Synthesis of Silyl Iron Dinitrogen Complexes for Activation of Dihydrogen and Catalytic Silylation of Dinitrogen

2021 ◽  
Author(s):  
Guoliang Chang ◽  
Peng Zhang ◽  
Wenjing Yang ◽  
Yanhong Dong ◽  
Shangqing Xie ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
Electronic Effect ◽  
Dinitrogen Complexes ◽  
First Time

Three novel iron dinitrogen hydrides, [FeH(iPr-PSiMeP)(N2)(PMe3)] (1), [FeH(iPr-PSiPhP)(N2)(PMe3)] (2), and [FeH(iPr-PSiPh)(N2)(PMe3)] (3), supported by silyl ligand are synthesized for the first time by changing the electronic effect and steric hindrance...

scholarly journals A Central Role for the Armadillo Protein Plakoglobin in the Autoimmune Disease Pemphigus Vulgaris

2001 ◽  
Vol 153 (4) ◽  
pp. 823-834 ◽  
Author(s):  
Reto Caldelari ◽  
Alain de Bruin ◽  
Dominique Baumann ◽  
Maja M. Suter ◽  
Christiane Bierkamp ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
In Vitro Model ◽  
Molecular Mechanisms ◽  
Pemphigus Vulgaris ◽  
Cell Types ◽  
Linear Distribution ◽  
Igg Binding ◽  
Vitro Model ◽  
First Time

In pemphigus vulgaris (PV), autoantibody binding to desmoglein (Dsg) 3 induces loss of intercellular adhesion in skin and mucous membranes. Two hypotheses are currently favored to explain the underlying molecular mechanisms: (a) disruption of adhesion through steric hindrance, and (b) interference of desmosomal cadherin-bound antibody with intracellular events, which we speculated to involve plakoglobin. To investigate the second hypothesis we established keratinocyte cultures from plakoglobin knockout (PG−/−) embryos and PG+/+ control mice. Although both cell types exhibited desmosomal cadherin-mediated adhesion during calcium-induced differentiation and bound PV immunoglobin (IgG) at their cell surface, only PG+/+ keratinocytes responded with keratin retraction and loss of adhesion. When full-length plakoglobin was reintroduced into PG−/− cells, responsiveness to PV IgG was restored. Moreover, in these cells like in PG+/+ keratinocytes, PV IgG binding severely affected the linear distribution of plakoglobin at the plasma membrane. Taken together, the establishment of an in vitro model using PG+/+ and PG−/− keratinocytes allowed us (a) to exclude the steric hindrance only hypothesis, and (b) to demonstrate for the first time that plakoglobin plays a central role in PV, a finding that will provide a novel direction for investigations of the molecular mechanisms leading to PV, and on the function of plakoglobin in differentiating keratinocytes.

scholarly journals On the nature of the electronic effect of multiple hydroxyl groups in the 6-membered ring – the effects are additive but steric hindrance plays a role too

2017 ◽  
Vol 15 (5) ◽  
pp. 1164-1173 ◽  
Author(s):  
Christian Marcus Pedersen ◽  
Mikael Bols
Keyword(s):  
Steric Hindrance ◽  
Electronic Effect ◽  
Membered Ring ◽  
Steric Effects ◽  
Hydroxyl Groups ◽  
Base Strength ◽  
Electronic And Steric Effects

Electronic and steric effects each play important roles in determining the base strength in piperidines.

scholarly journals Exceptionally Long Covalent CC Bonds—A Local Vibrational Mode Study

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 950
Author(s):  
Alexis Antoinette Ann Delgado ◽  
Alan Humason ◽  
Robert Kalescky ◽  
Marek Freindorf ◽  
Elfi Kraka
Keyword(s):  
Bond Strength ◽  
Radical Cation ◽  
Steric Hindrance ◽  
Force Constants ◽  
Electronic Effects ◽  
Future Design ◽  
Local Vibrational Mode ◽  
Negative Hyperconjugation ◽  
New Guidelines ◽  
First Time

