Coinage Metal Complexes Research Articles

A Configurationally Confined Thermally Activated Delayed Fluorescent Two-Coordinate CuI Complex for Efficient Blue Electroluminescence.

Thermally activated delayed fluorescence (TADF) from linear two-coordinate coinage metal complexes is sensitive to the geometric arrangement of the ligands. Herein we realize the tuning of configuration from coplanar to orthogonal gradually by variation of substituents. In a complex with confined twist configuration, its blue emission peaking at 458 nm presents a high ΦPL of 0.74 and a short τTADF of 1.9 μs, which indicates a fast enough kr,TADF of 3.9×105 s-1 and a depressed knr of 1.4×105 s-1 . Such outstanding luminescent properties are attributed to the proper overlap of HOMO and LUMO on CuI d orbitals that guarantees not only small ΔEST but also sufficient transition oscillator strength for fast . Vacuum-deposited blue OLEDs with either doped or host-free emissive layer present external quantum efficiencies over 20 % and 10 %, respectively, demonstrating the practicality of the configurationally confined strategy for efficient linear CuI TADF emitters.

Novel 1,2,3-triazolyl phosphine with a pyridyl functionality: synthesis, coinage metal complexes, photophysical studies and Cu(I) catalyzed C-O coupling of phenols with aryl bromides.

This manuscript describes the synthesis and coinage metal complexes of pyridine appended 1,2,3-triazolyl-phosphine [2-{(C6H4N)(C2(PPh2)N3C6H5)}] (1), photophysical studies and their catalytic application. The reactions of 1 with copper salts afforded dimeric complexes [{Cu(μ2-X)}2{2-(C6H4N)(C2(PPh2)N3C6H5)}2] (2, X = Cl; 3, X = Br; and 4, X = I). The crystal structure indicates that the Cu⋯Cu distance in 4 (2.694 Å) is significantly shorter than that in complexes 3 (3.0387 Å) and 2 (3.104 Å), indicating strong cuprophilic interactions which is also supported by NBO calculations, signifying the involvement of 3dz2 orbitals from each Cu atom contributing to the bonding interaction. The fluorescence studies on complexes 2-4 carried out in the solid state showed broad emission bands around 560 nm on excitation at λex = 420 nm. Complex 4 on treatment with two equivalents of 1,10-phenanthroline yielded a mononuclear complex 5 which showed almost complete quenching of fluorescence in the solid state, clearly indicating that the emissive properties of 4 are mainly due to the Cu⋯Cu interaction, along with (M + X)LCT. The reactions of 1 with silver salts led to the isolation of dimeric complexes [{Ag(μ2-X)}2{2-(C6H4N)(C2(PPh2)N3C6H5)}2] (6, X = Cl; 7, X = Br; and 8, X = I) in good yield. The reaction between 1 and [AuCl(SMe2)] yielded [{AuCl}{2-(C6H4N)(C2(PPh2)N3C6H5)}] (9). The molecular structures of 2-5 and 7-9 were confirmed by single crystal X-ray analysis. The complex 4 is found to be an excellent catalyst for C-O coupling under mild conditions.

New cationic coinage metal complexes featuring silyl group functionalized phosphine: syntheses, structures and catalytic studies in alkyne-azide cycloaddition reactions.

A series of coinage metal complexes bearing rarely explored ortho-silylated phosphine is reported. The treatment of diphenyl(2-(trimethylsilyl)phenyl)phosphine (1) with CuCl and [Cu(CH3CN)4]BF4 furnished the corresponding neutral [(1)CuCl]2 (2) and mono-cationic [(1)2Cu(CH3CN)]BF4 (3) complexes, respectively. The reactions of 1 with AgX (X = BF4-, NO3-) in 2 : 1 ratio furnished the corresponding mono cationic dicoordinate silver(I) complexes of the type [(1)2Ag]X (X = BF4- (4a), NO3- (4b)). The ortho-silylated phosphine ligand (1) was conveniently converted into the corresponding sulfide (5a) and selenide (5b) species, and their reactions with [Cu(CH3CN)4]BF4 yielded mono-cationic, homoleptic tris(silylphosphinochalcogenide)copper(I) complexes of the type [(5a/5b)3Cu]BF4 (6a/6b). The molecular structures of 2-4 and 6 were established by single-crystal X-ray diffraction analysis. The copper complexes 2, 3, and 6a were employed as catalysts in azide-alkyne cycloaddition reactions. Among these complexes, 3 was extensively used in the preparation of various mono- and bis-triazoles consisting of tolyl, benzyl, carbazolyl, and propargylic ether groups. Three sets of substituted triazole derivatives were achieved under mild conditions by employing copper(I) catalytic systems. The mechanistic studies indicated the formation of a heteroleptic copper(I) triazolide intermediate which was detected by high-resolution mass spectral analysis.

