Alkynyl Ligands Research Articles

Asymmetric Alkynylation of β‐Ketoesters and Naphthols Promoted by New Chiral Biphenylic Iodanes

The preparation of new chiral biphenylic λ3 -iodane reagents bearing transferable alkynyl ligands is described. These reagents transfer their carbon-based ligands onto β-ketoesters with an enantiomeric excess (ee) up to 68 %, and most remarkably, enable the dearomative alkynylation of naphthols in good to high yields up to 84 % ee.

Synthesis and Characterization of Luminescent Cyclometalated Platinum(II) Complexes with Tunable Emissive Colors and Studies of Their Application in Organic Memories and Organic Light-Emitting Devices.

A series of luminescent cyclometalated N^C^N [N^C^N = 1,3-bis(N-alkylbenzimidazol-2'-yl)benzene]platinum(II) alkynyl and carbazolyl complexes has been prepared. The structure of one platinum(II) carbazolyl complex has been characterized by X-ray crystallography. The corresponding electrochemical and photophysical properties have been explored and analyzed. The N^C^N platinum(II) complexes displayed rich luminescence in degassed dichloromethane solution, with their emission profiles dependent on the coordinated alkynyl and carbazolyl ligands. Their emission energies are correlated to the electronic properties of the alkynyl and carbazolyl ligands. By varying the electronic properties of the alkynyl and carbazolyl ligands, emission energies could be fine-tuned to cover a wide range of the visible spectrum, as supported by computational studies. A donor-acceptor platinum(II) complex has been utilized to fabricate memory devices that exhibit binary memory performances with low operating voltages, high ON/OFF ratios, and long retention times. Solution-processable OLEDs have been fabricated based on another platinum(II) carbazolyl complex, resulting in a maximum external quantum efficiency of up to 7.2%, which is comparable to that of the vacuum-deposited devices based on the small-molecule counterpart, illustrating the multifunctional nature of the platinum(II)-containing materials.

Sky-Blue-Emitting Dendritic Alkynylgold(III) Complexes for Solution-Processable Organic Light-Emitting Devices.

A new class of tridentate ligand-containing cyclometalated gold(III) complexes featuring dendritic alkynyl ligands with carbazole moieties as dendrons and peripheral groups has been synthesized up to the third generation. High-performance solution-processable organic light-emitting devices (OLEDs) with maximum current efficiency of up to 23.7 cd A-1 and external quantum efficiency of up to 6.9% have been realized by a simple spin-coating technique. With the incorporation of bulky carbazole moieties to form higher generation dendrimers, the undesirable excimeric emission could be effectively reduced, allowing the fine-tuning of the emission color toward the blue region. This represents the first successful demonstration of sky-blue-emitting alkynylgold(III) complexes and its application in solution-processable OLEDs.

Intermediates and Reactivity in Iron-Catalyzed Cross-Couplings of Alkynyl Grignards with Alkyl Halides.

Iron-catalyzed cross-coupling reactions using alkynyl nucleophiles represent an attractive approach for the incorporation of alkynyl moieties into organic molecules. In the present study, a multitechnique approach combining inorganic spectroscopic methods, inorganic synthesis, and reaction studies is applied to iron-SciOPP catalyzed alkynyl-alkyl cross-couplings, providing the first detailed insight into the effects of variation from sp2- to sp-hybridized nucleophiles on iron speciation and reactivity. Reaction studies demonstrate that reaction of FeBr2(SciOPP) with 1 equiv (triisopropylsilyl)ethynylmagnesium bromide (TIPS-CC-MgBr) leads to a distribution of mono-, bis-, and tris-alkynylated iron(II)-SciOPP species due to rapid alkynyl ligand redistribution. While solvents such as THF promote these complex redistribution pathways, nonpolar solvents such as toluene enable increased stabilization of these iron species and further enabled assessment of their reactivity with electrophile. While the tris-alkynylated iron(II)-SciOPP species was found to be unreactive with the cycloheptyl bromide electrophile over the average turnover time of catalysis, the in situ formed neutral mono- and bis-alkynylated iron(II)-SciOPP complexes are consumed upon reaction with the electrophile with concomitant generation of cross-coupled product at catalytically relevant rates, indicating the ability of one or both of these species to react selectively with the electrophile. The nature of the reaction solvent and Grignard reagent addition rate were found to have broader implications in overall reaction selectivity, reaction rate, and accessibility of off-cycle iron(I)-SciOPP species. Additionally, the effects of steric substitution of the alkynyl Grignard reagent on catalytic performance were investigated. Fundamental insight into iron speciation and reactivity with alkynyl nucleophiles reported herein provides an essential foundation for the continued development of this important class of reactions.