For decades one has strived to synthesize a compound with the longest covalent C−C bond applying predominantly steric hindrance and/or strain to achieve this goal. On the other hand electronic effects have been added to the repertoire, such as realized in the electron deficient ethane radical cation in its D3d form. Recently, negative hyperconjugation effects occurring in diamino-o-carborane analogs such as di-N,N-dimethylamino-o-carborane have been held responsible for their long C−C bonds. In this work we systematically analyzed CC bonding in a diverse set of 53 molecules including clamped bonds, highly sterically strained complexes such as diamondoid dimers, electron deficient species, and di-N,N-dimethylamino-o-carborane to cover the whole spectrum of possibilities for elongating a covalent C−C bond to the limit. As a quantitative intrinsic bond strength measure, we utilized local vibrational CC stretching force constants ka(CC) and related bond strength orders BSO n(CC), computed at the ωB97X-D/aug-cc-pVTZ level of theory. Our systematic study quantifies for the first time that whereas steric hindrance and/or strain definitely elongate a C−C bond, electronic effects can lead to even longer and weaker C−C bonds. Within our set of molecules the electron deficient ethane radical cation, in D3d symmetry, acquires the longest C−C bond with a length of 1.935 Å followed by di-N,N-dimethylamino-o-carborane with a bond length of 1.930 Å. However, the C−C bond in di-N,N-dimethylamino-o-carborane is the weakest with a BSO n value of 0.209 compared to 0.286 for the ethane radical cation; another example that the longer bond is not always the weaker bond. Based on our findings we provide new guidelines for the general characterization of CC bonds based on local vibrational CC stretching force constants and for future design of compounds with long C−C bonds.

Electronic Effect of Fluoro Substituents on Chromium(III) Complexes bearing β-Diketiminate Ligands for Ethylene Polymerization

2012 ◽  
Vol 476-478 ◽  
pp. 2201-2204 ◽  
Author(s):  
Guang Yong Xie ◽  
Xiang Zhang ◽  
Xiao Hang Xu ◽  
Ting Cheng Li ◽  
Ai Qing Zhang
Keyword(s):  
Reaction Temperature ◽  
Ethylene Polymerization ◽  
Electronic Effect ◽  
Reaction Parameters ◽  
Catalytic Activities ◽  
Alkyl Groups ◽  
Elemental Analyses ◽  
First Time ◽  
Catalytic Performances

A series of new chromium(III) complexes bearing fluoro-substituted β-diketiminate ligands have been synthesized and characterized by IR and elemental analyses. When activated by modified methylaluminoxane (MMAO), these Cr complexes exhibited moderate or high activities for ethylene polymerization (up to 370 g.mmol-1.h-1). Various reaction parameters such as reaction temperature and Al/Cr ratio were investigated in detail. Further more, it was found for the first time that the catalytic behaviors of Cr complexes can be greatly influenced by the electronic effect of fluoro substituents. The introduction of electron-withdrawing fluoro groups to ligands can improve the catalytic performances compared with those bearing alkyl groups, but incorporation of more fluoro atoms would then decrease the catalytic activities.

scholarly journals A Theoretical Analysis of the Contributions to the Internal Rotation Barrier in N-Benzylideneanilines

1990 ◽  
Vol 45 (9-10) ◽  
pp. 1199-1204
Author(s):  
K. Figueroa ◽  
M. Campos-Vallette ◽  
R. Contreras R.
Keyword(s):  
Total Energy ◽  
Internal Rotation ◽  
Steric Hindrance ◽  
Electronic Effect ◽  
Energy Surface ◽  
Rotation Barrier ◽  
Absolute Minimum ◽  
Internal Rotation Barrier ◽  
The Stability ◽  
Net Charges

Abstract An analysis, using CNDO wave functions, has been carried out on the different contributions to the internal rotation barrier in N-benzylideneaniline (1) and p-dimethylaminobenzylidene-p-nitro-aniline (2) in several conformations. The stability of the different structures has been expressed in terms of a partition of the total energy into electronic, net charges and steric hindrance contributions. Based on the shape of the total energy surface it appears that the barrier composition may be reasonably well described without approaching the absolute minimum. Rotation of the aniline group in both molecules is mainly governed by steric hindrance. Rotation of the benzylidene group shows a prevalent destabilizing electronic effect. The donor strength of the substituent in the benzylidene ring seems to play an important role in stabilizing a less nonplanar structure.

