Dimerization Of Alkynes Research Articles

Syntheses of Arylphosphonium Salts from Cyclotrimerization of Terminal Aryl Alknyes by a Ruthenium Pentadienyl Complex and Revisiting the Catalytic Dimerization

The synthesis of polyaryl phosphonium salts by cyclotrimerization of aryl alkynes is induced by a stoichiometric amount of the ruthenium η5-pentadienyl complex (η5-C5H7)(PPh3)2RuCl (1). With only 1 mol % quantity, complex 1 efficiently catalyzed the dimerization of aryl alkynes at room temperature to afford the corresponding (Z)-1,4-diarylbut-1-en-3-yne derivatives as the major products.

Continuous Hydrogenation of Monovinylacetylene for 1,3-Butadiene Production Catalyzed by Ionic Liquid Stabilized Pd Nanoparticles

The production of 1,3-butadiene from acetylene includes the dimerization of acetylene and hydrogenation of the dimer. This work investigated the hydrogenation process catalyzed by ionic liquid stabilized Pd nanoparticles. The Pd nanoparticles were dispersed uniformly the in ionic liquid phase by the N-heterocyclic carbene species adsorbed on the surface of the nanoparticles. However, during the reaction, the N-heterocyclic carbene layer was replaced by a hydrophobic byproduct, which caused the Pd nanoparticles to separate from the [BMIm][BF4] phase and the loss of the catalyst from the reaction phase. To solve this, n-heptane was introduced into the reaction system to re-disperse the Pd nanoparticles in n-heptane, and due to this, the Pd nanoparticles maintained a high catalytic activity for a long term. .

Observation of mixed acetylene – Nitrous oxide trimers: Infrared spectra of C2H2–(N2O)2 and (C2H2)2–N2O

Infrared spectra of the lowest energy isomers of C2H2–(N2O)2 and (C2H2)2–N2O were observed in the region of the ν1 fundamental band of the N2O monomer (∼2224cm−1) using a tunable diode laser and/or a CW quantum cascade laser to probe a pulsed supersonic slit jet expansion. One infrared band was measured for each trimer. The band for C2H2–(N2O)2 corresponds to the out-of-phase vibrations of the pair of equivalent N2O monomers. It is blue shifted by about 10cm−1with respect to the free N2O monomer. The band for (C2H2)2–N2O is slightly less blue shifted (centered at 2232.81cm−1). It can be simulated as a predominately a-type band. In addition to the normal isotopologues,the corresponding bands for C2D2–(N2O)2 and (C2D2)2–N2Owere also observed. The structures of these trimers are similar to those of the lowest energy isomers of the analogous OCS – acetylene trimers reported previously, that is, a twisted barrel with C2 symmetry for C2H2–(N2O)2 and a distorted T-shaped acetylene dimer with a coplanar N2O beside the stem of the T for (C2H2)2–N2O. Here, we present our observation and experimental results, which agree well with calculations based on distributed multipole pair potentials.

Synthesis and reactivity of water-soluble arene–ruthenium(II) complexes and dimerization of terminal alkynes in organic and aqueous media

Treatment of the dimeric precursor [{RuCl(μ-Cl) (η6-C6H5OCH2CH2OH)}2] (1) with HNCPh2 in the presence of H2O afforded the arene–ruthenium(II) complex [(η6-C6H5OCH2CH2OH) (HN]CPh2)RuCl2] (2), as well as the aquo-species [(η6-C6H5OCH2CH2OH) (H2O)RuCl2] (3). The hydroxyethoxy substituent on the arene induces water-solubility of the resulting complexes. Reaction of 2 with HCC(O)OR1 in R2OH afforded the chelate vinyl ether complexes [Tp(PPh3)Ru–C(OR2)CHC(O)OR1] (4a, R1 = Me, R2 = Me; 4b, R1 = Et, R2 = Me; 4c, R1 = Et, R2 = Et; 4d, R1 = Me, R2 = Et), respectively. Preliminary results on the catalytic activity of 2 are also accessible. Intriguingly, complex 2 catalyzes the dimerization of some terminal alkynes HCCR in organic and aqueous medium. Whereas with R = COOMe, E-selective head-to-head dimerization takes place exclusively, in the case of R = SiMe3, t-Bu isomeric mixtures of head-to-head and head-to-tail coupling products are obtained. The structure of 3 has been determined by X-ray diffraction analysis.

Experimental and theoretical studies into the formation of C4-C6 products in partially chlorinated hydrocarbon pyrolysis systems: a probabilistic approach to congener-specific yield predictions.

