Alkyne Ligands Research Articles

Stereochemical control of the diphosphine and alkyne ligands in triruthenium clusters: The effect of reversible CO loss/addition on the ligand distribution in [Ru3(µ3,η2-PhCCPh){µ-Ph2PCH(Me)PPh2}(CO)7,8

Thermolysis of [Ru3{µ-Ph2PCH(Me)PPh2}(CO)10] (1) in the presence of diphenylacetylene affords the corresponding alkyne-substituted cluster [Ru3(µ3,η2-PhCCPh){µ-Ph2PCH(Me)PPh2}(CO)8] (2) and its unsaturated counterpart [Ru3(µ3,η2-PhCCPh){µ-Ph2PCH(Me)PPh2}(CO)7] (3), along with the alkyne-coupled complexes [Ru3{κ2-Ph2PCH(Me)PPh2}{µ3,η4-(CPh)4}(CO)4(µ-CO)2] (4) and [Ru2{µ-Ph2PCH(Me)PPh2}{µ,η4-(CPh)4}(CO)4] (5). The backbone-modified diphosphine in 2 has facilitated the growth of single crystals of the same and whose molecular structure was established by X-ray crystallography. The Ph2PCH(Me)PPh2 ligand bridges two ruthenium centers and occupies adjacent axial sites at one of the metallic faces. The diphosphine is situated trans to the alkyne ligand that caps the opposite metallic face. X-ray structural analysis of 3 reveals a perpendicular conformation of the alkyne relative to the metal triangle and a bridging diphosphine that coordinates the adjacent equatorial sites of the alkyne-bisected Ru–Ru bond. The kinetics for the conversion of 2 → 3 + CO under argon have been investigated over the temperature range 298–343 K in toluene. The calculated activation parameters [ΔHǂ = 13.3(3) kcal/mol; ΔSǂ = − 31(1) eu] are inconsistent with a rate-limiting step involving a dissociative loss of CO. Consistent with earlier reports on the related analog [Ru3(µ3,η2-PhCCPh)(µ-Ph2PCH2PPh2)(CO)7] by Lavigne and coworkers, the addition of CO to 3 (1 atm CO) at 258 K is rapid and affords 2 with a rate constant of 1.12(2) e−1s−1. Cluster 3 exhibits high reactivity toward 2e donors. Control experiments confirm that 3 reacts with additional PhCCPh (66 °C, 1 h) to give the diruthenium derivative 5 and that 4 also gives 5 in refluxing THF. The reaction of 3 with hydrogen gas (1 atm, 25 °C, 20 min) yields the dihydride [H2Ru3(µ3,η2-PhCCPh){µ-Ph2PCH(Me)PPh2}(CO)7] (6) in 85% yield. Clusters 2−6 were characterized by IR, 1H, and 31P NMR spectroscopies, and the solid-state structures of 2−5 were established by single-crystal X-ray crystallography. The bonding in clusters 2 and 3 and the thermodynamics for the equilibrium involving 2 ⇆ 3 + CO have been evaluated by electronic structure calculations.

Binuclear Alkyne Manganese Carbonyls: Their Rearrangements to Allene, Allyl, and Vinylcarbene Derivatives by Hydrogen Migration from Methyl Substituents

