Alkyne Complexes Research Articles

Site-Selective Labeling of Native Proteins by a Multicomponent Approach.

Chemical functionalization of proteins is an indispensable tool. Yet, selective labeling of native proteins has been an arduous task. The limited success of chemical methods allows N-terminus protein labeling, but the examples with side-chain residues are rare. Herein, we surpass this challenge through a multicomponent transformation that operates under physiological conditions in the presence of a protein, aldehyde, acetylene, and Cu-ligand complex. The methodology results in the labeling of a single lysine residue in nine distinct proteins.

How different is the borazine–acetylene dimer from the benzene–acetylene dimer? A matrix isolation infrared and ab initio quantum chemical study

ABSTRACTThe 1:1 dimer of borazine–acetylene has been studied for the first time, both experimentally and computationally. The borazine–acetylene dimer was trapped in Ar and N2 matrices, and studied using infrared spectroscopy. Our experiments clearly revealed two isomers of the borazine–acetylene complex, one in which the N–H of borazine interacted with the carbon of acetylene, and another in which the C–H of acetylene formed a hydrogen bond with a nitrogen atom of borazine. The formation of both isomers in the matrix was evidenced by shifts in the vibrational frequencies of the appropriate modes. Reassuringly, the experimental observations were corroborated by our computations using the second-order Møller–Plesset perturbation theoretic method and coupled-cluster singles, doubles and perturbative triples method in conjunction with different Dunning basis sets, which indicated both these isomers to be stable minima, with the N–H⋅⋅⋅C complex being the global minimum. Atoms-in-molecules and energy decomposition analysis were also carried out for the different isomers of the dimer. These studies reveal that replacing the three C–C linkages in benzene with three B–N linkages in borazine modifies the interaction in the dimer sufficiently, to result in a different potential energy landscape for the borazine–acetylene system when compared with the benzene–acetylene system.

Decamethyltitanocene hydride intermediates in the hydrogenation of the corresponding titanocene-(η2-ethene) or (η2-alkyne) complexes and the effects of bulkier auxiliary ligands.

1H NMR studies of reactions of titanocene [Cp*2Ti] (Cp* = η5-C5Me5) and its derivatives [Cp*(η5:η1-C5Me4CH2)TiMe] and [Cp*2Ti(η2-CH2[double bond, length as m-dash]CH2)] with excess dihydrogen at room temperature and pressures lower than 1 bar revealed the formation of dihydride [Cp*2TiH2] (1) and the concurrent liberation of either methane or ethane, depending on the organometallic reactant. The subsequent slow decay of 1 yielding [Cp*2TiH] (2) was mediated by titanocene formed in situ and controlled by hydrogen pressure. The crystalline products obtained by evaporating a hexane solution of fresh [Cp*2Ti] in the presence of hydrogen contained crystals having either two independent molecules of 1 in the asymmetric part of the unit cell or cocrystals consisting of 1 and [Cp*2Ti] in a 2 : 1 ratio. Hydrogenation of alkyne complexes [Cp*2Ti(η2-R1C[triple bond, length as m-dash]CR2)] (R1 = R2 = Me or Et) performed at room temperature afforded alkanes R1CH2CH2R2, and after removing hydrogen, 2 was formed in quantitative yields. For alkyne complexes containing bulkier substituent(s) R1 = Me or Ph, R2 = SiMe3, and R1 = R2 = Ph or SiMe3, successful hydrogenation required the application of increased temperatures (70-80 °C) and prolonged reaction times, in particular for bis(trimethylsilyl)acetylene. Under these conditions, no transient 1 was detected during the formation of 2. The bulkier auxiliary ligands η5-C5Me4tBu and η5-C5Me4SiMe3 did not hinder the addition of dihydrogen to the corresponding titanocenes [(η5-C5Me4tBu)2Ti] and [(η5-C5Me4SiMe3)2Ti] yielding [(η5-C5Me4tBu)2TiH2] (3) and [(η5-C5Me4SiMe3)2TiH2] (4), respectively. In contrast to 1, the dihydride 4 did not decay with the formation of titanocene monohydride, but dissociated to titanocene upon dihydrogen removal. The monohydrides [(η5-C5Me4tBu)2TiH] (5) and [(η5-C5Me4SiMe3)2TiH] (6) were obtained by insertion of dihydrogen into the intramolecular titanium-methylene σ-bond in compounds [(η5-C5Me4tBu)(η5:η1-C5Me4CMe2CH2)Ti] and [(η5-C5Me4SiMe3)(η5:η1-C5Me4SiMe2CH2)Ti], respectively. The steric influence of the auxiliary ligands became clear from the nature of the products obtained by reacting 5 and 6 with butadiene. They appeared to be the exclusively σ-bonded η1-but-2-enyl titanocenes (7) and (8), instead of the common π-bonded derivatives formed for the sterically less congested titanocenes, including [Cp*2Ti(η3-(1-methylallyl))] (9). The molecular structure optimized by DFT for compound 1 acquired a distinctly lower total energy than the analogously optimized complex with a coordinated dihydrogen [Cp*2Ti(η2-H2)]. The stabilization energies of binding the hydride ligands to the bent titanocenes were estimated from counterpoise computations; they showed a decrease in the order 1 (-132.70 kJ mol-1), 3 (-121.11 kJ mol-1), and 4 (-112.35 kJ mol-1), in accordance with the more facile dihydrogen dissociation.