Coinage metal complexes of BN analogues of m-terphenyl ligands.

We report the synthesis of a series of group 11 metal complexes with sterically demanding anionic nitrogen ligands based on the 1,2-azaborinine motif. The ligands, which share structural similarities with m-terphenyls, have been used to stabilize two-coordinate phosphine complexes and dimeric complexes with close contacts between the metal centers. Spectroscopic, crystallographic, and theoretical investigations reveal close parallels to the related m-terphenyl complexes, including metallophilic interactions in the dimers.

Coinage metal complexes of multidentate Pacman phosphane ligands.

We present the extension of Pacman ligands to bidentate phosphane ligands enabling them to bind metals in their sterically protected cavity. The coordination of coinage metals shows the ability of the ligand to adopt different coordination modes by distortion, of which some additionally include the imine nitrogen atoms. Besides the coordinated metal, the substitution on the phosphorus atoms influences the type of coordination.

Finding Design Principles of OLED Emitters through Theoretical Investigations of Zn(II) Carbene Complexes.

In this work, Zn(II) carbene complexes carrying a dianionic 1,2-dithiolbenzene (dtb) or 1,2-diolbenzene (dob) ligand were investigated regarding their suitability as organic light-emitting diode (OLED) emitter. For the optimization of the complexes, density functional-based methods were used and frequency analyses verified the obtained structures as minima. All calculations were carried out including a polarizable continuum model to mimic solvent-solute interactions. Multireference configuration interaction methods were used to determine excitation energies, spin-orbit couplings, and luminescence properties. Rate constants of spin-allowed and spin-forbidden transitions were calculated according to a Fermi golden rule expression. Using carbene ligands with varying σ-donor and π-acceptor strengths, the luminescence is found to be tunable from yellow to orange/red to deep red/near-infrared. The calculated intersystem crossing (ISC) time constants indicate thermally activated delayed fluorescence (TADF) to be the main decay channel. In contrast to many d10 coinage metal complexes, a parallel orientation of dtb or dob and the carbene ligand is found to be highly favorable. For the complexes with a cyclic (alkyl)(amino) carbene (CAAC) or cyclic (amino)(aryl) carbene (CAArC) ligand, the S1 and T1 states have ligand-to-ligand charge-transfer (LLCT) character and are energetically close. The complex with a classical N-heterocyclic carbene (NHC) ligand has S1 and T1 states with mixed ligand-to-metal charge-transfer (LMCT)/LLCT character and is a very rare example in which the zinc ion contributes to the excitation.

Mechanistic Study of Alkyne Insertion into Cu–Al and Au–Al Bonds: A Paradigm Shift for Coinage Metal Chemistry

