Binding multidentate ligands to Ni²⁺: kinetic identification of preferential binding sites

Abstract

The kinetics of the reactions between [Ni(MeOH)6](2+) (hereafter Ni(2+)) and a variety of neutral Schiff base multidentate ligands have been measured in methanol at 25.0 °C using stopped-flow spectrophotometry. The ligands contain a variety of different potential donor sites (phenolic OH, imine N, pyridyl N and NH groups), different structural components and substituents. The kinetic studies explore how systematic changes to the composition of the ligands affect the rates of binding. The results are consistent with the Eigen-Wilkins mechanism in which the ligand initially forms an outer-sphere association with Ni(2+) prior to dissociation of a coordinated solvent molecule and binding to the metal ion. The general features that emerge from these studies are as follows. (i) For ligands with the same donor set, the rates of binding are all similar irrespective of changes to the ligand framework (bridge and substituents). (ii) Comparison of structurally analogous ligands shows that the presence of pyridyl or NH groups in the multidentate results in significantly faster reactions. (iii) With ligands containing multiple NH groups, the rate of ligand binding increases as the number of NH groups increases. The extent to which these kinetic features can be attributed to preferential binding of particular donor groups is discussed.

A Straightforward Electrochemical Approach to Imine- and Amine-bisphenolate Metal Complexes with Facile Control Over Metal Oxidation State

“…At the outset, scope and generality of the method were evaluated; therefore, ligand precursors 1 a – 1 h were prepared using literature procedures and fully characterized (Scheme ) . Cyclic voltammetry of ligands 1 a – 1 e indicated reduction potentials in the range −2.04 to −2.55 V (vs. FeCp 2 /FeCp 2 + ), similar to those found for imidazolium salts (see Supporting Information).…”

Synthesis of a Crizotinib Intermediate via Highly Efficient Catalytic Hydrogenation in Continuous Flow

“…According to the study on the mechanism of nitro-catalyzed hydrogenation in the references, the direction of catalyst design and the improvement of reaction selectivity and conversion were indicated. − We speculated that there might have been two pathways for the reduction of compound I to compound II (Scheme ).…”

Evulation of Antimutagenic Activity of Ni(II) Complexes with Unsymmetric Schiff Bases

“…First time, a new two step method for the synthesis of these type diimines with respect to the unsymmetrical nature of the imine bond were reported by one of us [11,12]. Thus, potentiometric, tautomeric and antimicrobial studies of these type unsymmetric Schiff bases were started to be investigated [13][14][15][16][17].…”