Diimine Complexes Research Articles

Copolymerization of 1-Decene with Alkyl and Alkenyl Methacrylates Catalyzed by Palladium–diimine Complexes

Copolymerization of 1-Decene with Alkyl and Alkenyl Methacrylates Catalyzed by Palladium–diimine Complexes

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 CuI 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, Structures, Dna-Binding, Cytotoxicity and Molecular Docking of Cubr(Pph3)(Diimine) Complexes

A set of copper(I) complexes with the general formula [CuBr(PPh3)(N^N)] (N^N = 2,2’-bipyridine (1), 1,10-phenanthroline (2), 4,4’-dimethyl-2,2’-bipyridine (3), 4,4’-dimethoxy-2,2’-bipyridine (4), 3-(2-pyridyl)-4,5-diphenyl-1,2,4-triaine (5), 4,7-diphenyl-1,10-phenanthroline (6), 5-nitro-1,10-phenanthroline (7), dipyrido[3,2-a:2',3'-c]phenazine(8)) have been synthesized and characterized by elemental analysis, 31P-NMR spectroscopy and mass spectrometry. The structure of complexes 5 and 7 were confirmed by X-ray crystallography. Complex 5 is the second example to be reported with an unusual 4N-triazine-ligated coordination mode of the 3-(2-pyridyl)-4,5-diphenyl-1,2,4-triazine. Calculated energies of the two possible bidentate modes of the ligand (2N- and 4N-triazine) at the copper center showed no significant difference, rationalizing that with the absence of the steric hindrance effect around the metal center. Preliminary biological studies were conducted, highlighting the effect of the diimine ligands. Complexes 5 and 8 exhibited good cytotoxicity against prostate (PC-3), leukemia (MOLT-4) and breast (MCF-7) cancer cell lines, consistent with the presence of nitrogen heteroatoms and extended delocalized systems correlating with strong cytotoxic performance. Binding affinity studies against ct-DNA and docking studies with B-DNA and MDM2 protein highlighted the strong p interactions of 5 and 8, with the planarity of the diimine ligand of the latter contributing to its better binding and cytotoxicity. The current results afford structural requirements for the design of new copper(I) complexes with enhanced biological/physiochemical properties.

Catalytic Chain Transfer Polymerization to Functional Reactive End Groups for Controlled Free Radical Growth

Alkoxyamine-functionalized silane functions as a chain transfer reagent in ethylene polymerization catalyzed by cationic palladium diimine complexes, without significant adverse effects in producti...

Photophysical and Electrocatalytic Properties of Rhenium(I) Triazole-Based Complexes

A series of [Re(N^N)(CO)3(Cl)] (N^N = diimine) complexes based on 4-(pyrid-2-yl)-1,2,3-triazole (1), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (2), and 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (3) diimine ligands were prepared and their photophysical and electrochemical properties were characterized. The ligand-based reduction wave is shown to be highly sensitive to the nature of the triazole-based ligand, with the peak potential shifting by up to 600 mV toward more positive potential from 1 to 3. All three complexes are phosphorescent in solution at room temperature with λmax ranging from 540 nm (1) to 638 nm (3). Interestingly, the complexes appear to show inverted energy-gap law behaviour (τ = 43 ns for 1 versus 92 ns for 3), which is tentatively interpreted as reduced thermal accessibility of metal-centred (3MC) states from photoexcited metal to ligand charge transfer (3MLCT) states upon stabilisation of the N^N-centred lowest unoccupied molecular orbital (LUMO). The photophysical characterisation, supported by computational data, demonstrated a progressive stabilization of the LUMO from complex 1 to 3, which results in a narrowing of the HOMO–LUMO energy gap (HOMO = highest occupied molecular orbital) across the series and, correspondingly, red-shifted electronic absorption and photoluminescence spectra. The two complexes bearing pyridyl (1) and pyrimidyl (2) moieties, respectively, showed a modest ability to catalyse the electroreduction of CO2, with a peak potential at ca. −2.3 V versus Fc/Fc+. The catalytic wave that is observed in the cyclic voltammograms is slightly enhanced by the addition of water as a proton source.

