Remarkable Inertness of Copper(II) Chelates of Cyclen-Based Macrobicycles with Two trans-N-Acetate Arms

Abstract

Two cross-bridged cyclen-based macrocycles with two trans-N-acetic acid arms, one having a dibenzofuran (DBF) moiety as the bridge, H2L1, and the other a diphenyl ether (DPE) one, H2L2, were synthesized. Both compounds behave as "proton sponges." The thermodynamic stability constants for the Cu(2+), Zn(2+), Al(3+), and Ga(3+) complexes of both compounds were determined. They exhibit an excellent thermodynamic selectivity for copper(II), ensuring that metal ions largely present in the human body do not interfere with the copper(II) chelates. All complexes are very slow to form, and [CuL2] and [CuL1] are extremely inert to demetallate, especially [CuL2]. The acid-assisted dissociation of [CuL1] led to a half-life of 4.28 h in 5 M HCl at 363.2 K, while [CuL2] needed harsher conditions of 12 M HCl at 363.2 K with a half-life of 30.8 days. To the best of our knowledge, [CuL2] exhibits the highest half-life value for a copper(II) complex of a polyazamacrocycle derivative reported in the literature until now. Single crystal X-ray diffraction determined for [Cu(H2L1)](ClO4)2 showed the copper center in a distorted octahedral environment bound to the N4O donors of the macrobicycle and one oxygen atom from a carboxylic arm, while for [CuL2] it showed the copper center in a trigonal bipyramid geometry only bound to the donors of the macrobicycle and leaving the carboxylate arms away from the coordination sphere. UV-vis-NIR and X-band EPR spectra showed that in [CuL1] the copper center adopts a distorted compressed octahedral environment, which is the only structure found in solution for this complex, while in [CuL2] a similar environment was found in the first stages of its slow formation but reached a square-pyramidal geometry upon stabilization. The acetate arms play therefore an important role during the formation of the complex, as revealed by the comparison of its complexation behavior with the corresponding parent compounds.

Pycup—A Bifunctional, Cage-like Ligand for 64Cu Radiolabeling

“…Recently published work on new Cu(II) chelators has shown that highly inert Cu-complexes can be obtained by modification of CB-TE2A-type structures, either by extension of the cross-bridge 20 or integration of a donor atom into the cross bridge. 21 We also took the potent copper chelator cyclam as a base and used the previously established synthesis of 1,8-(2,6-Pyridinedimethylene)-1,4,8,11-tetraazacyclo-tetradecane (here abbreviated as pycup) by Brandes et al, 22 to furnish ligand that incorporates a pyridyl nitrogen donor atom into the cross-bridge. Incorporation of this donor group for the purpose of building a more sturdy ligand is based on the well-documented preference of Cu(II) for softer nitrogen donors.…”

Catalytic Cooperativity, Nuclearity, and O2/H2O2 Specificity of Multi‐Copper(II) Complexes of Cyclen‐Tethered Cyclotriphosphazene Ligands in Aqueous Media

“…The spectrum of Cu 2 L1 is quite different from that of Cu 1 L1 and is best simulated with three components: 48 % of component A with g ∥ = 2.202, A ∥ = 554 MHz, g ⊥ = 2.056, and A ⊥ = 47 MHz similar to the spectrum of Cu 1 L1 , 12 % of component B with g ∥ = 2.416, A ∥ = 389 MHz, g ⊥ = 2.0832, and A ⊥ = 14.5 MHz, and 40 % of a broad component C with g ∥ = 2.262, A ∥ = 178 MHz, g ⊥ = 2.0480, and A ⊥ = 7.5 MHz and H‐strain broadenings in the order of 400 MHz (Figure C). The second component with relatively large g ∥ would indicate coordination to four oxygen ligands according to the Peisach–Blumberg rules if it could be considered to have only four ligands but this is unlikely for Cu II –cyclen complexes as seen from recent structural data of similar complexes , . It only accounts for 12 % of the spectral intensity and was included in the simulation because it was quite pronounced in the echo‐detected field sweep spectra of the same sample (cf.…”

A family of [Cu2], [Cu4] and [Cu5] aggregates: alteration of reaction conditions, ancillary bridges and capping anions

“…Figure S2 ( transfer transition (LMCT) is observed at 368 nm (ε = 7600 L mol -1 cm -1 ) for 1, 374 nm (ε = 10500 L mol -1 cm -1 ) for 2, and 371 nm (ε max = 13700 L mol -1 cm -1 ) for 3. 26 Interestingly the other ligand based strong absorption bands were seen at 259 nm with ε values of 3510, 52400…”