AbstractBinuclear alkyne manganese carbonyls of the type (RC≡CR')Mn2(CO)n (R and R'=methyl or dimethylamino; n=8, 7, 6) and their isomers related to the experimentally known (MeC2NEt2)Mn2(CO)n (n=8, 7) structures have been investigated by density functional theory. The alkyne ligand remains intact in the only low energy (Me2N)2C2Mn2(CO)8 isomer, which has a central Mn2C2 tetrahedrane unit and is otherwise analogous to the well‐known (alkyne)Co2(CO)6 derivatives except for one more CO group per metal atom. The low‐energy structures of the unsaturated (Me2N)2C2Mn2(CO)n (n=7, 6) systems include isomers in which the nitrogen atom of one of the dimethylamino groups as well as the C≡C triple bond of the alkyne is coordinated to the central Mn2 unit. In other low‐energy (Me2N)2C2Mn2(CO)n (n=7, 6) isomers the alkyne C≡C triple bond has broken completely to form two separate bridging dimethylaminocarbyne Me2NC ligands analogous to the experimentally known iron carbonyl complex (Et2NC)2Fe2(CO)6. The (alkyne)Mn2(CO)n (n=8, 7, 6) systems of the alkynes MeC≡CMe and Me2NC≡CMe with methyl substituents have significantly more complicated potential surfaces. In these systems the lowest energy isomers have bridging ligands derived from the alkyne in which one or two hydrogen atoms have migrated from a methyl group to one or both of the alkyne carbon atoms. These bridging ligands include allene, manganallyl, and vinylcarbene ligands, the first two of which have been realized experimentally in research by Adams and coworkers. Theoretical studies suggest that the mechanism for the conversion of the simple alkyne octacarbonyl (MeC2NMe2)Mn2(CO)8 to the dimethylaminomanganaallyl complex Mn2(CO)7[μ‐η4‐C3H3Me2] involves decarbonylation to the heptacarbonyl and the hexacarbonyl complexes. Subsequent hydrogen migrations then occur through intermediates with C−H−Mn agostic interactions to give the final product. Eight transition states for this mechanistic sequence have been identified with activation energies of ∼20 kcal/mol for the first hydrogen migration and ∼14 kcal/mol for the second hydrogen migration.

Acetylenic Sulfones and Acetylenic Sulfonamide Analogs: A Novel and Preferable Antimicrobial Drugs Based on Computational Strategies

This study was done to report virtual screening and molecular docking studies of sulfacetamide derivatives as new antimicrobial drugs, belonging to the pharmacological class of sulfonamides. For this purpose, sulfonamide functional groups from a library of chemical structures were converted into acetylenic sulfone and acetylenic sulfonamide functional groups to introduce a new class of antimicrobial drugs with mechanisms of action of dihydropteroate synthase inhibitors (DHPS). Initially, a library of compounds containing approximately 170 acetylenic sulfone ligands was created by similarity search method, and a library containing 170 acetylenic sulfonamide ligands was designed to be administered as new inhibitors. After designing, their molecular docking energies were calculated by three software programs including Arguslab4.0.1, AutoDock Vina and Molegro Virtual Docker and the results were compared in terms of binding energy. Although acetylenic sulfonamide compounds showed better results, acceptable results were observed in both groups of compounds. Adsorption, distribution, metabolism and excretion (ADME) properties of acetylenic sulfones/acetylenic sulfonamide analogs were also analyzed using the admetSAR program. These new derivatives can be used in drug improvement processes for the treatment of antibacterial infections after performing further studies.

Case Study of N-i Pr versus N-Mes Substituted NHC Ligands in Nickel Chemistry: The Coordination and Cyclotrimerization of Alkynes at [Ni(NHC)2