Improved Photostability of a CuI Complex by Macrocyclization of the Phenanthroline Ligands.

The development of molecular materials for conversion of solar energy into electricity and fuels is one of the most active research areas, in which the light absorber plays a key role. While copper(I)‐bis(diimine) complexes [CuI(L)2]+ are considered as potent substitutes for [RuII(bpy)3]2+, they exhibit limited structural integrity as ligand loss by substitution can occur. In this article, we present a new concept to stabilize copper bis(phenanthroline) complexes by macrocyclization of the ligands which are preorganized around the CuI ion. Using oxidative Hay acetylene homocoupling conditions, several CuI complexes with varying bridge length were prepared and analyzed. Absorption and emission properties are assessed; rewardingly, the envisioned approach was successful since the flexible 1,4‐butadiyl‐bridged complex does show enhanced MLCT absorption and emission, as well as improved photostability upon irradiation with a blue LED compared to a reference complex.

The effect of group-substitution on the sensitization properties of alkynylrhenium(I) tricarbonyl diimine complexes adsorbed to TiO2(101) film surface: a theoretical study.

A series of dyes are designed by adding the different electron-donating (-CH3, -NH2, -OH) and electron-withdrawing groups (-Br, -Cl, -NO2) to the different ancillary ligands in the alkynylrhenium(I) tricarbonyl diimine complexes [Re(CO)3(N^N){C≡C-C6H4-CH=C(CN)(COOH)}], where N^N = 1,10-phenanthroline (phen)(1) and then investigated the sensitization properties of dyes linked to the TiO2(101) surface. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to study the electronic structure, frontier molecular orbitals, and absorption spectral properties. The effect of group-substitution on sensitization properties is obvious. When the dye molecules are combined with TiO2(101) surface, not only the absorptions of some sensitizers containing -CH3 or -OH groups have red shift but also the electrons can be directly injected into the TiO2 conduction band from the dye molecules compared with the parent molecular 1. The results indicate that the designed dyes containing electron-donating groups have smaller energy gaps, better light-harvesting efficiency, sufficient driving force, and higher charge transfer efficiency as appropriate dye sensitizers. We hope it can provide valuable hints so that we can design more efficient dye sensitizers in DSSCs.

Synthesis and Photochemical Properties of Manganese(I) Tricarbonyl Diimine Complexes Bound to Tetrazolato Ligands

Ten manganese(I) tricarbonyl diimine complexes bound to variably functionalised 5‐aryl‐tetrazolato ligands were prepared, and their photochemical properties were investigated. Upon exposure to light at 365 nm, each complex decomposed to its free diimine and tetrazolato ligands, simultaneously dissociating three CO ligands, as evidenced by changes in the IR spectra of the irradiated complexes over time. The anti‐bacterial properties of one of these complexes were tested against Escherichia coli. While the complex displayed no effect on the bacterial growth in the dark, pre‐irradiated solutions inhibited bacterial growth. Comparative studies revealed that the antibacterial properties originate from the presence of free 1,10‐phenanthroline.

A Robust Visible-Light-Harvesting Cyclometalated Ir(III) Diimine Sensitizer for Homogeneous Photocatalytic Hydrogen Production

A cyclometalated Ir(III) diimine complex [Ir(NBI)2(phen)]PF6, NBI = 1,8-naphthalenebenzimidizole and phen = 1,10-phenanthroline, exhibits excellent photostability as a sensitizer in a three-compone...

Cu(i) diimine complexes as immobilised antibacterial photosensitisers operating in water under visible light

A simple complex of copper immobilised on silica exemplifies how lighter transition metal complexes can efficiently kill both Gram-positive and Gram-negative bacteria in water – in some cases in only 15 min – under visible light.

Octahedral copper(ii)-diimine complexes of triethylenetetramine: effect of stereochemical fluxionality and ligand hydrophobicity on CuII/CuI redox, DNA binding and cleavage, cytotoxicity and apoptosis-inducing ability.