This work presents a study of the pyrolytic formation of vinylacetylene and benzene congeners formed from chlorinated hydrocarbon precursors, a complex, multipath polymerization system formed in a monomer-rich environment. (Co-)pyrolyses of dichloro- and trichloroethylene yield a rich array of products, and assuming a single dominant underlying growth mechanism, this (on comparing expected and observed products) allows a number of potentially competing channels to C4 and C6 products to be ruled out. Poor congener/isomer descriptions rule out even-carbon radical routes, and the absence of C3 and C5 products rule out odd-carbon processes. Vinylidenes appear unable to describe the increased reactivity of acetylenes with chlorination noted in our experiments, leaving molecular acetylene dimerization processes and, in C6 systems, the closely related Diels-Alder cyclization as the likely reaction mechanism. The feasibility of these routes is further supported by ab initio calculations. However, some of the most persuasive evidence is provided by congener-specific yield predictions enabled by the construction of a probability tree analogue of kinetic modeling. This approach is relatively quick to construct, provides surprisingly accurate predictions, and may be a very useful tool in screening for important reaction channels in poorly understood congener- or isomer-rich reaction systems.

A Series of Pincer-Ligated Rhodium Complexes as Catalysts for the Dimerization of Terminal Alkynes

A series of pincer complexes of Rh has been prepared and tested as catalysts for the dimerization of terminal alkynes. The pincers included aryl/bis(phosphinite) POCOP, aryl/bis(phosphine) PCP, and diarylamido/bis(phosphine) PNP ligands. RhI complexes of the general form (pincer)Rh(SiPr2) or (pincer)Rh(H2) were used as catalysts. In addition, the apparent donating ability of the pincer ligands was gauged through the carbonyl stretching frequencies in (pincer)Rh(CO) complexes by IR spectroscopy. All surveyed Rh complexes acted as catalysts for dimerization of 4-ethynyltoluene, 1-hexyne, or trimethysilylacetylene. The products were a mixture of E- and gem-enyne isomers, with small amounts of oligomers in some cases. The Z-enyne isomers were not observed except in two reactions. None of the catalysts showed useful selectivity for either the E- or the gem-enyne product. However, the POCOP-based catalysts bearing PiPr2 donor arms performed faster and possessed apparently greater longevity (up to 20 000 TON) than the previously reported pincer Rh catalysts.

Formation of unsaturated vicinal Zr(+)/P frustrated Lewis pairs by the unique 1,1-carbozirconation reactions.

Treatment of the metallocene cation complexes [Cp*2MCH3](+)[B(C6F5)4](-) (M = Zr or Hf) with trimethylsilyl(diarylphosphino)acetylenes Ar2P-C≡C-SiMe3 (Ar = Ph or p-tolyl) resulted in the formation of internal phosphane stabilized cations [Cp*2M-C(CH3)═C(SiMe3)PAr2](+) 4 through the unique 1,1-carbometalation reaction under mild conditions. In contrast, when the low Lewis basicity phosphane containing alkyne (C6F5)2P-C≡C-SiMe3 was used, normal 1,2-carbometalation occurred to produce complexes 5, which show agostic coordination of a Me-Si group to the metal center. Complex 4a reacts with n-butyl isocyanide to give the coordination product 6, which has the Zr-P bond retained. Treatment of 4a with N2O gave the five-membered metallaheterocycle 7 by oxidation of the phosphane. The vicinal M(+)/P complexes 4 also show some typical FLP reactivity. They add to cinnamaldehyde or paraformaldehyde, for example, to produce carbonyl addition products 8 and 9, respectively. Complex 4a adds to the N═O functionality of nitrosobenzene with formation of 10. The vicinal M(+)/P systems 4 behave as reactive frustrated Lewis pairs toward hetercumulenes, undergoing 1,2-addition to the C═O bond of CO2 and the S═O bond of SO2 to form the respective adducts 11 and 12. The Zr(+)/P FLP 4a reacts with PhN═S═O to give the addition product 13, in which the phosphane Lewis base has added to the nitrogen atom and the Zr(+) Lewis acid to both atoms of the S═O unit. The reaction of complex 4a with the metal complex [Ir(COD)Cl]2 affords a heterobimetallic Zr/Ir product 14. The vicinal M(+)/P complexes 4 can be also used as efficient catalysts for the regioselective dimerization of phenyl acetylene.

Inside Cover: Carboxylate Switch between Hydro- and Carbopalladation Pathways in Regiodivergent Dimerization of Alkynes (Chem. Eur. J. 31/2014)

Inside Cover: Carboxylate Switch between Hydro- and Carbopalladation Pathways in Regiodivergent Dimerization of Alkynes (Chem. Eur. J. 31/2014)

Carboxylate switch between hydro- and carbopalladation pathways in regiodivergent dimerization of alkynes.

