An Electron-Poor Dioxa-[2.1.1]-(2,6)-pyridinophane Ligand and Its Application in Cu-Catalyzed Olefin Aziridination

A novel macrocyclic 1,7-dioxa-[2.1.1]-(2,6)-pyridinophane ligand has been synthesized and crystallographically characterized. Two derived metal complexes, dichloropalladium(II) and chlorocopper(I), were prepared. In the palladium(II) complex LPdCl₂, both in the solid state, according to its crystallographic characterization, and in CH₂Cl₂ solutions at -40 °C, according to ¹H NMR spectroscopy, the ligand adapts a C₁-symmetric κ²-N,N-coordination mode in which the metal atom binds to two nonequivalent pyridine fragments of the macrocycle. The complex is fluxional at 20 °C. In the crystalline copper(I) complex LCuCl, the macrocyclic ligand is also κ²-N,N-coordinated to the metal, but it utilizes two equivalent pyridine fragments for the binding. The copper(I) complex is fluxional in CH₂Cl₂ solutions in the temperature range between 20 and -70 °C and is proposed to be involved in a fast intermolecular macrocyclic ligand exchange which is slowed down below -40 °C. DFT calculations predict a lower thermodynamic stability of the dioxapyridinophane-derived complexes LPdCl₂ and LCuCl, as compared to their [2.1.1]-(2,6)-pyridinophane analogs containing bridging CH₂ groups instead of the oxygen atoms. The electron poor dioxapyridinophane chlorocopper(I) complex, in combination with NaBAr^F₄ (BAr^F₄ = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) in dichloromethane solutions, can serve as an efficient catalyst for aziridination of various olefins with PhINTs at 0-22 °C.