Redox-Disproportionation of a Decamethyltitanocene(III) Isonitrile Alkynyl Complex.

A mixed decamethyltitanocene(III) isonitrile alkynyl complex (7) was synthesized by the sequential introduction of the isonitrile and alkynyl ligands. Direct synthesis results in the formation of the diamagnetic decamethyltitanocene bis(isonitrile) (2) and bis(alkynyl) (3) complexes. Compound 7 undergoes disproportionation at room temperature to give 2 and 3. All complexes were fully characterized by IR, NMR, and EPR spectroscopy, and mass spectrometry. Molecular structures for complexes 2 and 7 are reported. The stability and reactivity of these complexes are rationalized by DFT computations.

Coordinating Tectons. Experimental and Computational Infrared Data as Tools To Identify Conformational Isomers and Explore Electronic Structures of 4-Ethynyl-2,2′-bipyridine Complexes

4-Ethynyl-2,2′-bipyridyl-substituted ruthenium alkynyl complexes have been prepared and used to access a range of binuclear homometallic ruthenium and heterometallic ruthenium–rhenium complexes. These have been characterized by a variety of spectroscopic and single-crystal X-ray diffraction experiments. The IR spectra of a number of these ruthenium alkynyls display multiple ν(C≡C) bands in the IR spectra, which are rationalized in terms of putative conformational isomers, whose calculated infrared stretching frequencies are comparable to those obtained experimentally. The mononuclear alkynyl ruthenium complexes undergo reversible one-electron oxidations centered largely on the alkynyl ligands, as inferred from the significant shift in ν(C≡C) frequency on oxidation, while the binuclear complex [Ru{C≡C-4-bpy-κ2-N,N′-RuClCp}(dppe)Cp*]+ undergoes initial oxidation at the very electron rich {RuCl(bpy)Cp} fragment, causing only a small change in ν(C≡C). A combination of IR and UV–vis spectroelectrochemical expe...

Amphiphilic oligo(ethylene glycol)- and poly(ethyleneoxide)-block-poly(propylene oxide)-block-poly-(ethylene oxide)-containing cyclometalated alkynylgold(III) complexes: From basic photophysics to self-assembly and stimuli-responsive properties

A class of luminescent cyclometalated gold(III) complexes with oligo(ethylene glycol)- and poly(ethyleneoxide)-block-poly(propylene oxide)-block-poly-(ethylene oxide)-based (PEO-PPO-PEO) alkynyl ligands has been synthesized and characterized. Their photophysical and electrochemical properties have been studied. Cyclometalated gold(III) complexes with oligo(ethylene glycol)-based alkynyl ligands are found to show different aggregation morphologies in DMSO while those with PEO-PPO-PEO-based alkynyl ligand exhibited lower critical solution temperature (LCST) properties in methanol−water (1:1 v/v). Their self-assembly properties have been studied by scanning electron microscopy, transmission electron microscopy, variable-temperature 1H NMR and UV–vis absorption spectroscopy.

Synthesis, characterization and computational studies of luminescent rhenium(I) tricarbonyl diimine complexes with 8-hydroxyquinoline-containing alkynyl ligands

A series of 8-hydroxyquinoline-containing alkynylrhenium(I) tricarbonyl diimine complexes has been designed and synthesized. Their UV-vis absorption, emission as well as electrochemical properties have been studied. Computational studies have also been performed to provide insights into the electronic transitions, excited state origins and electrochemical properties of the complexes.