Experimental and theoretical investigation of the regiodivergent palladium-catalyzed dimerization of terminal alkynes is presented. Employment of N-heterocyclic carbene-based palladium catalyst in the presence of phosphine ligand allows for highly regio- and stereoselective head-to-head dimerization reaction. Alternatively, addition of carboxylate anion to the reaction mixture triggers selective head-to-tail coupling. Computational studies suggest that reaction proceeds via the hydropalladation pathway favoring head-to-head dimerization under neutral reaction conditions. The origin of the regioselectivity switch can be explained by the dual role of carboxylate anion. Thus, the removal of hydrogen atom by the carboxylate directs reaction from the hydropalladation to the carbopalladation pathway. Additionally, in the presence of the carboxylate anion intermediate, palladium complexes involved in the head-to-tail dimerization display higher stability compared to their analogues for the head-to-head reaction.

ChemInform Abstract: Reactivity Switch Enabled by Counterion: Highly Chemoselective Dimerization and Hydration of Terminal Alkynes.

AbstractThis approach features the combination of a Pd(0) catalyst with a Broensted acid, with a neat tuning of reactivity between dimerization and hydration.

ChemInform Abstract: 1,3‐Diyne Chemistry: Synthesis and Derivations

AbstractReview: [58 refs.

ChemInform Abstract: Ligand Mediated Iron Catalyzed Dimerization of Terminal Aryl Alkynes: Scope and Limitations.

AbstractThe regioselective dimerization of terminal aryl alkynes gives only head‐to‐head dimers.

Reactivity Switch Enabled by Counterion: Highly Chemoselective Dimerization and Hydration of Terminal Alkynes

A counterion-controlled reactivity tuning in Pd-catalyzed highly chemoselective and regioselective dimerization and hydration of terminal alkynes is reported. The use of acetate as counterion favors the formation of an alkenyl alkynyl palladium intermediate which forms hitherto less reported 1,3-diaryl-substituted conjugated enynes after reductive elimination. Using chloride, which is a better leaving group, leads to anion exchange on the alkenylpalladium intermediate with hydroxide which after reductive elimination and tautomerization delivered the hydration products.

POP–Pincer Ruthenium Complexes: d6 Counterparts of Osmium d4 Species

A wide range of ruthenium complexes stabilized by the POP-pincer ligand xant(P(i)Pr2)2 (9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) were prepared starting from cis-RuCl2{κ-S-(DMSO)4} (1; DMSO = dimethyl sulfoxide). Treatment of toluene solutions of this adduct with the diphosphine under reflux leads to RuCl2{xant(P(i)Pr2)2}(κ-S-DMSO) (2), which reacts with H2 in the presence of a Brønsted base. The reaction in the presence of Et3N affords RuHCl{xant(P(i)Pr2)2}(κ-S-DMSO) (3), whereas NaH removes both chloride ligands to give RuH2{xant(P(i)Pr2)2}(κ-S-DMSO) (4). The stirring of 3 in 2-propanol under 3 atm of H2 for a long time produces the elimination of DMSO and the coordination of H2 to yield the dihydrogen derivative, RuHCl(η(2)-H2){xant(P(i)Pr2)2} (5). In contrast to H2, PPh3 easily displaces DMSO from the metal center of 3 to afford RuHCl{xant(P(i)Pr2)2}(PPh3) (6), which can be also obtained starting from RuHCl(PPh3)3 (7) and xant(P(i)Pr2)2. In contrast to 3, complex 4 does not undergo DMSO elimination to give RuH2(η(2)-H2){xant(P(i)Pr2)2} (8) under a H2 atmosphere. However, the latter can be prepared by hydrogenation of Ru(COD)(COT) (9; COD = 1,5-cyclooctadiene and COT = 1,3,5-cyclooctatriene) in the presence of xant(P(i)Pr2)2. A more efficient procedure to obtain 8 involves the sequential hydrogenation with ammonia borane of the allenylidene derivative RuCl2(═C═C═CPh2){xant(P(i)Pr2)2} (10), which is formed from the reaction of 2 with 1,1-diphenyl-2-propyn-1-ol. The hydrogenation initially gives RuCl2(═C═CHCHPh2){xant(P(i)Pr2)2} (11), which undergoes the subsequent reduction of the Ru-C double bond to yield the hydride-tetrahydroborate complex, RuH(η(2)-H2BH2){xant(P(i)Pr2)2} (12). The osmium complex, OsCl2{xant(P(i)Pr2)2}(κ-S-DMSO) (13), reacts with 1,1-diphenyl-2-propyn-1-ol in a similar manner to its ruthenium counterpart 2 to yield the allenylidene derivative, OsCl2(═C═C═CPh2){xant(P(i)Pr2)2} (14). Ammonia borane also reduces the Cβ-Cγ double bond of the allenylidene of 14. However, the resulting vinylidene species, OsCl2(═C═CHCHPh2){xant(P(i)Pr2)2} (15), is inert. Complex 12 is an efficient catalyst precursor for the hydrogen transfer from 2-propanol to ketones, the α-alkylations of phenylacetonitrile and acetophenone with alcohols, and the regio- and stereoselective head-to-head (Z) dimerization of terminal alkynes.

