Crystallographic Characterization of Stepwise Changes in Ligand Conformations as Their Internal Topology Changes and Two Novel Cross-Bridged Tetraazamacrocyclic Copper(II) Complexes

Abstract

The parallel syntheses of two new cross-bridged tetraazamacrocyclic complexes whose ligands are derived from 1,4,8,11-tetraazacyclotetradecane (cyclam = 14N4) and rac-1,4,8,11-tetraaza-5,5,7,12,12,14-hexamethylcyclotetradecane (tetB = 14N4Me(6)) have been characterized through the crystal structure determination of every stepwise intermediate ligand in the multistep ligand syntheses. These structures show that although the final ligand skeletons are nearly identical, the immediate precursors differ greatly because of the six additional methyl groups of the 14N4Me(6) macrocycle. The inversion from one diastereomer to another of the tetracycle derived from rac-14N4Me(6) has been chemically induced through the successive addition of methyl groups to the reactive tertiary nitrogens, and the novel heterocycles produced have been crystallographically characterized with one showing a conformation not previously known for these systems. The structures of the two copper(II) complexes have significant geometrical differences, and accordingly, their electrochemical and spectroscopic properties are compared. The complexes exhibit remarkable kinetic stability under harsh conditions.

Aspartate‐Based CXCR4 Chemokine Receptor Binding of Cross‐Bridged Tetraazamacrocyclic Copper(II) and Zinc(II) Complexes

“…The electronic spectra of the Cu 2+ acetate complexes of ligands 1 – 6 in acetonitrile show the expected ligand field transitions for d 9 Cu 2+ (see Table S1 in the Supporting Information), similar to those of other Cu 2+ complexes with cross‐bridged cyclam and cyclen ligands 1 – 4 in the presence of the acetate, which does not cause significant differences from other bound monodentate ligands …”

“…Cu 2+ complexes of ligands 1–3 and 5 are known {[Cu 1 Cl]PF 6 , [Cu 2 Cl]Cl and [Cu 2 (CH 3 CN) 2 ][PF 6 ] 2 , [Cu 3 (OH 2 )][ClO 4 ] 2 , [Cu 5 (CH 3 CN)][PF 6 ] 2 } as are Zn 2+ complexes of ligands 1–2 {[Zn 1( L) 2 ] and [Zn 2( L) 2 ]} . However, none of these involve acetate as a coordinated ligand.…”

“…Our own experience with growing crystals of these complexes has been similarly unproductive. However, producing X‐ray quality crystals of bridged mono‐macrocycle transition‐metal complexes has been much more successful in our hands ,. We have synthesised a number of dimethyl, monobenzyl‐monomethyl and dibenzyl pendant‐arm‐containing cross‐bridged tetraazamacrocycles to provide the best models for our bis‐macrocycle antagonists, which are linked through a xylene moiety (Figure ).…”

Selectively Functionalized Constrained Polyazamacrocycles: Building Blocks for Multifunctional Chelating Agents

“…8,43.1,43.2,45.7,46.5,47.3,48.9,51.7,52.6,55.2 (CH 2 Acetone (100 mL) was added and a precipitate was formed immediately.…”

“…13 C{ 1 H} NMR (125 MHz, CDCl 3 , 300 K): δ = 25.3 (CH 2 β), 38 8,. 1 H NMR (300 MHz, CDCl 3 , 300 K): δ = 1.57-1.67 (m, 2 H), 2.11-2.19 (m, 2 H), 2.39-2.97 (m, 21 H), 3.09-3.14 (m, 1 H), 3.30-3.35 (m, 1 H) ppm.…”