Luminescent Bis-Cyclometalated Gold(III) Complexes with Alkynyl Ligands of Hexaphenylbenzene and Hexabenzocoronene Derivatives and Their Supramolecular Assembly.

A series of luminescent bis-cyclometalated gold(III) complexes with different nuclearities and various alkynyl ligands derived from hexaphenylbenzene (HPB) and hexabenzocoronene (HBC) have been synthesized. The energies of the low-energy metal-perturbed intraligand (IL) π-π*(R-C^N^C) absorptions of the HPB-alkynyl gold(III) complexes have been fine-tuned by attaching various substituent groups to the bis-cyclometalating ligands. Similarly, the metal-perturbed 3 IL [π→π*(R-C^N^C)] emissions of the complexes show energy shifts according to the electronic nature of the bis-cyclometalating ligands. On the contrary, the absorption and emission spectra of the HBC-alkynyl gold(III) complex have been assigned as dominated by the IL transitions of the HBC-alkynyl unit, as supported by transient absorption studies. The supramolecular assembly morphologies of the gold(III) complexes have been studied by TEM and SEM, along with comparisons across different complexes based on the molecular structures, and their assembly processes monitored by concentration-dependent and variable-temperature 1 H NMR spectroscopy studies.

Silver Alkynyl-Phosphine Clusters: An Electronic Effect of the Alkynes Defines Structural Diversity

The face-capping triphosphine, 1,1,1-tris(diphenylphosphino)methane (tppm), together with bridging alkynyl ligands and the counterions, facilitates the formation of a family of silver complexes, which adopt cluster frameworks of variable nuclearity. The hexanuclear compounds [Ag6(C2C6H4-4-X)3(tppm)2(An–)3] (X = H (1), CF3 (2), OMe (3), An– = CF3SO3–; X = OMe (4), An– = CF3COO–) are produced for the electron-accepting to moderately electron-donating alkynes and the appropriate stoichiometry of the reagents. 1 and 3 undergo an expansion of the metal core when treated with 1 equiv of Ag+ to give the species [Ag7(C2C6H4-4-X)3(tppm)2(CF3SO3)3](CF3SO3) (X = H (5), OMe (6)). The electron-donating substituent (X = NMe2) particularly favors this Ag7 arrangement (7) that undergoes geometry changes upon alkynylation, resulting in the capped prismatic cluster [Ag7(C2C6H4-4-NMe2)4(tppm)2(CF3SO3)](CF3SO3)2 (8). Alternatively, for the aliphatic tBu-alkyne, only the octanuclear complex [Ag8(C2But)4{(PPh2)3CH}2(CF3SO3)2](CF3SO3)2 (9) is observed. The structures of 1–4 and 6–9 were determined by X-ray diffraction analysis. In solution, all the studied compounds were found to be stereochemically nonrigid that prevented their investigation in the fluid medium. In the solid state, clusters 2, 3, 5–8 exhibit room temperature luminescence of triplet origin (maximum Φem = 27%, λem = 485–725 nm). The observed emission is assigned mainly to [d(Ag) → π*(alkyne)] electronic transitions on the basis of TD-DFT computational analysis.

Alkynyl-protected gold and gold-silver nanoclusters.

Ligand-protected metal nanoclusters as unique nanomaterials have attracted great attention. The protecting ligands that directly bind on the cluster surfaces are crucial in dictating the structures and properties of the clusters. In contrast to the extensively studied thiolates, alkynyl ligands have been found recently to be important ligands for passivating gold/silver cluster surfaces. In this Frontier article, recent advances in alkynyl-protected metal nanoclusters are overviewed, and the structures, luminescence and catalytic activities are also discussed. It is demonstrated that alkynyls are very promising ligands in the control of the structures and properties of gold/silver nanoclusters.

A stable gold(i)-enyne species obtained by alkyne carboauration in a complex rearrangement.

