Heteroleptic Copper Complexes Research Articles

Sulfonamido-Pincer Complexes of Cu(II) and the Electrocatalysis of O2 Reduction.

Heteroleptic copper complexes of an asymmetrical pincer ligand containing a central anionic sulfonamide donor (pyridine-2-yl-sulfonyl)(quinolin-8-yl)-amide (psq), which contains a central anionic sulfonamido donor have been prepared. Meridional κ3-N,N″,N‴ binding with the co-ligands acetate, chloride, or acetonitrile (MeCN), trans to the central sulfonamido N-donor, is revealed by the X-ray crystal structures of [Cu(OAc)(psq)(H2O)], [CuCl(psq)]2, and [Cu(psq)(MeCN)](PF6). Either overall distorted square pyramidal or octahedral geometries of the copper atom are satisfied by coordinated water in the case of the acetate complex or interactions with periphery sulfonamido oxygen atoms on adjacent molecules in the dimeric chloride and 1D polymeric acetonitrile complexes. The cyclic voltammogram (CV) of [Cu(OAc)(psq)(H2O)] shows a quasi-reversible CuII/CuI reduction at -0.930 V (vs Fc+/Fc0, MeCN), and an irreversible CuII/CuI reduction for [Cu(psq)(MeCN)](PF6) is seen at -0.838 V. This signal is split into two quasi-reversible redox processes on the addition of 2,2,2-trifluoroethanol (TFE). This suggests that TFE pushes a solution equilibrium toward a dimeric acetate complex analogous to [CuCl(psq)]2, which shows two quasi-reversible waves at -0.666 V and -0.904 V vs Fc+/Fc0 consistent with its dimeric solid-state structure. A comparison of the CVs of [Cu(OAc)(psq)(H2O)] under either a N2 or an O2 atmosphere revealed that this complex catalyzes turnover electro-reduction of O2 to H2O2 and H2O. The rate of reaction increases on addition of a weak organic acid, and a coulombic efficiency of 48% for H2O2 was determined by iodometric titration. We propose that a CuI complex formed on electroreduction binds O2 to yield an intermediate superoxide complex. On electron and proton transfer to this species, a bifurcated route back to the O2-activating CuI complex is feasible with either release of H2O2 or O-O cleavage resulting in the liberation of H2O. The CuI complex is regenerated by subsequent reduction and protonation to close the cycle.

Fungicidal and Stimulating Effects of Heteroleptic Copper Complex on the Germination and Phytosafety of Plants

At present, when the whole world is intensively switching to organic farming, the refusal or minimization of the usage of chemical plant protection products and synthesized fertilizers is a very urgent issue for the agro-industrial complex (AIC). Accordingly, the solution to the problems of increasing yields and ensuring the fight against pathogenic components should be carried out in accordance with the principles of “green” chemistry. In this regard, the usage of heteroleptic complexes based on carboxylic and amino acids with biogenic metals is dictated not only by their availability, low cost, and ability to increase crop yields but also by fungicidal activity, lower toxicity, and easy biodegradability, which lists them among the “green” and cost-effective plant biostimulants. In the present work, for the first time, a heteroleptic complex based on succinic acid and glycine, with the formula [Cu(succ)(gly)], was developed for usage as a fungicidal biostimulant, which has the ability to significantly reduce the number of pathogens. We found that this compound has a layered structure and was able to increase soybean germination up to 100%.

Chemoenzymatic Dynamic Kinetic Resolution of Secondary Alcohols and Amines Employing Copper-Based Photocatalysis

A tandem photo- and biocatalytic dynamic kinetic resolution of secondary alcohols and amines was achieved employing a commercially available lipase, Candida antarctica lipase B (CALB), and a heteroleptic copper complex. The process is an example of using copper-based photocatalysis to promote hydrogen atom transfer (HAT) processes employing thiyl radicals. Screening of 48 complexes and 5 disulfides identified Cu(dtbbpy)(DPEPhos)BF4 and (Ph3SiS)2 as an optimal catalyst system to promote the HAT process. The catalytic system represents a general system for radical-mediated racemization applicable to both aliphatic and aromatic alcohols and amines (18 examples, 60 → 97% yield, 76 → 99% ee).

