Organolithium compounds species

The 1 1 zincate reagent is believed to be dimeric. At higher ratios of organolithium compounds, 2 1 and 3 1 species can be formed.174... 

Dehydrohalogenation reactions appeared to be a convenient route to double bond germanium nitrogen species and were commonly carried out with an organolithium compound as a base.3,4 5b 6 7 96,97 123 Accordingly, the synthesis of two moderately hindered stable germanimines Mes2Ge = NR 136 and 137 has been reported.59 Stabilization in these cases is achieved... 

As is implicit in the fact that the products of the (stoichiometric) 1,6-cuprate addition - the lithium allenyl enolate and the organocopper compound - are formed as independent species, it is also possible to conduct the reaction catalytically through in situ regeneration of the cuprate. The reaction can thus be run in a continuous mode, with only catalytic amounts of the preformed cuprate being necessary (with simultaneous addition of the substrate and the organolithium compound) enabling the desired allenes to be prepared even on larger scales (Eq. 4.17) [3oj. 

There are multiple systems for naming organolithium compounds. In one, CeHsLi is named phenyl lithium and w-C4H9Li is w-butyl lithium. In another, these species are named Uthiobenzene and 1-lithiobutane, respectively, when the lithium atom is regarded as a substituent on the hydrocarbon parent. A third nomenclature approach assumes these species are ionic salts, e.g. the above two compounds are called lithium phenylide and lithium butylide. We will bypass any questions of aggregation by referring to these compounds by their monomeric names (e.g. phenyl lithium and not dimeric phenyl lithium, phenyl lithium dimer nor diphenyl dilithium), and where monomeric species are actually meant, we will make this explicit. 

Only the most reactive organolithium compound, e.g. f-BuLi, is able to attack the carbon-nitrogen triple bond at temperatures below —20°C. For the other less reactive species, namely PhLi and n-BuLi, higher temperatures in ordinary solvents like pentane would be more appropriate to synthesize their lithiated Schiff bases. Flowever, for their detection IR spectroscopy seems to be unsuitable, since the relevant C=N stretching mode will be hidden by strong CH deformation modes of the solvent. 

In order to determine the strnctnres of the intermediate organolithium compounds, 1-phenylpropyne was metalated with 4 equivalents of w-butyllithium in refluxing cyclohexane . One hour later, no absorption due to lithiated phenylpropynes was detected. The IR spectrum showed only a strong peak at 1775 cm due to a trilithioallene, which gradually became much stronger. Apparently, the introduction of the first Li atom is much slower than subsequent lithiations, so no mono- and dilithiated species were observed in the IR spectrum. 

Organolithium compounds tend to associate into dimers, higher oligomers and polymers of two types Complexes where the Li atoms are linked to each other by a chain of one or more atoms of other elements (C, N, O etc.), and complexes where the Li and other metallic atoms are close to each other, forming clusters. Section V presents examples of application of instrumental methods—mainly NMR and XRD—to structural elucidation of these associated species. 

A study of the state of association of the functionalized organolithium compounds 204a-d was carried out by multinuclear ( H, Li, Li, C, N and P) NMR spectroscopy, using Li- and N-enriched species. Spectral evidence, supported in part by XRD crystallographic evidence, points to compounds 204a-c being dimerically associated in etheric solutions in three different forms (205-207). The interconversion among these three... 

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