Alkynyl Complexes Research Articles

Synthesis, characterizations, and anticancer properties of bifunctional system based on gold(I) alkynyl and antipyrine

A Gold(I)-antipyrine conjugate compound {Au(PPh3)(CCC6H4–4-CHN-antipyrine) (4) was synthesized and the new complex was characterized by different spectroscopic techniques. DNA-binding and BSA-binding were performed for the Au-antipyrine compound (4), showing that the synthesized complex exhibits better binding affinities against BSA compared to Au(PPh3)(CCPh) (5) while both have comparable DNA-binding. The gold(I)-antipyrine compound was tested against HepG2 and MCF-7 human cancer cell lines, exhibiting better cytotoxic effects compared to its ligand but comparable to that of Au(PPh3)(CCPh) (5). Despite the comparable anticancer properties of both 4 and 5 described herein, the presence of the antipyrine moiety altered the biomolecule-binding of gold(I) alkynyl complexes. Compared to cisplatin, the gold(I) complexes possess slightly less anticancer properties against both cell lines. Flow cytometry analysis was performed for Au-antipyrine complex, indicating apoptotic cell death pathway (late apoptosis) but via different mechanisms from that of cisplatin (early apoptosis) as can be seen from the differences in the cell cycle analysis at different cell phases.

Endeavoring Cerium(IV)-Alkyl, -Aryl and -Alkynyl Complexes by an Energy-Level Match Strategy

Endeavoring Cerium(IV)-Alkyl, -Aryl and -Alkynyl Complexes by an Energy-Level Match Strategy

Synthesis and antitumor activity of gold(I) N-heterocyclic carbene with dithiocarbamate and alkynyl complexes

A series of new type gold(I) N-heterocyclic carbene (NHC) complexes bearing a paeonol ligand in the side chain of NHC and bearing dithiocarbamate or alkynyl groups as a second ligand have been synthesized and structurally characterized by spectroscopic methods. The structure of Pa-NHC-Au-Cl has been established by X-ray crystallography. Their antitumor activities in vitro were investigated by CCK8 assay against two tumor cell lines (A549 and Hela). The gold(I) NHC with dithiocarbamate (DTC) complexes showed good to excellent antiproliferative activity and strongly inhibited the selenoenzyme thioredoxin reductase (TrxR).

Thermally Activated Delayed Fluorescent Binuclear Copper(I) Alkynyl Complexes with Cuprophilic Interactions.

Copper(I)-based thermally activated delayed fluorescence (TADF) emitters have been conceived to be promising candidates for display and lighting applications because of their multifarious structures and strong photoluminescence. Herein a string of binuclear Cu(I) complexes bearing pronounced cuprophilic interactions have been designed and synthesized. [Cu2(dppb)2(μ2-η1-C≡C-Ph)2] (1 a) and [Cu2(dppb)2(μ2-η1-C≡C-PPXZ)2] (1 b) display photoluminescence quantum yields of up to 67 % in doped films and solid states via TADF and exhibit reversible bicolor luminescence switching upon mechanical stimuli. Computational studies manifest that the metal-to-ligand charge transfer predominant transitions ensure a small energy splitting (ΔEST) between the lowest singlet (S1) and triplet (T1) excited states and cuprophilic interactions promote the spin-orbit coupling (SOC), favoring the reverse intersystem crossing (RISC) process. This study provides a new strategy for the construction of stimuli-responsive metal-based TADF materials.

Dinuclear NHC-gold(I)-thiolato and -alkynyl complexes: synthesis, anticancer activity, and catalytic activity in lactonization reactions.

A series of novel dinuclear NHC-gold-thiolato and -alkynyl complexes bearing aromatic linkers were successfully synthesized by an efficient and simple synthetic route. The catalytic activity of these complexes was tested in a lactonization reaction. The reaction proceeds in high efficiency, in short reaction time and under mild conditions, and is complementary to existing methods. Furthermore, the digold(I)-thiolato derivatives exhibit remarkable cytotoxicity towards several cancer cell lines.

Stereoregular polymerization of phenylacetylene using alkynyl and methyl rhodium(i) complexes with functionalized phosphine ligands: linear vs. branched poly(phenylacetylene)s

Alkynyl rhodium(i) complexes with functionalized phosphine ligands efficiently catalyze the polymerization of phenylacetylene to give a highly stereoregular linear poly(phenylacetylene) with a fraction of high molecular weight branched polymer.

Mechanistic study of the atomic layer deposition of cobalt: a combined mass spectrometric and computational approach.