A case study on the effect of the employment of two different NHC ligands in complexes [Ni(NHC)2] (NHC= i Pr2ImMe 1Me , Mes2Im 2) and their behavior towards alkynes is reported. The reaction of a mixture of [Ni2( i Pr2ImMe)4(μ‐(η 2 : η2)‐COD)] B/ [Ni( i Pr2ImMe)2(η4‐COD)] B’ or [Ni(Mes2Im)2] 2, respectively, with alkynes afforded complexes [Ni(NHC)2(η2‐alkyne)] (NHC= i Pr2ImMe: alkyne=MeC≡CMe 3, H7C3C≡CC3H7 4, PhC≡CPh 5, MeOOCC≡CCOOMe 6, Me3SiC≡CSiMe3 7, PhC≡CMe 8, HC≡CC3H7 9, HC≡CPh 10, HC≡C(p‐Tol) 11, HC≡C(4‐ t Bu‐C6H4) 12, HC≡CCOOMe 13; NHC=Mes2Im: alkyne=MeC≡CMe 14, MeOOCC≡CCOOMe 15, PhC≡CMe 16, HC≡C(4‐ t Bu‐C6H4) 17, HC≡CCOOMe 18). Unusual rearrangement products 11 a and 12 a were identified for the complexes of the terminal alkynes HC≡C(p‐Tol) and HC≡C(4‐ t Bu‐C6H4), 11 and 12, which were formed by addition of a C−H bond of one of the NHC N‐ i Pr methyl groups to the C≡C triple bond of the coordinated alkyne. Complex 2 catalyzes the cyclotrimerization of 2‐butyne, 4‐octyne, diphenylacetylene, dimethyl acetylendicarboxylate, 1‐pentyne, phenylacetylene and methyl propiolate at ambient conditions, whereas 1Me is not a good catalyst. The reaction of 2 with 2‐butyne was monitored in some detail, which led to a mechanistic proposal for the cyclotrimerization at [Ni(NHC)2]. DFT calculations reveal that the differences between 1M e and 2 for alkyne cyclotrimerization lie in the energy profile of the initiation steps, which is very shallow for 2, and each step is associated with only a moderate energy change. The higher stability of 3 compared to 14 is attributed to a better electron transfer from the NHC to the metal to the alkyne ligand for the N‐alkyl substituted NHC, to enhanced Ni‐alkyne backbonding due to a smaller CNHC−Ni−CNHC bite angle, and to less steric repulsion of the smaller NHC i Pr2ImMe.

Synthesis of [(CO)5MS=CFcCH3] and exploration of the nature of M-S vs. M-O bonds in [(CO)5ME=CFcCH3]; (M = Cr, Mo, W and E = O, S) complexes

Photolysis of a methanol solution containing substituted alkyne, group VI metal hexacarbonyl and P4S10 at low temperature under an inert atmosphere leads to metal-sulfur coordinated complexes of chromium, molybdenum, and tungsten. The structure of pentacarbonylthioacetylferrocene-S-chromium (1) is confirmed by single crystal x-ray diffraction study and both the complexes (1 and 2) are confirmed using IR and NMR spectral studies. The sulfur-coordinated metal carbonyl complexes are thought to be formed by the initial activation of metal carbonyl with acetylenic ligand which then rearranges into metal coordinated thioacetylferrocene by dithiophosphoryl radical (formed in situ by reaction of P4S10 and methyl alcohol under photolytic condition). The stability of pentacarbonylthioacetylferrocene of group VI metal complexes are further compared with their acetylferrocene derivatives of Group VI metal complexes using DFT studies. Density functional theory was performed on six complexes [(CO)5ME=CFcCH3] (where M = Cr, Mo and W; while E = O and S) to assess their geometry and electronic structure aspects. Natural bonding orbital (NBO) and energy-decomposition analysis (EDA) were carried out to probe the nature and strength of the M-E interactions. NBO and EDA analysis predict M-E bond strength in the following order: Cr-E < Mo-E < W-E. The M-E bond covalency increases as we move down the group from Cr, Mo to W, which rationalizes the observed trends in the M-E bonds. While comparing the nature of the E (O and S) linkage in bonding, we found that -S analogue shows exceptionally robust σ and π interactions compared to the -O analogue. The reasonably strong M-S interactions resulted in the isolation of these -thio analogues.

Threefold Collaborative Stabilization of Ag14‐Nanorods by Hydrophobic Ti16‐Oxo Clusters and Alkynes: Designable Assembly and Solid‐State Optical‐Limiting Application

AbstractAg nanoclusters have received increasing attention due to their atomically precise and diverse structures and intriguing optical properties. Nevertheless, the inherent instability of Ag nanoclusters has seriously hindered their practical application. In this work, for the first time, Ag clusters are collaboratively protected by hydrophobic Ti‐oxo clusters and alkyne ligands. Initially, a pyramidal Ag5 cluster terminated with tBuC≡C− and CH3CN was inserted into the cavity of a Ti8‐oxo nanoring to form Ag5@Ti8. To overcome the instability of acetonitrile‐terminated silver site, such two Ag5@Ti8 clusters could sandwich an Ag4 unit to form Ag14‐nanorod@Ti16‐oxo‐nanoring (Ag14@Ti16), which is peripherally protected by fluorophenyl groups and alkyne caps. This threefold protected (hydrophobic fluorinated organic layer, Ti‐O shell, and terminal alkyne ligands) Ag14@Ti16 exhibits superhydrophobicity and excellent ambient stability, endowing it with solid‐state optical limiting characteristics.

