Effect Of Ancillary Ligands Research Articles

The effect of ancillary ligands on hydrocarbon C-H bond functionalization by uranyl photocatalysts.

The aqueous uranyl dication has long been known to facilitate the UV light-induced decomposition of aqueous VOCs (volatile organic compounds), via the long-lived highly efficient, uranyl excited state. The lower-energy visible light excited uranyl ion is also able to cleave unactivated hydrocarbon C-H bonds, yet the development of this reactivity into controlled and catalytic C-H bond functionalization is still in its infancy, with almost all studies still focused on uranyl nitrate as the precatalyst. Here, hydrocarbon-soluble uranyl nitrate and chloride complexes supported by substituted phenanthroline (Ph2phen) ligands are compared to each other, and to the parent salts, as photocatalysts for the functionalization of cyclooctane by H atom abstraction. Analysis of the absorption and emission spectra, and emission lifetimes of Ph2phen-coordinated uranyl complexes demonstrate the utility of the ligand in light absorption in the photocatalysis, which is related to the energy and kinetic decay profile of the uranyl photoexcited state. Density functional theory computational analysis of the C-H activation steps in the reaction show how a set of dispersion forces between the hydrocarbon substrate and the Ph2phen ligand provide control over the H atom abstraction, and provide predictions of selectivity of H atom abstraction by the uranyl oxo of the ring C-H over the ethyl C-H in an ethylcyclohexane substrate.

Computational Insights into the Influence of Ligands on Hydrogen Generation with [Cp*Rh] Hydrides.

This work reports a computational investigation of the effect of ancillary ligands on the activity of an Rh catalyst for hydrogen evolution based on the [Cp*Rh] motif (Cp* = η5-pentamethylcyclopentadienyl). Specifically, we investigate why a bipyridyl (bpy) ligand leads to H2 generation but diphenylphosphino-based (dpp) ligands do not. We compare the full ligands to simplified models and systematically vary structural features to ascertain their effect on the reaction energy of each catalytic step. The calculations based on density functional theory show that the main effect on reactivity is the choice of linker atom, followed by its coordination. In particular, P stabilizes the intermediate Rh-hydride species by donating electron density to the Rh, thus inhibiting the reaction toward H2 generation. Conversely, N, a more electron-withdrawing center, favors H2 generation at the price of destabilizing the hydride intermediate, which cannot be isolated experimentally and makes determining the mechanism of this reaction more difficult. We also find that the steric effects of bulky substituents on the main ligand scaffold can lead to large effects on the reactivity, which may be challenging to fine-tune. On the other hand, structural features like the bite angle of the bidentate ligand have a much smaller impact on reactivity. Therefore, we propose that the choice of linker atom is key for the catalytic activity of this species, which can be further fine-tuned by a proper choice of electron-directing groups on the ligand scaffold.

Effects of ancillary ligands in acceptorless benzyl alcohol dehydrogenation mediated by phosphine-free cobalt complexes

Effects of ancillary ligands in acceptorless benzyl alcohol dehydrogenation mediated by phosphine-free cobalt complexes

Augmentation of photophysical features and Judd-Ofelt analysis of extensively green glowing terbium (III) complexes with nitrogen donor ancillary ligands.

Six green glowing terbium (III) complexes were fabricated via grinding method utilizing a prime organic ligand (L) and nitrogen donor ancillary ligands. Characterization of synthesized complexes was accomplished through various spectroscopic techniques. The significant thermal stability was determined by thermogravimetric analysis while the energy bandgap and Urbach energy were investigated through diffused reflectance spectra of these complexes. The peak observed at 548nm in emission spectra is responsible for the virescent color of these complexes. Color purity, decay time, quantum yield, and emission intensities of ternary complexes were significantly improved as compared to binary ones due to the synergistic effect of ancillary ligands. Judd-Ofelt parameters were determined by the NIR absorption spectrum, which claims the asymmetric environment around the terbium (III) ion. CCT values advocate the applicability of these complexes in green light-emitting materials as a cool light source. The biological assignments reveal the significance of these complexes as potent antioxidants and antimicrobial agents. The energy transfer process highlights the enhancement of luminescence in these complexes via the synergic effect of ligands. Our investigation portrays that these complexes can be employed in laser technology, display devices, semiconductors, biological fields, and optoelectronic devices.

