NMR spectroscopy of organolithium compounds, part XIX1 reaction of (Z)-1,2-Bis(trimethylsilyl)-1-phenylethene with lithium: Dianion formation, schlenk dimerization, and 13C,6Li coupling in a benzyllithium system

Böhler, Bernd; Hüls, Dietmar; Günther, Harald

doi:10.1016/s0040-4039(96)02036-9

Cited by 10 publications

(6 citation statements)

References 20 publications

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“…At the same time, using a similar strategy, Fraenkel and Martin 104 found 13 C α , 6 Li couplings of 2.8 and 3.4 Hz in THF at 250 K for the two compounds 25a and 25b and we observed 13 C, 6 Li couplings (2.7 Hz) for the lithium cation trapped in the organic ligand of the Schlenk dimer 26 where the second lithium exists as a solvent separated ion 105 . Even more interesting, Fraenkel and Martin 104 were able to meas-ure a 13 C α , 6 Li coupling of 3.8 Hz for the parent compound itself in the presence of TMEDA, using 13 C and 6 Li labeling, low concentration (0.005 M in THF), and low temperature (180 K).…”

Section: H Rsupporting

confidence: 64%

Selected topics from recent NMR studies of organolithium compounds

Günther¹

1999

J. Braz. Chem. Soc.

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Após uma breve introdução à espectroscopia de RMN de metais alcalinos e alcalino terrosos, esta revisão concentra-se nas investigações de RMN em compostos organo-lítios. O método de impressão digital isotópica, que baseia-se no deslocamento das ressonâncicas de 6 Li induzido por deutério, é apresentado e exemplificado com aplicações sobre o comportamento de agregação de sistemas de ciclopropil-lítio e formação de agregados mistos entre metil-lítio e sais de lítio. No capítulo seguinte discutem-se experimentos uni-e bidimensionais, tanto para sistemas de spin homonucleares quanto heteronucleares. Finalmente, descrevem-se os aspectos estruturais associados ao benzil-lítio e a formação de sistemas poli-lítio pela redução de bifenilas por lítio. After a short introduction to NMR spectroscopy of alkali and alkaline earth metals the review concentrates on NMR investigations of organolithium compounds. The isotopic fingerprint method, which rests on deuterium-induced isotope shifts for 6 Li resonances, is introduced and exemplified with applications from the aggregation behavior of cyclopropyllithium systems and mixed aggregate formation between methyllithium and lithium salts. In the following chapter, one-and two-dimensional pulse experiments, both for homo-and for heteronuclear spin systems are discussed. Finally, the structural aspects associated with benzyllithium are outlined and the formation of polylithium systems by lithium reduction of biphenylenes is described.

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Section: H Rsupporting

confidence: 64%

Selected topics from recent NMR studies of organolithium compounds

Günther¹

1999

J. Braz. Chem. Soc.

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“…Such a dimer can explain the observed NMR spectra, the rehybridization of carbon atom C2 and the absence of the above-mentioned coupling constants. The ability of lithium cations to interact with numerous carbanionic centers has been extensively studied; however, such a coordinative dimerization of a PAH has never been observed previously 3 Calculated structure (PM3) of the coordinative dimer, 4 4- ·2Li + · 4 4- /6Li + .…”

Section: Resultsmentioning

confidence: 99%

“…One way of proving the existence of C−Li−C bonds would be to measure the 1 J 13 C, Li coupling that such a bond would yield . For this purpose a sample of 4 was reduced using lithium[6]; however, the recorded spectra ( 6 Li and 13 C NMR) did not show any such couplings, probably due to the broadness of the peaks .…”

Section: Resultsmentioning

confidence: 99%

Reduction of Bowl-Shaped Hydrocarbons: Dianions and Tetraanions of Annelated Corannulenes

et al. 2005

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[structure: see text] The reduction of several annelated corannulene derivatives was undertaken using lithium and potassium metals. It was found that annelation affects the annulenic character of corannulene by changing its charge distribution; the dianions of derivatives that are annelated with six-membered rings have less annulenic character and are less paratropic than corannulene dianion. This effect is even more pronounced in corannulenes that are peri-annelated with five-membered rings. The alkali metal used in the reduction process has a great influence on the outcome, especially on the degree of reduction. Most derivatives get reduced to tetraanions only with potassium, and not with lithium, the exception being systems that can stabilize the tetraanion with lithium by special means, such as aggregation or dimerization. One such system is cyclopenta[bc]corannulene (acecorannulylene), which gives a coordinative dimer that consists of two cyclopentacorannulene tetraanions, bound together in a convex-convex fashion by lithium cations. The points of contact in this dimer are two rehybridized carbons from each cyclopentacorannulene unit, which are bridged together by two lithium cations.