Steric effects in quaternizations. Alkylation of pyridine, thiazole, isothiazole and some benzologues with methyl, ethyl and isopropyl iodides

1976 ◽  
Vol 29 (8) ◽  
pp. 1745 ◽  
Author(s):  
LW Deady ◽  
DC Stillman
Keyword(s):  
Steric Hindrance ◽  
Electronic Effect ◽  
Alkyl Halide ◽  
Steric Effects ◽  
Methyl Ethyl ◽  
Rate Retardation

Results of quaternization reactions in sulpholane at 65� are reported. A large steric hindrance is noted for quinoline relative to pyridine. A much smaller variation in rate with change in alkyl halide is seen in the benzothiazole/thiazole pair. Steric effects are very small and the rate retardation resulting from benzofusion is ascribed largely to an electronic effect. 2,l-Benzisothiazole reacts at essentially the same rate as isothiazole under these conditions.

Hexamethylazoxybenzene. Structure, Basicity, and Rearrangement

1973 ◽  
Vol 51 (18) ◽  
pp. 3143-3149 ◽  
Author(s):  
Robin A. Cox ◽  
Erwin Buncel
Keyword(s):  
Sulfuric Acid ◽  
Steric Hindrance ◽  
Reaction Mechanisms ◽  
Electronic Effect ◽  
Two Factors ◽  
Large Distortion ◽  
Concentrated Sulfuric Acid ◽  
Steric Inhibition Of Resonance

2,2′,4,4′,6,6′-Hexamethylazoxybenzene (1) has been prepared and characterized. The u.v. spectrum is indicative of large distortion from coplanarity. 1 is only slightly more basic than azoxybenzene despite expectations due to electronic effect of the methyl substituents. Two factors are considered responsible for this: steric inhibition of resonance in the unprotonated species and steric hindrance to hydration in the conjugate acid.Rearrangement of 1 in moderately concentrated sulfuric acid gives rise to the alcohol 4-hydroxymethyl-2,2′,4′,6,6′-pentamethylazobenzene (6). A Bamberger type phenolic product which would result from methyl migration is not observed. Possible reaction mechanisms are given.

Reactions between N-Heterocyclic Carbene and Lutetium–Metallofullerenes: High Regioselectivity Directed by Electronic Effect in Addition to Steric Hindrance

2018 ◽  
Vol 84 (2) ◽  
pp. 606-612 ◽  
Author(s):  
Wangqiang Shen ◽  
Le Yang ◽  
Yongbo Wu ◽  
Lipiao Bao ◽  
Ying Li ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
Electronic Effect

Synthesis and optical properties of trifluoroethoxy-substituted double-decker phthalocyanines

2014 ◽  
Vol 18 (10n11) ◽  
pp. 1034-1041 ◽  
Author(s):  
Satoru Mori ◽  
Naoya Ogawa ◽  
Etsuko Tokunaga ◽  
Norio Shibata
Keyword(s):  
Optical Properties ◽  
Steric Hindrance ◽  
Fluorescence Spectra ◽  
Absorption And Fluorescence Spectra ◽  
Double Decker ◽  
First Time

The synthesis of trifluoroethoxy-substituted double-decker phthalocyanines was investigated for the first time. Trifluoroethoxy-substituted phthalonitriles reacted with lanthanide acetylacetonate hydrate in n-octanol in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene when refluxed. La and Eu were chosen as central metals. Phthalonitriles, including one trifluoroethoxy substituent at the α- or β-position, were nicely induced to double-decker phthalocyanines. Phthalonitrile having two trifluoroethoxy substituents at α-positions did not react, although we succeeded in leading β-di-substituted phthalonitrile to double-decker phthalocyanines. Fully trifluoroethoxy-coated phthalonitrile did not react at all. Fluorophobic repulsion and steric hindrance caused by outlying trifluoroethoxy groups could be responsible for the difficulty in the formation of a double-decker structure. Absorption and fluorescence spectra of trifluoroethoxy-substituted double-decker phthalocyanines obtained were also investigated.

Sign in / Sign up

Export Citation Format

Share Document