Controlled formation and topologies of thiophenolate-based macrocycles: rings, cylinders and bowls

Abstract

The Schiff-base condensations of 1,3-diaminopropane with a protected thiophenol dialdehyde in the presence of Ni²⁺, Pd²⁺ or Zn²⁺ can be controlled to yield either mononuclear acyclic, or 2 + 2 and 4 + 4 macrocyclic complexes by the choice of both metal cation and counteranion. The Ni²⁺ complex of the 2 + 2 macrocycle contains two square-planar nickel ions and shows an arrangement similar to one observed previously: the μ-S atoms of the thiophenolate groups are pyramidal and lie on the same side of the plane defined by the four N atoms of the macrocycle to give a V-shaped molecule. By contrast, the Zn²⁺ complex of the 2 + 2 macrocycle undergoes oligomerisation to yield a bowl-shaped hexanuclear complex that includes a μ₃-carbonate anion. Essential for this topology is the presence of three μ₃-S-thiophenolato groups that link the three macrocyclic units to form a Zn₃S₃ ring that seals the bottom part of the bowl. In this arrangement, one of the pyramidal μ₃-S atoms in each dinuclear Zn²⁺ complex is inverted relative to the arrangement observed for the dinickel complexes. Molecular modelling suggests that inversion about the μ-S atoms of the 2 + 2 macrocyclic complexes is readily accessible at room temperature and that the contrasting arrangements observed for the Ni²⁺ and Zn²⁺ complexes are those energetically most favourable for the respective metal ions. Rare 4 + 4 macrocyclic complexes are isolated as neutral dinuclear complexes for Ni²⁺ and Pd²⁺ and as a tetranuclear complex cation for Zn²⁺. The topologies of these systems contrast significantly: those with two square-planar Ni²⁺ or Pd²⁺ ions form extended rings, while that with Zn²⁺ forms a sulfur-lined cylinder which hosts acetonitrile molecules in the crystalline state. Reaction conditions can also be optimised to produce 2 + 1 acyclic ligands as their mononuclear Ni²⁺ and Pd²⁺ complexes, providing potentially useful building blocks for production of more complicated macrocyclic and supramolecular systems.