Synthesis, characterization and copper chemistry of a non-symmetric phenanthroline ligand: 2-Methyl-9-(3,5-dimethyl- N-pyrazolylmethyl)-1,10-phenanthroline

Abstract

The synthesis of an unsymmetrical phenanthroline-based ligand, 2-methyl-9-(3,5-dimethylpyrazolylmethyl)-1,10-phenanthroline ( L), and its cupric [Cu(II)] ( 1) and cuprous [Cu(I)] ( 2) complexes, are reported. The X-ray structures of each of these Cu complexes show distinct changes in coordination environments consistent with the geometrical preferences of the two oxidation states. In the solid-state, the Cu(II) complex ( 1) adopts a geometry best described as trigonal bipyramidal, while the Cu(I) complex ( 2) consists of a single dicationic dimer in which the ligand bridges between two copper ions, separated by 4.26 Å. The two Cu(I) coordination sites differ in 2 with one copper center complexed in a trigonal planar geometry and the other copper in a distorted tetrahedral environment; the latter coordination results from an additional CH 3CN ligand. Complex 1 exhibits a reversible redox process at −0.34 V versus Fc/Fc + in CH 3CN, attributable to the Cu 2+/Cu + couple, while the dimeric Cu(I) complex ( 2) does not display this redox couple on the CV timescale. Over minutes however, complex 1 does oxidize in the presence of dioxygen to 2 in CH 3CN.