Dimerization Of Alkynes Research Articles

Variable Mechanisms for Cobalt-Catalyzed Alkyne Dimerization Pinpointed by Quasi-Classical Trajectory Simulations

Variable Mechanisms for Cobalt-Catalyzed Alkyne Dimerization Pinpointed by Quasi-Classical Trajectory Simulations

Influence of η1‐Acetylide Ligands on the Spin State and Catalytic Activity of Iron(II) PNP Pincer Complexes

Here, we report the preparation, structures and reactivity of iron(II) PNP pincer complexes bearing one, two or three η1‐acetylide ligands bound to the metal center. The described complexes are accessible through the reaction of either one, two or ≥ 3 equivalent of LiCCR (R = SiMe3, Ph) with the dibromide complex [Fe(PNP)Br2] (1). Through increasing the number of η1‐acetylides the overall ligand field strength can be modulated resulting in S = 2, S = 1 and S = 0 spin states for mono‐, bis‐ and tris‐acetylated complexes, respectively. These findings are supported by DFT calculations on the spin state spitting in these complexes and appear to affect their binding affinity towards additional co‐ligands. The Fe(II) mono‐, bis‐ and tris‐acetylides were tested as catalyst in the catalytic dimerization of terminal alkynes. These test reactions revealed that only the bis‐acetylated complexes are catalytically competent while mono‐acetylated species are inactive. The tris‐acetylated complexes were found to be off‐cycle intermediates in the presence of lithium acetylides.

Palladium-Catalyzed Synthesis of β-Alkynyl Ketones via Selective 1,3-Alkynyl Migration of α,α-Disubstituted Allylic Alcohols.

Herein, a palladium-catalyzed 1,3-alkynyl migration of allylic alcohol for the synthesis of β-alkynyl ketone was described. This intramolecular rearrangement reaction demonstrated an enhanced reactivity compared to the traditional intermolecular alkynylation by circumventing the dimerization of alkynes, exhibiting a specific selectivity toward β-alkynyl elimination. Moreover, this reaction featured wide substrate scope, good functional group tolerance, and 100% atom economy.

Aluminium in der Chemie der Frustrierten Lewis‐Paare

AbstractDieser Übersichtsartikel beschreibt die Entwicklung der Verwendung von Aluminiumverbindungen in der Chemie der frustrierten Lewis‐Paare (FLPs) in den letzten 14 Jahren. Es werden die Synthese, die Reaktivität und die katalytischen Anwendungen von intermolekularen, intramolekularen und sogenannten versteckten FLPs mit Phosphor‐, Stickstoff‐ und Kohlenstoff‐Lewis‐Basen erörtert. Die intrinsisch höhere Acidität von Aluminiumverbindungen im Vergleich zu ihren Bor‐Analoga eröffnet unterschiedliche Reaktionswege. Die Ergebnisse werden in einer mehr oder weniger chronologischen Reihenfolge präsentiert. Es wird gezeigt, dass Al‐FLPs mit einer Vielzahl von polaren und unpolaren Substraten reagieren und sowohl stabile Addukte bilden als auch reversibel Bindungen aktivieren. Folglich werden einige katalytische Anwendungen der Titelverbindungen vorgestellt, wie z. B. die Dimerisierung von Alkinen, die Hydrierung von tert‐butylethylen und Iminen, die Aktivierung von C−F‐Bindungen, die Reduktion von CO2, die Dehydrierung von Aminboran und der Transfer von Ammoniak. Darüber hinaus wurden verschiedene Al‐FLPs als Initiatoren in Polymerisationsreaktionen eingesetzt.

Aluminum in Frustrated Lewis Pair Chemistry.

This review article describes the development of the use of aluminum compounds in the chemistry of frustrated Lewis pairs (FLPs) over the last 14 years. It also discusses the synthesis, reactivity and catalytic applications of intermolecular, intramolecular and so-called hidden FLPs with phosphorus, nitrogen and carbon Lewis bases. The intrinsically higher acidity of aluminum compounds compared to their boron analogs opens up different reaction pathways. The results are presented in a more or less chronological order. It is shown that Al FLPs react with a variety of polar and non-polar substrates and form both stable adducts and reversibly activate bonds. Consequently, some catalytic applications of the title compounds were presented such as dimerization of alkynes, hydrogenation of tert-butyl ethylene and imines, C-F bond activation, reduction of CO2, dehydrogenation of amine borane and transfer of ammonia. In addition, various Al FLPs were used as initiators in polymerization reactions.

