scholarly journals Hoveyda–Grubbs catalysts with an N→Ru coordinate bond in a six-membered ring. Synthesis of stable, industrially scalable, highly efficient ruthenium metathesis catalysts and 2-vinylbenzylamine ligands as their precursors

2019 ◽  
Vol 15 ◽  
pp. 769-779 ◽  
Author(s):  
Kirill B Polyanskii ◽  
Kseniia A Alekseeva ◽  
Pavel V Raspertov ◽  
Pavel A Kumandin ◽  
Eugeniya V Nikitina ◽  
...  
Keyword(s):  
Ring Opening ◽  
The Novel ◽  
Ring Closing Metathesis ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cross Metathesis ◽  
Grubbs Catalysts ◽  
Coordinate Bond ◽  
Metathesis Catalysts ◽  
Hofmann Cleavage

A novel and efficient approach to the synthesis of 2-vinylbenzylamines is reported. This involves obtaining 2-vinylbenzylamine ligands from tetrahydroisoquinoline by alkylation and reduction followed by the Hofmann cleavage. The resultant 2-vinylbenzylamines allowed us to obtain new Hoveyda–Grubbs catalysts, which were thoroughly characterised by NMR, ESIMS, and X-ray crystallography. The utility of this chemistry is further demonstrated by the tests of the novel catalysts (up to 10−2 mol %) in different metathesis reactions such as cross metathesis (CM), ring-closing metathesis (RCM) and ring-opening cross metathesis (ROCM).

scholarly journals Halide exchanged Hoveyda-type complexes in olefin metathesis

2010 ◽  
Vol 6 ◽  
pp. 1091-1098 ◽  
Author(s):  
Julia Wappel ◽  
César A Urbina-Blanco ◽  
Mudassar Abbas ◽  
Jörg H Albering ◽  
Robert Saf ◽  
...  
Keyword(s):  
Olefin Metathesis ◽  
Ring Opening ◽  
Catalytic Performance ◽  
Ring Closing Metathesis ◽  
Cross Metathesis ◽  
Metathesis Reactions ◽  
Metathesis Catalysts

The aims of this contribution are to present a straightforward synthesis of 2nd generation Hoveyda-type olefin metathesis catalysts bearing bromo and iodo ligands, and to disclose the subtle influence of the different anionic co-ligands on the catalytic performance of the complexes in ring opening metathesis polymerisation, ring closing metathesis, enyne cycloisomerisation and cross metathesis reactions.

New pseudohalide ligands in Ru-catalyzed olefin metathesis — A robust, air-activated iminopyrrolato catalyst

2005 ◽  
Vol 83 (6-7) ◽  
pp. 748-754 ◽  
Author(s):  
Samantha D Drouin ◽  
Heather M Foucault ◽  
Glenn PA Yap ◽  
Deryn E Fogg
Keyword(s):  
Key Words ◽  
Olefin Metathesis ◽  
High Reactivity ◽  
Ring Closing Metathesis ◽  
Grubbs Catalyst ◽  
X Ray ◽  
X Ray Crystallography

Reaction of the Grubbs catalyst RuCl2(PCy3)2(CHPh) (1) with lithium 2-[(2,6-diisopropylphenyl)imino]pyrrolide·Et2O (LiNN′·Et2O) gives alkylidene complex 5, containing a chelating, σ-bound iminopyrrolato unit. The structure of 5 is confirmed by X-ray crystallography. Treatment of 5 with pyridine generates RuCl(NN′)(py)2(CHPh) (6) via displacement of PCy3. Complex 5 effects ring-closing metathesis in air, displaying high reactivity relative to 6.Key words: ruthenium, alkylidene, metathesis, pyrrolimine, iminopyrrolato.

