Synthesis, Structure, and Spectroscopic and Electrochemical Properties of Copper(II/I) Complexes with Symmetrical and Unsymmetrical 2,9-Diaryl-1,10-phenanthroline Ligands

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.

Red Light-Based Dual Photoredox Strategy Resembling the Z-Scheme of Natural Photosynthesis

Photoredox catalysis typically relies on the use of single chromophores, whereas strategies, in which two different light absorbers are combined, are rare. In photosystems I and II of green plants, the two separate chromophores P₆₈₀ and P₇₀₀ both absorb light independently of one another, and then their excitation energy is combined in the so-called Z-scheme, to drive an overall reaction that is thermodynamically very demanding. Here, we adapt this concept to perform photoredox reactions on organic substrates with the combined energy input of two red photons instead of blue or UV light. Specifically, a Cu^I bis(α-diimine) complex in combination with in situ formed 9,10-dicyanoanthracenyl radical anion in the presence of excess diisopropylethylamine catalyzes ca. 50 dehalogenation and detosylation reactions. This dual photoredox approach seems useful because red light is less damaging and has a greater penetration depth than blue or UV radiation. UV-vis transient absorption spectroscopy reveals that the subtle change in solvent from acetonitrile to acetone induces a changeover in the reaction mechanism, involving either a dominant photoinduced electron transfer or a dominant triplet-triplet energy transfer pathway. Our study illustrates the mechanistic complexity in systems operating under multiphotonic excitation conditions, and it provides insights into how the competition between desirable and unwanted reaction steps can become more controllable.

Non-Symmetrical Sterically Challenged Phenanthroline Ligands and Their Homoleptic Copper(I) Complexes with Improved Excited-State Properties

A strategy is presented to improve the excited state reactivity of homoleptic copper-bis(diimine) complexes CuL₂ ⁺ by increasing the steric bulk around Cu^I whereas preserving their stability. Substituting the phenanthroline at the 2-position by a phenyl group allows the implementation of stabilizing intramolecular π stacking within the copper complex, whereas tethering a branched alkyl chain at the 9-position provides enough steric bulk to rise the excited state energy E⁰⁰ . Two novel complexes are studied and compared to symmetrical models. The impact of breaking the symmetry of phenanthroline ligands on the photophysical properties of the complexes is analyzed and rationalized thanks to a combined theoretical and experimental study. The importance of fine-tuning the steric bulk of the N-N chelate in order to stabilize the coordination sphere is demonstrated. Importantly, the excited state reactivity of the newly developed complexes is improved as demonstrated in the frame of a reductive quenching step, evidencing the relevance of our strategy.

Synthesis and characterisation of homoleptic 2,9-diaryl-1,10-phenanthroline copper(i) complexes: influencing selectivity in photoredox-catalysed atom-transfer radical addition reactions

Novel bis(2,9-diaryl-1,10-phenanthroline)copper(i) complexes were prepared to study a photoredox-catalysed reaction.

Colorimetric and fluorescent chemosensor for highly selective and sensitive relay detection of Cu2+ and H2PO4- in aqueous media

In this manuscript, a new colorimetric and fluorescent chemosensor (T) was designed and synthesized, it could successively detect Cu²⁺ and H₂PO₄^- in DMSO/H₂O (v/v=9:1, pH=7.2) buffer solution with high selectivity and sensitivity. When added Cu²⁺ ions into the solution of T, it showed a color changes from yellow to colorless, meanwhile, the green fluorescence of sensor T quenched. This recognition behavior was not affected in the presence of other cations, including Hg²⁺, Ag⁺, Ca²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺, and Mg²⁺ ions. More interestingly, the Cu²⁺ ions contain sensor T solution could recover the color and fluorescence upon the addition of H₂PO₄^- anions in the same medium. And other surveyed anions (including F^-, Cl^-, Br^-, I^-, AcO^-, HSO₄^-, ClO₄^-, CN^- and SCN^-) had nearly no influence on the recognition behavior. The detection limits of T to Cu²⁺ and T-Cu²⁺ to H₂PO₄^- were evaluated to be 1.609×10^-8M and 0.994×10^-7M, respectively. In addition, the sensor T also could be served as a recyclable component and the logic gate output was also defined in sensing materials. The test strips based on sensor T were fabricated, which acted as a convenient and efficient Cu²⁺ and H₂PO₄^- test kits.

Copper (II) complexes possessing alkyl-substituted polypyridyl ligands: Structural characterization and in vitro antitumor activity