Sterically encumbered metalla-diphosphines: unlocking alkyne rotation by PtII coordination.

We present the synthesis and coordination chemistry of a series of WII alkyne complexes with symmetric and asymmetric acetylene diphosphines. Chelate-like P,P'-coordination of PtCl2 cause a drastic potential change of the W centered oxidation proving intermetallic cooperativity. The choice of peripheric P-substituents has a measurable influence on the potential itself as well on the respective potential change upon coordination. The enlarged deviation of the diphosphino alkyne from linearity in the dinuclear complexes unlock alkyne rotation making different isomers accessible.

Probing C-H⋯N interaction in acetylene-benzonitrile complex using matrix isolation infrared spectroscopy and DFT computations

Hydrogen-bonded complexes of acetylene (C2H2) and the benzonitrile (C6H5CN) have been investigated using matrix isolation infrared spectroscopy and DFT computations. The structure of the complexes and the energies were computed at B3LYP and B3LYP+D3 levels of theory using 6–311++G (d, p) and aug-cc-pVDZ basis sets. DFT computations indicated two minima corresponding to the C-H⋯N (global) and C-H⋯π interactions (local) of 1:1 C2H2-C6H5CN complexes, where C2H2 is the proton donor in both complexes. Experimentally, the 1:1 C-H⋯N complex identified from the shifts in the C-H and CN stretching modes corresponding to the C2H2 and C6H5CN sub-molecules in N2 and Ar matrices. Atoms in Molecules and Natural Bond Orbital analyses were performed to understand the nature of interaction and to unravel the reasons for red-shifting of the C-H stretching frequency in these complexes. Energy decomposition analysis was carried out to discern the various stabilizing and destabilizing components as a result of hydrogen bonding in the C2H2-C6H5CN complexes.

Supt20 is required for development of the axial skeleton

Somitogenesis and subsequent axial skeletal development is regulated by the interaction of pathways that determine the periodicity of somite formation, rostrocaudal somite polarity and segment identity. Here we use a hypomorphic mutant mouse line to demonstrate that Supt20 (Suppressor of Ty20) is required for development of the axial skeleton. Supt20 hypomorphs display fusions of the ribs and vertebrae at lower thoracic levels along with anterior homeotic transformation of L1 to T14. These defects are preceded by reduction of the rostral somite and posterior shifts in Hox gene expression. While cycling of Notch target genes in the posterior presomitic mesoderm (PSM) appeared normal, expression of Lfng was reduced. In the anterior PSM, Mesp2 expression levels and cycling were unaffected; yet, expression of downstream targets such as Lfng, Ripply2, Mesp1 and Dll3 in the prospective rostral somite was reduced accompanied by expansion of caudal somite markers such as EphrinB2 and Hes7. Supt20 interacts with the Gcn5-containing SAGA histone acetylation complex. Gcn5 hypomorphic mutant embryos show similar defects in axial skeletal development preceded by posterior shift of Hoxc8 and Hoxc9 gene expression. We demonstrate that Gcn5 and Supt20 hypomorphs show similar defects in rostral-caudal somite patterning potentially suggesting shared mechanisms.