Cobaltcarbonyl-tert-butylacetylene (CCTBA) is a conventional precursor for the selective atomic layer deposition of Co onto silicon surfaces. However, a limited understanding of the deposition mechanism of such cobalt precursors curbs rational improvements on their design for increased efficiency and tuneable selectivity. The impact of using a less reactive internal alkyne instead of a terminal alkyne was investigated using experimental and computational methods. Using electrospray-ionization mass spectrometry, the formation of CCTBA analogs and their gas phase decomposition pathways were studied. Decomposition experiments show very similar decomposition pathways between the two complexes. The internal alkyne dissociates from the Co complex at slightly lower energies than the terminal alkyne, suggesting that an internal alkynyl ligand may be more suited to low temperature ALD. In addition, transition state calculations using the nudged elastic band method confirm an increased reaction barrier between the internal alkyne and the Si-H surface bonds on Si(111). These results suggests that using a less reactive internal alkyne will result in fewer embedded carbon impurities during deposition onto Si wafers. DFT calculations using the PBE functional and periodic boundary conditions also predict increased surface binding with the metal centers of the internal alkynyl complex.

Photoinduced Reductive C-C and C-Heteroatom Couplings from Bis-cyclometalated Pt(IV) Alkynyl Complexes.

Unsymmetrical dicarboxylato complexes [Pt(tpy)2(O2CR)2] [tpy = cyclometalated 2-(p-tolyl)pyridine, R = Me, CF3] react with the terminal alkynes 4-methoxyphenylacetylene, phenylacetylene, 4-(trifluoromethyl)phenylacetylene or 3,5-difluorophenylacetylene in the presence of a base to produce complexes mer-[Pt(tpy)2(O2CR)(CCAr)], in which the metalated carbon atoms are in a meridional arrangement. Irradiation of the trifluoroacetato derivatives with a 365 nm LED source leads to isomerization to the facial complexes, which can be converted to chlorido derivatives upon reaction with NH4Cl. In contrast, irradiation of the acetato derivatives leads to four different processes, namely, reduction to cis-[Pt(tpy)2], annulations involving one of the tpy ligands and the Cα and Cβ atoms of the alkynyl to give benzoquinolizinium derivatives, isomerization to the facial geometry, or C-O couplings between the acetato ligand and one tpy. The first two processes are favored by the presence of electron-donating groups on the alkynyl, whereas electron-withdrawing groups favor the last two. Irradiation of complexes fac-[Pt(tpy)2(O2CCF3)(CCAr)] with a medium-pressure Hg UV lamp leads to a reductive C-C coupling involving the alkynyl Cα atom and one of the tpy ligands to give pyridoisoindolium derivatives, except for the methoxyphenylacetylide derivative, which is photostable. On the basis of TDDFT calculations, the photoreactivity of the mer complexes is attributed to 3LLCT [π(alkynyl) → π*(tpy)] excited states for annulations or 3LMCT [π(alkynyl) → dσ*] excited states for the rest of the processes, which are accessible through thermal population from 3LC(tpy) states. The C-C couplings from the fac complexes are attributed to photoreactive pentacoordinate intermediates.

Multistate Switching of Some Ruthenium Alkynyl and Vinyl Spiropyran Complexes.

To study the switching properties of photochromes, we undertook the synthesis and characterization of several ruthenium organometallic complexes of the type [Ru(Cp*)(dppe)(C≡C-SP)] or [Ru(CO)(dppe)(PPh3)Cl(CH═CH-SP)], where SP = spiropyran. The spectroscopic and electrochemical properties of the complexes were determined by careful cyclic voltammetric and spectroelectrochemical experiments. Whereas the mononuclear alkynyl ruthenium complexes undergo one-electron oxidations localized over the metal alkynyl moiety, the oxidation of the mononuclear vinyl ruthenium complexes is centered on the indoline moiety of the spiropyran. Through these studies, we demonstrate access to several stable redox states, in addition to switching states attained via acidochromism and/or photoisomerization.

Dinitrogen Binding and Functionalization from a Low-Coordinate Alkynyliron Complex

Alkynyl complexes of low-coordinate transition metals offer a sterically open environment and interesting bonding opportunities. Here, we explore the capacity of iron(I) alkynyl complexes to bind N2 and isolate a N2 complex including its X-ray crystal structure. Silylation of the N2 complex gives an isolable, formally iron(IV) complex with a disilylhydrazido(2−) ligand, but natural bond orbital analysis indicates that an iron(II) formulation is preferable. The structure of this compound is similar to an earlier reported phenyl complex in which phenyl migration forms a new N–C bond, but the alkynyl group does not migrate. DFT calculations are used to test the possible reasons why the alkynyl is resistant to migration, and these show that the large Fe–C bond energy in the alkynyl complex is a factor that could contribute to the lack of migration.

