Novel Non-Symmetric Nickel-Diimine Complexes for the Homopolymerization of Ethene: Control of Branching by Catalyst Design

2002 ◽  
Vol 57 (10) ◽  
pp. 1141-1146 ◽  
Author(s):  
Markus Schmid ◽  
Robert Eberhardt ◽  
Jürgen Kukral ◽  
Bernhard Rieger
Keyword(s):  
Nmr Spectroscopy ◽  
Catalyst Design ◽  
Methyl Groups ◽  
Degree Of Branching ◽  
Diimine Ligands ◽  
Melting Transitions ◽  
Diimine Complexes ◽  
C Nmr ◽  
Ethene Polymerization

Non-symmetric diimine ligands (Ar-N=C(CH3)-(CH3)C=NAr*; Ar: 2,6-diisopropyl-phenyl; Ar*: 2,6-di(4-tert-butyl-phenyl)phenyl (4b), 2,6-di(4-OCH3)-phenyl)phenyl (4c)) were synthesized and converted in-situ into the corresponding nickel dibromo complexes (5b, c) by reaction with (DME)NiBr2. The complexes were activated for ethene polymerization by treatment with MAOat ambient temperature. The resulting highmolecular weight polymer products (MW > 4.0 x 106 g mol-1) have a branched microstructure (predominantly methyl groups), as indicated by 13C NMR spectroscopy. The degree of branching can be controlled by a proper choice of the 2,6-diphenyl modified aniline moieties resulting in melting transitions ranging from 92 - 130 °C.

2,5-Bridged 1-Carba-arachno-pentaborane(10) Derivatives – Intermediates on the Way to Pentaalkyl-1,5-dicarba-closo-pentaboranes(5)

2015 ◽  
Vol 70 (10) ◽  
pp. 741-745 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Hans-Joerg Schanz
Keyword(s):  
Nmr Spectroscopy ◽  
Low Temperature ◽  
Thermal Degradation ◽  
Dft Calculations ◽  
Large Excess ◽  
Thermally Induced ◽  
Independent Synthesis ◽  
Induced Decomposition ◽  
C Nmr

AbstractStimulated by a report from (R. Köster, G. Benedikt, M. A. Grassberger, Liebigs Ann. Chem. 1968, 719, 187.) on a carbaborane, for which the structure of 2,3,4,5,-tetraethlyl-1-methyl-2,5-μ-(ethyl-1′,1′-diyl)-1-carba-arachno-pentaborane(10) 1 was proposed, an independent synthesis was developed. Diethyl(ethynyl)borane was generated in situ in the presence of a large excess of “Et2B–H” (hydride bath) by ethynyl/H exchange, using ethynyl(trioctyl)tin to react in a mixture with diethyl(vinyl)borane at low temperature. Hydroboration and Et2B–H-catalysed condensation afforded 1, as shown by 11B, 13C NMR spectroscopy and DFT calculations. Thermal degradation of 1 gave 2,3,4-triethyl-1,5-dimethyl-1,5-dicarba-closo-pentaborane(5), whereas the pentaethyl-1,5-dicarba-closo-pentaborane(5) resulted from thermally induced decomposition of other suitably substituted arachno carbaboranes.

In situ preparation of cyclopropanones with the bicyclo[3.1.0]hexan-6-one skeleton (substituted examples of the Loftfield intermediate). Confirmation of a very facile intramolecular alkyl cyclopropanone – dienol rearrangement

1996 ◽  
Vol 74 (1) ◽  
pp. 79-87 ◽  
Author(s):  
T. S. Sorensen ◽  
F. Sun
Keyword(s):  
Nmr Spectroscopy ◽  
Sigmatropic Rearrangement ◽  
Unsaturated Ketone ◽  
Tert Butyl ◽  
H Nmr ◽  
In Situ Preparation ◽  
Rate Determining Step ◽  
Enol Formation ◽  
C Nmr

