Helical Figure-of-Eight Loop Dicopper(I) Compounds:  Syntheses, Structures, and Dynamics

Abstract

The synthesis of a series of nine large macrocyclic ligands with two N(2)S(2) (thioether and Schiff-base imine) binding sites each, with different bridges between the donor atoms of each site (ethylene, o-xylylene, propylene, butylene) and different spacer groups between the two binding sites (p-xylylene, 2,5-dimethyl-p-xylylene, 2,5-dimethoxy-p-xylylene), and the synthesis of a similar ligand with a preorganized double-helical geometry, based on a paracyclophane spacer group, are reported, together with the syntheses and characterizations of the corresponding dicopper(I) compounds. The solid state structures of the dicopper(I) complexes have two tetrahedral copper(I) sites, separated by ca. 8 Å, and a figure-of-eight loop configuration of the ligand with a parallel arrangement of the two substituted benzene spacer groups (benzene.benzene distance of ca. 3.5 Å). All the dicopper(I) compounds have the same double-helical configuration ("twisted ring figure-of-eight loop"). NMR spectroscopy indicates that the monocyclic metal-free ligands have an open, cyclic structure in solution, while the dicopper(I) compounds are folded as in the solid. In acetonitrile there is a fast dynamic equilibrium between two enantiomeric forms of the double-helical dicopper(I) compounds. The fact that copper(I)-donor atom bond breaking is involved in this process is supported by (1)H NMR data and by the X-ray crystal structure analysis of a putative intermediate with each of the two copper(I) centers coordinated to one acetonitrile and three donors of the macrocycle. A second fast dynamic, solvent independent process (epimerization) has been identified in nitromethane and acetonitrile, involving helix inversion with full conservation of the copper(I) coordination.

Metal‐coordinated Hydroxide as a Nucleophile: a Brief History

“…Indeed they do. In an extensive series of papers Comba and his group have studied the Cu II and Zn II complexes of analogues of the patellamides . What is most significant in the sense of this present article is that the Cu II and Zn II complexes of these patellamide analogues exhibit hydrolytic activity towards a number of substrates through a nucleophilic M –OH moiety (Scheme ).…”

“…We end by highlighting some work involving metal‐coordinated hydroxide carried out by the dedicatee of this review, Professor Peter Comba. Comba and his associates have studied the chemistry of cyclic octapeptides, synthetic analogues of marine metabolites found in ascidians of the Pacific and Indian Oceans and originally isolated from genus Lissoclinum bistratum and Lissoclinum patella , . The ascidians (or tunicates) are filter‐feeding animals, found as individuals or in colonies on the ocean floor and importantly metabolites isolated from these animals exhibit antiviral, antitumor and cytotoxic properties.…”

Supramolecular Circular Helicates Formed by Destabilisation of Supramolecular Dimers

“…Table 1. Crystallographic data and details of refinement for [Cu 3 (L) 3 (3) a [8] 90.00 102.5900(10) b [8] 90.00 91.9340(10) g [8] 120.00 113.5150(10) m [ 3] 5100.3 (2) 5826.55 (13)…”

“…Keywords: circular helicates · dinuclear double helicates · N ligands · pyridylimine ligands · supramolecular chemistry in a cyclic (rather than linear) arrangement. [7,8,[12][13][14][15][16][17][18][19] In nature cyclic motifs occur in plasmid DNA and elsewhere. [3] In some systems, a mixture of different circular helicates may be formed in solution, which leads to a real or virtual library of structures.…”

Linked macrocyclic systems. Interaction of copper(I) with tris-ring N2S2-donor macrocycles and their single-ring analogues

“…The counter ion in this case is triflate. Related copper(I) complexes of double ring, N 2(imine) -S 2 -macrocycles have also been reported [19].…”