Mechanistic Insights into Multisilver-Mediated Synergistic Activation of Terminal Alkynes.

Synergistic effect extensively exists in multimetal-involved catalytic or mediated processes of group 11 metals due to their remarkable metallophilic interactions. Herein, we present a multiple synergism model for alkynyl substrates and conduct theoretical investigations on various multimetallic bonding modes and the corresponding synergistic activations. We computationally screen nine alkynyl multisilver coordination modes and sequence their reactivity shown in an intramolecular nucleophilic addition reaction by the trend of active μ4-η1η1η2η2 and μ3-η1η1η2 to the relatively inert μ2-η1η2. The transition-state (TS) stabilization of the high-nuclearity mode mainly comes from the significant negative interaction energies between Agn and the substrate based on the distortion/interaction analysis. Energy decomposition analysis-natural orbitals for chemical valence (EDA-NOCV) analysis further reveals the charge-accepting reservoir effect of the polysilver moiety and the orbital match between the alkynyl group and specific spatial arrangement of silver atoms to account for this efficient activation. In addition, tests on different ligands coordinated to silver atoms show a correlation of the ligand conformation adjustability with the reactivity of the alkynyl unit, and the accommodable η2 activation unit embodies a lower deformation energy than the other homonuclear synergistic modes. Privileged multiple synergistic models have been further evidenced based on on-bench experiments by isolating trisilver and tetrasilver alkynyl complexes. This study not only systematically evaluates the multimetallic synergism of different coordination modes in alkyne activation but also provides a guidance for the future design of multimetallic catalysts.

High Seebeck Coefficient Achieved by Multinuclear Organometallic Molecular Junctions.

This paper describes the thermoelectric properties of molecular junctions incorporating multinuclear ruthenium alkynyl complexes that comprise Ru(dppe)2 [dppe = 1,2-bis(diphenylphosphino)ethane] fragments and diethylnyl aromatic bridging ligands with thioether anchors. Using the liquid metal technique, the Seebeck coefficient was examined as a function of metal nuclearity, oxidation state, and substituent on the organic ligand backbone. High Seebeck coefficients up to 73 μV/K and appreciable thermal stability with thermovoltage up to ∼3.3 mV at a heating temperature of 423 K were observed. An unusually high proximity of the highest occupied molecular orbital (HOMO) energy level to the Fermi level was revealed to give the remarkable thermoelectric performance as suggested by combined experiments and calculations. This work offers important insights into the development of molecular-scale devices for efficient thermoregulation and heat-to-electricity conversion.

Dinuclear gold(I) Complexes with Bidentate NHC Ligands as Precursors for Alkynyl Complexes via Mechanochemistry.

The use of alkynyl gold(I) complexes covers different research fields, such as bioinorganic chemistry, catalysis, and material science, considering the luminescent properties of the complexes. Regarding this last application, we report here the synthesis of three novel dinuclear gold(I) complexes of the general formula [(diNHC)(Au-C≡CPh)2]: two Au-C≡CPh units are connected by a bridging di(N-heterocyclic carbene) ligand, which should favor the establishment of semi-supported aurophilic interactions. The complexes can be easily synthesized through mechanochemistry upon reacting the pristine dibromido complexes [(diNHC)(AuBr)2] with phenylacetylene and KOH. Interestingly, we were also able to isolate the monosubstituted complex [(diNHC)(Au-C≡CPh)(AuBr)]. The gold(I) species were fully characterized by multinuclear NMR spectroscopy and mass spectrometry. The emission properties were also evaluated, and the salient data are comparable to those of analogous compounds reported in the literature.

Unlocking Air- and Water-Stable Technetium Acetylides and Other Organometallic Complexes.

