolerated and the C–N coupling products were afforded in good to excellent yields (up to 96 % yield).