Structural and Electrochemical Studies of Copper(I) Complexes with Diethoxyphosphoryl-1,10-phenanthrolines

Two series of copper(I) complexes with diethoxyphosphoryl-substituted 1,10-phenanthroline ligands were synthesized and characterized in the solid state and in solution. The first comprised mixed-ligand CuI complexes with phenanthroline and triphenylphosphine. The second series includes bis-chelates with two phenanthroline ligands. According to the Xray data for the six complexes, the ditopic phenanthroline ligands exhibit bidentate coordination to the copper(I) atom through two nitrogen atoms in both series. Solution equilibria involving different phenanthroline copper(I) species were studied by H-1 and P-31 NMR spectroscopy, electrochemistry, and spectroelectrochemistry. The solution speciation of these labile complexes is different for these two series and depends on the nature of solvent and the location of the phosphorus substituent on the phenanthroline backbone. Coordinating solvents can replace a bromide, triphenylphosphine, and even a phenanthroline ligand in the inner coordination sphere of the metal center. Copper(I) complexes with alpha-substituted phenanthrolines easily dissociate even in noncoordinating solvents such as CH2Cl2 and CHCl3. Ligand-exchange reactions leading to less sterically hindered species were observed under the utilized solution conditions. The coordination mode of the phenanthroline chelators does not change under any of the utilized solution conditions, and binding of the phosphoryl group to the metal center was never observed by spectroscopic or spectroelectrochemical methods.