Noncovalent Interactions in Organometallic Compounds: Formation of an Intramolecular Metal–Carbon Ion Pair in Zirconium Borate Betaines

Abstract From the above results it would certainly appear that the ionic character of the growing ion pair (polymer−M+) is a very important factor in governing the structure of isoprene homopolymers. Another factor which may be sufficient or necessary for the formation of the unique cis-1,4-eonfiguration is the presence of an orienting surface or complex. It is well known that organolithium compounds are associated in hydrocarbon media, whereas they are probably monomolecularly dispersed in ethers and amines. It is apparent, then, that in hydrocarbon solutions the carbon-lithium chain end may be associated with other carbon-lithium pairs from unreacted initiator molecules or even with other chain ends or, in some cases, it may be associated with the lithium atoms on the surface of lithium particles. The fact that greater than 90 per cent cis-1,4-structure is obtained in hydrocarbons by use of either an apparently clear solution of filtered n-butyllithium or a heterogeneous system of lithium dispersion suggests that the massive surface of the lithium particle is not a necessary factor for the stereospecificity of the reaction. Whether we should consider the butyllithium or the lithium-initiated polymerizations as homogeneous solution reactions or heterogeneous surface reactions depends on the definition of a surface, since an associated complex or micelle may also conceivably serve as an orienting specie in the same way as a surface does. We emphasize this since so many stereospecific polymerizations such as the Ziegler system and the Phillips system appear to occur under heterogeneous conditions, presumably on an orienting surface of rather gross dimensions.

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Organometallic compounds of Group III. 52. Active sites for ethylene polymerization with titanium(IV) catalysts in homogeneous media: multinuclear NMR study of ion-pair equilibria and their relation to catalyst activity

Organometallics ◽

10.1021/om00034a018 ◽

1993 ◽

Vol 12 (10) ◽

pp. 3856-3863 ◽

Cited By ~ 65

Author(s):

John J. Eisch ◽

Sofya I. Pombrik ◽

Guo Xiu Zheng

Keyword(s):

Ethylene Polymerization ◽

Active Sites ◽

Catalyst Activity ◽

Organometallic Compounds ◽

Ion Pair ◽

Group Iii ◽

Multinuclear Nmr ◽

Nmr Study ◽

Homogeneous Media

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Simultaneously improving the ductility and strength of aromatic thermoset films

High Performance Polymers ◽

10.1177/09540083211017189 ◽

2021 ◽

pp. 095400832110171

Author(s):

Cheng Wang ◽

Long Fei Zhang ◽

Wa Li ◽

Li Rong Yang ◽

Jia Jun Ma ◽

...

Keyword(s):

Electrostatic Interactions ◽

Large Scale ◽

Noncovalent Interactions ◽

Ion Pair ◽

Special Group ◽

Covalent Bonds ◽

New Class ◽

Wide Range ◽

Potential Applications ◽

Mechanical Strengths

Aromatic thermoset materials have shown great potential applications in various fields owing to their excellent mechanical strengths. However, their poor ductility is still hinders their large-scale applications. In this study, a new class of aromatic thermosets consisting of two types of crosslinks was successfully developed by incorporating the special group imidazole into a type of crosslinked thermoset. One crosslink is constituted of reversible multiple noncovalent interactions containing “face-face” π–π stacking, “point-point” hydrogen bonds, and ion-pair electrostatic interactions, whereas the other is composed of permanent covalent bonds. Most importantly, the synergetic interplay among these reversible multiple noncovalent interactions enables them to evade the restrictions from the aromatic polymer skeletons to proceed with their dynamic dissociating-rebuilding processes, which can timely and effectively dissipate the internal stress. Finally, owing to the coefficient of these two types of crosslinks, a significantly enhanced ductility was successfully obtained on these aromatic thermosets and their tensile strengths were also improved. Such thermosets having simultaneously enhanced strengths and ductility are predicted to be eventually used in a wide range of applications.

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ESR- und ENDOR-Untersuchungen von p-Benzosemichinon-Diarylthallium-Ionenpaaren / ESR- and ENDO R-Investigations of p-Benzosemiquinone-Diarylthallium Ion Pairs

Zeitschrift für Naturforschung B ◽

10.1515/znb-1984-1019 ◽

1984 ◽

Vol 39 (10) ◽

pp. 1416-1424 ◽

Cited By ~ 7

Author(s):

Hartmut B. Stegmann ◽

Karl B. Ulmschneider ◽

Paul Schuler ◽

Thomas Jülich ◽

Klaus Scheffler

Keyword(s):