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“…Some of the L factors may turn out to be much smaller than those given in Tables and and Tables S1 and S2 in the Supporting Information. For example, we did not analyze RLi species with more delocalized anionic charges and small 1 J ( 13 C, 6 Li) values, such as benzyllithium compounds (2.6−3.8 Hz) − and allyllithium species (2.3−3.0 Hz). , …”

Section: Discussionmentioning

confidence: 99%

“…Some of the L factors may turn out to be much smaller than those given in Tables 1 and 2 and Tables S1 and S2 in the Supporting Information. For example, we did not analyze RLi species with more delocalized anionic charges and small 1 J( 13 C, 6 Li) values, 32 such as benzyllithium compounds (2.6-3.8 Hz) [52][53][54] and allyllithium species (2.3-3.0 Hz). 55,56 As a tempting extension, 57 a roughly inverse relationship between 1 J( 15 N, 6 Li) and the number of coordinating donor ligands was noted recently, 58 in accord with earlier computational results; 59 however, it may be less straightforward to formulate a quantitative dependence because of the smaller magnitudes of many 1 J NLi values and occasional overlaps of their ranges.…”

Section: Discussionmentioning

confidence: 99%

Microsolvation and ¹³C−Li NMR Coupling

et al. 2008

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The empirical expression (1)J(CLi) = L[n(a + d)](-1) is proposed; it claims a reciprocal dependence of the NMR coupling constant (1)J((13)C, Li) in a C-Li compound on two factors: (i) the number n of lithium nuclei in bonding contact with the observed carbanion center and (ii) the sum (a + d) of the numbers a of anions and d of donor ligands coordinated at the Li nucleus that generates the observed (1)J(CLi) value. The expression was derived from integrations of separate NMR resonances of coordinated and free monodentate donor ligands (t-BuOMe, Et2O, or THF) in toluene solutions of dimeric and monomeric 2-(alpha-aryl-alpha-lithiomethylidene)-1,1,3,3-tetramethylindan at moderately low temperatures. This unusually slow ligand interchange is ascribed to steric congestion in these compounds, which is further characterized by measurements of nuclear Overhauser correlations and by solid-state structures of the dimers bearing only one donor per lithium atom (d = 1). Increasing microsolvation numbers d are also accompanied by typical changes of the NMR chemical shifts delta (positive for the carbanionic (13)C(alpha), negative for C(para) and p-H). The aforementioned empirical expression for (1)J(CLi) appears to be applicable to other cases of solvated monomeric, dimeric, or tetrameric C-Li compounds (alkyl, alkenyl, alkynyl, and aryl) and even to unsolvated (d approximately 0) trimeric, tetrameric, or hexameric organolithium aggregates, indicating that (1)J(CLi) might serve as a tool for assessing unknown microsolvation numbers. The importance of obtaining evidence about the (13)C NMR C-Li multiplet splitting of both the nonfluxional and fluxional aggregates is emphasized.

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NMR spectroscopy of organolithium compounds, part XIX1 reaction of (Z)-1,2-Bis(trimethylsilyl)-1-phenylethene with lithium: Dianion formation, schlenk dimerization, and 13C,6Li coupling in a benzyllithium system

Cited by 10 publications

References 20 publications

Selected topics from recent NMR studies of organolithium compounds

Selected topics from recent NMR studies of organolithium compounds

Reduction of Bowl-Shaped Hydrocarbons: Dianions and Tetraanions of Annelated Corannulenes

Microsolvation and ¹³C−Li NMR Coupling

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NMR spectroscopy of organolithium compounds, part XIX1 reaction of (Z)-1,2-Bis(trimethylsilyl)-1-phenylethene with lithium: Dianion formation, schlenk dimerization, and 13C,6Li coupling in a benzyllithium system

Cited by 10 publications

References 20 publications

Selected topics from recent NMR studies of organolithium compounds

Selected topics from recent NMR studies of organolithium compounds

Reduction of Bowl-Shaped Hydrocarbons: Dianions and Tetraanions of Annelated Corannulenes

Microsolvation and 13C−Li NMR Coupling

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Microsolvation and ¹³C−Li NMR Coupling