Synthesis of Carbene-Metal-Amido (CMA) Complexes and Their Use as Precatalysts for the Activator-Free, Gold-Catalyzed Addition of Carboxylic Acids to Alkynes.

A straightforward synthetic protocol leading to carbene-metal-amido (CMA) complexes (metal=Au, Cu) using a mild base and an environmentally desirable solvent (EtOH) has been explored, with a focus on complexes bearing backbone-substituted N-heterocyclic carbene (NHC) ligands, including BIAN-NHCs (BIAN=bis(imino)acenaphthene). The novel CMAs were structurally characterized, and gold-based CMAs bearing diverse NHCs were screened as simple, Brønsted-basic precatalysts. The readily accessible complexes display high catalytic activity in the intermolecular and intramolecular hydrocarboxylation of internal alkynes and alkynoic acids respectively, while the screening reveals the ancillary ligand effect of NHCs in these catalytic systems.

Ancillary ligand effects and microwave‐assisted enhancement on the catalytic performance of cationic ruthenium(II)‐CNC pincer complexes for acceptorless alcohol dehydrogenation

The application of cationic Ru(II)‐CNC pincer complexes [Ru(CNC)(CO)(PPh3)Cl]PF6 (1), [Ru(CNC)(PPh3)2Cl]PF6 (2), [Ru(CNC)(η2:η2‐COD)Cl]PF6 (4), and [Ru(CNC)(DMSO)2Cl]PF6 (5) in acceptorless dehydrogenation of alcohols is reported under conventional “oil‐bath” and microwave heating conditions. The effect of different ancillary ligands (CO, PPh3, COD, and DMSO) have been demonstrated during catalysis. Complexes with more π‐acid ligands CO and COD perform better compared with those with PPh3 and DMSO ligands. A plausible mechanism is proposed based on NMR and mass investigation during the catalysis. The catalytic performance matches with the order of trans effect among the four ancillary ligands studied in these complexes. Further, a significant reduction in reaction time, as well as reaction temperature, was observed for catalytic reactions under the microwave‐assisted reaction compared with the oil‐bath heating reaction.

Gold-Aluminyl and Gold-Diarylboryl Complexes: Bonding and Reactivity with Carbon Dioxide.

The unconventional carbon dioxide insertion reaction of a gold-aluminyl [tBu3PAuAl(NON)] complex has been recently shown to be related to the electron-sharing character of the Au–Al bond that acts as a nucleophile and stabilizes the insertion product through a radical-like behavior. Since a gold-diarylboryl [IPrAuB(o-tol)2] complex with similar reactivity features has been recently reported, in this work we computationally investigate the reaction of carbon dioxide with [LAuX] (L = phosphine, N-heterocyclic carbene (NHC); X = Al(NON), B(o-tol)2) complexes to get insights into the Al/B anionic and gold ancillary ligand effects on the Au–Al/B bond nature, electronic structure, and reactivity of these compounds. We demonstrate that the Au–Al and Au–B bonds possess a similar electron-sharing nature, with diarylboryl complexes displaying a slightly more polarized bond as Au(δ+)–B(δ–). This feature reduces the radical-like reactivity toward CO2, and the Al/B anionic ligand effect is found to favor aluminyls over boryls, despite the greater oxophilicity of B. Remarkably, the ancillary ligand of gold has a negligible electronic trans effect on the Au–X bond and only a minor impact on the formation of the insertion product, which is slightly more stable with carbene ligands. Surprisingly, we find that the modification of the steric hindrance at the carbene site may exert a sizable control over the reaction, with more sterically hindered ligands thermodynamically disfavoring the formation of the CO2 insertion product.

