UNUSUAL STRUCTURAL AND REACTIVITY TYPES FOR COPPER(I) - EQUILIBRIUM-CONSTANTS FOR THE BINDING OF MONODENTATE LIGANDS TO SEVERAL 4-COORDINATE COPPER(I) COMPLEXES

Equilibrium binding constants KI were measured for the reaction CuI(mac)n++L⇌Cu1(mac)(L)n+, in which CuI(mac)n+is a four-coordinate Cu(I) complex of a polydentate ligand, L is a monodentate ligand, and CuI(mac)(L)n+is a five-coordinate Cu(I) complex. Equilibrium constants have been obtained for reactions between isocyanides, phosphites, CO, phosphines, and amines with a single, four-coordinate, copper(I) macrocyclic ligand complex. Reactions between CO and 12 different four-coordinate copper(I) complexes were also studied. In all cases equilibrium constants were obtained by using a simple electrochemical technique. Sampled dc polarography was used to obtain E1/2 for the CuII/I(mac)n+redox couple in the absence and in the presence of a monodentate ligand L. The observed shift in E1/2 was then used to calculate equilibrium constants. In general, five-coordination for Cu(I) was found to be favored for π-acid ligands, such as isocyanides, phosphites, CO, and phosphines. Five-coordinate adducts are apparently accessible from a variety of four-coordinate Cu(I) complexes. Tetradentate ligands which enforce a near-square-planar, yet flexible, ligand geometry for Cu(I) seem to promote five-coordination. © 1979, American Chemical Society. All rights reserved.