Threefold Collaborative Stabilization of Ag14 -Nanorods by Hydrophobic Ti16 -Oxo Clusters and Alkynes: Designable Assembly and Solid-State Optical-Limiting Application.

Ag nanoclusters have received increasing attention due to their atomically precise and diverse structures and intriguing optical properties. Nevertheless, the inherent instability of Ag nanoclusters has seriously hindered their practical application. In this work, for the first time, Ag clusters are collaboratively protected by hydrophobic Ti-oxo clusters and alkyne ligands. Initially, a pyramidal Ag5 cluster terminated with t BuC≡C- and CH3 CN was inserted into the cavity of a Ti8 -oxo nanoring to form Ag5 @Ti8 . To overcome the instability of acetonitrile-terminated silver site, such two Ag5 @Ti8 clusters could sandwich an Ag4 unit to form Ag14 -nanorod@Ti16 -oxo-nanoring (Ag14 @Ti16 ), which is peripherally protected by fluorophenyl groups and alkyne caps. This threefold protected (hydrophobic fluorinated organic layer, Ti-O shell, and terminal alkyne ligands) Ag14 @Ti16 exhibits superhydrophobicity and excellent ambient stability, endowing it with solid-state optical limiting characteristics.

Synthesis, Electrochemistry, and Optical Properties of Highly Conjugated Alkynyl-Ferrocenes and -Biferrocenes

Sonogashira reactions are utilized herein to react iodo-ferrocenes and -biferrocenes with terminal alkyne ligands, functionalized with both pyridine and thioanisole groups. High-yielding reactions generate both monoalkynyl and dialkynyl derivatives, the ratio of which can be altered through changes in the reaction stoichiometry. This methodology allowed us to synthesize a large family of derivatives, comprising four symmetrical derivatives (3xx, where x represents a phenyl-substituted terminal alkyne) and six less-studied asymmetrical derivatives (3xy, where x and y represent two different phenyl-substituted terminal alkynes), as well as a number of their biferrocenyl analogues (6x, 7xx, and 7xy), including the first known examples of asymmetrically disubstituted biferrocenes. We examined the electrochemical behavior of all the systems in solution through the use of cyclic voltammetry and demonstrate that these highly conjugated alkynyl ligands exert delicate redox control over the central ferrocene motif. We also note that these substituents display some control over the mixed-valence character present in biferrocene monocations, with thioanisole substituents imparting almost an order of magnitude higher Kc than their pyridyl analogues, and asymmetric systems displaying rare characteristic properties of mixed-valence isomers. The electronic structure of these systems was further elucidated through a combination of UV/vis spectroscopy and density functional theory calculations. Our methodology provides a facile and adaptable route toward the isolation of a number of novel ferrocene and biferrocene derivatives. From our perspective, the asymmetric nature of these systems, along with the delicate and predictable redox control that these ligands exert on the central ferrocene unit(s), could lead to applications in molecular electronics, where these properties have previously shown promise in the fabrication of diodes and rectifiers, as well as in the synthesis of donor-π-acceptor systems.

DFT Study on Dinuclear Palladium Complex Catalyzed Pyrrole Formation From tert‐Butyl Isocyanide and Alkynes

AbstractDensity functional theory calculations were carried out to study the mechanisms of Pd‐catalyzed reactions of alkynes with tert‐butyl isocyanide forming pyrroles. In the case of di‐palladium catalysis, the calculations indicated that alkyne insertion, isocyanide insertion, intramolecular cyclization, isocyanide insertion, isomerization and ligand substitution were involved in the mechanism. The intramolecular cyclization process was calculated to be the rate‐determining step in the catalytic cycle. The substituent effects on the regioselectivity of reaction were also analyzed. In addition, detailed calculations on mono‐palladium catalysis showed that the activity of mononuclear catalysis was not as high as that of di‐palladium catalysis. These calculation results were in good agreement with the experimental results.

