Copper(II) environments in some macrobicycle complexes at room and low temperatures: some novel binuclear chloro-bridged systems

Computational Insights on the Geometrical Arrangements of Cu(II) with a Mixed-Donor N3S3 Macrobicyclic Ligand

“…7 ] t r i c o s a n e (Me 8 tricosaneN 6 ), have been found to differ in this behavior and encapsulate transition metal atoms in a variety of geometries where the ligand acts as either hexadentate or pentadentate. 13,14 The chemistry of the first type of these species has shown unique physical properties, such as enhanced thermodynamic stability and extreme resistance to dissociation, which have, for instance, important applications in medicinal chemistry by complexation of 64 Cu(II) for diagnostic positron emission tomography (PET) imaging. 15 Indeed, demetalation of hexadentate cage complexes requires harsh reaction conditions such as concentrated acid, extraction of the metal with highly competitive ligands, or redox processes that liberate the metal center.…”

“…amine (coordinated to a trivalent metal ion) and generates an intermediate that undergoes inversion of the nitrogen configuration. For instance, detailed studies on the isomerization kinetics of Cu(II) complexes of both meso and rac isomers of the tetraamine macrocyclic ligand Me 6 [14]aneN 4 from a folded to a planar conformation have shown that the processes are catalyzed by base. 30 On the other hand, in water the acid-catalyzed N inversion involves dissociation of the nitrogen donor and rapid proton equilibration of the amino group; ring closure ultimately leads to the N-inverted product.…”

“…In this sense, it is known that complex [Cu(sar)] 2+ undergoes a relatively facile detachment of a ligand strap in acid solution, giving a species with a different bound-N configuration. 14,31,32 However, in nonprotic solvents N inversion might be facilitated by abstraction of a proton to form a temporary amide ion in which the nitrogen can invert and be reprotonated (Figure 2a) in a process rather similar to the above-mentioned internal conjugate base mechanism. Since proton abstraction is not a facile process in solvents with poor protophilicity such as MeCN or DMSO and the fact that the metal ion is only divalent thus having little influence on the N−H bond strength, this reaction is expected not to be favored under these conditions.…”

“…Conversely, ligands from the sarcophagine family (sar, Chart ) are not prone to such behavior, − and generally only one molecular structure, which features the metal totally encapsulated by the hexadentate ligand, is found for a range of transition and d-block metal ions. Notably, expanded versions of these cage complexes, i.e., 1,5,5,9,13,13,20,20-octamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane (Me 8 tricosaneN 6 ), have been found to differ in this behavior and encapsulate transition metal atoms in a variety of geometries where the ligand acts as either hexadentate or pentadentate. , The chemistry of the first type of these species has shown unique physical properties, such as enhanced thermodynamic stability and extreme resistance to dissociation, which have, for instance, important applications in medicinal chemistry by complexation of 64 Cu(II) for diagnostic positron emission tomography (PET) imaging . Indeed, demetalation of hexadentate cage complexes requires harsh reaction conditions such as concentrated acid, extraction of the metal with highly competitive ligands, or redox processes that liberate the metal center .…”

An Unusually Flexible Expanded Hexaamine Cage and Its CuII Complexes: Variable Coordination Modes and Incomplete Encapsulation

“…Recently it has been shown that [Cu(Me 5 tricosaneN 6 )] 2+ (as its CF 3 SO 3 À salt) is also capable of adopting a pentadentate coordinated structure, even without ligand protonation, although in that case the CF 3 SO 3 À anion was found to be coordinated in the solid state. 46 Previously [Cu(Me 5 tricosaneN 6 )] 2+ was crystallized and structurally characterized in a six-coordinate form, 19 so it also appears that five and six-coordinate [Cu(Me 5 trico-saneN 6 2+ shows a facile and quasi-reversible Cu II/I couple at À690 mV vs Ag/AgCl with the anodic/cathodic peak current ratio (i pa /i pc ) being essentially unity at all sweep rates from 20 to 1000 mV s À1 . Representative voltammograms are shown in Figure 7 recorded at pH 7.…”