Heteroleptic Copper Complexes as Catalysts for the CuAAC Reaction: Counter-Ion Influence in Catalyst Efficiency

A series of nine cationic heteroleptic aryl-BIAN-copper(I) (BIAN = bis-iminoacenaphthene) complexes with the general formula [Cu((E-C6H4)2BIAN)(PPh3)2][X] (E = p-Me, p-iPr, o-iPr; X = BF4, OTf, NO3) 1X–3X were synthesized and fully characterized using several analytical techniques, including NMR spectroscopy and single-crystal X-ray diffraction. Except for complexes 2BF4 and 3BF4, which were already reported in our previous works, all remaining complexes are herein described for the first time. Two different strategies were used for the preparation of the complexes: complexes bearing BF4− or OTf− counter-ions (1BF4, 1OTf, 2OTf, and 3OTf) were obtained using the appropriate copper(I) precursors [Cu(NCMe)4][BF4] or [Cu(NCMe)4][OTf], whereas for derivatives 1NO3–3NO3, [Cu(PPh3)2NO3] was used. Their activity as catalysts for the copper azide-alkyne cycloaddition (CuAAC) was assessed alongside other high activity, previously reported Cu(I) complexes. Comparative studies to determine the influence of the counter-ion and of the aryl substituents were performed. All complexes behaved as active catalysts under neat reaction conditions, at 25 °C and in short reaction times without requiring the use of any additive, with complex 2NO3 being the most efficient derivative, along with other NO3−-bearing complexes.

A general synthesis of azetidines by copper-catalysed photoinduced anti-Baldwin radical cyclization of ynamides

A general anti-Baldwin radical 4-exo-dig cyclization from nitrogen-substituted alkynes is reported. Upon reaction with a heteroleptic copper complex in the presence of an amine and under visible light irradiation, a range of ynamides were shown to smoothly cyclize to the corresponding azetidines, useful building blocks in natural product synthesis and medicinal chemistry, with full control of the regioselectivity of the cyclization resulting from a unique and underrated radical 4-exo-dig pathway.

Decomposition of lignin models enabled by copper-based photocatalysis under biphasic conditions

A heteroleptic copper complex, Cu(bathocup)(XantPhos)BF4 promotes the fragmentation of lignin models of the β-O-4 linkage under aqueous biphasic reaction conditions using catalytic amounts of NABnH, a hydrogen atom donor.

Comparative Study of Antioxidant and Pro-Oxidant Properties of Homoleptic and Heteroleptic Copper Complexes with Amino Acids, Dipeptides and 1,10-Phenanthroline: The Quest for Antitumor Compounds.

In a search for new antitumoral agents, a series of homoleptic copper(II) complexes with amino acids and dipeptides, as well as heteroleptic complexes containing both dipeptides and 1,10-phenanthroline, were studied. Furthermore, a single-crystal structure containing alanyl-leucinato ([Cu3(AlaLeu)3(H2O)3(CO3)]·PF6·H2O), which is the first homotrinuclear carbonato-bridged copper(II) complex with a dipeptide moiety, is presented. To assess possible antitumor action mechanisms, we focused on the comparative analysis of pro- and antioxidant behaviors. Pro-oxidant activity, in which the reactive oxygen species (ROS) formed by the reaction of the complexes with H2O2 produce oxidative damage to 2-deoxy-d-ribose, was evaluated using the TBARS method. Additionally, the antioxidant action was quantified through the superoxide dismutase (SOD)-like activity, using a protocol based on the inhibitory effect of SOD on the reduction of nitrobluetetrazolium (NBT) by the superoxide anion generated by the xanthine/xanthine oxidase system. Our findings show that Cu–amino acid complexes are strong ROS producers and moderate SOD mimics. Conversely, Cu–dipeptide–phen complexes are good SOD mimics but poor ROS producers. The activity of Cu–dipeptide complexes was strongly dependent on the dipeptide. A DFT computational analysis revealed that complexes with high SOD-like activity tend to display a large dipole moment and condensed-to-copper charge, softness and LUMO contribution. Moreover, good ROS producers have higher global hardness and copper electrophilicity, lower copper softness and flexible and freely accessible coordination polyhedra.