Effect of N-donor ancillary ligand on zinc/cadmium-organic arsonates: Structural analysis and photoluminescence

The design and construction of metal organic frameworks (MOFs) or coordination polymers (CPs) with tunable structures is of great interest in recent years, owing to their intriguing structural diversity and potential applications. The mixed-ligand approach is widely used as an effective synthesis method to fabricate CPs. By precise regulation of the structure of N-donor co-ligands, in this work, a series of zinc/cadmium-organic arsonates are successfully synthesized, namely, [Zn2(OH)(L-As)(4,4′-Bipy)⋅H2O]n (1), [Zn3(L-As)2(2,2′-Bipy)(H2O)2⋅2H2O]n (2), [Cd(HL-As)(4,4′-Bipy)0.5]n (3), [Cd(HL-As)(2,2′-Bipy)(H2O)⋅H2O]n (4) (H3L-As ​= ​2-(carboxymethylamino)phenylarsonic acid; 4,4′-Bipy ​= ​4,4′-bipyridine; 2,2′-Bipy ​= ​2,2′-bipyridine). We demonstrate that N-donor co-ligands significantly affect the coordination environment of metal centers and the structure of these compounds. Compound 1 is a three-dimension (3D) hydrogen-bond network via C–H···π interactions between the aromatic rings of L-As ligand, whereas 3 exhibits a 3D framework with 6-connected pcu topological network. By contrast, 2 and 4 are two-dimension (2D) layered structures by adopting chelated 2,2′-Bipy Co-ligand. All compounds display a luminescence from ligand-to-metal charge transfer (LMCT) which depends on the coordination environment of metal centers. The results show that N-donor co-ligands can effectively regulate the structures and luminescent properties of the formed CPs.

Effect of ancillary ligand on the photoluminescent and electroluminescent properties of blue Ir(III) complexes bearing main bipyridine ligand

Homoleptic and heteroleptic cyclometalated blue iridium(III) complexes, namely, 1 and 2, incorporating 2′,6′-dimethoxy-5-trimethylsilyl-2,3′-bipyridine (OMe2py-TMSpy) as the main ligand and acetylacetonate (acac) as the ancillary ligand, are developed for the comparison of their structure, photophysical properties, and electroluminescent characteristics. Both 1 and 2 exhibit distorted octahedral geometries around the iridium center, and the aspect ratios are 1.0 for 1 and 0.76 for 2, respectively. The interatomic contacts involving hydrogen bond interactions (H···N/O) in 1 are greater than those in 2, based on Hirshfeld surface analysis. TD-DFT calculations reveal that the electronic transition for 1 may be attributed to intra-ligand charge transfer (ILCT, πbpy−π*bpy) mixed with metal-to-ligand charge transfer (MLCT, Ird−π*bpy), while for 2, it is attributed to the combination of ILCT/MLCT and additional ligand-to-ligand charge transfer (LLCT, πacac−π*bpy). Owing to the introduction of the ancillary ligand, the emission of complex 2 is red-shifted by only 6 nm compared to complex 1. However, the photoluminescent quantum efficiency of 2 is higher than that of 1 owing to the high radiative decay rate. Furthermore, phosphorescent organic light-emitting diodes (PhOLEDs) based on 2 achieve a high external quantum efficiency of 26.7%, which is one of the highest performances observed among reported blue PhOLEDs.

Effects of Ancillary Ligands on Deep Red to Near-Infrared Cyclometalated Iridium Complexes.

The design of organometallic compounds with efficient phosphorescence in the deep red to near-infrared portions of the spectrum is a long-standing fundamental challenge. Here we describe a series of heteroleptic bis-cyclometalated iridium complexes with phosphorescence in these low-energy regions of the spectrum. The cyclometalating ligands in this study feature a metalated benzothiophene aryl group substituted with a quinoline, isoquinoline, or phenanthridine heterocycle. Increasing the conjugation on the heterocycle stabilizes the ligand-centered LUMO, decreases the HOMO-LUMO gap, and enables phosphorescence to occur at long wavelengths. These cyclometalating ligands are paired with a variety of electron-rich ancillary ligands, such as dithiocarbamate (dipdtc), β-ketoiminate (acNac), β-diketiminate (NacNac), amidinate (dipba), and hexahydropyrimidopyrimidine (hpp), some of which have significant influences on the phosphorescence wavelength and excited-state dynamics. The syntheses of seven compounds in this series are described, three of which are structurally validated by single-crystal X-ray diffraction. Cyclic voltammetry reveals the effects of ligand modification on the frontier orbital energies. The photophysical properties of all compounds are thoroughly characterized by UV-vis absorption spectroscopy and steady-state photoluminescence at room-temperature and 77 K. Photoluminescence quantum yields and lifetimes of all compounds are reported.