Synthesis, characterization, and structures of zircona- and boracyclosiloxanes with ferrocenyl substituents

2002 ◽  
Vol 80 (11) ◽  
pp. 1469-1480 ◽  
Author(s):  
Karena Thieme ◽  
Sara C Bourke ◽  
Juan Zheng ◽  
Mark J MacLachlan ◽  
Fojan Zamanian ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Differential Scanning Calorimetry ◽  
Thermogravimetric Analysis ◽  
Ring Opening ◽  
Ring Opening Polymerization ◽  
The Novel ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Multinuclear Nmr Spectroscopy

The novel zirconatetraferrocenylcyclotrisiloxane Cp2Zr(OSiFc2)2O (6), dizirconatetraferrocenylcyclotetrasiloxane [Cp2Zr(OSiFc2)O]2 (7), boratetraferrocenylcyclotrisiloxane (C6H5)B(OSiFc2)2O (8), and diboratetraferrocenylcyclotetrasiloxane [(C6H5)B(OSiFc2)O]2 (9) with ferrocenyl (Fc = Fe(η-C5H4)(η-C5H5)) substituents at silicon have been prepared from the reactions of Cp2Zr(NMe2)2 and PhBCl2 with diferrocenylsilanediol Fc2Si(OH)2 (3) and tetraferrocenyldisiloxanediol [Fc2SiOH]2O (5). The compounds were characterized by mass spectrometry, elemental analysis, UV–vis, IR, Raman, and multinuclear NMR spectroscopy, as well as single crystal X-ray diffraction. Thermogravimetric analysis and differential scanning calorimetry investigation of 6–9 showed that the cycles decompose before they can undergo any thermal ring-opening polymerization. In addition, no polymerization was detected in the presence of either KOSiMe3 or HOTf. The bulky ferrocenyl substituents on the Si atoms are likely to be at least partially responsible for the inability of these heterocycles to undergo ring-opening polymerization. Key words: heterocyclosiloxanes, ferrocenyl.

scholarly journals Übergangsmetall-Carben-Komplexe, CXXXIV [1]. Synthese neuer Mono- und Biscarben-Komplexe der VI. Nebengruppe; Röntgenstruktur des ersten Bis[amino(alkoxy)carben]-Komplexes / Transition Metal Carbene Complexes, CXXXIV [1]. Synthesis of New Mono- and Bis-Carbene Complexes of Group VIb Elements; Structure of the First Bis[amino(alkoxy)carbene]-Complex

1984 ◽  
Vol 39 (5) ◽  
pp. 668-674 ◽  
Author(s):  
Ernst Otto Fischer ◽  
Rudolf Reitmeier ◽  
Klaus Ackermann
Keyword(s):  
Molecular Structure ◽  
Transition Metal ◽  
Spectroscopic Data ◽  
The Novel ◽  
Nucleophilic Agent ◽  
Reaction Conditions ◽  
Carbene Complexes ◽  
X Ray ◽  
X Ray Crystallography ◽  
New Compounds

The hexacarbonyl compounds of chromium, molybdenum and tungsten react with the highly nucleophilic agent Li NiPr2 and in a subsequent alkylation with (Et3O)BF4 to give the carbene complexes (CO)5M[C(N′Pr2)OEt] (1, 3, 4). In case of W(CO)6 and Mo(CO)6 the novel biscarbene complexes cis(CO)4M[C(NiPr2)OEt]2 (2, 5) are additionally obtained. Reaction conditions, properties and spectroscopic data of the new compounds are reported. The molecular structure of cis(CO)4W[C(NiPr2)OEt]2 (4) was determined by X-ray crystallography

1,4,8,11-Tetra[2-aryl-1-diazenyl]-1,4,8,11-tetraazacyclotetradecanes — Synthesis, characterization, and X-ray crystallography of the first tetrakistriazenes to be reported

2006 ◽  
Vol 84 (10) ◽  
pp. 1280-1289 ◽  
Author(s):  
Jeffery D Clarke ◽  
Keith Vaughan ◽  
Valerio Bertolasi
Keyword(s):  
Mass Spectrometry ◽  
High Resolution ◽  
Electrospray Mass Spectrometry ◽  
Diazonium Salt ◽  
Diazonium Salts ◽  
The Novel ◽  
Analogous Reaction ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Mean