Synthesis, Characterization, and Catalytic Activity of Bimetallic Ti/Cr Complexes

We report herein the reactions of the Rosenthal complexes, Cp2Ti(BTMSA) and Cp*2Ti(BTMSA) (BTMSA: bis(trimethylsilyl)acetylene), with CpCr(CO)3H. Those complexes are known to dissociate their alkyne ligands and to exhibit the reactivities of the putative titanocenes “Cp2Ti” and “Cp*2Ti”. Our reactions appear to proceed through the addition of CpCr(CO)3H to these titanocenes, giving rise to TiIV-H intermediates that lose H2 to form the TiIII–Cr complexes 1 and 2. In the solid state, 1 and 2 both adopt a dimeric geometry, involving a 12-membered “Ti2Cr2” ring held together with Ti–O–C–Cr bridging carbonyls. The terminal carbonyls in 1 and 2 are trans. DFT calculations confirm that the loss of H2 from the TiIV-H intermediate—forming the TiIII-Cr dimer—is exergonic by 14.2 kcal mol–1 in the gas phase. The Bercaw compound Cp* (C5Me4CH2)TiCH3 reacts with CpCr(CO)3H to form a TiIV-CH3 species with a coordinated CpCr(CO)3– anion (3). The Ti-Cr dimer 1 is capable of catalyzing the hydrogenation of an epoxide to an anti-Markovnikov alcohol, avoiding the use of Cp2TiX2 (X = Cl– or mesylate), NaCpCr(CO)3, and HCpCr(CO)3 separately as in our previous catalyst system.

A Homoleptic Alkynyl-Ligated [Au13 Ag16 L24 ]3- Cluster as a Catalytically Active Eight-Electron Superatom.

A new alkynylated cluster [Au13 Ag16 (C10 H6 NO)24 ]3- is prepared by a NaBH4 mediated reduction method. The AuAg clusters are confirmed by sophisticated characterization techniques. It has a unique "Aucenter @Ag12 @Au12 Ag4 " metal framework which is protected by 24 atypical alkyne ligands L (L=C10 H6 NO). The ligands construct a unique type of motif L-(Ag)-Au-(Ag)-L at the cluster interface, where the alkyne (C≡C) group of each L was linked by sharing an Au atom through the σ bonds and each C≡C group was discretely connected to a chemically different Ag atom (Agicosahedral /Agcap ) through π bonds. The electronic and optical properties of [Au13 Ag16 L24 ]3- were studied. DFT characterized the cluster as a clear 8-electron superatom, and peaks in the optical absorption spectrum were interpreted in terms of the P and D superatom states. The supported Au13 Ag16 L24 /CeO2 catalyst exhibited high catalytic activity and selectivity towards the A3 -coupling reaction involving benzaldehyde, diethylamine, and phenylacetylene.

A Homoleptic Alkynyl‐Ligated [Au13Ag16L24]3− Cluster as a Catalytically Active Eight‐Electron Superatom

AbstractA new alkynylated cluster [Au13Ag16(C10H6NO)24]3− is prepared by a NaBH4 mediated reduction method. The AuAg clusters are confirmed by sophisticated characterization techniques. It has a unique “Aucenter@Ag12@Au12Ag4” metal framework which is protected by 24 atypical alkyne ligands L (L=C10H6NO). The ligands construct a unique type of motif L‐(Ag)‐Au‐(Ag)‐L at the cluster interface, where the alkyne (C≡C) group of each L was linked by sharing an Au atom through the σ bonds and each C≡C group was discretely connected to a chemically different Ag atom (Agicosahedral/Agcap) through π bonds. The electronic and optical properties of [Au13Ag16L24]3− were studied. DFT characterized the cluster as a clear 8‐electron superatom, and peaks in the optical absorption spectrum were interpreted in terms of the P and D superatom states. The supported Au13Ag16L24/CeO2 catalyst exhibited high catalytic activity and selectivity towards the A3‐coupling reaction involving benzaldehyde, diethylamine, and phenylacetylene.