The first technetium complexes containing anionic alkynido ligands in an end-on coordination mode have been prepared by using the nonprotic, cationic precursor mer,trans-[Tc(SMe2)(CO)3(PPh3)2]+. This cation acts as a functional analogue of the highly reactive 16-electron metallo Lewis acid {Tc(CO)3(PPh3)2}+ in reactions with alkynes, acetylides, and other organometallic reagents. Such reactions give a variety of organometallic technetium complexes in excellent yields and enable the preparation of [Tc(CH3)(CO)3(PPh3)2], [Tc(Ph)(CO)3(PPh3)2], [Tc(Cp)(CO)2(PPh3)], [Tc(═CCH2CH2CH2O)(CO)3(PPh3)2]+, [Tc(═CCH2CH2CH2CH2O)(CO)3(PPh3)2]+, [Tc(C≡C-H)(CO)3(PPh3)2], [Tc(C≡C-Ph)(CO)3(PPh3)2], [Tc(C≡C-tBu)(CO)3(PPh3)2], [Tc(C≡C-nBu)(CO)3(PPh3)2], [Tc(C≡C-SiMe3)(CO)3(PPh3)2], and [Tc{C≡C-C6H3(CF3)2}(CO)3(PPh3)2]. The bonding situation in the alkynyl complexes is compared to that in corresponding alkyl- and arylnitrile and -isonitrile complexes. [Tc(N≡C-Ph)(CO)3(PPh3)2](BF4), [Tc(C≡N-Ph)(CO)3(PPh3)2](BF4), [Tc(N≡C-tBu)(CO)3(PPh3)2](BF4), and [Tc(C≡N-tBu)(CO)3(PPh3)2](BF4) were prepared in high yields by ligand exchange reactions starting from mer,trans-[Tc(OH2)(CO)3(PPh3)2](BF4). The novel complexes were characterized by single-crystal X-ray diffraction and spectroscopic methods. In particular, 99Tc nuclear magnetic resonance spectroscopy proved to be an invaluable and sensitive tool for the characterization of the complexes. Density functional theory calculations strongly suggest similar bonding situations for the related alkynyl, nitrile, and isonitrile complexes of technetium.

Au(I) Fluorido Phosphine Complexes: Tools for the Hydrofluorination of Alkynes

AbstractThe reactivity of the Au(I) fluorido complex [Au(F)(SPhos)] (SPhos=dicyclohexyl(2’,6’‐dimethoxy[1,1’‐biphenyl]‐2‐yl)phosphine) (1) towards several alkynes was studied. The formation of fluorovinyl species by formal insertion of the alkyne in the metal‐fluorine bond was observed. Addition of HCl to vinyl complexes resulted in protodeauration and elimination of the hydrofluorinated alkynes. Treatment of1with the terminal alkyne 1‐hexyne resulted in clean formation of the alkynyl complex [Au(C≡CC4H9)(SPhos)] (15), whereas with an excess alkyne hydrofluorination was also observed. Various Au(I) phosphine complexes including1were then compared in their ability to catalyze hydrofluorination reactions of 1‐phenyl‐1‐propyne with Et3N ⋅ 3HF as HF source. Model reactions suggested a reaction mechanism, which imparts a pre‐coordination of an alkyne to a cationic gold center followed by nucleophilic addition of a fluoride. Mechanistic investigations included reactivity studies at [Au(SPhos)][B(C6F5)4)] (17), which was treated with 4‐phenyl‐3‐butyn‐2‐one and TMAF (TMAF=tetramethylammonium fluoride). The reaction led to the formation of the complex [Au(CH3C(O)C=C(F)Ph)(SPhos)] (13), but not the fluorido complex1.

Photodegradation of tetracycline by asymmetrical zinc(II)phthalocyanines conjugated to cobalt tungstate nanoparticles

This work focused on syntheses of novel asymmetrically tetra substituted Zn phthalocyanines (ZnPc) each containing a single carboxyl group, with the other substituents bearing alkynyl (complex 1) and fluorine containing groups (complexes 2 and 3). The complexes were conjugated to cobalt tungstate nanoparticles and employed as efficient photocatalysts for degradation of tetracycline in water. ZnPc complexes and their conjugates showed good photophysical and photochemical properties behaviour with complex 1 giving higher triplet and singlet oxygen quantum yields compared to 2 and 3. Complex 1 showed higher activity towards the photodegradation of tetracycline compared to complexes 2 and 3, with higher kobs and initial rates for the former. The photocatalysis obeyed the Langmuir-Hinshelwood kinetic model.

Synthesis and Structure Diversity of Half‐Sandwich Rare Earth Dialkynyl Complexes