In this work, the mechanism of the insertion reaction of 3-hexyne into Cu-Al and Au-Al bonds in M-aluminyl (M = Cu, Au) complexes is computationally elucidated. The mechanism is found to be radical-like, with the Cu-Al and Au-Al bonds acting as nucleophiles toward the alkyne, and predicts a less efficient reactivity for the gold-aluminyl complex. The proposed mechanism well rationalizes the kinetic (or thermodynamic) control on the formation of the syn (or anti) insertion product into the Cu-Al bond (i.e., dimetallated alkene) which has been recently reported. A comparative analysis of the electronic structure reveals that the reduced reactivity at the gold site─usually showing higher efficiency than copper as a "standard" electrophile in alkyne activation─arises from a common feature, i.e., the highly stable 6s Au orbital. The relativistic lowering of the 6s orbital, making it more suitable for accepting electron density and thus enhancing the electrophilicity of gold complexes, in the gold-aluminyl system is responsible for a less nucleophilic Au-Al bond and, consequently, a less efficient alkyne insertion. These findings demonstrate that the unconventional electronic structure and the electron-sharing nature of the M-Al bond induce a paradigm shift in the properties of coinage metal complexes. In particular, the peculiar radical-like reactivity, previously shown also with carbon dioxide, suggests that these complexes might efficiently insert/activate other small molecules, opening new and unexplored paths for their reactivity.

Luminescent Complexes of Platinum, Iridium, and Coinage Metals Containing N-Heterocyclic Carbene Ligands: Design, Structural Diversity, and Photophysical Properties.

The employment of N-heterocyclic carbenes (NHCs) to design luminescent metal compounds has been the focus of recent intense investigations because of the strong σ-donor properties, which bring stability to the whole system and tend to push the d-d dark states so high in energy that they are rendered thermally inaccessible, thereby generating highly emissive complexes for useful applications such as organic light-emitting diodes (OLEDs), or featuring chiroptical properties, a field that is still in its infancy. Among the NHC complexes, those containing organic chromophores such as naphthalimide, pyrene, and carbazole exhibit rich emission behavior and thus have attracted extensive interest in the past five years, especially carbene coinage metal complexes with carbazolate ligands. In this review, the design strategies of NHC-based luminescent platinum and iridium complexes with large spin-orbit-coupling (SOC) are described first. Subsequent paragraphs illustrate the recent advances of luminescent coinage metal complexes with nucleophilic- and electrophilic-based carbenes based on silver, gold, and copper metal complexes that have the ability to display rich excited state emissions in particular via thermally activated delayed fluorescence (TADF). The luminescence mechanism and excited state dynamics are also described. We then summarize the advance of NHC-metal complexes in the aforementioned fields in recent years. Finally, we propose the development trend of this fast-growing field of luminescent NHC-metal complexes.

Highly Efficient Au(I) Alkynyl Emitters: Thermally Activated Delayed Fluorescence and Solution-Processed OLEDs.

Two-coordinate donor-metal-acceptor type coinage metal complexes displaying efficient thermally activated delayed fluorescence (TADF) have been unveiled to be highly appealing candidates as emitters for organic light-emitting diodes (OLEDs). Herein a series of green to yellow TADF gold(I) complexes with alkynyl ligands has been developed for the first time. The complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 0.76 in doped films (5 wt % in PMMA) at room temperature. The modifications of alkynyl ligands with electron-donating amino groups together with the use of electron-deficient carbene ligands induce ligand-to-ligand charge transfer excited states that give rise to TADF emission. Spectroscopic and density functional theory (DFT) calculations reveal the roles of electron-donating capability of the alkynyl ligand in tuning the excited-state properties. Solution-processed organic light-emitting diodes (OLEDs) using the present complexes as emitters achieve maximum external quantum efficiency (EQE) of up to 20 %.

Silver(I) N–heterocyclic carbene complex encapsulated in cellulose acetate membranes for hydrogen gas purification

Coinage metal complexes bearing N–heterocyclic carbene (NHC) ligands are important in discovery of new metal-based drugs, however, their usage in homogenous and heterogeneous catalysis, photocatalysis, gas purification, etc., are scarce. In this report, the performance of a silver(I)–NHC encapsulated membrane for hydrogen gas purification is reported. Gas purification materials or membranes play a crucial role in the manufacture of pure hydrogen gas, a green fuel, at industrial levels. The purification of hydrogen gas has been carried out conventionally following solid-state diffusion method using silver-palladium metal alloy-based membranes. Though the efficiency of these membranes is acceptable, their cost of preparation is economically nonviable, and hence a new method has been developed to purify hydrogen gas using silver(I)-NHC complex encapsulated cellulose acetate membranes. The complex encapsulated membranes possess promising elongation strength and tensile modulus. The optimum composite membrane showed good separation efficiency with ideal selectivity of 2.0, 65 and 32 for H2/CO2, H2/CH4 and CO2/CH4, respectively.