The silent information regulator 1 (Sirt1) is a positive regulator of the Notch pathway in Drosophila.

The silent information regulator 1 (Sirt1) has been shown to have negative effects on the Notch pathway in several contexts. We bring evidence that Sirt1 has a positive effect on Notch activation in Drosophila, in the context of sensory organ precursor specification and during wing development. The phenotype of Sirt1 mutant resembles weak Notch loss-of-function phenotypes, and genetic interactions of Sirt1 with the components of the Notch pathway also suggest a positive role for Sirt1 in Notch signalling. Sirt1 is necessary for the efficient activation of enhancer of split [E(spl)] genes by Notch in S2N cells. Additionally, the Notch-dependent response of several E(spl) genes is sensitive to metabolic stress caused by 2-deoxy-d-glucose treatment, in a Sirt1-dependent manner. We found Sirt1 associated with several proteins involved in Notch repression as well as activation, including the cofactor exchange factor Ebi (TBL1), the RLAF/LAF histone chaperone complex and the Tip60 acetylation complex. Moreover, Sirt1 participates in the deacetylation of the CSL transcription factor Suppressor of Hairless. The role of Sirt1 in Notch signalling is, therefore, more complex than previously recognized, and its diverse effects may be explained by a plethora of Sirt1 substrates involved in the regulation of Notch signalling.

SAGA complex and Gcn5 are necessary for respiration in budding yeast

In budding yeast, growth through fermentation and/or respiration is dependent on the type of carbon source present in the medium. SAGA complex is the main acetylation complex and is required, together with Rtg factors, for nucleus-mitochondria communication and transcriptional activation of specific nuclear genes. Even though acetylation is necessary for mitochondria activity and respiratory pathways the direct role of histone acetyltransferases and SAGA complex has never been investigated directly. In this study we demonstrate, for the first time, that Gcn5 and SAGA are needed for respiratory metabolism and oxygen consumption. According to a central role for acetylation in respiration we find that the Gcn5 inhibitor CPTH2 had higher efficacy on cells grown in glycerol containing media. We also demonstrated that the opposing activities of Gcn5 and Hda1 modify selectively H3-AcK18 and are essential for respiration. Taken together our results suggest a novel paradigm coupling acetyltransferase activity to respiratory metabolism. Correspondingly we propose the selective utilization of KAT inhibitor CPTH2, combined to the modulation of the respiratory metabolism of the cell, as a promising novel tool of intervention in cancer cells.

Computational Insights into the Mechanism of Pd(0) and Ben-zoic Acid Co-Catalyzed Hydroamination of Internal Alkynes

Computational studies were carried out to investigate the detailed mechanism of Pd(0) and benzoic acid co-catalyzed hydroamination of internal alkynes. In the presence of the benzoic acid, the formation of a hydridopalladium intermediate via the oxidative addition (OA) of the O-H bond of benzoic acid into the Pd(0) complex center might not be a favorable reaction pathway to start the reaction. Instead, after the coordination of benzoic acid with the Pd(0)-alkyne complex, a proton transfer process from the acid to carbon of alkyne is found to be a favorable pathway, leading to the alkenyl(PhCOO)Pd(II) intermediate. Next, the resulting alkenyl(PhCOO)Pd(II) species would produce phenylallene intermediate via a β-H elimination step assisted by the formed benzoate anion. Subsequently, the benzoic acid might undergo a second proton step to the yielded phenylallene intermediate to produce the π-allylpalladium species. Finally, the amine substrate could undergo a nucleophilic addition to the terminal carbon of the π-allylpalladium species to produce the hydroamination product.

The Outer‐Sphere Mechanism of Nitrene Transfer onto Gold(I) Alkyne Complexes

AbstractThe recently developed nitrene transfer reaction onto gold‐activated alkynes provides a route to safe and accessible synthons of α‐diazo imides. This reaction is rather unique in that it requires AuI in catalytic amounts; however, this promiscuous metal is only used to activate the alkyne moiety. After such activation is obtained, the nitrene‐transfer process occurs through an outer‐sphere mechanism, in which the metal acts only as a spectator. Density functional theory was applied to elucidate this peculiar reaction and to provide a mechanistic explanation for the experimentally observed isomers at the double bond and imine sites.