Four substituted bicyclo[3.1.0]hexan-6-ones (cyclopropanones) were prepared in situ, starting from the corresponding 2,6-dibromocyclohexanone and reductively removing the bromine atoms with the organometallic salt PPN+Cr(CO)4NO− The reaction is essentially instantaneous at −78 or−100 °C, and can be conveniently carried out in an NMR tube for easy characterization of the products by low-temperature 1H and 13C NMR spectroscopy. The1,5-di-tert-butyl and 1-tert-butyl analogs were thermally stable to ca. 0 °C, but the 1-tert-butyl-5-methyl and 1-tert-butyl-5-ethyl derivatives were extremely labile, rearranging at ca. −80 °C into a cross-conjugated enol, where the methyl (or ethyl) substituent was converted into an exomethylene group. These enols were also characterized as in situ species using 1H and 13C NMR spectroscopy, and by allowing the enol → α,β-unsaturated ketone rearrangement to take place at about 25 °C. The mechanism of the enol formation was investigated using a 1 -tert-butyl-5-CD3 analog, and the kH/kD ratio for enol formation was determined to be 6 ± 2. From this, the rate-determining step in the enol formation was postulated as a C-H → H-O transfer of a hydrogen atom in a cyclohexyl oxyallyl intermediate. The 1,5-di-tert-butylbicyclohexanone shows dynamic 1H NMR line broadening, the origin of which is also proposed to involve a cyclohexyl oxyallyl intermediate. Key words: cyclopropanone, oxyallyl, bicyclo[3.1.0]hexan-6-one, dienol, sigmatropic rearrangement.

Characterization of photo-intermediates in the photo-reaction pathways of a bacteriorhodopsin Y185F mutant using in situ photo-irradiation solid-state NMR spectroscopy

2015 ◽  
Vol 14 (9) ◽  
pp. 1694-1702 ◽  
Author(s):  
Kyosuke Oshima ◽  
Arisu Shigeta ◽  
Yoshiteru Makino ◽  
Izuru Kawamura ◽  
Takashi Okitsu ◽  
...  
Keyword(s):  
Solid State ◽  
Nmr Spectroscopy ◽  
Solid State Nmr ◽  
Reaction Pathways ◽  
Solid State Nmr Spectroscopy ◽  
C Nmr

Photo-reaction pathways of a Y185F-bR mutant and, CS*- and O-intermediates were examined using in situ photo-irradiation solid-state 13C NMR spectroscopy.

1H and 13C nuclear magnetic resonance assignment of fluorescent olefinic sterol derivatives for use as membrane probes

1987 ◽  
Vol 65 (8) ◽  
pp. 1784-1794 ◽  
Author(s):  
Jacinta Drew ◽  
Jean-Robert Brisson ◽  
Peter Morand ◽  
Arthur G. Szabo
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Nmr Spectroscopy ◽  
Chemical Shifts ◽  
Methyl Groups ◽  
Coupling Constant ◽  
13C Nuclear Magnetic Resonance ◽  
High Degree ◽  
Degree Of Similarity ◽  
C Nmr ◽  
Membrane Probes

A number of fluorescent steroids with unsaturated sidechains have been analyzed by high resolution 1H and 13C nmr spectroscopy. The geometry of the olefinic systems was assigned on the basis of 1H–1H shift-correlated spectra (COSY) and selected nOe difference experiments. For one of these compounds, a 13C–1H shift-correlated spectrum, a COSY spectrum, a 1H J-resolved spectrum as well as nOe experiments on the angular methyl groups permitted complete ring proton assignment and coupling constant analysis. The high degree of similarity of the ring carbon 13C chemical shifts of these steroids and cholesterol would indicate that the former have the potential for use as fluorescent probes of cholesterol domains in membranes.

Article

1998 ◽  
Vol 76 (3) ◽  
pp. 254-259
Author(s):  
Mehmet Karatas ◽  
Serap Koni ◽  
Ilknur Dogan
Keyword(s):  
Nmr Spectroscopy ◽  
Ground States ◽  
Rotational Isomerism ◽  
Optically Active ◽  
Chiral Auxiliary ◽  
Methyl Groups ◽  
Racemic Mixtures ◽  
Sterically Hindered ◽  
C Nmr

Sterically hindered N-(o-aryl)-rhodanines (a) (N-(o-aryl)-2-thioxo-4-thiazolidinones) have been synthesized and the N-(o-tolyl) and N-(o-chlorophenyl) derivatives have been converted to their dioxo analogs (b) (N-(o-aryl)-2,4-thiazolidine- diones). The chirality of the compounds in their conformational ground states was proved by detection of the diastereotopic protons or methyl groups at C-5 of the heteroring using 1H and 13C NMR spectroscopy. In the presence of the optically active auxiliary (S)-(+)-1-(9-anthryl)-2,2,2-trifluoroethanol the enantiomers of the racemic mixtures formed diastereomeric association complexes via H-bonding.Key words: chirality, chiral auxiliary, rotational isomerism, N-(o-aryl)-rhodanines, N-(o-aryl)-2,4-thiazolidinediones, 1H and 13C NMR.

scholarly journals A straightforward implementation of in situ solution electrochemical 13C NMR spectroscopy for studying reactions on commercial electrocatalysts: ethanol oxidation

2015 ◽  
Vol 51 (38) ◽  
pp. 8086-8088 ◽  
Author(s):  
L. Huang ◽  
E. G. Sorte ◽  
S.-G. Sun ◽  
Y. Y. J. Tong
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
Ethanol Oxidation ◽  
13C Nmr Spectroscopy ◽  
Nmr Study ◽  
C Nmr

The first in situ solution electrochemical 13C NMR study of ethanol oxidation on commercial Pt/C and PtRu/C was reported.

