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-(CF 3 ) 2 Pz) 3 ]Cu(C 2 H 4 ), [HB(3-(CF 3 ),5-(C 6 H 5 )Pz) 3 ]Cu(C 2 H 4 ), and [HB(3-(CF 3 )Pz) 3 ]Cu(C 2 H 4 ), have been prepared by reacting the corresponding sodium derivative with CF 3 SO 3 Cu in the presence of ethylene. They were characterized both in the solid state and in solution using 1 H, 13 C, and 19 F 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 1 H NMR chemical shifts of the copper(I)-bonded ethylene protons appear in the 4.8−5.2 ppm region. The 13 C 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 η 2 -bonded ethylene units and relatively unperturbed ethylene C−C distances. The copper adducts [HB(3,5-(CF 3 ) 2 Pz) 3 ]Cu(C 2 H 4 ) and [HB(3-(CF 3 ),5-(C 6 H 5 )Pz) 3 ]Cu(C 2 H 4 ) are competent aziridination catalysts, readily converting a variety of olefins into the corresponding N -tosyl aziridines with N -tosyl phenyliodinane.