Ion Pairs ◽

Organometallic Compounds ◽

Ion Pair ◽

Coupling Constants ◽

Paramagnetic Species ◽

Contact Ion Pair ◽

Basic Solutions ◽

G Value ◽

Contact Ion Pairs ◽

Doublet Splitting

Diarylthallium hydroxides react very smoothly in organic solvents with hydroquinones to stable paramagnetic complexes. This reaction has been investigated with two ligands and several organometallic compounds in 8 different solvents. In basic solutions clearly two paramagnetic species can be detected by ESR spectroscopy. One component exhibits a large doublet splitting assigned to the thallium counterion and the second radical does not show any metal coupling. The relative concentrations of both radicals depend strongly on the solvent and the temperature. Therefore, a slow equilibrium betw een a contact ion pair and a solvent separated ion pair is assumed. The thermodynamic parameters are determined to ⊿H = 0.8 kcal/mol, ⊿G293 = -0.1 kcal/mol, ⊿S = 3.04 cl/mol. The proton and thallium coupling constants as well as the g-value of the contact ion pair show a rem arkable temperature dependence. The signs of proton splitting constants are determined by ENDOR-TRIPLE investigations. The change of the electronic structure of the radical anion by formation of a contact ion pair is discussed. For interpretation of these results we assumed a fast equilibrium between different conformations of the contact ion pair according to behaviour of comparable aroxyl radicals. Therefore, the systems investigated allow a simultaneous observation of solvent separated and different contact ion pairs.

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Solid State NMR for Nonexperts: An Overview of Simple but General Practical Methods

Solids ◽

10.3390/solids2020009 ◽

2021 ◽

Vol 2 (2) ◽

pp. 139-154

Author(s):

Ilya G. Shenderovich ◽

Hans-Heinrich Limbach

Keyword(s):

Noncovalent Interactions ◽

Theoretical Calculations ◽

Heterogeneous Systems ◽

Organometallic Compounds ◽

Ease Of Use ◽

Specific System ◽

Main Research ◽

Specialized Equipment ◽

Technical Simplicity ◽

Analytical Tools

There are varieties of methods available for the exploration of solids using nuclear magnetic resonance (NMR) spectroscopy. Some of these methods are quite sophisticated, others require specialized equipment. This review is addressed to those for whom NMR is not the main research method. It discusses simple methods that can be applied to solids with little or no adaptation to a specific system. Despite their technical simplicity and ease of use, these methods are powerful analytical tools that provide unique insights into the structure, dynamics, and noncovalent interactions in homo- and heterogeneous systems. Particular attention is paid to the characterization of porous materials and solids containing phosphorus. 31P NMR of organometallic compounds has been used as an example of how theoretical calculations can help in deeper analysis of experimental data.

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Cooperative Noncovalent Interactions Induce Ion Pair Separation in Diphenylsilanides

Chemistry - A European Journal ◽

10.1002/chem.201704217 ◽

2017 ◽

Vol 23 (62) ◽

pp. 15633-15637 ◽

Cited By ~ 9

Author(s):

Eric A. Marro ◽

Eric M. Press ◽

Tapas K. Purkait ◽

Daniel Jimenez ◽

Maxime A. Siegler ◽

...

Keyword(s):

Noncovalent Interactions ◽

Ion Pair ◽

Pair Separation ◽

Ion Pair Separation

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The Reactions of Organometallic Compounds Involving Silicon. Reactions of Methyldiphenyl-, Triphenylsilyl-sodium, -potassium, -rubidium, and -caesium with 9-Methylfluorene in Tetrahydrofuran

Canadian Journal of Chemistry ◽

10.1139/v73-412 ◽

1973 ◽

Vol 51 (16) ◽

pp. 2759-2764 ◽

Cited By ~ 4

Author(s):

Muhammad Abdul Hamid

Keyword(s):

Dipole Moment ◽

Binding Energy ◽

Electronic Transition ◽

Low Temperatures ◽

Organometallic Compounds ◽

Ion Pair ◽

Sodium Potassium ◽

Metal Compounds ◽

Thermodynamic Constants ◽

Stop Flow

The reactions of triphenylsilyl-sodium(Ph3SiNa), diphenylmethylsilyl-sodium(Ph2MeSiNa), triphenylsilyl-potassium (Ph3SiK), triphenylsilyl-rubidium (Ph3SiRb), and triphenylsilyl-caesium (Ph3SiCs) with 9-methylfluorene in tetrahydrofuran (THF) were studied using the stop-flow technique at low temperatures. The rate constant k (1 mol−1 s−1) depends on the nature of the cation; at −50 °C k is 11.5 for Ph3SiNa, 29.5 for Ph2MeSiNa, 26.8 for Ph3SiK, 35.6 for Ph3SiRb, and 47.9 for Ph3SiCs. It seems that the organosilylalkali–metal compounds (R3SiM) exist in the form of contact ion-pair and therefore the reactivity of an ion-pair is determined by the Coulombic binding energy of the pair. The thermodynamic constants of activation for these reactions were calculated for −50 °C and compared with the corresponding values of triphenylsilyl-lithium Ph3SiLi reaction with 9-methylfluorene in THF. The plots of log k, ΔS≠, and ΔH≠ against 1/(rc + 2) and ΔS≠ against ΔH≠ were drawn to show that Li+ due to its existence as solvent separated ion-pair behaves differently to its Na+, K+, Rb+, and Cs+ counterparts.The electronic spectra of R3SiM, 9-methyl-fluoren-9-yl-sodium, -potassium, -rubidium and -caesium were determined at temperatures varying from 20 to −80 °C. A red shift was observed in spectra of R3SiNa at low temperatures; this was attributed to the increase in dipole moment which occurs during the electronic transition. The spectra of 9-methylfluoren-9-yl-sodium, -potassium, -rubidium, and -caesium were compared with their lithium counterpart to explain the effects of gegenion on the solvation of these species.

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