- Canopy Catalysts for Alkyne Metathesis: Investigations into a Bimolecular Decomposition Pathway and the Stability of the Podand Cap
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Molybdenum alkylidyne complexes with a trisilanolate podand ligand framework (“canopy catalysts”) are the arguably most selective catalysts for alkyne metathesis known to date. Among them, complex 1 a endowed with a fence of lateral methyl substituents on the silicon linkers is the most reactive, although fairly high loadings are required in certain applications. It is now shown that this catalyst decomposes readily via a bimolecular pathway that engages the Mo≡CR entities in a stoichiometric triple-bond metathesis event to furnish RC≡CR and the corresponding dinuclear complex, 8, with a Mo≡Mo core. In addition to the regular analytical techniques, 95Mo NMR was used to confirm this unusual outcome. This rapid degradation mechanism is largely avoided by increasing the size of the peripheral substituents on silicon, without unduly compromising the activity of the resulting complexes. When chemically challenged, however, canopy catalysts can open the apparently somewhat strained tripodal ligand cages; this reorganization leads to the formation of cyclo-tetrameric arrays composed of four metal alkylidyne units linked together via one silanol arm of the ligand backbone. The analogous tungsten alkylidyne complex 6, endowed with a tripodal tris-alkoxide (rather than siloxide) ligand framework, is even more susceptible to such a controlled and reversible cyclo-oligomerization. The structures of the resulting giant macrocyclic ensembles were established by single-crystal X-ray diffraction.
- Hillenbrand, Julius,Korber, J. Nepomuk,Leutzsch, Markus,N?thling, Nils,Fürstner, Alois
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- "canopy Catalysts" for Alkyne Metathesis: Molybdenum Alkylidyne Complexes with a Tripodal Ligand Framework
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A new family of structurally well-defined molybdenum alkylidyne catalysts for alkyne metathesis, which is distinguished by a tripodal trisilanolate ligand architecture, is presented. Complexes of type 1 combine the virtues of previous generations of silanolate-based catalysts with a significantly improved functional group tolerance. They are easy to prepare on scale; the modularity of the ligand synthesis allows the steric and electronic properties to be fine-tuned and hence the application profile of the catalysts to be optimized. This opportunity is manifested in the development of catalyst 1f, which is as reactive as the best ancestors but exhibits an unrivaled scope. The new catalysts work well in the presence of unprotected alcohols and various other protic groups. The chelate effect entails even a certain stability toward water, which marks a big leap forward in metal alkylidyne chemistry in general. At the same time, they tolerate many donor sites, including basic nitrogen and numerous heterocycles. This aspect is substantiated by applications to polyfunctional (natural) products. A combined spectroscopic, crystallographic, and computational study provides insights into structure and electronic character of complexes of type 1. Particularly informative are a density functional theory (DFT)-based chemical shift tensor analysis of the alkylidyne carbon atom and 95Mo NMR spectroscopy; this analytical tool had been rarely used in organometallic chemistry before but turns out to be a sensitive probe that deserves more attention. The data show that the podand ligands render a Mo-alkylidyne a priori more electrophilic than analogous monodentate triarylsilanols; proper ligand tuning, however, allows the Lewis acidity as well as the steric demand about the central atom to be adjusted to the point that excellent performance of the catalyst is ensured.
- Copéret, Christophe,Fürstner, Alois,Gordon, Christopher P.,Hillenbrand, Julius,Leutzsch, Markus,N?thling, Nils,Wille, Christian,Yiannakas, Ektoras
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supporting information
p. 11279 - 11294
(2020/07/13)
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- Steric, conjugation and electronic impacts on the photoluminescence and electroluminescence properties of luminogens based on phosphindole oxide
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Aggregation-induced emission (AIE) is currently receiving intense interest because of its important implications in photophysics. The structure-property relationship decipherment of AIE luminogens is of crucial importance for the fundamental understanding and application exploration. In this research, a series of novel luminogens based on phosphindole oxide (PIO), including a peculiar one with a folded conformation and apparent through-space conjugation, were synthesized and studied as models to elucidate the AIE mechanism. The significant impacts of steric, conjugation and electronic effects on the AIE property are presented based on the results of crystallography analysis, optical spectra measurements and theoretical computation. Non-doped yellow organic light-emitting diodes were fabricated with the new PIO-based luminogens, and they exhibited high brightness, good electroluminescence efficiencies and low efficiency roll-off.
