Copper(I) Ethylene Adducts and Aziridination Catalysts Based on Fluorinated Tris(pyrazolyl)borates [HB(3-(CF3),5-(R)Pz)3]- (where R = CF3, C6H5, H; Pz = pyrazolyl)

The ethylene adducts of copper(I) tris(pyrazolyl)borates, [HB(3,5-(CF3)2Pz)3]Cu(C2H4), [HB(3-(CF3),5-(C6H5)Pz)3]Cu(C2H4), and [HB(3-(CF3)Pz)3]Cu(C2H4), have been prepared by reacting the corresponding sodium derivative with CF3SO3Cu in the presence of ethylene. They were characterized both in the solid state and in solution using 1H, 13C, and 19F NMR and IR spectroscopy and by X-ray crystallography. Solid samples of these nonionic copper complexes featuring fluorinated tris(pyrazolyl)borate ligands display notably high stability toward air oxidation and ethylene loss. The 1H NMR chemical shifts of the copper(I)-bonded ethylene protons appear in the 4.8−5.2 ppm region. The 13C signal of copper-coordinated ethylene shows an upfield shift of about 35 ppm, whereas the 1 J C - H shows a minor change (an increase of about 2−5 Hz) compared to the values for free ethylene. X-ray structural data show the presence of pseudo-tetrahedral copper ions and η2-bonded ethylene units and relatively unperturbed ethylene C−C distances. The copper adducts [HB(3,5-(CF3)2Pz)3]Cu(C2H4) and [HB(3-(CF3),5-(C6H5)Pz)3]Cu(C2H4) are competent aziridination catalysts, readily converting a variety of olefins into the corresponding N-tosyl aziridines with N-tosyl phenyliodinane.