Ancillary ligand effects on α-olefin polymerization catalyzed by zirconium metallocene: a computational study.

The polymerization of α-olefins catalyzed by zirconium metallocene catalyst was systematically studied through experiments and density functional theory (DFT) calculations. Having achieved an agreement between theory and experiment, it was found that the effect of the catalyst ligand on the C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C insertion reaction was significantly greater than that on the β-H elimination reaction. Therefore, the molecular weight of polymers can be increased by improving the activity of the CC insertion. In addition, in comparison with propylene, the chain length of α-olefins can directly affect the stereotacticity of polymerization products, owing to steric hindrance between the polymer chain and monomer.

Understanding the ancillary ligand effect on luminescent cyclometalated Ir(III) complex as a reporter for 2-acetylaminofluorene DNA(AAF-dG) adduct.

Mutagenic agents such as aromatic amines undergo metabolic activation and produce DNA adducts at C8 position of guanine bases. N-2-acetylaminofluorene (AAF) generates different mutational outcomes when placed at G1, G2, and G3 of a NarI sequence (-G1G2CG3CC/T-). These outcomes are dictated by the conformations adopted by these adducts. Detection of such lesions is of considerable interest owing to their hazardous effects. Here, we report the synthesis of three cyclometalated [Ir(L)2dppz]+ complexes (L = 2-phenylpyridine (ppy) 1; benzo[h]quinoline (bhq) 2; 2-phenylquinoline (pq) 3; dppz = dipyrido[3,2-a:2',3'-c]phenazine) and their interaction with AAF adducted NarI DNA. Remarkably, complexes 1 and 2 displayed dominant 3LC transition characteristic of polar environment despite binding to the adducted sites. On the other hand, complex 3 binds to NarI sequences and behaves as a luminescent reporter for AAF-modified DNA. The results reported here emphasize that molecular light switching phenomenon can be stimulated by switching ancillary ligands and might act as potential probes for covalent-DNA defects.

Effect of ancillary ligand on DNA and protein interaction of the two Zn (II) and Co (III) complexes: experimental and theoretical study

In the present work we have developed one mononuclear Zn(II) complex [Zn(L)(H2O)] (Complex 1) by utilizing a tetracoordinated ligand H2L, formed by simple condensation of 2, 2 dimethyl 1,3 diamino propane and 3- ethoxy salicylaldehyde and one newly designed mononuclear Co (III) complex [Co(L)(L1)] (complex 2) by utilizing (H2L) and 3- ethoxy salicylaldehyde(HL1) as an ancillary ligand. The newly developed complex 2 have been spectroscopically characterized. An interesting phenomenon has been noticed that in presence of ancillary ligand, the solubility in buffer solution and the thermal stability of complex 2 comparatively increases than 1. To check the effect of ancillary ligand, present in complex 2 towards the DNA and HSA binding efficacy, both the complexes have been taken into consideration to inspect their binding potentiality with the macromolecules. The ‘on’, ‘off’ fluorescence changes in presence of DNA and HSA, the binding constant values, obtained from electronic spectral titration, iodide induced quenching, competitive binding assay, circular dichroism (CD) spectral titration, time resolved fluorescence experiment unambiguously assure the better binding efficacy of complex 2 with the signal of minor groove binding mode with DNA along with no significant conformational changes of the macromolecules. The strong and spontaneous binding of complex 2 with CT-DNA is further supported by the Isothermal Titration Calorimetry (ITC) study. Furthermore TDDFT calculation of DNA with and without complex 2 significantly authorize the formation of complex 2-DNA adduct during the association. Finally Molecular Docking study properly verifies the experimental findings and provides justified explanation behinds experimental findings.