- Zhuang, Zeyan,Bu, Fan,Luo, Wenwen,Peng, Huiren,Chen, Shuming,Hu, Rongrong,Qin, Anjun,Zhao, Zujin,Tang, Ben Zhong
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p. 1836 - 1842
(2017/02/23)
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- Pd(NHC)PEPPSI-diazonium salts: An efficient blend for the decarboxylative Sonogashira cross coupling reaction
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An efficient N-heterocyclic carbene based Pd complex is described for the de-carboxylative Sonogashira coupling reaction with diazonium salts under ligand and co-catalyst free conditions. Pd(NHC)PEPPSI not only offers an air and moisture stable pre-cataly
- Bhojane, Jeevan Manohar,Jadhav, Vilas Gangadhar,Nagarkar, Jayashree Milind
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supporting information
p. 6775 - 6780
(2017/07/17)
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- Synthesis of diarylalkynes via tandem Sonogashira/decarboxylative reaction of aryl chlorides with propiolic acid
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A facile and efficient protocol for one-pot synthesis of diarylalkynes via tandem Sonogashira/decarboxylative coupling has been developed. The remarkable features of this reaction include using commercially available aryl chlorides as starting materials and taking the propiolic acid instead of expensive terminal alkynes as an acetylene source. This journal is the Partner Organisations 2014.
- Li, Xiang,Yang, Fan,Wu, Yangjie
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p. 13738 - 13741
(2014/04/03)
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- A versatile and efficient palladium-meta-terarylphosphine catalyst for the copper-free sonogashira coupling of (hetero-)aryl chlorides and alkynes
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A novel meta-terarylphosphine ligand, CyPhine, was developed and found to be a highly active promoter of copper-free Sonogashira cross-coupling reactions when combined in situ with a palladium source. The evolutionary m-terarylphosphine ligand architectur
- Yang, Yong,Chew, Xinying,Johannes, Charles W.,Robins, Edward G.,Jong, Howard,Lim, Yee Hwee
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p. 7184 - 7192
(2015/01/16)
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- Microwave-promoted copper-free Sonogashira-Hagihara couplings of aryl imidazolylsulfonates in water
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Aryl imidazol-1-ylsulfonates have been efficiently cross-coupled with aryl-, alkyl-, and silylacetylenes in neat water under copper-free conditions at 110 °C assisted by microwave irradiation. Using 0.5mol% of an oxime palladacycle as precatalyst, 2-dicyclohexylphosphino-2′,6′- dimethoxybiphenyl (SPhos, 2mol%) as ligand, hexadecyltrimethylammonium bromide (CTAB) as additive, and triethylamine (TEA) as base, a wide array of disubstituted alkynes has been prepared in good to high yields in only 30min. Copyright
- Civicos, Jose F.,Alonso, Diego A.,Najera, Carmen
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supporting information
p. 203 - 208
(2013/03/14)
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- Synthesis of symmetrical diarylalkyne from palladium-catalyzed decarboxylative couplings of propiolic acid and aryl bromides under water
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Symmetric diarylalkynes were obtained from the decarboxylative coupling reactions of aryl bromides and propiolic acid in water solvent condition. In the presence of phase transfer surfactant C18H37N(CH 3)3Cl, the catalytic system of both Pd(PPh 3)2Cl2/dppb and Pd(TPPMS)2Cl 2/TPPMS afforded the desired coupled products in good yields.
- Park, Kyungho,Bae, Goun,Park, Ahbyeol,Kim, Yong,Choe, Jaehoon,Song, Kwang Ho,Lee, Sunwoo
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experimental part
p. 576 - 580
(2011/03/18)
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- Synthesis of symmetrical and unsymmetrical diarylalkynes from propiolic acid using palladium-catalyzed decarboxylative coupling
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Figure presented. Symmetrical diarylalkynes were obtained from propiolic acid (or 2-butynedioic acid) and aryl halides in good yields. The optimized reaction conditions were 2.0 equiv of aryl halide, 1.0 equiv of propiolic acid, 5.0 mol % Pd(PPh3/su
- Park, Kyungho,Bae, Goun,Moon, Jeongju,Choe, Jaehoon,Song, Kwang Ho,Lee, Sunwoo
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experimental part
p. 6244 - 6251
(2010/12/20)
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- The use of calcium carbide in one-pot synthesis of symmetric diaryl ethynes
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An efficient Pd-catalyzed copper and amine free coupling reaction of acetylene and aryl bromides was achieved with calcium carbide as an acetylene source, using inorganic base and easily prepared, air-stable aminophosphine ligand in common organic solvents, providing symmetric diaryl ethynes in one-pot with yields ranged from moderate to excellent. The Royal Society of Chemistry 2006.
- Zhang, Weiwei,Wu, Huayue,Liu, Zhiqing,Zhong, Ping,Zhang, Lin,Huang, Xiaobo,Cheng, Jiang
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p. 4826 - 4828
(2007/10/03)
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