Effect of Constrained Donor Atom Orientations on the Stabilities, Complexation Kinetics, Redox Potentials, and Structures of Macrocyclic Polythiaether Complexes. Copper(II) Complexes with Cyclopentanediyl Derivatives of [14]aneS₄ in 80% Methanol

Abstract

The two ethylene bridges in the macrocyclic tetrathiaether 1,4,8,11-tetrathiacyclotetradecane ([14]aneS(4)) have been systematically replaced by cis- or trans-1,2-cyclopentane to generate a series of new ligands that exhibit differing preferences for the orientation of the sulfur donor atoms while maintaining constant inductive effects. The resulting five dicyclopentanediyl derivatives, along with two previously synthesized monocyclopentanediyl analogues, have been complexed with Cu(II), and their stability constants, formation and dissociation rate constants, and redox potentials have been determined in 80% methanol/20% water (by weight). The crystal structures of the Cu(II) complexes with the five dicyclopentanediyl-[14]aneS(4) diastereomers as well as the structures for a representative Cu(I) complex and one of the free ligands have also been determined. The properties of these complexes are compared to previous data obtained for the corresponding cyclohexanediyl derivatives in an attempt to shed additional light on the influence of sterically constraining substituents upon the properties of macrocyclic ligand complexes.

Kinetically Controlled Photoinduced Electron Transfer Switching in Cu(I)-Responsive Fluorescent Probes

“…The formal potential of the Cu(II/I) couple coordinated to the ligand can be readily measured by cyclic voltammetry of the Cu(II)-complex. 25 To determine the amount of Cu(II) needed to saturate ligand 3 , we first performed a mol-ratio titration with Cu(OTf) 2 in methanol. Only at a large excess of Cu(II) were we able to discern changes in the UV-vis absorption spectrum, indicating a very low affinity of 3 towards Cu(II).…”

Macrocyclic coordination chemistry

“…The effects of backbone constraint on thioether macrocycles and their copper(II) complexes was investigated with ligands incorporating a 1,2-cyclopentane unit in the backbone such as L 45 and both cis and trans units were included. 81 The donor atom orientation effects were proposed to be the key characteristic in the reduced stability of these complexes compared to those formed with [14]aneS 4 . Monomeric and dimeric complexes have been characterised with ruthenium(II) and [12]aneS 4 , in both cases the ruthenium is six coordinate.…”

Zinc(ii) complexes of constrained antiviral macrocycles

“…11 There are several examples in the literature of the effects of ligand constraints on the properties of macrocyclic complexes. [12][13][14][15][16][17][18] A side-bridged macrocycle incorporating a coordinating acetate pendant arm displays only trans-II or trans-IV configurations, showing how constraining substituents affect the preferred geometry of the ring. 13 Reducing the flexibility of the ring through the addition of constraining substituents may result in a potential increase in kinetic stability, an important advance when addressing problems of increased kinetic lability in vivo of existing bifunctional radiopharmaceutical chelators.…”

“…Studies on the effect on stability constants for complexes with comparable constraining substituents have been reported. 14 Similarly, Nfunctionalised derivatives of cyclam that contain cross-bridge linking of symmetrical nitrogens in the ring can show increased in vivo stability in radiolabelled complexes when compared with analogues with no cross-bridge. 19,20 In this work we have investigated the configurations of zinc cyclam complexes constrained with cyclohexyl substituents and with N-methyl substituents in the cyclam ring, Scheme 1.…”