In an effort to find alternatives to the antitumor drug cisplatin, a series of copper (II) complexes possessing alkyl-substituted polypyridyl ligands have been synthesized. Eight new complexes are reported herein: μ-dichloro-bis{2,9-di-sec-butyl-1,10-phenanthrolinechlorocopper(II)} {[(^di-sec-butylphen)ClCu(μ-Cl)₂CuCl(^di-sec-butylphen)]}(1), 2-sec-butyl-1,10-phenanthrolinedichlorocopper(II) {^{[mono-sec-butyl}phen) CuCl₂} (2), 2,9-di-n-butyl-1,10-phenanthrolinedichlorocopper(II) {[^di-n-butylphen) CuCl₂}(3), 2-n-butyl-1,10-phenanthrolinedichlorocopper(II) {[^mono-n-butylphen) CuCl₂} (4), 2,9-di-methyl-1,10-phenanthrolineaquadichlorocopper(II) {[^di-methylphen) Cu(H₂O)Cl₂}(5), μ-dichloro-bis{6-sec-butyl-2,2'-bipyridinedichlorocopper(II)} {(^{mono-sec-butyl}bipy) ClCu(μ-Cl)₂CuCl(^{mono-sec-butyl}bipy)} (6), 6,6'-di-methyl-2,2'-bipyridinedichlorocopper(II) {^{6,6'-di-methyl}bipy) CuCl₂} (7), and 4,4'-dimethyl-2,2'-bipyridinedichlorocopper(II) {^{4,4'-di-methyl}bipy) CuCl₂} (8). These complexes have been characterized via elemental analysis, UV-vis spectroscopy, and mass spectrometry. Single crystal X-ray diffraction experiments revealed the complexes synthesized with the ^di-sec-butylphen ligand (1) and ^{mono-sec-butyl}bipy ligand (6) crystallized as dimers in which two copper(II) centers are bridged by two chloride ligands. Conversely, complexes 2, 7, and 8 were isolated as monomeric species possessing distorted tetrahedral geometries, and the [(^di-methylphen)Cu(H₂O)Cl₂] (5) complex was isolated as a distorted square pyramidal monomer possessing a coordinating aqua ligand. Compounds 1-8 were evaluated for their in vitro antitumor efficacy. Compounds 1, 5, and 7 in particular were found to exhibit remarkable activity against human derived lung cancer cells, yet this class of copper(II) compounds had minimal cytotoxic effect on non-cancerous cells. In vitro control experiments indicate the activity of the copper(II) complexes most likely does not arise from the formation of CuCl₂ and free polypyridyl ligand, and preliminary solution state studies suggest these compounds are generally stable in biological buffer. The results presented herein suggest further development of this class of copper-based drugs as potential anti-cancer therapies should be pursued.

A trefoil knotted polymer produced through ring expansion

A synthetic strategy is reported for the production of a trefoil knotted polymer from a copper(I)-templated helical knot precursor through ring expansion. The expected changes in the properties of the knotted polymer compared to a linear analogue, for example, reduced hydrodynamic radius and lower intrinsic viscosity, together with an atomic force microscopy (AFM) image of individual molecular knots, confirmed the formation of the resulting trefoil knotted polymer. The strategies employed here could be utilized to enrich the variety of available polymers with new architectures.

Polymeric catenanes synthesized via “click” chemistry and atom transfer radical coupling

A novel route for the synthesis of polymeric catenanes was domonstrated by grafting to strategy via CuAAC reaction followed by ring closure via ATRC. The polymeric catenane was characterized by GPC and AFM imaging.

In-house and synchrotron X-ray diffraction studies of 2-phenyl-1,10-phenanthroline, protonated salts, complexes with gold(III) and copper(II), and an orthometallation product with palladium(II)

Different salts of the 2-phenyl-1,10-phenanthrolin-1-ium cation, (pnpH)(+), are obtained by reacting 2-phenyl-1,10-phenanthroline (pnp), C18H12N2, (I), with a variety of anions, such as hexafluoridophosphate, C18H13N2(+)·PF6(-), (II), trifluoromethanesulfonate, C18H13N2(+)·CF3SO3(-), (III), tetrachloridoaurate, (C18H13N2)[AuCl4], (IV), and bromide (as the dihydrate), C18H13N2(+)·Br(-)·2H2O, (V). Compound (I) crystallizes with Z' = 2, with both independent molecules adopting a coplanar conformation. In (II)-(IV), a hydrogen bond exists between the cation and anion, while one of the lattice water molecules serves as a hydrogen-bonded bridge between the cation and anion in (V). Reaction of (I) with HAuCl4 gives the salt complex (IV); however, reaction with KAuCl4 produces the monodentate complex trichlorido(2-phenyl-1,10-phenanthroline-κN(10))gold(III), [AuCl3(C18H12N2)], (VI). Dichlorido(2-phenyl-1,10-phenanthroline-κ(2)N,N')copper(II), [CuCl2(C18H12N2)], (VII), results from the reaction of CuCl2·2H2O and (I), in which the Cu(II) center adopts a tetrahedrally distorted square-planar geometry. The pendent phenyl ring twists to a bisecting position relative to the phenanthroline plane. The square-planar Pd(II) complex, bromido[2-(phenanthrolin-2-yl)phenyl-κ(3)C(1),N,N']palladium(II), [PdBr(C18H11N2)], (VIII), is obtained from the reaction of (I) with [PdCl2(cycloocta-1,5-diene)], followed by addition of bromine. A coplanar geometry for the pendent ring is adopted as a result of the tridentate bonding motif.

Stability of disubstituted copper complexes in the gas phase analyzed by electrospray ionization mass spectrometry

A series of nitrogen ligand (L)/copper complexes of the type [Cu(I)L](+), [Cu(II)L(X)](+) and [Cu(I)L(2)](+) (X = Cl(-), BF(4) (-), acac(-), CH(3)COO(-) and SO(3)CF(3) (-)) was studied in the gas phase by electrospray ionization mass spectrometry. The following ligands (L) were employed: 1,12-diazaperylene (dap), 1,1'-bisisoquinoline (bis), 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 2,11-disubstituted 1,12-diazaperylenes (dap), 3,3'-disubstituted 1,1'- bisisoquinoline (bis), 5,8-dimethoxy-substituted diazaperylene (meodap), 6,6'- dimethoxy-substituted bisisoquinoline (meobis) and 2,9-dimethyl-1,10-phenanthroline (dmphen). Collision-induced decomposition measurements were applied to evaluate the relative stabilities of the different copper complexes. The influence of the spatial arrangement of the ligands, of the type of substituents and of the counter ion of the copper salts employed for the complexation was examined. Correlations were found between the binding constants of the [ML(2)](+) complexes in solution and the relative stabilities of the analogous complexes in the gas phase. Furthermore, complexation with the ligands 2,11-dialkylated 1,12-diazaperylenes [alkyl = ethyl (dedap) and isopropyl (dipdap)] was studied in the solvents CH(3)OH and CH(3)CN.