The reactions of a series of arene diazonium salts with 1,4,8,11-tetraazacyclotetradecane (cyclam) afford the novel compounds, the 1,4,8,11-tetra[2-aryl-1-diazenyl]-1,4,8,11-tetraazacyclotetradecanes (1a–1f), which are the first examples of tetrakistriazenes to be reported. The tetrakistriazenes were characterized by IR spectroscopy, proton and carbon NMR, elemental analysis, high resolution electrospray mass spectrometry, and X-ray crystallography. The analogous reaction of a diazonium salt with 1,4,7-triazacyclononane or 1,5,9-triazacyclododecane yields the tristriazenes 2, 3a, and 3b. The structures of compounds 1c and 1e were solved by X-ray crystallography at low temperature (150 K). Both molecules display a conformation where the four phenyltriazenyl groups point alternately upwards and downwards with respect to the mean macrocyclic plane.Key words: triazene, tetrakistriazene, cyclam, tetraazacyclotetradecane, X-ray, NMR, cyclic polyamines.

PLP undergoes conformational changes during the course of an enzymatic reaction

2014 ◽  
Vol 70 (2) ◽  
pp. 596-606 ◽  
Author(s):  
Ho-Phuong-Thuy Ngo ◽  
Nuno M. F. S. A. Cerqueira ◽  
Jin-Kwang Kim ◽  
Myoung-Ki Hong ◽  
Pedro Alexandrino Fernandes ◽  
...  
Keyword(s):  
Conformational Change ◽  
Conformational Changes ◽  
Catalytic Mechanism ◽  
Enzymatic Reaction ◽  
Nucleophilic Attack ◽  
The Novel ◽  
X Ray ◽  
X Ray Crystallography ◽  
Starting Point ◽  
High Level

Numerous enzymes, such as the pyridoxal 5′-phosphate (PLP)-dependent enzymes, require cofactors for their activities. Using X-ray crystallography, structural snapshots of the L-serine dehydratase catalytic reaction of a bacterial PLP-dependent enzyme were determined. In the structures, the dihedral angle between the pyridine ring and the Schiff-base linkage of PLP varied from 18° to 52°. It is proposed that the organic cofactor PLP directly catalyzes reactions by active conformational changes, and the novel catalytic mechanism involving the PLP cofactor was confirmed by high-level quantum-mechanical calculations. The conformational change was essential for nucleophilic attack of the substrate on PLP, for concerted proton transfer from the substrate to the protein and for directing carbanion formation of the substrate. Over the whole catalytic cycle, the organic cofactor catalyzes a series of reactions, like the enzyme. The conformational change of the PLP cofactor in catalysis serves as a starting point for identifying the previously unknown catalytic roles of organic cofactors.

Structural studies of some 1-polymethyleneimino-2,4-dinitrobenzenesand related compounds; crystal structure of 1-(cis-2′,6′-dimethylpiperidin-1′-yl)-2,4-dinitrobenzene

2000 ◽  
Vol 53 (8) ◽  
pp. 715 ◽  
Author(s):  
Maureen F. Mackay ◽  
Douglas J. Gale ◽  
John F. K. Wilshire
Keyword(s):  
Crystal Structure ◽  
Phenyl Ring ◽  
Ring Opening ◽  
Boat Conformation ◽  
Structural Studies ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Mean ◽  
Related Compounds ◽  
Solid State Conformation

The ultraviolet and 1H n.m.r. spectra of some 1-polymethyleneimino-2,4-dinitrobenzenes and related compounds are discussed. The effect of trifluoroacetic acid on these spectra was also investigated; with 1-azetidinyl-2,4-dinitrobenzene, acid-catalysed ring opening was observed. The solid-state conformation of 1-(cis-2′,6′-dimethylpiperidin-1′-yl)-2,4-dinitrobenzene has been defined by single-crystal X-ray crystallography. Triclinic crystals belong to the space group P–1 with a 8.165(1), b 7.865(1), c 11.148(1) Å, α 95.23(1), β 106.00(1), γ 92.63(1)˚ and Z 2. The structure was refined to a final R of 0.048 for the 2222 observed data. In the crystal, the phenyl ring adopts a slight boat conformation, while the amino and o-nitro groups are significantly twisted from the mean plane of the ring.