Significant π bonding in coinage metal complexes OCTMCCO- from infrared photodissociation spectroscopy and theoretical calculations.

A series of coinage metal complexes in the form of TMC(CO)n - (TM = Cu, Ag, Au; n = 0-3) were generated using a laser-ablation supersonic expansion ion source in the gas phase. Mass-selected infrared photodissociation spectroscopy in conjunction with quantum chemical calculations indicated that the TMC(CO)3 - complexes contain a linear OCTMCCO- core anion. Bonding analyses suggest that the linear OCTMCCO- anions are better described as the bonding interactions between a singlet ground state TM+ metal cation and the OC/CCO2- ligands in the singlet ground state. In addition to the strong ligands to metal σ donation bonding components, the π-bonding components also contribute significantly to the metal-ligand bonds due to the synergetic effects of the CO and CCO2- ligands. The strengths of the bonding of the three metals show a V-shaped trend in which the second-row transition metal Ag exhibits the weakest interactions whereas the third-row transition metal Au shows the strongest interactions due to relativistic effects.

Asymmetrically Substituted Phospholes as Ligands for Coinage Metal Complexes.

A series of coinage metal complexes asymmetrically substituted 2,5-diaryl phosphole ligands is reported. Structure, identity, and purity of all obtained complexes were corroborated with state-of-the-art techniques (multinuclear NMR, mass spectrometry, elemental analysis, X-ray diffraction) in solution and solid state. All complexes obtained feature luminescence in solution as well as in the solid state. Additionally, DOSY-MW NMR estimation experiments were performed to achieve information about the aggregation behavior of the complexes in solution allowing a direct comparison with their structures observed in the solid state.

Cover Feature: Role of Anionic Backbone in NHC‐Stabilized Coinage Metal Complexes: New Precursors for Atomic Layer Deposition (Chem. Eur. J. 16/2022)

A series of new N-heterocyclic carbene (NHC) based Cu(I) and Ag(I) complexes were synthesized, analyzed, and evaluated for their potential usage in atomic layer deposition (ALD) of coinage metal thin films. Employing the same set of diketonate-type ligands for both metals did result in thermally stable Cu(I) complexes suitable for ALD, while the Ag(I) complexes exhibit an inherently unstable nature and different bonding features. More information can be found in the Research Article by Anjana Devi et al. (DOI: 10.1002/chem.202103798).

Role of Anionic Backbone in NHC-Stabilized Coinage Metal Complexes: New Precursors for Atomic Layer Deposition.

Cu and Ag precursors that are volatile, reactive, and thermally stable are currently of high interest for their application in atomic‐layer deposition (ALD) of thin metal films. In pursuit of new precursors for coinage metals, namely Cu and Ag, a series of new N‐heterocyclic carbene (NHC)‐based CuI and AgI complexes were synthesized. Modifications in the substitution pattern of diketonate‐based anionic backbones led to five monomeric Cu complexes and four closely related Ag complexes with the general formula [M( tBuNHC)(R)] (M=Cu, Ag; tBuNHC=1,3‐di‐tert‐butyl‐imidazolin‐2‐ylidene; R=diketonate). Thermal analysis indicated that most of the Cu complexes are thermally stable and volatile compared to the more fragile Ag analogs. One of the promising Cu precursors was evaluated for the ALD of nanoparticulate Cu metal deposits by using hydroquinone as the reducing agent at appreciably low deposition temperatures (145–160 °C). This study highlights the considerable impact of the employed ligand sphere on the structural and thermal properties of metal complexes that are relevant for vapor‐phase processing of thin films.

Coinage Metal Complexes of Germylene and Stannylene.