Synthesis and molecular structures of platinum(II) and platinum(IV) diimine complexes possessing fluoroalkyl ligands

2003 ◽  
Vol 81 (11) ◽  
pp. 1270-1279 ◽  
Author(s):  
Russell P Hughes ◽  
Antony J Ward ◽  
Arnold L Rheingold ◽  
Lev N Zakharov
Keyword(s):  
Reductive Elimination ◽  
Molecular Structures ◽  
Aryl Group ◽  
Organometallic Synthesis ◽  
Diimine Ligands ◽  
Diimine Complexes

A range of Pt-diimine complexes possessing fluoroalkyl and hydrofluoroalkyl ligands were synthesized from the readily prepared [Pt(diimine)Me2] complexes and the appropriate iodofluoroalkane. For complexes with diimine ligands containing substituents in the 2,6-positions of the aryl group, Pt(II) complexes were obtained due to in situ reductive elimination of MeI, while for complexes with diimine ligands of smaller steric demands (possessing substituents in the 3,5-positions or the 4-position), Pt(IV) complexes were obtained. Attempts to convert the Pt(IV) complexes to the desired Pt(II) species via reductive elimination of MeI, methane, or ethane resulted in either no reaction or degradation of the starting complex. Fluoroalkyl(methyl)platinum(II) complexes were then converted to the fluoroalkyliodoplatinum(II) complexes via addition of I2 or by reaction with aq HI. Several complexes have been characterized crystallographically.Key words: fluoroalkyl, organometallic synthesis, structure, platinum.

Unexpected Keto-enol Tautomerism in the Cyclopyridinophane Class Direct and indirect proofs

2008 ◽  
Vol 59 (10) ◽  
Author(s):  
Paul Ionut Dron ◽  
Neculai Doru Miron ◽  
Gheorghe Surpateanu
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
Stable Conformer ◽  
Ph Measurements ◽  
Theoretical Methods ◽  
Nmr Data ◽  
Tautomeric Forms ◽  
New Compounds

The paper presents the synthesis of cyclo (bis-paraquat p-phenylene p-phenylene-carbonyl) tetrakis (hexafluorophosphate), named �CETOBOX�, and the closely related structural determinations. This compound exists in three tautomeric forms. These forms were evidentiated by NMR-data (1H-NMR, TOCSY, COSY, NOESY), UV-Vis spectra coupled with pH measurements and by synthesis. As the �CETOBOX� gives �in situ� only the corresponding monoylide, the synthesis of a new fluorescent indolizine cyclophane has been performed by a 3+2 cycloaddition. All structures of the new compounds presented herein have been established by NMR spectroscopy. Also, theoretical methods (MM3, AM1, AM1-COSMO and B88LYPDFT) have been used to determine the most stable conformer structures.

The mechanism of formation of 2,7-dimethyl-2,6-octadiene in the synthesis of 3-methylene-7-methyl-1,6-octadiene

1983 ◽  
Vol 48 (7) ◽  
pp. 1864-1866
Author(s):  
Jan Bartoň ◽  
Ivan Kmínek
Keyword(s):  
Mass Spectrometry ◽  
Nmr Spectroscopy ◽  
Alkali Metal ◽  
Chromatographic Analysis ◽  
Solid Phase ◽  
Reaction Pathway ◽  
Mechanism Of Formation ◽  
Gas Chromatographic Analysis ◽  
C Nmr ◽  
Visual Observations

2,7-Dimethyl-2,6-octadiene is formed in the catalytic solution for the dimerization of 2-methyl-1,3-butadiene to β-myrcene (3-methylene-7-methyl-1,6-octadiene), as revealed by mass spectrometry and 13C NMR spectroscopy. Visual observations together with the results of gas chromatographic analysis of the catalytic solution suggest that the formation of 2,7-dimethyl-2,6-octadiene is associated with the transition of the alkali metal (sodium) from the solid phase into the solution. A reaction pathway is suggested accounting for the formation of 2,7-dimethyl-2,6-octadiene in the system.

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