592-47-2Relevant academic research and scientific papers
Switching the Reactivity of Palladium Diimines with “Ancillary” Ligand to Select between Olefin Polymerization, Branching Regulation, or Olefin Isomerization
Jones, Glen R.,Basbug Alhan, Hatice E.,Karas, Lucas J.,Wu, Judy I.,Harth, Eva
supporting information, p. 1635 - 1640 (2020/11/30)
Coordinating solvents are commonly employed as ancillary ligands to stabilize late transition metal complexes and are conventionally considered to have little effect on the reaction products. Our work identifies that the presence of ancillary ligand in Pd-diimine catalyzed polymerizations of α-olefins can drastically alter reactivity. The addition of different amounts of acetonitrile allows for switching between distinct reaction modes: isomerization–polymerization with high branching (0 equiv.), regular chain-walking polymerization (1 equiv.), and alkene isomerization with no polymerization (>20 equiv.). Optimization of the isomerization reaction mode led to a general set of conditions to switch a wide variety of diimine complexes into efficient alkene isomerization catalysts, with catalyst loading as low as 0.005 mol %.
Precursor Nuclearity and Ligand Effects in Atomically-Dispersed Heterogeneous Iron Catalysts for Alkyne Semi-Hydrogenation
Faust Akl, Dario,Ruiz-Ferrando, Andrea,Fako, Edvin,Hauert, Roland,Safonova, Olga,Mitchell, Sharon,López, Núria,Pérez-Ramírez, Javier
, p. 3247 - 3256 (2021/05/31)
Nanostructuring earth-abundant metals as single atoms or clusters of controlled size on suitable carriers opens new routes to develop high-performing heterogeneous catalysts, but resolving speciation trends remains challenging. Here, we investigate the potential of low-nuclearity iron catalysts in the continuous liquid-phase semi-hydrogenation of various alkynes. The activity depends on multiple factors, including the nuclearity and ligand sphere of the metal precursor and their evolution upon interaction with the mesoporous graphitic carbon nitride scaffold. Density functional theory predicts the favorable adsorption of the metal precursors on the scaffold without altering the nuclearity and preserving some ligands. Contrary to previous observations for palladium catalysts, single atoms of iron exhibit higher activity than larger clusters. Atomistic simulations suggest a central role of residual carbonyl species in permitting low-energy paths over these isolated metal centers.
Seed-mediated Growth of Alloyed Ag-Pd Shells toward Alkyne Semi-hydrogenation Reactions under Mild Conditions?
Zheng, Yuqin,Tan, Taixing,Wang, Cheng
, p. 3071 - 3078 (2021/09/13)
Ag@Ag-Pdx core-shell nanocomposites with various Ag/Pd ratio were deposited on Ag nanoplates using a seed growth method. When physically loaded on C3N4, Ag@Ag-Pd0.077/C3N4 with optimized Ag/Pd ratio could accomplish high catalytic performance for the semi-hydrogenation of phenylacetylene as well as other aliphatic (both terminal and internal alkynes) alkynes and phenylcycloalkynes containing functional groups (such as ester, hydroxyl, ethyl groups) under room temperature and 1 atm H2. The alloying and ensemble effects are used to interpret such catalytic performance.
Deoxygenation of Epoxides with Carbon Monoxide
Maulbetsch, Theo,Jürgens, Eva,Kunz, Doris
supporting information, p. 10634 - 10640 (2020/07/30)
The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer-iridium(I) complex in combination with a Lewis acid co-catalyst to achieve a pre-activation of the epoxide substrate, as well as the elimination of CO2 from a γ-2-iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate-dependent change in the mechanism for the epoxide C?O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration.
Transfer hydrogenation of alkynes into alkenes by ammonia borane over Pd-MOF catalysts
Bakuru, Vasudeva Rao,Samanta, Debabrata,Maji, Tapas Kumar,Kalidindi, Suresh Babu
supporting information, p. 5024 - 5028 (2020/05/08)
Ammonia borane with both hydridic and protic hydrogens in its structure acted as an efficient transfer hydrogenation agent for selective transformation of alkynes into alkenes in non-protic solvents. Catalytic synergy between the μ3-OH groups of the UiO-66(Hf) MOF and Pd active sites in Pd/UiO-66(Hf) furnished an elusive >98% styrene selectivity and full phenylacetylene conversion at room temperature. Such performance is not achievable by a Pd + UiO-66(Hf) physical mixture or by a commercial Pd/C catalyst.
Fast and Selective Semihydrogenation of Alkynes by Palladium Nanoparticles Sandwiched in Metal–Organic Frameworks
Choe, Kwanghak,Li, Guodong,Qiu, Xueying,Ri, Myonghak,Shi, Xinghua,Tang, Zhiyong,Wang, Hui,Wang, Yinglong,Xue, Guangxin,Yuan, Yi,Zhao, Wenshi,Zheng, Fengbin
supporting information, p. 3650 - 3657 (2020/02/04)
The semihydrogenation of alkynes into alkenes rather than alkanes is of great importance in the chemical industry. Unfortunately, state-of-the-art heterogeneous catalysts hardly achieve high turnover frequencies (TOFs) simultaneously with almost full conversion, excellent selectivity, and good stability. Here, we used metal–organic frameworks (MOFs) containing Zr metal nodes (“UiO”) with tunable wettability and electron-withdrawing ability as activity accelerators for the semihydrogenation of alkynes catalyzed by sandwiched palladium nanoparticles (Pd NPs). Impressively, the porous hydrophobic UiO support not only leads to an enrichment of phenylacetylene around the Pd NPs but also renders the Pd surfaces more electron-deficient, which leads to a remarkable catalysis performance, including an exceptionally high TOF of 13835 h?1, 100 % phenylacetylene conversion 93.1 % selectivity towards styrene, and no activity decay after successive catalytic cycles. The strategy of using molecularly tailored supports is universal for boosting the selective semihydrogenation of various terminal and internal alkynes.
Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
Eyselein, Jonathan,F?rber, Christian,Grams, Samuel,Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Martin, Johannes,Thum, Katharina,Wiesinger, Michael
supporting information, p. 9102 - 9112 (2020/03/30)
Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2]2 (1-Ae) and Ae[N(TRIP)(DIPP)]2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3, DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.
Transition metal complexes of a bis(carbene) ligand featuring 1,2,4-triazolin-5-ylidene donors: structural diversity and catalytic applications
Donthireddy, S. N. R.,Illam, Praseetha Mathoor,Rit, Arnab,Singh, Vivek Kumar
, p. 11958 - 11970 (2020/09/21)
Dialkylation of the 1,3-bis(1,2,4-triazol-1-yl)benzene with ethyl bromide results in the formation of [L-H2]Br2which, upon salt metathesis with NH4PF6, readily yields the bis(triazolium) salt [L-H2](PF6)2with non-coordinating counterions. [L-H2](PF6)2and Ag2O react in a 1?:?1 ratio to yield a binuclear AgI-tetracarbene complex of the composition [(L)2Ag2](PF6)2which undergoes a facile transmetalation reaction with [Cu(SMe2)Br] to deliver the corresponding CuI-NHC complex [(L)2Cu2](PF6)2. In contrast, the [L-H2]Br2reacts with [Ir(Cp*)Cl2]2to generate a doubly C-H activated IrIII-NHC complex5. Similarly, the triazolinylidene donor supported diorthometalated RuII-complex6is also obtained. Complexes5and6represent the first examples of a stable diorthometalated binuclear IrIII/RuII-complex supported by 1,2,4-triazolin-5-ylidene donors. The synthesized IrIII-NHC complex5is found to be more effective than its RuII-analogue (6) for the reduction of a range of alkenes/alkynesviathe transfer hydrogenation strategy. Conversely, RuII-complex6is identified as an efficient catalyst (0.01 mol% loading) for the β-alkylation of a wide range of secondary alcohols using primary alcohols as alkylating partnersviaa borrowing hydrogen strategy.
Selective α,δ-hydrocarboxylation of conjugated dienes utilizing CO2and electrosynthesis
Buckley, Benjamin R.,Elmorsy, Saad S.,Malkov, Andrei V.,Mashaly, Mohammad A.,Said, Samy B.,Sheta, Ahmed M.
, p. 9109 - 9114 (2020/09/17)
To date the majority of diene carboxylation processes afford the α,δ-dicarboxylated product, the selective mono-carboxylation of dienes is a significant challenge and the major product reported under transition metal catalysis arises from carboxylation at the α-carbon. Herein we report a new electrosynthetic approach, that does not rely on a sacrificial electrode, the reported method allows unprecedented direct access to carboxylic acids derived from dienes at the δ-position. In addition, the α,δ-dicarboxylic acid or the α,δ-reduced alkene can be easily accessed by simple modification of the reaction conditions. This journal is
Olefin Dimerization and Isomerization Catalyzed by Pyridylidene Amide Palladium Complexes
Navarro, Miquel,Rosar, Vera,Montini, Tiziano,Milani, Barbara,Albrecht, Martin
, p. 3619 - 3630 (2018/10/05)
A series of cationic palladium complexes [Pd(N^N′)Me(NCMe)]+ was synthesized, comprising three different N^N′-bidentate coordinating pyridyl-pyridylidene amide (PYA) ligands with different electronic and structural properties depending on the PYA position (o-, m-, and p-PYA). Structural investigation in solution revealed cis/trans isomeric ratios that correlate with the donor properties of the PYA ligand, with the highest cis ratios for the complex having the most donating o-PYA ligand and lowest ratios for that with the weakest donor p-PYA system. The catalytic activity of the cationic complexes [Pd(N^N′)Me(NCMe)]+ in alkene insertion and dimerization showed a strong correlation with the ligand setting. While complexes bearing more electron donating m- and o-PYA ligands produced butenes within 60 and 30 min, respectively, the p-PYA complex was much slower and only reached 50% conversion of ethylene within 2 h. Likewise, insertion of methyl acrylate as a polar monomer was more efficient with stronger donor PYA units, reaching a 32% ratio of methyl acrylate vs ethylene insertion. Mechanistic investigations about the ethylene insertion allowed detection, for the first time, by NMR spectroscopy both cis- and trans-Pd-ethyl intermediates and, furthermore, revealed a trans to cis isomerization of the Pd-ethyl resting state as the rate-limiting step for inducing ethylene conversion. These PYA palladium complexes induce rapid double-bond isomerization of terminal to internal alkenes through a chain-walking process, which prevents both polymerization and also the conversion of higher olefins, leading selectively to ethylene dimerization.