Alkyne reactions with trimethylphosphine complexes of iridium: Lessons for the catalysis of vinyl ester formation and alkyne dimerization

The combination of iridium with trimethylphosphine ligands yields very electron rich iridium compounds that are active for terminal alkyne dimerization chemistry as well as the addition of carboxylic acids to alkynes. The structures, catalytic and stoichiometric chemistry of some iridium tris-trimethlyphosphine compounds with benzoate ligands are detailed in this paper. The roles that these compounds may play in the catalytic cycles involved in the dimerization of terminal alkynes and the addition of benzoic acid to terminal alkynes are examined and possible mechanisms for these catalytic reactions are proposed.

Ligand mediated iron catalyzed dimerization of terminal aryl alkynes: scope and limitations

Regioselective dimerization of terminal aryl alkynes to produce conjugated enynes has been achieved using FeCl3 and KO(t)Bu in the presence of either DMEDA or dppe. The reaction proceeds smoothly in toluene at 145 °C for 2 h to give the corresponding head-to-head dimers in good to excellent yields (54 to 99%) with high E-selectivity (67 : 33 to 83 : 17 E/Z). Both strongly electron-donating and electron-withdrawing groups are compatible with this procedure. The bidentate phosphine (dppe) ligand exhibits better catalytic activity than the bidentate amine (DMEDA). The aliphatic acetylene fails to react under this catalytic system which suggests that potassium tertiary butoxide activates the conjugated system of aryl acetylene through cation-pi interaction and pi-pi interaction. A radical inhibitor (galvinoxyl or TEMPO) completely suppresses the reaction. Employing FeCl2 as a catalyst instead of FeCl3, only phenyl acetylene afforded the corresponding head to head dimer in good yield. Mechanistic pathways for both FeCl3 catalyzed dimerization of aryl alkynes and FeCl2 catalyzed dimerization of phenyl acetylene have been proposed.

Microwave-assisted palladium-catalyzed highly regio- and stereoselective head to head dimerization of terminal aryl alkynes in water

A highly regio- and stereoselective oxime palladacycle/imidazolinium-catalyzed head to head dimerization of terminal aryl alkynes in water is presented.

Benzene⋯acetylene: a structural investigation of the prototypical CH⋯π interaction

The structure of a prototype CH···π system, benzene···acetylene, has been determined in the gas phase using Fourier-transform microwave spectroscopy. The spectrum is consistent with an effective C(6v) structure with an H···π distance of 2.4921(1) Å. The HCCH subunit likely tilts by ~5° from the benzene symmetry axis. The dipole moment was determined to be 0.438(11) D from Stark effect measurements. The observed intermolecular distance is longer than in similar benzene···HX complexes and than the distances observed in the benzene···HCCH cocrystal and predicted by many high level ab initio calculations; however, the experimentally estimated binding energy of 7.1(7) kJ mol(-1) is similar to previously studied benzene···HX complexes. Several additional sets of transitions were observed in the rotational spectrum, likely corresponding to excited states arising from low energy intermolecular vibrational modes of the dimer.

Dispersible and discrete metalloporphyrin-based CMP nanoparticles enabling colorimetric detection and quantitation of gaseous SO2

Metalloporphyrin-based CMP nanoparticles synthesized by the oxidative dimerization of terminal alkynes in the toluene-in-water miniemulsion possess native porosity, outstanding solution processability and uniform nanosized distribution. Also, they exhibit the sensitive color-switching ability for quantitative assay of gaseous SO2 by the noncovalent complex-displacement reaction at liquid-solid or gas-solid interfaces.

ChemInform Abstract: A Broensted Acid‐Catalyzed Generation of Palladium Complexes: Efficient Head‐to‐Tail Dimerization of Alkynes.

AbstractA highly selective head‐to‐tail dimerization of aliphatic and aromatic alkynes (I) and (III) is reported.