Octahedral copper(ii) complexes of the type [Cu(trien)(diimine)](ClO4)2 (1-4), where trien is triethylenetetramine and diimine is 2,2'-bipyridine (1), 1,10-phenanthroline (2), 5,6-dimethyl-1,10-phenanthroline (3), and 3,4,7,8-tetramethyl-1,10-phenanthroline (4), have been isolated. Single crystal X-ray structures of 1 and 2 reveal that the coordination geometry around Cu(ii) is tetragonally distorted octahedral. The stereochemical fluxionality of the complexes illustrates the observed trend in CuII/CuI redox potentials and DNA binding affinity (Kb: 1, 0.030 ± 0.002 < 2, 0.66 ± 0.01 < 3, 1.63 ± 0.10 < 4, 2.27± 0.20 × 105 M-1), determined using absorption spectral titration. All complexes effect oxidative DNA cleavage more efficiently than hydrolytic DNA cleavage. The bpy complex 1 with stereochemical fluxionality lower than its phen analogue 2 shows a higher cytotoxicity against both A549 lung (IC50, 3.3 μM) and MCF-7 human breast (IC50, 3.9 μM) cancer cells, and induces the generation of the highest amount of ROS in A549 cells. Complex 3 with a higher stereochemical fluxionality and higher ligand hydrophobicity exhibits a higher DNA binding and cleavage ability and higher cytotoxicity (IC50, 2.1 μM) towards MCF-7 cells. Complex 4 with a still higher stereochemical fluxionality displays the highest DNA binding and cleavage ability but a lower cytotoxicity towards both A549 and MCF-7 cell lines due to its tendency to form a five-coordinated complex with the uncoordinated amine group. Annexin V.Cy3 staining and immunoblot analysis demonstrate the mechanism of cell death caused by 1 and 2. The finding of the up-regulation of the pro-apoptotic Bax protein and down-regulation of PARP protein in western blot analysis confirms the induction of apoptosis by these complexes.

Activated carbon fibers as a support for nickel diimine complexes and their application in ethylene oligomerization

In this work, we demonstrate the synthesis and characterization of a new class of β-diimine ligand combined with the alkoxysilane group CPTMS ((3-chloropropyl)trimethoxysilane), covalently anchored to the surface of activated carbon fibers (ACF).

Influence of anion variation and cation modification on the packing of tetraazamacrocyclic Au(III) complexes

Abstract The work presents the analysis of the packings of crystal structures of unsaturated tetraazamacrocyclic gold(III) complexes with different anions ([Au(С14H22N4)]X (X = Br (I), ReO4 (II), BPh4 (III), AuBr2 (IV)) and with modified (halogenated [Au(С14Н20N4Y2)]ClO4 (Y = Cl (V), Br (VI), protonated [Au(С14H23N4)](ClO4)2 (VII), [Au(С14H24N4)](H3O)(ClO4)4 (VIII) cations. Crystal-chemical regularities and features of the packings depend on the composition and structure of cations, as well as on the nature and geometry of counter-anions. In the packings of the complexes I–VII whose ligands contain one or two iminate six-membered rings, the 3D supramolecular architecture of the crystal lattice is determined and stabilized by an extensive network of secondary non-covalent intermolecular interactions (non-classical H-bonds C–H…A (A = π, Br, Cl, O, Au) and contacts Au⋯Au (O, N, π); O⋯Cl (Br, N). In the iminate complexes with nonlinear inorganic anions Br−, ClO4−, ReO4−, the main structure-forming role belongs to the cations which are interconnected by non-classical H-bonds C–H…π. The halogenation of iminate rings of the cation and the protonation of one of the rings do not cause profound changes in the packing. In the structures of the complexes with a bulky organic anion BPh4– (III) and with a coordinatively unsaturated linear anion AuBr2− (IV), the decisive role belongs to the anions which prevent the association of cations by forming H-bonds and contacts with them. The linear acceptor-active anion AuBr2− has the greatest influence on the packing of diiminate macrocyclic gold(III) complexes by providing the parquet packing of the structure. The 1D crystal structure of the diprotonated diimine complex VIII is stabilized by classical H-bonds Ow–H...O of the oxonium ion and by the contacts of the central atom of the macrocyclic cation Au⋯O.