Bioactivity studies of two copper complexes based on pyridinedicarboxylic acid N-oxide and 2,2′-bipyridine

Bioactivity of two heteroleptic copper complexes based on pyridinedicarboxylic acid N-oxide and 2,2′-bipyridine which benefit from extensive hydrogen bonds and π-interactions is reported. Anti-cancer activities of 1 and 2 were evaluated by MTT assay against a panel of murine and human cancer cell lines. Moreover, the synergistic effects of 1 in combination with cisplatin, paclitaxel, and topotecan were investigated on HeLa cells. Cell death mechanism induced by 1 was also assessed using FITC-annexin V/PI staining. MTT results indicated that 1inhibited the proliferation of cancerous cells as compared with normal cells. Complex 2 also exerted selective toxicity towards both murine and human colon cancer cells. Moreover, the strongest synergistic effect was obtained from the combination of 1 with topotecan, and apoptosis was the main mechanism of cell death. Our results indicated that both complexes significantly inhibited the proliferation of cancerous cells. Furthermore, complex 1 can be a promising chemotherapeutic agent to be used in combination with other drugs for treatment of cervical cancer, although more studies are required to confirm this.

Panchromatic Copper Complexes for Visible Light Photopolymerization

In this work, eleven heteroleptic copper complexes were designed and studied as photoinitiators of polymerization in three-component photoinitiating systems in combination with an iodonium salt and an amine. Notably, ten of them exhibited panchromatic behavior and could be used for long wavelengths. Ferrocene-free copper complexes were capable of efficiently initiating both the radical and cationic polymerizations and exhibited similar performances to that of the benchmark G1 system. Formation of acrylate/epoxy IPNs was also successfully performed even upon irradiation at 455 nm or at 530 nm. Interestingly, all copper complexes containing the 1,1′-bis(diphenylphosphino)ferrocene ligand were not photoluminescent, evidencing that ferrocene could efficiently quench the photoluminescence properties of copper complexes. Besides, these ferrocene-based complexes were capable of efficiently initiating free radical polymerization processes. The ferrocene moiety introduced in the different copper complexes affected neither their panchromatic behaviors nor their abilities to initiate free radical polymerizations.

Homoleptic and Heteroleptic Copper Complexes as Redox Couples in Dye‐Sensitized Solar Cells

AbstractTo gather a comprehensive understanding of copper complexes as redox couples in dye‐sensitized solar cells (DSSCs), a series of copper complexes were synthesized and thoroughly characterized. Characterization was undertaken using an arsenal of spectroscopic techniques, including steady‐state spectroscopy, electrochemical and spectroelectrochemical assays, current‐voltage measurements, electrochemical impedance spectroscopy (EIS), and transient absorption spectroscopy (TAS). Starting from a homoleptic copper complex featuring two bathocuproine ligands and replacing one of them by either another N‐ or a P‐coordinating ligand, a clear relationship between ligand size, on one hand, and charge transport, recombination as well as effective regeneration of the sensitizer, on the other hand, was established. With this information in hand, the future targeted synthesis of copper complexes to achieve maximum device performance may be achieved.