Coordination and Solvation in Gas-Phase Ag+(C2H2)n Complexes Studied with Selected-Ion Infrared Spectroscopy.

Silver-acetylene cation complexes of the form Ag+(C2H2)n (n = 1-9) were produced via laser ablation in a supersonic expansion of acetylene/argon. The ions were mass selected and studied via infrared laser photodissociation spectroscopy in the C-H stretching region (3000-3500 cm-1). Fragmentation patterns indicate that four ligands are strongly coordinated to the metal cation. Density functional theory calculations were performed in support of the experimental data. Together, infrared spectroscopy and theory provide insight into the structure and bonding of these complexes. The Ag+(C2H2)n (n = 1-4) species are shown to be η2-bonded, cation-π complexes with red-shifted C-H stretches on the acetylene ligands. Unlike Cu+(C2H2)n and Au+(C2H2)n complexes, which have a maximum coordination of three, silver cation is tetrahedrally coordinated to four acetylene ligands. Larger complexes (n = 5-9) are formed by solvation of the Ag+(C2H2)4 core with acetylene. Similar to Cu+(C2H2)n and Au+(C2H2)n complexes, acetylene solvation leads to new and interesting infrared band patterns that are quite distinctive from those of the smaller complexes.

Overall Structures of Two Metal Nanoclusters: Chloride as a Bridge Fills the Space between the Metal Core and the Metal Shell

In addition to using common ligands (phosphine, thiol, or acetylene ligands) to protect metal nanoclusters, halogens can also be used to participate in the formation of nanoclusters. In this study, we reported the formation of two new nanoclusters promoted by chlorides released from HAuCl4: one [Au1Ag26(SR)18Cl] with an icosahedral Au1Ag12 kernel, which is surrounded by the shell of Ag14(SR)18, and the special chlorine atom fills the space between the metal core and the metal shell; the other [Au6Ag33(Dppf)2(SR)16Cl6]+ with the kernel consisted of two icosahedral Au3Ag10 units by sharing one vertex Ag atom, which is protected by the complicated shell of Ag14(Dppf)2(SR)16Cl4, two special chlorine atoms also fill the space between the metal core and the metal shell. Thus, both two nanoclusters suggest that the chlorine atoms can exist in the space between the metal kernel and out shell, playing a critical role in maintaining the stability of the overall structures. These will deepen the comprehensive understanding of chlorine in constructing the structures of alloy nanoclusters and will also be helpful in mapping out the new strategies for core-shell nanocluster synthesis.

Alkyne/Ruthenium(II) Complex-Based Ratiometric Surface-Enhanced Raman Scattering Nanoprobe for In Vitro and Ex Vivo Tracking of Carbon Monoxide.

Here, we report a surface-enhanced Raman scattering (SERS) nanosensor for real-time ratiometric detection of carbon monoxide (CO) based on a ligand displacement mechanism. This nanoprobe consists of a gold-silver (Au-Ag) alloy nanoparticle core as the highly active SERS substrate, an alkyne/ruthenium(II) (alkyne/Ru(II)) complex immobilized on the surface as the CO-sensing element, and a porous silica shell to improve the stability and biocompatibility of the particle. Displacement of the alkyne ligand by CO results in a decrease of the alkyne vibrations and an increase of the metal carbonyl complex signals, thus allowing the effective ratiometric detection of CO in real-time. The great potential of this assay for CO detection is validated in clean buffer environments, live cells, and tissue slices.

