Electrochemical and spectroelectrochemical study of copper complexes with 1,10-phenanthrolines

Photoactive Copper Complexes: Properties and Applications

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

Photocatalytic Reduction of Nicotinamide Co-factor by Perylene Sensitized RhIII Complexes

The ambitious goal of artificial photosynthesis is to develop active systems that mimic nature and use light to split water into hydrogen and oxygen. Intramolecular design concepts are particularly promising. Herein, we firstly present an intramolecular photocatalyst integrating a perylene-based light-harvesting moiety and a catalytic rhodium center (RhIII phenPer). The excited-state dynamics were investigated by means of steady-state and time-resolved absorption and emission spectroscopy. The studies reveal that photoexcitation of RhIII phenPer yields the formation of a charge-separated intermediate, namely RhII phenPer⋅+ , that results in a catalytically active species in the presence of protons.

Copper Complexes with 1,10-Phenanthroline Derivatives: Underlying Factors Affecting Their Cytotoxicity

The interpretation of in vitro cytotoxicity data of Cu(II)-1,10-phenanthroline (phen) complexes normally does not take into account the speciation that complexes undergo in cell incubation media and its implications in cellular uptake and mechanisms of action. We synthesize and test the activity of several distinct Cu(II)-phen compounds; up to 24 h of incubation, the cytotoxic activity differs for the Cu complexes and the corresponding free ligands, but for longer incubation times (e.g., 72 h), all compounds display similar activity. Combining the use of several spectroscopic, spectrometric, and electrochemical techniques, the speciation of Cu-phen compounds in cell incubation media is evaluated, indicating that the originally added complex almost totally decomposed and that Cu(II) and phen are mainly bound to bovine serum albumin. Several methods are used to disclose relationships between structure, activity, speciation in incubation media, cellular uptake, distribution of Cu in cells, and cytotoxicity. Contrary to what is reported in most studies, we conclude that interaction with cell components and cell death involves the separate action of Cu ions and phen molecules, not [Cu(phen)_n] species. This conclusion should similarly apply to many other Cu-ligand systems reported to date.

Decarboxylative sp3 C-N coupling via dual copper and photoredox catalysis

Over the past three decades, considerable progress has been made in the development of methods to construct sp2 carbon-nitrogen (C-N) bonds using palladium, copper or nickel catalysis1,2. However, the incorporation of alkyl substrates to form sp3 C-N bonds remains one of the major challenges in the field of cross-coupling chemistry. Here we demonstrate that the synergistic combination of copper catalysis and photoredox catalysis can provide a general platform from which to address this challenge. This cross-coupling system uses naturally abundant alkyl carboxylic acids and commercially available nitrogen nucleophiles as coupling partners. It is applicable to a wide variety of primary, secondary and tertiary alkyl carboxylic acids (through iodonium activation), as well as a vast array of nitrogen nucleophiles: nitrogen heterocycles, amides, sulfonamides and anilines can undergo C-N coupling to provide N-alkyl products in good to excellent efficiency, at room temperature and on short timescales (five minutes to one hour). We demonstrate that this C-N coupling protocol proceeds with high regioselectivity using substrates that contain several amine groups, and can also be applied to complex drug molecules, enabling the rapid construction of molecular complexity and the late-stage functionalization of bioactive pharmaceuticals.

Catalytic fixation of atmospheric carbon dioxide by copper(ii) complexes of bidentate ligands

The copper(ii) complexes of simple bidentate ligands have shown selective fixation and sequestration of atmospheric CO₂. The fixation of CO₂ proceeds via copper(i) species and geometrical interconversions and afforded CO₃²⁻ bound complexes.

Antiproliferative activity and QSAR study of copper(II) mixed chelate [Cu(N-N)(acetylacetonato)]NO3 and [Cu(N-N)(glycinato)]NO3 complexes, (Casiopeínas)

Mixed chelate copper(II) complexes patented and mark title registered as Casiopeínas are antineoplastic agents with general formulas [Cu(N-N)(alpha-l-amino acidato)]NO(3) and [Cu(N-N)(O-O)]NO(3), where the N-N donor is an aromatic substituted diimine (1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy)) and the O-O donor is acetylacetonate (acac) or salicylaldehydate (salal). In the present work, the series of complexes [Cu(N-N)(acac)]NO(3) and [Cu(N-N)(gly)]NO(3) with several substituents on the diimine ligand were selected to perform a quantitative structure-activity relationship (QSAR) study. Two main analysis were performed: (1) the study of the influence of the substituents on diimine ligand on physicochemical properties such as half-wave potential (E(1/2)) and their relationship with medial lethal dose (LD50) or medial inhibitory concentration (IC50) on several tumor cell lines and (2) the study of the influence of the secondary ligand when acac is changed for glycinate (gly). Results showed that the presence of the central fused aromatic ring in the phen containing complexes is necessary to preserve the antiproliferative activity. The QSAR equations showed a strong relationship between the IC50 and E(1/2); the most active complexes are the weaker oxidants. The change of secondary ligand from acac to gly has less influence on biological activity than the changes on the diimine ligand.