An unprecedented tetranuclear gold derivative with unusual gold-enyne moieties is prepared by a mild and neat rearrangement of a dinuclear gold complex with a bridging bis(diphenylphosphino)alkyne and terminal alkynyl ligands. The complex originates as a consequence of an intramolecular addition of the AuC[triple bond, length as m-dash]CTol fragment to the internal diphosphine triple bond Ph2PC[triple bond, length as m-dash]CPPh2. The crystal structure of the tetranuclear complex shows a dinuclear metallacycle with a very short AuAu bond interaction and bridging phosphino-enyne ligands. This disposition clearly stabilises the elusive vinyl gold species omnipresent as intermediates in gold-catalysed reactions.

Insights into the chemistry of bismuth nanoparticles

Alkynyl ligands are proposed as new stabilizing agents for bismuth nanoparticles.

Supramolecular assembly of a phosphole-based moiety into nanostructures dictated by alkynylplatinum(ii) terpyridine complexes through non-covalent Pt···Pt and π-π stacking interactions: synthesis, characterization, photophysics and self-assembly behaviors.

A new class of platinum(ii) terpyridine complexes with a phosphole-derived bridging alkynyl ligand have been prepared. The X-ray crystal structure of complex 2 has been determined, and reveals a polymeric zig-zag chain structure with the existence of π-π stacking interactions. The photophysical properties have also been studied, with 3MLCT/3LLCT phosphorescence exhibited in degassed CH2Cl2; the energy of which is varied by the π-conjugation of the terpyridine ligands. The solvent-induced assembly of complex 1 has been studied. The incorporation of hydrophobic hydrocarbon chains has been shown to play an important role in assisting the formation of self-assembled nanostructures via Pt···Pt, π-π stacking and hydrophobic-hydrophobic interactions. It has been established that an isodesmic growth mechanism operates in polar media to give nanospheres, while fibrous networks originate from the self-assembly of the complexes in non-polar media, predominantly driven by π-π stacking interactions.

Assembly of strongly phosphorescent hetero-bimetallic and -trimetallic [2]catenane structures based on a coinage metal alkynyl system.

Homo-metallic metal alkynyl complexes exhibit interesting catenane structures, but their hetero-metallic catenane counterparts are under-developed. In this work, we report rare examples of bimetallic Au-Cu (DtbpC[triple bond, length as m-dash]C- ligand; Dtbp = 3,5-di-tert-butylphenyl), Au-Ag ( t BuC[triple bond, length as m-dash]C- ligand), and Au-Cu, Au-Ag (C6-FluoC[triple bond, length as m-dash]C- ligand; C6-Fluo = 9,9-dihexyl-9H-fluoren-2-yl) complexes as well as a trimetallic Au-Ag-Cu (C6-FluoC[triple bond, length as m-dash]C- ligand) complex, which feature [2]catenane structures. The formation of the [2]catenane structure is significantly affected by the coinage metal ion(s) and change of the structure of the alkynyl ligand. These hetero-metallic [2]catenane structures are strongly luminescent with tunable emission λ max from 503 to 595 nm and Φ values up to 0.83.

Luminescent Dinuclear Bis-Cyclometalated Gold(III) Alkynyls and Their Solvent-Dependent Morphologies through Supramolecular Self-Assembly.

A series of luminescent bis-cyclometalated gold(III) complexes containing bridging alkynyl ligands of different natures has been synthesised and characterised. The photophysical properties of the complexes have been investigated through electronic absorption spectroscopy and emission studies. The vibronic emission bands are found to originate from the triplet intraligand (IL) π-π* excited states of the bis-cyclometalating ligands with some mixing of 3 IL π-π* character of the alkynyl ligands. The electrochemical study of a nonsymmetric dinuclear complex shows two successive reduction processes originating from the reductions of the two different cyclometalating ligands. The complexes are found to undergo supramolecular self-assembly processes driven by π-π stacking and hydrophobic/hydrophilic interactions to give honeycomb nanostructures, as revealed from the SEM images. Solvent-dependent morphological transformations have also been observed, which have been studied by SEM and 1 H NMR spectroscopy.