Understanding the role of ancillary ligands in the interaction of Ru(II) complexes with covalent arylamine-DNA adducts

The interaction between Ru(II) complexes and covalent DNA-arylamine adduct has been studied using steady-state fluorescence spectroscopy. Here, we have used 16-mer NarI sequences with variation in next flanking bases i.e., -CG1G2CG3CX- in which X is either C or T and G is unmodified or N-acetylaminofluorene-dG (AAF-dG). To understand the effect of ancillary ligands, we used three Ru(II) complexes [Ru(phen)2(dppz)]2+ (Ru-1), [Ru(TMP)2(dppz)]2+ (Ru-2)and [Ru(DIP)2(dppz)]2+(Ru-3) [where phen: 1,10-phenanthroline; TMP: 3,4,7,8-tetramethyl-1,10-phenanthroline; DIP: 4,7-diphenyl-1,10-phenanthroline; dppz: dipyrido[3,2-a;2′,3′-c]phenazine]. Steady-state luminescence data shows that all the three complexes exhibit strong luminescence when it binds to AAF-dG adducts compared to unmodified control. The addition of sodium iodide to the binary mixture (Ru-oligo) improves the luminescence differential in G1 and G3 AAF adducts while it is minimal at G2. Competitive binding studies also show that the ancillary ligand in the complex Ru-2 alters the binding towards the adducted site compared to Ru-1 and Ru-3. Overall, the present study reveals that the probing of adducted site by Ru(II) complexes is dictated not only by the conformational heterogeneity of the AAF-dG adduct but ancillary ligands as well.

Structure-Based Relative Energy Prediction Model: A Case Study of Pd(II)-Catalyzed Ethylene Polymerization and the Electronic Effect of Ancillary Ligands.

Rapidly mapping a reaction energy profile to understand the reaction mechanism is of great importance and highly desired for the discovery of new chemical reactions. Herein, a combination of density functional theory (DFT) calculations and regression analysis has been applied to construct quantitative structures-based energy prediction models, considering Pd(II)-catalyzed ethylene polymerization as an example, for rapid construction of the reaction energy profile. It is inspiring that only geometrical parameters of the reaction center of one species are capable of predicting the whole energy profile with high accuracy. The reaction energies of ethylene insertion and β-H elimination, which directly correlate with polymerization activity and the possibility of branch formation, were studied to elucidate the electronic effects of ancillary ligands. Further analyses of these models from the statistical and chemical points of view afforded useful information on the design of the catalyst ligand. The current work is expected to methodologically shed new light on rapidly mapping the energy profile of chemical reactions and further provide useful information for the development of the reactions.

Two-photon absorption characterization and comparison of Au(I) fluorenyl benzothiazole complexes in the visible wavelength regime

We use the two-photon excited fluorescence method to determine the two-photon absorption (2PA) cross sections of three series of (fluorenyl benzothiazole) gold(I) complexes in the visible wavelength range from 570 to 700 nm. We compare the effect of ancillary ligand substitutions on the 2PA magnitudes and find that the ancillary ligand does not drastically affect either the magnitude or the shape of 2PA. Even so, moderate 2PA cross sections were measured that ranged from 10 to 1000 s of GM (Göppert-Mayer, =10-50cm4s/photon), making these types of complexes nonlinear optical materials for two-photon absorbing applications.

Structural Diversity and Argentophilic Interactions in Small Phosphine Silver(I) Thiolate Clusters

AbstractSilver(I) coordination compounds display an interesting geometrical diversity, the possibility of having distinct coordination numbers (typically from 2 to 4) and the capability of forming argentophilic (Ag⋅⋅⋅Ag) interactions. These properties complicate the accurate prediction of structures of silver complexes under certain experimental conditions. In this work, we show how subtle modifications in thiolate and phosphine ligands exert important effects on the nuclearity and geometry of phosphine caped clusters [Ag(SR)]n(n=4, 6 and 8). We rationalize these effects in terms of the electronic environment of silver centers by analyzing the electronic density of the single‐crystal X‐ray structures via the Quantum Theory of Atoms in Molecules (QTAIM) and the Non‐Covalent Interaction (NCI)‐Index. Furthermore, we characterized attractive and repulsive argentophilic contacts by means of the Interacting Quantum Atoms (IQA) energy partition. Our results provide insights on the effects of ancillary ligands in controlling the structure of silver‐thiolate clusters. Such control is relevant towards a bottom‐up approach to the atomic precise construction of higher nuclearity clusters.