Modular synthesis of silicon (IV) phthalocyanine conjugates bearing glycosylated axial ligands

Phthalocyanines (Pcs) are near-infrared photosensitizers with therapeutic potential for the treatment of bacterial infections and cancer. However, their clinical utility has been hindered by poor solubility in biological fluids, lack of specificity, and limited clearance from affected tissues. Glycosylated Pcs have the potential to overcome these issues by providing increased solubility and tumor specific targeting. However, reliable methods for their synthesis remains challenging. Here we present our first approach towards the synthesis of a series of silicon (IV) phthalocyanine conjugates bearing axial carbohydrate ligands (CPcCs). The novelty of our approach lies in the installation of axial alkyne ligands which can be functionalized with readily accessible acetyl protected azido glycosides, thus providing a modular approach for the synthesis of these complex macromolecules.

Selective Activation of CH Bonds in Polar Vinyl Olefins and Coupling of Ethylene to the Activated Carbon Atoms in Pentaruthenium Complexes.

Ru5(μ5-C)(CO)15, 1, has been found to activate CH bonds in the vinyl group of polar vinyl olefins, methyl acrylate (MA), and vinyl acetate (VAc), through a cluster opening process to yield the complexes Ru5(μ5-C)(CO)14[η2-O═C(OMe)CH═CH](μ-H), 2, and Ru5(μ5-C)(CO)14[η2-(MeCO2)C═CH2](μ-H), 4, respectively. The site of CH activation is dependent on the olefin substituent. In 2, the site of CH activation is the β-carbon atom of the vinyl group, while in 4 the CH activation has occurred exclusively at the α-carbon atom of the vinyl group. Compound 2 can be further decarbonylated to yield the complex Ru5(μ5-C)(CO)13[μ-η3-O═C(OMe)CHCH](μ-H), 3, which contains a η3-bridging acryloyl ligand. Compound 2 reacts with ethylene in the presence of Me3NO to yield three new Ru5 products: Ru5(μ5-C)(CO)13[η4-1- anti,3- syn-{O═C(OMe)}C(H)C(H)C(H)Me](μ-H), 5, Ru5(μ5-C)(CO)12(C2H4)[μ-η3- O═C(OMe)C(H)C(H)](μ-H), 6, and Ru5(μ5-C)(CO)13[η4- anti-O═C(OMe)H2CHCHCH2](μ-H), 7. Compounds 5 and 7 are isomers containing substituted η3-allyl ligands formed by the coupling of the ethylene to the CH-activated β-carbon atom of the acryloyl ligand accompanied by some metal-mediated H-shifts. Compound 6 contains an uncoupled π-coordinated ethylene ligand. Compound 7 was isomerized to 5 thermally at 80 °C. Compound 4 reacts with ethylene in the presence of Me3NO to yield two new Ru5 products: Ru5(μ5-C)(CO)13[η4-1,1- anti- syn-[(O2CMe)C(Me)CHCH2](μ-H), 8, and Ru5(μ5-C)(CO)13[η4-1- anti-CH(Me)C(O2CMe)(CH2)](μ-H), 9. Compounds 8 and 9 both contain substituted η3-allyl ligands formed by the coupling of the ethylene to the CH-activated α-carbon atom of the vinyl acetyl ligand. Compound 8 was isomerized to 9 thermally at 80 °C. All new products were characterized structurally by single-crystal X-ray diffraction analyses.

Luminescent NˆCˆN cyclometalated iridium(III) acetylide complexes with fluorene and carbazole motifs

NˆCˆN cyclometalated iridium(III) acetylide complexes in the 3 + 2+1 ligand mode were obtained and characterized. Cyclometalating ligands were bis(pyridyl)phenyl, bis(benzothiazolyl)phenyl and 2-phenylpyridine derivatives, while acetylene ligands represented 2-ethynylfluorene and 3-ethynylcarbazole derivatives. The HOMOs of the ethynyl iridium complexes are located on the ethynyl ligand and the iridium atom, whereas the LUMO is located exclusively on the NˆCˆN-cyclometalating ligand. All compounds showed phosphorescent properties, where the change of ligands significantly affects the wavelength of emission. Acetylide complexes emit light from the blue (∼ 400 nm) to orange (∼ 560 nm) range. Emission occurs from the mixed state 3 MLCT/ 3 LC, with a predominance of junction depending on the structure of the ligands. • Iridium acetylide complexes with fluorene and carbazole motifs were examined. • Detailed characterization of optical, thermal and electrochemical properties of new complexes has been carried out. • In the Ir(III) complexes the emission takes place from the mixed state 3 MLCT/ 3 LC.