Phosphoester binding, DNA binding, DNA cleavage and in vitro cytotoxicity studies of simple heteroleptic copper(II) complexes with bidentate ligands

Two mononuclear heteroleptic copper complexes, [Cu(±trans-dach)(bpy)](ClO4)2 1a and [Cu(±trans-dach)(phen)](ClO4)2 2a [dach = 1,2-diaminocyclohexane, bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline], were synthesized and analyzed by CHN analysis, electronic absorption, FT-IR spectroscopy, EPR, and SXRD. The molecular structures of 1a and 2a showed octahedral geometry around Cu(II). Both complexes interacted with phosphoesters and DNA. Their binding affinities with diphenylphosphate, di n-butylphosphate, trimethylphosphate, and triphenylphosphate were studied by UV–vis spectroscopy. For understanding the stereochemical role of dach ligand toward DNA interaction, enantiopure DACH complexes [Cu(R,R-trans-dach(bpy)](ClO4)2 1b, [Cu(S,S-trans-dach)(bpy)](ClO4)2 1c, [Cu(cis-dach)(bpy)](ClO4)2 1d, [Cu(R,R-trans-dach)(phen)](ClO4)2 2b, [Cu(S,S-trans-dach)(phen)](ClO4)2 2c, and [Cu(cis-dach)(phen)](ClO4)2 2d were synthesized and analyzed. All complexes interacted with calf thymus-DNA (CT-DNA) as studied by UV–vis spectroscopy. The nature of binding to CT-DNA was groove/electrostatic as supported by circular dichroism, cyclic voltammetry, and docking studies. Complexes were able to cleave plasmid DNA at 12.5 µM (1a–d) and 6 µM (2a–d), where 2d showed 64% Form II and 36% Form III. The in vitro cytotoxic studies of two different cancer cell lines showed inhibition with low IC50 value in comparison to reference control (cisplatin). These complexes are efficient in inducing apoptosis in cancer cells, making them viable for potent anticancer activity.

Heteroleptic copper(I) photosensitizers with carbazole-substituted phenanthroline ligands: Synthesis, photophysical properties and application to photocatalytic H2 generation

A series of novel 4,7-dicarbazol-1,10-phenanthroline bidentate N-ligands have been designed and synthesized, and applied in heteroleptic copper complexes [Cu(PˆP)(NˆN)]+ as photosensitizers (PS) for light-driven water reduction. In combination with a water reduction catalyst (WRC), Fe3CO12, photocatalytic performances up to 1036 turnover numbers (TON) were reached. This excellent performance can be attributed to the introduction of carbazole groups to the phenanthroline backbone, which can increase the fluorescence quantum yield, decrease the reduction potential of the copper complexes and switch the excited state quenching mechanism from reductive to oxidative. By means of DFT calculations, it has been established that the carbazole substituent contributes most significantly to the HOMO of these complexes.

Heteroleptic copper(I) photosensitizers of dibenzo[b,j]-1,10-phenanthroline derivatives driven hydrogen generation from water reduction

A series of dibenzo[b,j]-1,10-phenanthroline derivatives as N ligands was synthesized and their heteroleptic copper complexes obtained in-situ. These were applied as photosensitizer in photocatalyticCu-Fe water reduction system. Thixantphos as P ligand and 5,8-diphenyl-6,7-dihydrodibenzo[b,j] [1,10]phenanthroline as N ligands constitutes the most efficient photosensitizer among the tested photosensitizer. The highest turnover number of copper was up to 441 and the system achieved a stability of 15 h. Photophysical and electronic chemical character showed that the longer exited time of Cu complex is the reason for the higher photosensitive activity. By theoretical calculation it could be proven that ligand-to-ligand charge transfer is the main energy transition method. Noteworthy, for the first time it could be detected and explained why a C-C single bond at 6,7 positions of phenanthroline could significantly increase the light conversion efficiency. This is a result of the lower N ligand contribution in HOMO and the wider energy gap.