AbstractHalf‐sandwich rare‐earth dialkynyl complexes are of much interest in both structure and reactivity but have remained much underexplored to date. Here we report the synthesis and transformation of a new family of half‐sandwich dialkynyl complexes bearing the C5Me4SiMe3 ligand, which exhibited diverse structural features depending on metal ion size, alkyne substituent and with or without THF coordination. The acid‐base reactions between half‐sandwich rare earth dialkyl complexes (C5Me4SiMe3)Ln(CH2SiMe3)2(THF) (Ln=Sc, Y, Lu) and two equivalents of terminal alkynes such as phenylacetylene and trimethylsilylacetylene in THF generally gave the corresponding THF‐coordinated monomeric rare earth dialkynyl complexes, which upon recrystallization from toluene yielded further aggregated alkynyl complexes with partial or full dissociation of the THF ligands. In the case of phenylacetylene, trimeric yttrium and lutetium hexaalkynyl complexes were formed, in which each pair of the metal atoms was bridged by two alkynyl ligands in solid state but the alkynyl ligands underwent rapid site exchange in toluene solution. In the case of trimethylsilylacetylene with yttrium and lutetium, dimeric tetraalkynyl complexes bearing two terminal and two bridging alkynyl ligands were obtained from toluene. In contrast, recrystallization of the scandium trimethylsilylacetylide complex from toluene induced alkynyl coupling and yielded dimeric scandium complex with one butatrienediyl and two alkynyl bridging ligands. Upon dissolution in THF, all the aggregated alkynyl/butatrienediyl complexes were rapidly reconverted to the monomeric dialkynyl complexes as a result of THF coordination to the rare earth metal atoms.

Copper(I) Alkynyl Clusters with Crystallization-Induced Emission Enhancement.

Four copper(I) alkynyl complexes incorporating phosphate ligands, namely, [Cu16(tBuC≡C)12(PhOPO3)2]n (1; PhOPO3 = phenyl phosphate), [Cu16(tBuC≡C)12(1-NaphOPO3)2]n (2; 1-NaphOPO3 = 1-naphthyl phosphate), [VO4@Cu25(tBuC≡C)19(1-NaphOPO3)](PF6)0.5(F)0.5 (3), and [PO4@Cu25(tBuC≡C)19(1-NaphOPO3)](PF6)0.5(F)0.5 (4), were solvothermally synthesized and well-characterized by IR spectroscopy, powder X-ray diffraction, and single-crystal X-ray diffraction. Single-crystal X-ray analysis revealed that the Cu16 cluster-based coordination chain polymers 1 and 2 are formed by assembly during crystallization, while 3 and 4 contain high-nuclearity copper(I) composite clusters enclosing orthovanadate and phosphate template ions, respectively, that are supported by ROPO32- ligands. Complexes 1-4 exhibit crystallization-induced emission enhancement. Their crystalline state shows strong luminescence, in striking contrast to the weak emission of the amorphous state and solution phase. A detailed investigation of the crystal structure suggests that well-arranged C-H···π and π···π interactions between the ligands are the major factors for this enhanced emission. Clusters 3 and 4 also exhibit photocurrent responses upon visible-light illumination.

Syntheses and material applications of Ru(II)(bisphosphine)2 alkynyls

Described in this review are the synthetic methods to produce both mono- and bis-alkynyl Ru(II)(L-L)2 type complexes, where L-L is dppe, dppm, or dmpe. This synthetic tool kit encompasses reactions utilizing trimethylstannyl capped reagents, Ru-alkyl starting materials, or the 16 e− [RuCl(dppe)2]+ intermediate to produce the desired Ru(II)(L-L)2 alkynyl complexes. Advantages and drawbacks of each synthetic approach are touched upon. A brief overview of material applications of these complexes is also provided, highlighting their promises as efficient non-linear optical materials, wire-like molecules, molecular wires and switches, and active molecules in dye-sensitized solar cells.

Tuning the Gold(I)‐Carbon σ Bond in Gold‐Alkynyl Complexes through Structural Modifications of the NHC Ancillary Ligand: Effect on Spectroscopic Observables and Reactivity

AbstractUnderstanding the features of the gold(I)‐carbon σ bond and its modulation induced by an ancillary ligand has become fundamental for the purposes of ligand design, due to the increasing interest towards gold(I)‐alkynyl complexes and their wide range of applications. We carry out a systematic computational analysis of 16 gold(I)‐acetylide complexes bearing different N‐Heterocyclic Carbenes (NHCs) as ancillary ligands [NHC−Au(I)−CCH]. The results show that the strength and features of the Au−C bond can be efficiently tuned by performing specific structural modifications on the NHC, enabling a more efficient π communication between the alkynyl and the ancillary ligand. We also demonstrate that the effect of the bond modulation can be revealed via NMR spectroscopy, as highlighted by the tight correlation between the computed nuclear shielding constants and the bonding parameters. Finally, we show that, for the dual‐gold‐catalyzed Bergman cyclization as case study, suitable structural modifications on the NHC ligand, which modulate the π‐acidity of the metal fragment σ‐coordinated to an enediyne substrate, could affect the reaction barrier and the thermodynamic stability of the product. All the reported results can be well rationalized in the framework of distortion/interaction analysis, which has been recently extended to the dual (σ,π‐type) Au catalytic systems by Alabugin et al (J. Am. Chem. Soc. 2017, 137, 3406‐3416).