Activation and Photoinduced Release of Alkynes on a Biomimetic Tungsten Center: The Photochemical Behavior of the W-S-Phoz System.

The synthesis and structural determination of four tungsten alkyne complexes coordinated by the bio‐inspired S,N‐donor ligand 2‐(4′,4′‐dimethyloxazoline‐2′‐yl)thiophenolate (S‐Phoz) is presented. A previously established protocol that involved the reaction of the respective alkyne with the bis‐carbonyl precursor [W(CO)2(S‐Phoz)2] was used for the complexes [W(CO)(C2R2)(S‐Phoz)2] (R=H, 1 a; Me, 1 b; Ph, 1 c). Oxidation with pyridine‐N‐oxide gave the corresponding W‐oxo species [WO(C2R2)(S‐Phoz)2] (R=H, 2 a; Me, 2 b; Ph, 2 c). All W‐oxo‐alkyne complexes (2 a, b, c) were found to be capable of alkyne release upon light irradiation to afford five‐coordinate [WO(S‐Phoz)2] (3). The photoinduced release of the alkyne ligand was studied in detail by in situ 1H NMR measurements, which revealed correlation of the photodissociation rate constant (2 b>2 a>2 c) with the elongation of the alkyne C≡C bond in the molecular structures. Oxidation of [WO(S‐Phoz)2] (3) with pyridine‐N‐oxide yielded [WO2(S‐Phoz)2] (4), which shows highly fluxional behavior in solution. Variable‐temperature 1H NMR spectroscopy revealed three isomeric forms with respect to the ligand arrangement versus each other. Furthermore, compound 4 rearranges to tetranuclear oxo compound [W4O4(μ‐O)6(S‐Phoz)4] (5) and dinuclear [{WO(μ‐O)(S‐Phoz)}2] (6) over time. The latter two were identified by single‐crystal X‐ray diffraction analyses.

Dative and electron-sharing bonding in transition metal compounds.

Quantum chemical calculations using density functional theory at the BP86-D3(BJ)/def2-TZVPP level of theory are reported for transition metal compounds [TM]-L in high and low oxidation states involving carbene, carbyne, alkene, and alkyne ligands L. The nature of the [TM]-L bond is analyzed with the energy decomposition analysis - natural orbitals for chemical valence (EDA-NOCV) method. The calculations reveal that transition metal compounds with ligands, that are typically classified as donor-acceptor complexes possessing dative bonds (Fischer-type carbenes and carbynes, alkene, and alkyne complexes) or as TM compounds with electron-sharing bonds (Schrock-type carbenes and carbynes, metallacyclopropanes, and metallacyclopropenes), exhibit significant differences between the orbital interactions when closed-shell or open shell fragments are used. Fischer-type carbene complexes have much lower orbital interaction (ΔEorb ) values when singlet fragments are employed compared to triplet fragments. In contrast, singlet and triplet fragments of Schrock-type carbene complexes give similar ΔEorb values. The best description for Fischer-type carbyne complexes is found for neutral fragments in their electronic doublet state, which engage in a mixture of dative bonding (σ donation and π backdonation) and one electron-sharing π bond. The EDA-NOCV calculations of Schrock-type carbynes using open-shell species in their quartet electronic state give similar ΔEorb values as neutral fragments in their electronic doublet state. Alkene and alkyne complexes, but also metallacyclic species, are best described with singlet fragments, but the difference between the ΔEorb values for dative bonding and electron-sharing bonding using triplet fragments becomes much smaller for molecules that are considered as metallacycles. © 2018 Wiley Periodicals, Inc.