Synthesis and spectroelectrochemical studies of mixed heteroleptic chelate complexes of ruthenium(II) with 1,8-bis(2-pyridyl)-3,6-dithiaoctane (pdto) and substituted 1,10-phenanthrolines

Reaction of dichlorotris(triphenylphosphine) ruthenium(II) [RuCl(2)(PPh(3))(3)] with 1,8-bis(2-pyridyl)-3,6-dithiaoctane (pdto), a (N(2)S(2)) tetradentate donor, yields a new compound [Ru(pdto)(PPh(3))Cl]Cl (1), which has been fully characterized. (1)H and (31)P NMR studies of 1 in acetonitrile at several temperatures show the substitution of both coordinated chloride and triphenylphosphine with two molecules of acetonitrile, as confirmed by the isolation of the complex [Ru(pdto)(CH(3)CN)(2)]Cl(2) (2). Cyclic voltammetric and spectroelectrochemical techniques allowed us to determine the electrochemical behavior of compound 1. The substitution of the chloride and triphenylphosphine by acetonitrile molecules in the Ru(II) coordination sphere of compound 1 was also established by electrochemical studies. The easy substitution of this complex led us to use it as starting material to synthesize the substituted phenanthroline coordination compounds with (pdto) and ruthenium(II), [Ru(pdto)(4,7-diphenyl-1,10-phenanthroline)]Cl(2).4H(2)O (3), [Ru(pdto)(1,10-phenanthroline)]Cl(2).5H(2)O (4), [Ru(pdto)(5,6-dimethyl-1,10-phenanthroline)]Cl(2).5H(2)O (5), [Ru(pdto)(4,7-dimethyl-1,10-phenanthroline)]Cl(2).3H(2)O (6), and [Ru(pdto)(3,4,7,8-tetramethyl-1,10-phenanthroline)]Cl(2).4H(2)O (7). These compounds were fully characterized, and the crystal structure of 4 was obtained. Cyclic voltammetric and spectroelectrochemical techniques allowed us to determine their electrochemical behavior. The electrochemical oxidation processes in these compounds are related to the oxidation of ionic chlorides, and to the reversible transformation from Ru(II) to Ru(III). On the other hand, a single reduction process is associated to the reduction of the substituted phenanthroline in the coordination compound. The E(1/2) (phen/phen(-)) and E(1/2) (Ru(II)/Ru(III)) for the compounds (3-7) were evaluated, and, as expected, the modification of the substituted 1,10-phenanthrolines in the complexes also modifies the redox potentials. Correlations of both electrochemical potentials with pK(a) of the free 1,10-phenathrolines, lambda(max) MLCT transition band, and chemical shifts of phenanthrolines in these complexes were found, possibly as a consequence of the change in the electron density of the Ru(II) and the coordinated phenanthroline.

A density functional study of the reactivity and stability of mixed copper complexes. Is hardness the reason?

Mixed-ligand Cu2+ ternary complexes, formed by an aromatic diimine and a second ligand with O donor atoms, show a higher than expected stability. To understand the factors affecting the stability of these systems, we performed a density functional study of [Cu(H2O)5]2+, [Cu(N-N)(H2O)3]2+, and [Cu(N-N)(O-O)H2O] (N-N is 1,10-phenanthroline, 5-nitro-1,10-phenanthroline, or 3,4,7,8-tetramethyl-1,10-phenanthroline; and O-O is oxalate). In the present study, full geometry optimization (B3LYP/3-21G**) has been performed without symmetry constraints and a comparison with some available experimental results has been made. Bond distances, equilibrium geometries, harmonic frequencies, and net atomic charges from Mulliken populations are presented. Since the principle of hard and soft acids and bases has been widely used to explain the stability of these complexes, we also calculated and analyzed the global hardness and the local softness. The results of the global hardness do not support the commonly held idea that harder acids will preferably bind to harder ligands, while softer acids will bind to softer ligands. Interestingly, local softness and electron affinity correlate well with the formation constants of these compounds and provide an explanation of the reactivity behavior. The present results may help to rationalize the stability and reactivity of these systems.

An electron spin resonance study and antimicrobial activity of copper(II)-phenanthroline complexes

The antimicrobial activities of some copper(II) binary complexes with unsubstituted and different substituted phenanthroline ligands were investigated. A considerable increase in the biocidal activity of the ligands on being coordinated with the copper(II) ions was observed in terms of their minimum inhibitory concentration (MIC) values. EPR measurements were performed at room and low temperature with the aim of gaining an insight into the structure/activity relationship of these complexes. Subtle differences in the chemical arrangement result in appreciable differences in the antimicrobial activity. Copper(II) complexes with 2,9-dimethyl derivative phenanthrolines were observed to be more active against Staphylococcus aureus and Escherichia coli.