1,2-Addition or Enolization? Variable Reactivity of a Cerium Acetylide Complex toward Carbonyl Compounds

The reactions of the cerium alkyne complex bearing 2,6-bis(dimethylamino)-4-methylphenolate supporting ligands (bdmmp) and a terminal acetylide moiety, Na[Ce(C≡CPh)(bdmmp)3] (1), with benzaldehyde and a family of enolizable ketones led to different products depending on the acidity of the parent carbonyl compound. The reactions of 1 with benzaldehyde, acetone, benzylideneacetone, or 1,1-diphenylacetone (pKaDMSO = 26.5–19.4) gave the products of nucleophilic addition of type Na[Ce(O-CR2-C≡CPh)(bdmmp)3] featuring a new C–C bond. In contrast, the reaction of 1 with β-tetralone (pKaDMSO = 17.6) resulted in the enolization and deprotonation of β-tetralone with subsequent replacement of the acetylide ligand at the cerium ion by the enolate. Molecular structures for the cerium products were determined by X-ray diffraction studies, providing valuable information about the performance of organocerium reagents.

Multiple and Highly Selective Alkyne-Isonitrile C-C and C-N Couplings at Group 4 Metallocenes.

Reactions of the group 4 metallocene alkyne complexes [Cp'2 M(η(2) -Me3 SiC2 SiMe3 )] [Cp'2 =rac-(ebthi)=rac-1,2-ethylene-1,1'-bis(η(5) -tetrahydroindenyl): M=Ti, Zr, Hf; Cp'2 =Cp*2 (Cp*=η(5) -pentamethylcyclopentadienyl): M=Zr] with 2,6-dimethylphenyl isocyanide (2-xylyl isonitrile, XyNC) were investigated. Depending on the metal, the Cp' ligand, and/or the stoichiometry, as well as the reaction temperature and time, different products were obtained. The products included simple end-on coordination compounds of XyNC in addition to those of the coupling of Me3 SiC2 SiMe3 with two, three, or four isonitriles to form enimine complexes, aza-metallacycloallenes, and fused heterocyclic systems, respectively. One example of the latter tricyclic compounds was subject to demetalation by using HCl. Molecular structures of the heterometallacycles were determined by X-ray crystallography. The interconversion of the products was investigated by (1) H NMR spectroscopy.

Expanding the Phenotype Associated with NAA10-Related N-Terminal Acetylation Deficiency.

ABSTRACTN‐terminal acetylation is a common protein modification in eukaryotes associated with numerous cellular processes. Inherited mutations in NAA10, encoding the catalytic subunit of the major N‐terminal acetylation complex NatA have been associated with diverse, syndromic X‐linked recessive disorders, whereas de novo missense mutations have been reported in one male and one female individual with severe intellectual disability but otherwise unspecific phenotypes. Thus, the full genetic and clinical spectrum of NAA10 deficiency is yet to be delineated. We identified three different novel and one known missense mutation in NAA10, de novo in 11 females, and due to maternal germ line mosaicism in another girl and her more severely affected and deceased brother. In vitro enzymatic assays for the novel, recurrent mutations p.(Arg83Cys) and p.(Phe128Leu) revealed reduced catalytic activity. X‐inactivation was random in five females. The core phenotype of X‐linked NAA10‐related N‐terminal‐acetyltransferase deficiency in both males and females includes developmental delay, severe intellectual disability, postnatal growth failure with severe microcephaly, and skeletal or cardiac anomalies. Genotype–phenotype correlations within and between both genders are complex and may include various factors such as location and nature of mutations, enzymatic stability and activity, and X‐inactivation in females.

