To increase the number of potential materials for application as MRI contrast agents, several Cu(II) complexes were synthesized. Cu(II) complexes were chosen because they are less expensive in comparison with the presently used Gd(III), Mn(II) and other agents. Pyridine-2-carboximidamide (1), pyrimidine-2-carboximidamide (2) and pyrazole-2-carboximidamide (3) in the form of different salts along with CuCl2 and NaCl or CuBr2 and NaBr were used to obtain four Cu(II) complexes: dichloro-pyrimidine-2-carboximidamide copper(II) (4), dibromo-pyrimidine-2-carboximidamide copper(II) (5), dichloro-pirazole-2-carboximidamide copper(II) (6), and dibromo-pirazole-2-carboximidamide copper(II) (7). X-ray diffraction analysis revealed that molecular complexes 4–7 contain square planar coordinated Cu(II) atoms and their structures are very similar, as well as their packing in crystals, which allows us to consider them isomorphs. The same synthetic approach to complex preparation where NaCl or NaBr was not used brought us to the formation of dimeric complexes μ-chloro{chloro(pyridine-2-carboximidamide)copper(II)} (8) and μ-chloro{chloro(pyrimidine-2-carboximidamide)copper(II)} (9). In the dimeric complexes, two fragments which were the same as in monomeric complexes 4–7 are held together by bridging Cu-Cl bonds making the coordination of Cu equal to 5 (square pyramid). In dimeric complexes, axial Cu-Cl bonds are 2.7360 and 2.854 Å. These values are Cu-Cl bonds on the edge of existence according to statistical data from CSD. Synthesized complexes were characterized by IR spectroscopy, TGA, PXRD, EPR, and quantum chemical calculations. The higher thermal stability of monomer pyrimidine-based complexes with Cl and Br substituents makes them more prospective for further studies.
Multicopper active sites for small molecule activation in materials and enzymatic systems rely on controlled but adaptable coordination spheres about copper clusters for enabling challenging chemical transformations. To translate this constrained flexibility into molecular multicopper complexes, developments are needed in both ligand design for clusters and synthetic strategies for modifying the cluster cores. The present study investigates the chemistry of a class of pyridyldiimine-derived macrocycles with geometrically flexible aliphatic linkers of varying lengths (nPDI2, n = 2, 3). A series of dicopper complexes bound by the nPDI2 ligands are described and found to exhibit improved solubility over their parent analogs due to the incorporation of 4-tBu groups on the pyridyl units and the use of triflate counterions. The ensuing synthetic study investigated methods for introducing various bridging ligands (µ-X; X = F, Cl, Br, N3, NO2, OSiMe3, OH, OTf) between the two copper centers within the macrocycle-supported complexes. Traditional anion metathesis routes were unsuccessful, but the abstraction of bridging halides resulted in “open-core” complexes suitable for capturing various anions. The geometric flexibility of the nPDI2 macrocycles was reflected in the various solid-state geometries, Cu–Cu distances, and relative Cu coordination spheres on variation in the identity of the captured anion.
more » « less- Award ID(s):
- 1945265
- PAR ID:
- 10468711
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Inorganics
- Volume:
- 11
- Issue:
- 9
- ISSN:
- 2304-6740
- Page Range / eLocation ID:
- 348
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Homometallic copper complexes with alkenylidene ligands are discussed as intermediates in catalysis but the isolation of such complexes has remained elusive. Herein, we report the structural characterization of copper complexes with bridging and terminal alkenylidene ligands. The compounds were obtained by irradiation of CuIcomplexes with N‐heterocyclic diazoolefin ligands. The complex with a terminal alkenylidene ligand required isolation in a crystalline matrix, and its structural characterization was enabled by
in crystallo photolysis at low temperature. -
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Abstract Homometallic copper complexes with alkenylidene ligands are discussed as intermediates in catalysis but the isolation of such complexes has remained elusive. Herein, we report the structural characterization of copper complexes with bridging and terminal alkenylidene ligands. The compounds were obtained by irradiation of CuIcomplexes with N‐heterocyclic diazoolefin ligands. The complex with a terminal alkenylidene ligand required isolation in a crystalline matrix, and its structural characterization was enabled by
in crystallo photolysis at low temperature. -
null (Ed.)One-pot reaction of tris(2-aminoethyl)amine (TREN), [Cu I (MeCN) 4 ]PF 6 , and paraformaldehyde affords a mixed-valent [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 complex. The macrocyclic azacryptand TREN4 contains four TREN motifs, three of which provide a bowl-shape binding pocket for the [Cu 3 (μ 3 -OH)] 3+ core. The fourth TREN caps on top of the tricopper cluster to form a cryptand, imposing conformational constraints and preventing solvent interaction. Contrasting the limited redox capability of synthetic tricopper complexes reported so far, [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 exhibits several reversible single-electron redox events. The distinct electrochemical behaviors of [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 and its solvent-exposed analog [ TREN3 Cu II Cu II Cu II (μ 3 -O)](PF 6 ) 4 suggest that isolation of tricopper core in a cryptand enables facile electron transfer, allowing potential application of synthetic tricopper complexes as redox catalysts. Indeed, the fully reduced [ TREN4 Cu I Cu I Cu I (μ 3 -OH)](PF 6 ) 2 can reduce O 2 under acidic conditions. The geometric constraints provided by the cryptand are reminiscent of Nature's multicopper oxidases (MCOs). For the first time, a synthetic tricopper cluster was isolated and fully characterized at Cu I Cu I Cu I ( 4a ), Cu II Cu I Cu I ( 4b ), and Cu II Cu II Cu I ( 4c ) states, providing structural and spectroscopic models for many intermediates in MCOs. Fast electron transfer rates (10 5 to 10 6 M −1 s −1 ) were observed for both Cu I Cu I Cu I /Cu II Cu I Cu I and Cu II Cu I Cu I /Cu II Cu II Cu I redox couples, approaching the rapid electron transfer rates of copper sites in MCO.more » « less
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The 3d transition metal (Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)) complexes, supported by anions of sterically demanding β-diketones, 1,3-dimesitylpropane-1,3-dione (HLMes) and 1,3-bis(3,5-bis(trifluoromethyl)phenyl)-3-hydroxyprop-2-en-1-one (HLCF3), were synthesized and evaluated for their antitumor activity. To assess the biological effects of substituents on phenyl moieties, we also synthesized and investigated the analogous metal(II) complexes of the anion of the less bulky 1,3-diphenylpropane-1,3-dione (HLPh) ligand. The compounds [Cu(LCF3)2], [Cu(LMes)2] and ([Zn(LMes)2]) were characterized by X-ray crystallography. The [Cu(LCF3)2] crystallizes with an apical molecule of solvent (THF) and features a rare square pyramidal geometry at the Cu(II) center. The copper(II) and zinc(II) complexes of diketonate ligands, derived from the deprotonated 1,3-dimesitylpropane-1,3-dione (HLMes), adopt a square planar or a tetrahedral geometry at the metal, respectively. We evaluated the antitumor properties of the newly synthesized (Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)) complexes against a series of human tumor cell lines derived from different solid tumors. Except for iron derivatives, cellular studies revealed noteworthy antitumor properties, even towards cancer cells endowed with poor sensitivity to the reference drug cisplatin.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/inorganics11090348
