π‐Face Donor Properties of N‐Heterocyclic Carbenes in Grubbs II Complexes

Leuthäußer, Steffen; Schmidts, Volker; Thiele, Christina M.; Plenio, Herbert

doi:10.1002/chem.200800139

Cited by 138 publications

(97 citation statements)

References 99 publications

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“…[28] However, whereas this data can nicely be correlated with the one of the other classes of ligands, the LEP has not been determined for many NHC ligands, probably in part because of the requirement for less common electrochemical devices. [29] One established method for measuring the electron-donor ability of ligands is the synthesis of [Ni(CO) 3 (L)]. This method makes use of the fact that electron density from a ligand can not only be passed on to the metal, but also on to the p* orbital of CO ligands.…”

Section: Electronic Character Of Nhcsmentioning

confidence: 99%

The Measure of All Rings—N‐Heterocyclic Carbenes

2010

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Quantification and variation of characteristic properties of different ligand classes is an exciting and rewarding research field. N-Heterocyclic carbenes (NHCs) are of special interest since their electron richness and structure provide a unique class of ligands and organocatalysts. Consequently, they have found widespread application as ligands in transition-metal catalysis and organometallic chemistry, and as organocatalysts in their own right. Herein we provide an overview on physicochemical data (electronics, sterics, bond strength) of NHCs that are essential for the design, application, and mechanistic understanding of NHCs in catalysis.

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Section: Electronic Character Of Nhcsmentioning

confidence: 99%

The Measure of All Rings—N‐Heterocyclic Carbenes

2010

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“…J. 2009, 15, 585 -588 586 N-heterocyclic carbenes [12] (Figure 2 C) was to distinguish and quantify several dynamic processes in these complexes. It was especially important to distinguish the rotation of the benzylidene unit (k 3 ) from the rotation of mesityl flaps (k 1 and k 2 ).…”

mentioning

confidence: 99%

EASY ROESY: Reliable Cross‐Peak Integration in Adiabatic Symmetrized ROESY

Thiele

Petzold

Schleucher

2008

Chemistry A European J

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Determination of the 3D structure of small-to mediumsized organic and biomolecular compounds relies on the use of several NMR parameters. Information about dihedral angles from homo-and heteronuclear 3 J scalar couplings [1][2][3] is usually combined with information on distances from the nuclear Overhauser effect (NOE).[4] Even when using the recently (re)introduced (residual) dipolar couplings [5] to study flexible compounds, [6][7][8] distance information from the NOE is still essential for structure determination. The buildup rate of the NOE, however, depends on the correlation time t c of the compound and the observation frequency w. The NOE changes sign at wt c % 1.12, which leads to the well-known phenomenon that little or no NOE is observed for medium-sized compounds (MW % 1000 g mol À1). This impedes the extraction of distance information from NOESY spectra of these compounds.This problem can be solved by using rotating-frame nuclear Overhauser effect spectroscopy (ROESY), [9,10] which yields negative cross-peaks (corresponding to positive Overhauser enhancements) for all values of wt c . In the interpretation of ROESY, however, several experimental problems-namely direct cross-peaks due to J coupling, Hartmann-Hahn matching (leading to TOCSY, total correlation spectroscopy, cross-peaks) and offset dependence [11] -have to be avoided. The offset dependence influences the crosspeak integrals of all spins depending on their offset, whereas the other two phenomena can degrade the line shapes and integrals of ROESY cross-peaks. TOCSY artefacts also impede the use of ROESY for detecting chemical exchange.[12] These problems lead to serious complications, when distances or exchange rates are to be extracted from ROESY spectra.Several ROESY pulse sequences have been proposed for removing these artefacts, [13][14][15] but they are cumbersome to set up, reduce sensitivity too much, or show pronounced offset dependence. Thus a robust, convenient procedure is needed that yields high-quality, high-sensitivity spectra that can be reliably integrated even in the presence of J coupling.We have previously shown that jump-symmetrized ROESY (JS-ROESY) combines negligible offset dependence with close-to-optimal suppression of TOCSY, [14] but the experimental setup is quite laborious as pulses with finetuned power levels (gray in Figure 1 A) are needed. Here we show that by bracketing two off-resonance spin-lock pulses with adiabatic pulses [16] , we obtain high-quality, highsensitivity spectra with no need for a sample-specific setup (Figure 1 B). The resulting spectra can be reliably quantified and TOCSY transfer is as well suppressed as in conventional JS-ROESY. The superior performance of this convenient (gray) is needed to transfer magnetization from the low-to the high-field spinlock (SL). B) Adiabatic ramps at times a-d transfer magnetization to the spinlocks. After EASY ROESY has been set up once, parameters are calculated automatically. Gradient pulses (G z ) suppress unwanted signals. Solvent suppression can easi...

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“…Authors noted that unlike other NHC ligands, NHC ewg were characterized by electronwithdrawing substituents, which render their electron donation comparable to that of trialkylphosphines [65,66] . The process was carried out in Büchi miniclave using ethene and solution of natural rubber and catalyst in toluene at 120 °C and ethene pressure of 7 bar for 3 h. Importantly, the reaction mixture was transferred to a millipore cell and filtered over a nanofiltration membrane (Mw = 500 g/mol, flow = 1 mL/min, ∆p = 3 bar) to remove residual polymers [24] .…”

Section: Metathesis Reactionsmentioning

confidence: 99%

Degradation of non-vulcanized natural rubber renewable resource for fine chemicals used in polymer synthesis

Fainleib

Pires²,

Lucas³

et al. 2013

Polímeros

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In the current scenario, there is growing interest in the products of degradation of rubber (natural and synthetic) for specific applications in different industry sectors, whose benefits in replacing conventionally used products are mainly related to sustainability. Since the degradation products of rubber can be used in different areas, several research groups may have the interest aroused by these products, but are not familiar with the aspects related to the chemical behavior of rubber. This review aims to bring together the key information in the published literature on the degradation of natural rubber, emphasizing metatheses reactions, oxidative damage and splitting of the double bond, in order to serve as a reference source for researchers from different fields interested in obtaining such kind of products. The structures and properties as well as additional chemical transformations resulting in oligomers of isoprene, functionalised oligomers and polymers based on both are also described.

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π‐Face Donor Properties of N‐Heterocyclic Carbenes in Grubbs II Complexes

Cited by 138 publications

References 99 publications

The Measure of All Rings—N‐Heterocyclic Carbenes

The Measure of All Rings—N‐Heterocyclic Carbenes

EASY ROESY: Reliable Cross‐Peak Integration in Adiabatic Symmetrized ROESY

Degradation of non-vulcanized natural rubber renewable resource for fine chemicals used in polymer synthesis

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