Alkyne-Induced Facile C–C Bond Formation of Two η2-Alkynes on Dinuclear Tantalum Bis(alkyne) Complexes To Give Dinuclear Tantalacyclopentadienes

The dinuclear tantalum–alkyne complexes [(η2-RC≡CR)TaCl2]2(μ-OMe)2(μ-thf) (2a, R = Et; 2b, R = nPr) were synthesized by treating the mononuclear tantalum–alkyne complexes (η2-RC≡CR)TaCl3(dme) (1a, R = Et; 1b, R = nPr) with 1 equiv of NaOMe in THF. We found that adding a catalytic amount (20 mol %) of 3-hexyne to 2a induced the spontaneous formation of Ta2Cl4(OMe)2(μ-C4Et4)(thf) (4a). Similarly, Ta2Cl4(OMe)2(μ-C4nPr4)(thf) (4b) was obtained by treatment of 2b with a catalytic amount (20 mol %) of 4-octyne. Reaction of 4a,b with 4-dimethylaminopyridine gave 4-dimethylaminopyridine-coordinated complexes 6a,b, whose structures were elucidated by the X-ray structure of 6a. We conducted a control experiment in which 10 equiv of 4-octyne was added to 2a to give Ta2Cl4(OMe)2(μ-C4-2,3-nPr2-4,5-Et2)(thf) (7) in 90% yield, indicating that free 4-octyne reacted with the tantalacyclopropene moiety of 2a to form a dissymmetric tantalacyclopentadiene, followed by the release of 3-hexyne. The catalytic activity of 4a–6a ...

Well‐Defined Models for the Elusive Dinuclear Intermediates of the Pauson–Khand Reaction

AbstractThe mechanism of the Pauson–Khand reaction has attracted significant interest due to the unusual dinuclear nature of the Co2(CO)x active site. Experimental and computational data have indicated that the intermediates following the initial Co2(CO)6(alkyne) complex are thermodynamically unstable and do not build up in appreciable concentrations during the course of the reaction. As a consequence, the key steps that control the scope of viable substrates and various aspects of selectivity have remained largely uncharacterized. Herein, a direct experimental investigation of the dinuclear metallacycle‐forming step of the Pauson–Khand reaction is reported. These studies capitalize on well‐defined d9–d9 dinickel complexes supported by a naphthyridine–diimine (NDI) pincer ligand as functional surrogates of Co2(CO)8.

Well-Defined Models for the Elusive Dinuclear Intermediates of the Pauson-Khand Reaction.

The mechanism of the Pauson-Khand reaction has attracted significant interest due to the unusual dinuclear nature of the Co2 (CO)x active site. Experimental and computational data have indicated that the intermediates following the initial Co2 (CO)6 (alkyne) complex are thermodynamically unstable and do not build up in appreciable concentrations during the course of the reaction. As a consequence, the key steps that control the scope of viable substrates and various aspects of selectivity have remained largely uncharacterized. Herein, a direct experimental investigation of the dinuclear metallacycle-forming step of the Pauson-Khand reaction is reported. These studies capitalize on well-defined d(9) -d(9) dinickel complexes supported by a naphthyridine-diimine (NDI) pincer ligand as functional surrogates of Co2 (CO)8 .

Probing Ionic Complexes of Ethylene and Acetylene with Vacuum-Ultraviolet Radiation.

Mixed complexes of acetylene-ethylene are studied using vacuum-ultraviolet (VUV) photoionization mass spectrometry and theoretical calculations. These complexes are produced and ionized at different distances from the exit of a continuous nozzle followed by reflectron time-of-flight mass spectrometry detection. Acetylene, with a higher ionization energy (11.4 eV) than ethylene (10.6 eV), allows for tuning the VUV energy and initializing reactions either from a C2H2(+) or a C2H4(+) cation. Pure acetylene and ethylene expansions are separately carried out to compare, contrast, and hence identify products from the mixed expansion: these are C3H3(+) (m/z = 39), C4H5(+) (m/z = 53), and C5H5(+) (m/z = 65). Intensity distributions of C2H2, C2H4, their dimers and reactions products are plotted as a function of ionization distance. These distributions suggest that association mechanisms play a crucial role in product formation closer to the nozzle. Photoionization efficiency (PIE) curves of the mixed complexes demonstrate rising edges closer to both ethylene and acetylene ionization energies. We use density functional theory (ωB97X-V/aug-cc-pVTZ) to study the structures of the neutral and ionized dimers, calculate their adiabatic and vertical ionization energies, as well as the energetics of different isomers on the potential energy surface (PES). Upon ionization, vibrationally excited clusters can use the extra energy to access different isomers on the PES. At farther ionization distances from the nozzle, where the number densities are lower, unimolecular decay is expected to be the dominant mechanism. We discuss the possible decay pathways from the different isomers on the PES and examine the ones that are energetically accessible.