A highly efficient Lewis acid catalyst of F-doped activated carbon for acetylene dimerization

Doping carbon-based materials with heteroatoms is considered an effective strategy to enhance their catalytic activity by altering their electronic structure and chemical properties. In this study, fluorine doped activated carbon was synthesized and used in acetylene dimerization reaction. Fluorine has the highest electronegativity (3.98) and can induce neighboring carbon atoms to possess a stronger positive charge, thereby generating Lewis acid sites between the two atoms. The resulting carbon material exhibited abundant Lewis acid sites ensuring the ample exposure and availability of catalytic sites to facilitate notable activity in acetylene dimerization. Theoretical calculations indicated that the introduction of F could help to alleviate the progression of polymers. This research provides a promising approach to the development of solid acid catalysts with excellent catalytic performance by incorporating Lewis acid sites onto carbon materials.

Assessing the activity and stereoselectivity of heterobimetallic Zr/Co complexes catalyzed terminal alkyne dimerization: A DFT study

Early/late heterobimetallic complexes are widely recognized as one of the most effective catalysts for activating coupling reactions. Herein, DFT calculations were used to investigate the specific mechanisms of terminal alkyne dimerization facilitated by two types of Zr/Co complexes: the bis (phosphinoamide) complex B and the mono (phosphinoamide) complex C. In addition, their reaction activities were compared with that of three ligand‐bridged Zr/Co complex A. The results show that the activated mechanisms of the three reactions are similar, all of them contain inner‐ and outer‐sphere mechanisms, and the inner one is the optimal process. Compared to A, the terminal alkyne dimerizations activated by B and C have the lower energy barriers and better selectivity for the E‐isomer; thus, the mono‐ and bis‐(phosphinoamide) Zr/Co complexes are expected to show better activity and selectivity than tris (phosphinoamide) complexes. The stereoselectivity of E‐, Z‐, and gem‐isomers is controlled by the reductive elimination process. The IRI analysis reveals that the selectivity for E‐ and Z‐isomers is influenced due to the notable repulsion and vdW interaction between the second alkyne and the MeNPMe2 ligand. Our work provides a theoretical basis for experimental applications and offers inspiration for the design of high selectivity heterobimetallic complexes.

Influence of Brönsted Acid Sites on Activated Carbon-Based Catalyst for Acetylene Dimerization.

Activated carbon (AC) has been widely used as a support material with both tunable acidity and abundant functional groups for solid acid catalysts in various chemical processes such as acetylene dimerization. A facile, mild acid modification method that directly activates AC to generate rich defects and oxygen functional group surface structures with Brönsted acid sites and an enhanced conductivity is presented here. Impressively, the catalyst with optimized Brönsted acid sites and an enhanced dispersion of active components exhibited a superior acetylene dimerization catalytic activity. Moreover, theoretical calculations indicated that an increase in hydrogen concentration could inhibit the formation of coke. This research offered a feasible potential way to devise and construct a carbon-based solid acid catalyst with an excellent catalytic performance.

Z-selective dimerization of terminal alkynes by a (PNNP)FeII complex.

A tetradentate bis(amido)bis(phosphine) FeII complex, (PNNP)Fe, is shown to activate the terminal C-H bond of aryl alkynes across its Fe-Namide bonds. (PNNP)Fe is also shown to catalytically dimerize terminal aryl alkynes to produce 1,3-enynes with Z : E ratios as high as 96 : 4 with yields up to 95% and loadings as low as 1 mol% at 30 °C in 2 h. A plausible metal-ligand cooperative mechanism invoking a vinylidene intermediate is proposed.

Mechanism and Stereoselectivity Control of Terminal Alkyne Dimerization Activated by a Zr/Co Heterobimetallic Complex: A DFT Study.