Group 11 metal (M = Cu, Ag, Au) complexes of heavier tetrylenes (namely, germylene and stannylene) have been studied for several years now. However, the field is mainly unexplored for their potential application either in homogeneous catalysis or in photophysical properties regardless of how the current reports allude to the rich and fascinating chemistry of group 14 elements. In this mini-review, we attempted to summarize the recent advances of heavier tetrylene-stabilized coinage metal complexes, which are majorly dominated by structure elucidation studies. This comprehensive summary intends to help researchers design and fine-tune the tetrylene ligand framework that can lead to coinage metal complexes for future applications as photoemitters in organic light-emitting diode fabrication and efficient catalysts in homogeneous catalysis.

Coinage Metal Complexes of Bis(quinoline-2-ylmethyl)phenylphosphine-Simple Reactions Can Lead to Unprecedented Results.

The different coordination behavior of the flexible yet sterically demanding, hemilabile P,N ligand bis(quinoline‐2‐ylmethyl)phenylphosphine (bqmpp) towards selected CuI, AgI and AuI species is described. The resulting X‐ray crystal structures reveal interesting coordination geometries. With [Cu(MeCN)4]BF4, compound 1 [Cu2(bqmpp)2](BF4)2 is obtained, wherein the copper(I) atoms display a distorted square planar and square pyramidal geometry. The steric demand and π‐stacking of the ligand allow for a short Cu⋅⋅⋅Cu distance (2.588(9) Å). CuI complex 2 [Cu4Cl3(bqmpp)2]BF4 contains a rarely observed Cu4Cl3 cluster, probably enabled by dichloromethane as the chloride source. In the cluster, even shorter Cu⋅⋅⋅Cu distances (2.447(1) Å) are present. The reaction of Ag[SbF6] with the ligand leads to a dinuclear compound (3) in solution as confirmed by 31P{1H} NMR spectroscopy. During crystallization, instead of the expected phosphine complex 3, a tris(quinoline‐2‐ylmethyl)bisphenyl‐phosphine (tqmbp) compound [Ag2(tqmbp)2](SbF6)2 4 is formed by elimination of quinaldine. The Au(I) compound [Au2(bqmpp)2]PF6 (5) is prepared as expected and shows a linear arrangement of two phosphine ligands around AuI.

Cationic ligands between σ-donation and hydrogen-bridge-bond-stabilisation of ancillary ligands in coinage metal complexes with protonated carbodiphosphoranes.

A series of copper(I) and silver(I) complexes is reported containing the PCP-type tridentate ligand [(dppm)2CH]+ with a protonated carbodiphosphorane (CDPH) as cationic central donor group (dppm = 1,1-bis(diphenylphosphino)methane). In comparison to the previously reported gold complex [({dppm}2CH)AuCl]+ [Reitsamer et al., J. Organomet. Chem., 2017, 830, 150], the corresponding silver and copper complexes exhibit a κC-coordinated CDPH-group, which is absent in case of gold. For the series of silver complexes, we demonstrate that the κC-coordination of the CDPH-group is dependant on the ancillary ligand and that hydrogen bonding of the CDPH-group to the ancillary ligand can be competitive. The ability for such hydrogen bonding is a unique characteristic of protonated CDPs in comparison to other cationic ligands, which might offer benefits for applications in homogeneous catalysis by hemilability and substrate activation with this group.

Toward rational design of TADF two-coordinate coinage metal complexes: understanding the relationship between natural transition orbital overlap and photophysical properties

A series of twelve two-coordinate coinage metal, Cu, Ag and Au, complexes with carbene-metal-amide structures were prepared and used to study the correlation of the overlap between the hole and electron NTOs with the electronic and photophysical properties of these TADF emitters.