Trimerization of Acetylene Catalyzed by Ir(PH2CH2CH2PH2)Cl(cod): A Computational Study

Abstract The mechanisms for the trimerization of acetylene in the presence of (PH2CH2CH2PH2)IrCl as an active catalyst were investigated by density functional (B3LYP and M06) theory calculations. The reactant bis(acetylene)–Ir complex has a distorted trigonal bipyramid structure, and thus, there are three types of equilibrium structures connected by pseudorotation. The first oxidative coupling takes place between the acetylene molecule coordinating at the axial position and that in the equatorial plane in these reactant complexes to afford square pyramidal iridacyclopentadiene complexes through one of the two favorable transition states. Then, the third acetylene molecule attacks the iridacyclopentadiene intermediate, accompanied by Cl migration, to afford the iridacyclopentadiene–acetylene complex. The formation of a benzene complex from this acetylene complex involves reaction pathways based on intramolecular [4+2] cycloaddition and the Schore mechanism through iridacycloheptatriene, as well as the bicycle mechanism. The most favorable pathway for the formation of the benzene complex is through intramolecular [4+2] cycloaddition to form the η4-benzene–Ir complex, and finally, to the η2-benzene–Ir complex. This reaction mechanism is compared with that for reactions catalyzed by TpIr and CpIr systems.

Synthesis and conformational behavior of metallacyclicdipeptides derived from coordination of side chain alkynylamino acids to tungsten

Three dipeptides bearing alkynes on their side chains (9 (derived from dilysine), 14 (derived from dicysteine) and 17 (derived from diglycine)) were prepared and reacted with W(CO)3(dmtc)2 [dmtc = dimethyldithiocarbamate] to afford, respectively, three metallacyclicpeptides, 18, 19 and 20. The metallacyclicpeptides were characterized by HPLC, ES-MS, and 1H NMR. The conformational behavior of the alkynes about the tungsten center was assessed using 1H NMR. It was found that all three metallacyclicpeptides adopt multiple conformations of the alkynes relative to the tungsten. Both 18 and 19 appear to adopt all 8 possible conformations, while 20 adopts a limited number of conformations. The ability of the alkynes to equilibrate between the syn and anti conformations was assessed by examining the alkyne hydrogen resonances using variable temperature 1H NMR. It was found that the alkyne ligands in 18 and 19 will equilibrate between the syn and anti conformations. The alkyne hydrogen resonances in 18 coalesce to one signal around 343 K, while the alkyne hydrogen resonances in 19 do not completely coalesce even by 360 K. Complex 18 has a larger ring than complex 19, and the higher temperature of coalescence for 19 is attributed to its smaller ring size. In contrast, complex 20, which has the smallest ring size, cannot equilibrate between the syn and anti conformations, even at elevated temperatures. The results show that cyclic tungsten–bis(alkyne) complexes will form ring systems with ring sizes of approximately 10 atoms, that ring sizes of approximately 10 atoms are rigid, and that rigidity is lost as the ring size is increased.

Zwitterionic nickel(II) complexes: Synthesis, characterization, decomposition, and stoichiometric and catalytic reactivities

Zwitterionic nickel(II) compounds with a borate-containing anionic bidentate phosphine ligand (PBP−) have been synthesized and some of them crystallographically characterized. The methyl complex, (PBP−)Ni+CH3(NCCH3), reacts with H2 to form an 12-membered macrocycle containing three Ni nuclei and reacts with carbon monoxide (CO) to afford the acetyl complex (PBP−)Ni+COCH3(CO). The square planar acetyl complex is stable in solution under 1 atm of CO but undergoes irreversible decomposition under high CO pressure at room temperature. X-Ray crystallographic characterization of a decomposition product revealed fragmentation of the anionic borate under high pressure. (PBP−)Ni+COCH3(CO) is an active catalyst for ethylene-CO copolymerization, but its productivity is low likely due to its instability under high CO pressure.