Aromatic versus Aliphatic α-Diimine Ligands in Heteroleptic Copper(I) Emitters: Photophysical and Electrochemical Properties.

The electrochemical and photophysical properties of a heteroleptic Cu(I) complex bearing an aliphatic α-diimine ligand, [Cu(dab)(xantphos)]+ (Cu-dab; dab = N,N'-diphenyl-2,3-dimethyl-1,4-diazabutadiene, xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene), were evaluated together with those of complexes [Cu(dmp)(xantphos)]+ (Cu-dmp; dmp = 2,9-dimethyl-1,10-phenanthroline), [Cu(dmbpy)(xantphos)]+ (Cu-dmbpy; dmbpy = 5,5'-dimethyl-2,2'-bipyridine), and [Cu(bq)(xantphos)]+ (Cu-bq; bq = 2,2'-biquinoline), bearing aromatic diimine ligands. Cu-dab exhibited a two-step ligand-centered redox behavior, where the first wave corresponded to an electrochemically reversible one-electron reduction process. Although Cu(I)-aromatic diimine complexes Cu-dmp, Cu-dmbpy, and Cu-bq exhibited obvious luminescence from the metal-to-ligand charge transfer (MLCT) excited state, Cu-dab did not show any luminescence. Computational studies indicated that this non-luminescent property was caused by the large structural relaxation of Cu-dab during photoexcitation.

Asymmetric CuI-Catalyzed Insertion Reaction of 1-Aryl-2,2,2-trifluoro-1-diazoethanes into Si-H Bonds.

An asymmetric copper(I)-catalyzed Si-H insertion reaction of 1-aryl-2,2,2-trifluoro-1-diazoethanes in dimethyl carbonate as a green solvent alternative was developed. A C2-symmetric copper(I) diimine complex enabled the asymmetric insertion reaction to give enantioenriched (1-aryl-2,2,2-trifluoroethyl)silanes with excellent stereoselectivities (up to 98:2 er). Successful conversion of the silanes into the corresponding alcohols was performed with retention of stereochemistry. Mechanistic studies and DFT calculations support the proposed model for the observed stereoselectivities.

A Rare Type of Rhenium(I) Diimine Complexes with Unsupported Coordinated Phosphine Oxide Ligands: Synthesis, Structural Characterization, Photophysical and Theoretical Study

This paper presents synthesis and photophysical investigation of a very rare type of the ReI diimine complexes, [Re(diimine)(CO)3(OPR3)]+, R = Ph, Cy; diimine – phenanthroline and neocuproine, containing monodentate (unsupported) phosphine oxide ligands. The obtained compounds have been structurally characterized in solid phase by using XRD crystallography, which revealed unusual distortions in the pseudo octahedral rhenium environment, which may be ascribed to intramolecular interligand (phosphine oxide – diimine) interaction rather than to crystal packing effect. Optimization of the ground state structure of these molecules with the DFT method also confirmed intramolecular origin of the observed structural peculiarities. The complexes display phosphorescence in solution and in solid state with the quantum yield up to 11 % and 14 %, respectively, which originates from 3MLCT excited state as demonstrated by DFT calculations. Comparative analysis of the ligand (L) effect onto emission energy in the [Re(neocuproine)(CO)3(L)] complexes (L = PPh3, NCMe, OPPh3, Cl–) showed that the position of emission wavelength in the corresponding complexes qualitatively correlates with cumulative donor ability of these ligands that is in complete agreement with the 3MLCT character of emission.

Synthesis, Luminescence, and Structure of a Polymorphic Polyfluorinated Diiodoplatinum(II) Diimine Complex.