Intramolecular C–C Coupling Reactions of Alkynyl, Vinylidene, and Alkenylphosphane Ligands in Rhodium(III) Complexes

Electrophilic attack with methyl trifluoromethanesulfonate or tetrafluoroboric acid, to new alkynyl rhodium complexes containing alkenylphosphanes, leads to butenynyl coupling products or to the unprecedented rhodaphosphacycle complexes [Rh(η5-C5Me5){κ4-(P,C,C,C)-iPr2PCH2C(═CH2)C(CH2R)C═C(R)}][BF4] (R = Ph (11a), p-tol (11b)). These complexes 11a,b can be explained as a result of the coupling of three organic fragments in the molecule, the alkynyl, the vinylidene, generated in situ by reaction with HBF4 (A), and the C–C double bond from the alkenylphosphane. DFT computational studies on the formation of complex 11a suggest the [2 + 2] intramolecular cycloaddition between the double bond of the allylphosphane and the Cα–Cβ of the vinylidene A as the most plausible pathway for this reaction.

From Cluster to Polymer: Ligand Cone Angle Controlled Syntheses and Structures of Copper(I) Alkynyl Complexes.

Copper(I) alkynyl complexes have attracted tremendous attention in structural studies, as luminescent materials, and in catalysis, and homoleptic complexes have been reported to form polymers or large clusters. Herein, six unprecedented structures of Cu(I) alkynyl complexes and a procedure to measure the cone angles of alkynyl ligands based on the crystal structures of these complexes are reported. An increase of the alkynyl cone angle in the complexes leads to a modulation of the structures from polymeric [((PhC≡CC≡C)Cu)2 (NH3 )]∞ , to a large cluster [(TripC≡CC≡C)Cu]20 (MeCN)4 , to a relatively small cluster [(TripC≡C)Cu]8 (Trip=2,4,6-iPr3 -C6 H2 ). The complexes exhibit yellow-to-red phosphorescence at ambient temperature in the solid state and the luminescence behavior of the Cu20 cluster is sensitive to acetonitrile.

From Cluster to Polymer: Ligand Cone Angle Controlled Syntheses and Structures of Copper(I) Alkynyl Complexes

AbstractCopper(I) alkynyl complexes have attracted tremendous attention in structural studies, as luminescent materials, and in catalysis, and homoleptic complexes have been reported to form polymers or large clusters. Herein, six unprecedented structures of CuI alkynyl complexes and a procedure to measure the cone angles of alkynyl ligands based on the crystal structures of these complexes are reported. An increase of the alkynyl cone angle in the complexes leads to a modulation of the structures from polymeric [((PhC≡CC≡C)Cu)2(NH3)]∞, to a large cluster [(TripC≡CC≡C)Cu]20(MeCN)4, to a relatively small cluster [(TripC≡C)Cu]8 (Trip=2,4,6‐iPr3‐C6H2). The complexes exhibit yellow‐to‐red phosphorescence at ambient temperature in the solid state and the luminescence behavior of the Cu20 cluster is sensitive to acetonitrile.

Harnessing Fluorescence versus Phosphorescence Ratio via Ancillary Ligand Fine-Tuned MLCT Contribution

A series of gold(I) alkynyl-diphosphine complexes (XC6H4C2Au)PPh2—spacer—PPh2(AuC2C6H4X); spacer = —C2(C6H4)nC2— (A1, n = 2, X = CF3; A2, n = 2, X = OMe; A3, n = 3, X = CF3; A4, n = 3, X = OMe), —(C6H4)n— (B5, n = 3, X = OMe; B6, n = 4, X = OMe) were prepared, and their photophysical properties were investigated. The luminescence behavior of the titled compounds is dominated by the diphosphine spacer, which serves as an emitting ππ* chromophore. The complexes exhibit dual emission, comprising low and high energy bands of triplet (phosphorescence) and singlet (fluorescence) origins, respectively. The electron-donating characteristics of ancillary groups X significantly affect the LLCT/MLCT contribution of both alkynyl ligand and the metal center into the lowest lying excited state. In turn, it substantially influences the rate of intersystem crossing kisc S1 → Tm (m ≥ 1) that allows for tuning the ratio fluorescence vs phosphorescence without alteration of the chromophore core. Quantum chemical analysis of...