scholarly journals Synthesis, biophysical properties, and RNase H activity of 6’-difluoro[4.3.0]bicyclo-DNA

2019 ◽  
Vol 15 ◽  
pp. 79-88 ◽  
Author(s):  
Sibylle Frei ◽  
Adam K Katolik ◽  
Christian J Leumann
Keyword(s):  
Building Block ◽  
Ring Opening ◽  
Structural Investigation ◽  
Cyclopropane Ring ◽  
Cd Spectroscopy ◽  
Rnase H ◽  
Biophysical Properties ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cleavage Assay

Here we present the synthesis, the biophysical properties, and the RNase H profile of 6’-difluorinated [4.3.0]bicyclo-DNA (6’-diF-bc4,3-DNA). The difluorinated thymidine phosphoramidite building block was synthesized starting from an already known gem-difluorinated tricyclic glycal. This tricyclic siloxydifluorocyclopropane was converted into the [4.3.0]bicyclic nucleoside via cyclopropane ring-opening through the addition of an electrophilic iodine during the nucleosidation step followed by reduction. The gem-difluorinated bicyclic nucleoside was then converted into the corresponding phosphoramidite building block which was incorporated into oligonucleotides. Thermal denaturation experiments of these oligonucleotides hybridized to complementary DNA or RNA disclosed a significant destabilization of both duplex types (ΔT m/mod = −1.6 to −5.5 °C). However, in the DNA/RNA hybrid the amount of destabilization could be reduced by multiple insertions of the modified unit. In addition, CD spectroscopy of the oligonucleotides hybridized to RNA showed a similar structure than the natural DNA/RNA duplex. Furthermore, since the structural investigation on the nucleoside level by X-ray crystallography and ab initio calculations pointed to a furanose conformation in the southern region, a RNase H cleavage assay was conducted. This experiment revealed that the oligonucleotide containing five modified units was able to elicit the RNase H-mediated cleavage of the complementary RNA strand.

scholarly journals A Simple, Efficient, and Eco-Friendly Method for the Preparation of 3-Substituted-2,3-dihydroquinazolin-4(1H)-one Derivatives

Molecules ◽  
2019 ◽  
Vol 24 (22) ◽  
pp. 4052 ◽  
Author(s):  
Zainab Almarhoon ◽  
Kholood A. Dahlous ◽  
Rakia Abd Alhameed ◽  
Hazem A. Ghabbour ◽  
Ayman El-Faham
Keyword(s):  
Molecular Structure ◽  
Cost Effective ◽  
Environmentally Benign ◽  
Conventional Heating ◽  
Second Step ◽  
The Novel ◽  
Monoclinic Crystal ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cost Effective Method

A simple, cost-effective method under environmentally benign conditions is a very important concept for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives. The present work describes an efficient and eco-friendly protocol for the synthesis of 2-amino-N-(2-substituted-ethyl)benzamide and 3-substituted-2,3-dihydroquinazolin-4(1H)-one derivatives. The novel feature of this protocol is the use of 2-methyl tetrahydrofuran (2-MeTHF) as an eco-friendly alternative solvent to tetrahydrofuran (THF) in the first step. In the second step, methanol in the presence of potassium carbonate as a catalyst was used under conventional heating or microwave irradiation, which provided an eco-friendly method to afford the target products in excellent yields and purities. NMR (1H and 13C), elemental analysis, and LC-MS confirmed the structures of all compounds. X-ray crystallography further confirmed the structure of the intermediate 2-amino-N-(2-substituted-ethyl)benzamide 3a. The molecular structure of 3a was monoclinic crystal, with P21/c, a = 13.6879 (11) Å, b = 10.2118 (9) Å, c = 9.7884 (9) Å, β = 105.068 (7)°, V = 1321.2 (2) Å3, and Z = 4.

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