Synthesis and Characterization of Heteroleptic Copper and Zinc Complexes with Saccharinate and Aminoacids. Evaluation of SOD-like Activity of the Copper Complexes

Five new copper and zinc heteroleptic complexes with saccharin and aminoacids with general stoichiometry Na(2)[M(sac)(2)(aa)(2)].nH(2)O (M denotes Cu or Zn, sac the saccharinate ion, and aa the aminoacids) were synthesized and characterized by elemental and thermogravimetric analysis, conductimetric measurements and IR, Raman and UV-vis spectroscopies. In all the complexes, copper and zinc ions coordinated with the aminoacids through the terminal amine and carboxylate residues and with saccharin through the heterocyclic nitrogen atom. Besides, the superoxide dismutase-like activity of the heteroleptic copper complexes was evaluated and compared with the homoleptic copper amino acid complexes with the aim to observe the influence of the saccharin coordination.

Combination of hydrogen and coordination bonding for the construction of one-dimensional networks based on a 7-azaindole appended dipyrrin

A new ligand (L) incorporating a dipyrrin unit acting as a strong chelate under basic conditions and a 7-azaindole group offering a self-complementary hydrogen bonding site has been designed and synthesized. Both hetero- and homoleptic complexes have been prepared and their organization in the solid state investigated by single-crystal X-ray diffraction. As in the case of the dipyrromethane precursor, the heteroleptic copper complex (acac)CuL forms a H-bonded dimer featuring the well-known R22(8) hydrogen bonding motif between two 7-azaindole groups. Interestingly, in the case of the (salen)CoL complex offering a competing H-bond acceptor site, the dihapto mode of H-bonding is disrupted. However, the robustness of the formation of the R22(8) motif is demonstrated in a series of homoleptic complexes of the ML2 type (M = Zn(II), Cu(II), Ni(II)). In spite of the different coordination sphere around the divalent metal ions, the self-complementary R22(8) hydrogen bonding motif is observed in all three cases leading to 1D chains.

Assembly of Heteroleptic Copper Complexes with Silver Salts: From Discrete Trinuclear Complexes to Infinite Networks

The use of heteroleptic copper complexes functionalized with two differentiated coordinating groups for the elaboration of heterometallic extended networks is presented. Two novel 5-phenyl-dipyrrin (dpm) ligands appended with an imidazole or a pyrazole function, dpm-imid and dpm-pz, have been prepared and used as ligands for the synthesis of a series of heteroleptic (acacR)Cu(dpm) complexes (acacH = acetylacetonate; acacCN = 3-cyanoacetylacetonate). The X-ray crystal structures of these complexes revealed that, albeit no particular association mode is observed for the acac capping ligand, one-dimensional networks are formed with the acacCN capping ligand. Whereas the imidazole peripheral ligand is coordinated to the copper center of a neighboring complex in the structure of (acacCN)Cu(dpm-imid), such an interaction is absent for the pyrazole appended derivative, (acacCN)Cu(dpm-pz), leading to an association mode involving the peripheral nitrile group of the acacCN ligand. Upon reaction of the imidazole functionalized complexes, (acac)Cu(dpm-imid) and (acacCN)Cu(dpm-imid), with silver salts, trinuclear species, {[(acacR)Cu(dpm-imid)](2)Ag}(+), are formed as a result of the coordination of the azole nitrogen atom of two copper complexes to the silver ion. As expected, in the case of (acac)Cu(dpm-imid), these species do not self-assemble into an extended network owing to the absence of a peripheral coordinating group. However, for the (acacCN)Cu(dpm-imid) complex, the trinuclear species are equipped with peripheral nitrile groups, thus allowing the binding of metal centers. Consequently, these species self-assemble into one-dimensional polymers with association modes varying with the nature of the anion present in the silver salt.

Helical coordination polymers and cyclic dimers formed from heteroleptic thioether-dipyrrinato copper(ii) complexes

Heteroleptic copper complexes containing an acetylacetonato ligand and a thioether derivatized dipyrrinato ligand are shown to form oligomers and polymers in the solid state.