Substitution reactions of five-coordinate complexes. 2. Mechanism of ligand replacement in trigonal-bipyramidal nickel(II) and platinum(II) complexes containing the tetradentate ligand tris(o-(diphenylarsino)phenyl)arsine

Article abstract of DOI:10.1021/ic50204a046

Ligand replacement of the monodentate ligand in a series of trigonal-bipyramidal nickel(II) complexes containing the tetradentate ligand tris(o-(diphenylarsino)phenyl)arsine, QAS, is reported for methanol solutions. Entering ligands replacing Br^- in order of decreasing rate were SC(NH₂)² ? CN^-, > N3^- > SCN^- > I^- > NO₂^- ? PPh₃. CN^- replacement of leaving groups in order of decreasing rate were NCS^- > N₃^- > Cl^- > Br^- > NO₂^- > I^-. A second consecutive decomposition was observed to be several orders of magnitude slower than ligand replacement when CN^- was the entering ligand. The kinetic data obtained at 0.050 M ionic strength and 25.0°C are consistent with either an associative interchange, I_a, mechanism or a mechanism involving formation of a four-coordinate intermediate via partial dissociation of the tetradentate ligand.