Heterobimetallic complexes have recently garnered considerable attention in organic synthesis owing to their high activity and selectivity, which surpass those of monometallic complexes. In this study, the detailed mechanisms of terminal alkyne dimerization activated by the heterobimetallic Zr/Co complex, as well as the different stereoselectivities of Me3SiC≡CH and PhC≡CH dimerization, were investigated and elucidated by using density functional theory calculations. After excluding the three-molecule reaction and outer-sphere mechanisms, the inner-sphere mechanism was determined as the most optimal process. The inner-sphere mechanism involves four processes: THF dissociation and coordination of the first alkyne; ligand migration and C-H activation; N2 dissociation and insertion of the second alkyne; and reductive elimination. The stereoselectivity between the E-/Z- and gem-isomers is determined by the C-C coupling mode of the two alkynes and that of the E- and Z-isomers is determined by the sequence of the C-C coupling and hydrogen migration in the reductive elimination process. Me3SiC≡CH dimerization yields only an E-isomer owing to the large differences in the distortion and interaction energies, whereas PhC≡CH dimerization produces an E-, Z-, and gem-isomers owing to the reduced interaction energy differences.

Construction of Cu(DMF)2Cl Active Sites for Gas–Solid Acetylene Dimerization: Effects of DMF Ligand and Catalytic Mechanism

Construction of Cu(DMF)₂Cl Active Sites for Gas–Solid Acetylene Dimerization: Effects of DMF Ligand and Catalytic Mechanism

Reactive and deactivation mechanisms of acetylene dimerization on CuCl2/AC catalyst

Gas-solid acetylene dimerization has provided a facile and effective way to product MVA under mild conditions, whereas the copper-based catalysts using cuprous chloride as precursor are generally not regarded as ideal candidates, owing to its good ability for reaction with acetylene to produce explosive cuprous acetylide, and needs to help with other solvents and cosolvents for above process. Herein, we proposed a CuCl2/AC catalyst with CuCl2·H2O as the precursor. The reaction and deactivation mechanism of CuCl2/AC catalyst were investigated through experimental characterization and DFT calculation. Theoretical calculations revealed that the Cu(II) reduction, Cl dissociation (TS-1) was the rate-limiting step in CuCl2/AC catalyst for acetylene dimerization reaction, and the acetylene dimerization reaction prefers to the main-reaction path of generating MVA. Moreover, ICP analysis indicated that catalyst deactivation during acetylene dimerization could be attributed to active component loss. This work provides new theoretical insights into gas-solid acetylene dimerization.

Piano‐Stool Ruthenium N‐Heterocyclic Carbene Complexes for gem‐Specific Catalytic Dimerization of Terminal Alkynes

AbstractA series of piano‐stool Ru−NHC (NHC=N‐heterocyclic carbene) complexes have been prepared and characterized. The NHC ligands used herein have varying wingtip groups, showing the impact of steric congestion on the selectivity for the catalytic dimerization of terminal alkynes.

Efficient Fe-Catalyzed Terminal Alkyne Semihydrogenation by H2: Selectivity Control via a Bulky PNP Pincer Ligand

We report an efficient semihydrogenation of terminal alkynes with H2, catalyzed by a modified, tetramethylated PNP pincer Fe hydride complex. The reactivity contrasts with an analogous classical PNP Fe hydride complex containing CH2 arms, which catalyzes predominantly terminal alkyne dimerization even in the presence of H2, and with an N-Me arm PNP Fe complex, which is known to cause overreduction to alkanes and requires the presence of a trimethylsilyl protective group. Such straightforward PNP ligand modification is a convenient tool that switches reactivity and leads to selective alkene formation, with no dimerization side products observed and only a minor contribution from overreduction.

Deactivation Mechanism and Regeneration of the CuCl/Activated Carbon Catalyst for Gas-Solid Acetylene Dimerization.