Optical Properties of New Terbium(III) Ternary Complexes Containing Anionic 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and Neutral Sensitizers in Solution, Solid and PMMA Thin Films: Intra and Interphase Colour Tuning.

Four new terbium(III) ternary complexes, [Tb(fod)3 (indazole)] (1), [Tb(fod)3 (tptz)] (2), [Tb(fod)3 (impy)] (3) and [Tb(fod)3 (tppo)2 ] (4) with 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, (Hfod) and N and O donors are synthesized and structurally characterized. The photoluminescence of the complexes are studied in solid, chloroform solution and thin PMMA hybrid films (PMMA is a poly(methyl methacrylate)). The ligand-based emission is dominant in solution of 3 and 4. The effect of ancillary ligands on the photoluminescence of terbium(III) ion is investigated. The mechanism of energy transfer is discussed and correlates the luminescence of acceptor terbium ion with the triplet state energy level of donor ligands. Among the four complexes studied, the luminescence from 1 is most intense followed by 2, 4 and 3. The Commission International de I'Eclairage (CIE) color coordinates of these complexes are calculated and presented. The complexes 3 and 4 show intraphase color tuning when excited under different UV wavelengths. The emission color of [Tb(fod)3 (tppo)2 ] (4) changes from pure blue to turquoise green via almost pure white under 360, 328 and 280nm UV excitation wavelengths respectively. The [Tb(fod)3 (impy)] (3) show similar results. The complex [Tb(fod)3 (tptz)] (2) displays interphase color tuning from yellow (solution) to turquoise green (solid) and fascinatingly incorporation of complex in PMMA polymer generates white light under same excitation wavelength (360nm).

Ancillary ligand effect with methyl and t-butyl for deep blue and high EQE blue phosphorescent organic light-emitting diodes

Novel phosphorescent emitters, FIr4mpic and FIr4tpic were designed and prepared synthetically to improve the chromaticity and emission efficiency of FIrpic, one of the main blue phosphor. Apparently, methyl and tert-butyl on 4-position of picolinic acid of FIrpic were installed attaining FIr4mpic and FIr4tpic, respectively. With these new ancillary ligand-tuned cyclometalated iridium(III) complexes, phosphorescent organic light-emitting diodes (PHOLEDs) devices were constructed. The ultraviolet–visible (UV–vis) and photoluminescence (PL) spectra of FIr4mpic and FIr4tpic were similar to those of FIrpic; however, in terms of their electroluminescent properties, higher luminance was observed with FIr4mpic device. FIr4mpic and FIr4tpic exhibited deeper blue light emission than that of FIrpic. Once optimized, a maximum external quantum efficiency (EQE) of 18.77% and a maximum current efficiency (CE) of 36.17 cd/A were achieved with the FIr4mpic-based PHOLED. Along with the experimental information we also investigated the electronic properties by means of density functional theory (DFT) calculations being keen to explain the improved quantum yield of FIr4mpic over the other emitters.

Ancillary Ligand Effects on Heteroleptic IrIII Dye in Dye‐Sensitized Photocatalytic CO2 Reduction: Photoaccumulation of Charges on Arylated Bipyridine Ligand and Its Control on Catalytic Performance

Herein, we report the synthesis, and photochemical and -physical properties, as well as the catalytic performance, of a series of heteroleptic IrIII photosensitizers (IrPSs), [Ir(C^N)2 (N^NAryl )]+ , possessing ancillary ligands that are varied with aryl-substituents on bipyridyl unit [C^N=(2-pyridyl)benzo[b]thiophen-3-yl (btp); N^NAryl =4,4'-Y2 -bpy (Y=-Ph or -PhSi(Ph)3 ]. We found that the π-extension of bipyridyl ligand by aryl-substitution put bipyridyl ligand in use as an electron relay unit that performed charge accumulation before delivering to the catalytic center, greatly improving the overall CO2 -to-CO conversion activities. In a typical run, the aryl-substituted IrPS (tBu IrP-PhSi )-sensitized homogeneous systems (IrPS+ReI catalyst) gave a turnover number of 1340 (ΦCO =24.2 %) at the early stage of photolysis (<5 h). This study demonstrates that the π-character modulation on the ancillary bipyridyl ligand is critical for forthcoming catalytic performance.