PtI2(5,5'-bis(HCF2CH2OCH2)-2,2'-bpy)], 55-2FH-PtI2, is the first example of a substituted fluorinated diiodoplatinum diimine complex that exhibits polymorphism. The complex, upon recrystallization, forms two different polymorphs, denoted as α and β forms. The luminescence of the α and β forms are the same in glassy solution at 77 K; however, in the solid state, they differ significantly. The major difference between them lies in the solid-state packing of the crystalline structure. The α form is a square planar polyfluorinated PtI2-containing complex. Its extended herringbone structure consists of two neighboring stacked bipyridyl planes that do not overlap. The α form emits stronger than its parent molecule, [PtI2bpy], and much stronger than the β polymorph. The β form has a slight tetrahedral distortion about the metal center that ultimately changes the geometry of the complex and decreases the d-orbital splitting from square planar. Furthermore, overlapping bipyridine rings in the extended structure of the β form quench the emission thus resulting in a lower energy emission. Additionally, the β form shows only one type of C-H···O intermolecular stacking interaction that can cause the moderate distortion of the metal core.

Generation of Microsecond Charge-Separated Excited States in Rhenium(I) Diimine Complexes: Driving Force Is the Dominant Factor in Controlling Lifetime.

A transition-metal-based donor-(linker)-acceptor system can produce long-lived charge transfer excited states using visible excitation wavelengths. The ground- and excited-state photophysical properties of a series of [ReCl(CO)3(dppz-(linker)-TPA)] complexes, with varying donor and acceptor energies, have been systematically studied using spectroscopic techniques (both vibrational and electronic) supported by computational chemistry. The long-lived excited state is 3ILCT in nature for all complexes studied, characterized through transient absorption and emission, transient resonance Raman (TR2), and time-resolved infrared (TRIR) spectroscopy and TDDFT calculations. Modulation of the donor and acceptor energies results in changes of the 3ILCT lifetime by 1 order of magnitude, ranging from 6.1(±1) μs when a diphenylamine donor is used to 0.6(±0.2) μs when a triazole linker and triphenylamine donor is used. The excited-state lifetime may be rationalized by consideration of the driving force within the framework of Marcus theory and appears insensitive to the nature of the linker.

Pd-Promoted Copolymerization of Methallyl and Isoprenyl Ethers and Acetate with α-Olefins

1,1-Disubstituted ethylene derivatives with oxygen functionalities, such as methallyl and isoprenyl ethers and acetate, were employed as comonomers with α-olefins catalyzed by Pd–diimine complexes. A mixture of a chloro(methyl)palladium complex with α-diimine ligand having 2,4,6-trimethylphenyl groups at the coordinated N atoms (I) and Na+B{C6H3(CF3)2-3,5}4– catalyzes the copolymerization of 1-decene with methallyl tert-butyl ether (1) at 0 °C to produce copolymers with comonomer content of 9.7 mol %. Methallyl acetate (2) undergoes copolymerization with 1-decene to afford the corresponding copolymers with comonomer content of 1.0 to 3.3 mol %. Nuclear magnetic resonance analyses of the copolymers of 1-decene with 1 and 2 revealed that no significant β-alkoxy or β-acetate elimination takes place during the polymerization and that the insertion mode of the comonomer determines the location of the monomer on either the main chain or the terminal of the copolymer. Related compounds, isoprenyl tert-butyl ether (3), isoprenyl acetate (4), and isoprenyl trimethylsilyl ether (5), undergo copolymerization with 1-decene or 1-hexene to afford the corresponding copolymers with comonomer content of 1.0 to 6.2 mol %. The reaction with a higher concentration of a comonomer results in the formation of polymers with higher comonomer content.

Synthesis and electrochemiluminescence of a new iridium(III) complex

A new water-soluble iridium(III) diimine complex with appended glucose was synthesized and characterized. The photophysical properties and electrogenerated chemiluminescence (ECL) behavior of the complex were studied. The new iridium(III) complex displayed good emission under the UV-light excitation in aqueous solution and gave out the strongest ECL signals on the glass carbon electrode in the presence of high concentration of tri-n-propylamine (TPA, 20 mM) compared to that on Au and Pt electrodes in phosphate buffer (pH = 7.5). But at low concentration of TPA (1.0 mM), the ECL intensity of the complex was close on the GC, Au and Pt electrodes. The ECL of the system had a good linearity with the TPA concentration from 0.1 μM to 1 mM with a limit of determination of 50 nM (S/N = 3).