On the nature of M[sbnd]L bond and the puckering of some B-heterocyclic carbenes and silylenes in their relevant complexes with coinage metals: A theoretical quest

Boron heterocyclic divalents (BHEs; EC, Si) are organometallic ligands, and their coordination chemistry with transition metals, particularly coinage (G11) metals (Cu, Ag, Au), is interesting. Here, quantum chemical calculations at M06/def2-tzvp level of theory are performed to study the BHEs; EC, Si along with BP86/TZ2P level of theory for the calculation of its corresponding complexes of coinage metals (X2BHE-MCl; MCu(I), Ag(I), Au(I)) with selected halogen and alkyl side groups (XF, Cl, Br, Me, iPr, tBu). Results display that the interaction energies (∆Eint) for EM bond in X2BHE−MCl complexes (MCu(I), Au(I), Ag(I); EC, Si; XF, Cl, Br, Me, iPr, tBu) are significant and follow the familiar trend for the G11 transition metals as Au(I) > Cu(I) > Ag(I). The nature of EM bond in the complexes is evaluated using natural bond orbital (NBO), energy decomposition analysis (EDA), and excited transition state-natural orbitals for chemical valance (ETS-NOCV). The interaction energy (Eint) in X2BHE−MCl complexes studied here is largely electrostatic, and this feature accounts for about 65% of the total interaction energy. Furthermore, it is found that in carbene (1X−MCl) complexes with electron-withdrawing side groups (XF, Cl, Br), the group 11 metals form stronger bonds with X2BHEs rather than their corresponding silylenes (2X−MCl). The comparison of EDA-NOCV results for EM bond with the same M atom and X side groups in 1X−MCl and 2X−MCl indicates that the silylenes are typically stronger σ donors and weaker π acceptors than the corresponding carbene ligands.

Can One Novel Series of Transition Metal Complexes of Oxy-dianiline Schiff Base Afford Advances in Both Biological Inorganic Chemistry and Materials Science?

ABSTRACT This paper provides a manifestation of a new tradition by which Comments on Inorganic Chemistry starts publishing original research content that, nonetheless, preserves the Journal’s identity as a niche for a critical discussion of contemporary literature in inorganic chemistry; for previous manifestations, see Comments Inorg. Chem. 2020, 40, 277-303 and references cited in the abstract thereof as Yaseen W. K.; Sanders S. F.; Almotawa R. M.; Otten B. M.; Bhat S.; Alamo D. C.; Marpu S. B.; Golden T. D.; Omary M. A. “Are Metal Complexes” Organic, Inorganic, Organometallic, or Metal-Organic Materials? A case Study for the Use of Trinuclear Coinage Metal Complexes as “Metal-Organic Coatings” for Corrosion Suppression on Aluminum Substrates Comments Inorg. Chem. 2019, 39, 1-26 and also, Mohapatra R. K.; Das P. K.; Pradhan M. K.; El-Ajaily M. M.; Das D.; Salem H. F.; Mahanta U.; Badhei G.; Parhi P. K.; Maihub A. A.; Kudrat -E-Zahan Md. “Recent Advances in Urea- and Thiourea-Based Metal Complexes: Biological, Sensor, Optical, and Corrosion Inhibition Studies” Comments Inorg. Chem. 2019, 39, 127-147). In this work, the Schiff base 1-(6-(1-((4-(4-aminophenoxy)phenyl)imino)ethyl)-pyridin-2-yl)ethan-1-one (L) and eight transition metal complexes were synthesized. The reaction of 4,4-oxy-dianiline with 2,6-diacetylpyridine in 1:1 molar ratio affords to the ligand which was employed in the synthesis of the corresponding metal complexes by reacting with the Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) chlorides in 1:1 molar ratio. All the compounds were characterized by using different analytical methods. Structures of complexes were found to be octahedral as deduced from the spectroscopic and magnetic moment measurements. The ligand behaves as a neutral tridentate ligand where it coordinated to metal ions through N-azomethine, N-pyridine, and O-carbonyl group. Besides, experimental investigations for their antibacterial activity against different bacteria species were studied, molecular docking studies were reported with receptors 4ME7, 4K3V, 3T88 and 4WJ3. Density functional theory (DFT) calculations for ligand were reported. Finally, the evaluation of corrosion inhibition efficiency was measured by using different techniques such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and electrochemical frequency modulation (EFM). Scanning electron microscope (SEM) and energy dispersive X-Ray analysis (EDX) were measured to affirm the presence of barrier film on the carbon steel surface by inspecting the surface morphologies and elemental composition of corrosion products.