Acetylene dimerization is necessary to the coal chemical industry for producing monovinylacetylene, while the deactivation mechanism and regeneration of catalysts have not been studied in detail, which is crucial to the design of high-efficiency catalysts for acetylene dimerization. Herein, the deactivation mechanism and regeneration methods of CuCl/activated carbon catalysts in gas-solid acetylene dimerization were studied in detail. The catalysts with different reaction times were analyzed by temperature-programmed desorption of ammonia (NH3-TPD), Fourier transform infrared (FT-IR), thermogravimetry (TG), pyridine-FTIR, and X-ray photoelectron spectroscopy (XPS) analyses. NH3-TPD results demonstrated that as the time went on, the strong acid in the samples was enhanced, while the weak acid was weakened. Similarly, pyridine-FTIR results indicated that both Brönsted and Lewis acids in the samples were decreased. TG and XPS results showed that the reasons for deactivation for acetylene dimerization in the gas-solid reaction were significantly affected by coke deposition and the change of Cu valence. The more the content of Cu+, the higher the acetylene conversion rate, implying that Cu+ may be the active center of the acetylene dimerization reaction. Thus, removing carbon deposition through calcining and increasing the content of Cu+ was an effective way of regenerating the catalyst. This work strengthened the understanding of the deactivation behavior and provides a practicable regeneration method for the catalyst in gas-solid acetylene dimerization.

Tuning the Product Distribution of Acetylene Dimerization through Bimetallic Metal–Organic Framework-Supported Nanoporous Systems

Tuning the Product Distribution of Acetylene Dimerization through Bimetallic Metal–Organic Framework-Supported Nanoporous Systems

Palladium-Catalyzed Three-Component Cross-Coupling of Conjugated Dienes with Indoles Using Ethynylbenziodazolones as Electrophilic Alkynylating Reagents.

A palladium-catalyzed regioselective 1,2-alkynyl-carbonalization of conjugated dienes with ethynylbenziodazolone (EBZ) and indoles has been developed for the first time. Various molecules containing alkenyl, alkynyl, and indole groups were readily obtained. Moreover, the resulting products can be applied to various derivatizations. This protocol uses EBZ as an electrophilic alkynylating reagent, avoiding the byproduct of dimerization of alkynes.

Synthesis and Reactivity of Iron(II) Acetylide Complexes Relevant to Alkyne Dimerization

Synthesis and Reactivity of Iron(II) Acetylide Complexes Relevant to Alkyne Dimerization

Dimerization of aryl alkynes by Grubbs-Hoveyda complex: investigation of factors affecting the efficiency of the process based on experimental and theoretical approaches

The 2nd generation Grubbs-Hoveyda complex in the presence of slight excess of triphenylphosphine was found as an efficient catalyst for the synthesis of 1,4-disubstituted enynes with preference for head-to-head coupling and Z-selectivity form in the dimerization of various terminal aryl alkynes. Selective product formation was affected by the steric and the electronic properties of the phosphine used as well as the substituents of the alkynes. In order to shed some light on the properties of the alkynes that may affect the yield of desired products a set of 14 alkyne derivatives was characterized on the basis of Density Functional Theory (DFT) using ωB97XD functional and 6-311++G(d,p) basis set. The Atoms in Molecules (AIM) theory was employed for electronic structure and topological analyses of the investigated compounds. The quantitative description of the substituent effect was carried out with assistance of the Harmonic Oscillator Model of Aromaticity (HOMA), charge of the Substituent Active Region (cSAR(X)) and Substituent Effect Stabilization Energy (SESE). It was found that substituents in the phenyl ring are able to affect the geometric and electronic structure of the alkynyl moiety. The experimental and theoretical results revealed that high activity of the investigated ruthenium complex towards dimerization of alkynes is related with σ-donor ability and bulkiness of added phosphine combined with small size aryl alkyne bearing electron-withdrawing group. However, the influence of the structure of aryl alkyne on the catalyst activity could not be easily explained only on the basis of steric and electronic factors.

Regio‐ and Stereoselective Synthesis of Ynenamides through Gold(I)‐Catalyzed Hydroalkynylation of Ynamides

AbstractTransition metal catalysis is a useful tool for C−C bond‐forming reactions. Of special interest is the hydroalkynylation reaction of alkynes, which provides a simple method for the synthesis of enynes representing interesting structural motifs in organic chemistry. So far, there are only a few examples of gold(I)‐catalyzed hydroalkynylation reactions. Herein, we were able to show experimentally that the gold(I)‐catalyzed hydroalkynylation of ynamides leads regio‐ and stereoselectively to the corresponding ynenamides, a rather unknown type of molecule. A wide range of products could be generated with yields up to 90 % and, in contrast to many other gold‐catalyzed alkyne dimerization reactions, alkyl groups are tolerated. Quantum chemical calculations and NMR labelling experiments reveal a mechanism via dual gold catalysis.