Organolithium complexes

Preliminary experiments prove that the substitution pattern of the /V-aryl moiety of imine 1 is crucial for the stereoselectivity of this reaction. The 2-substituent on the aryl group is of special importance. Namely, introduction of a methoxy group leads to a considerable decrease of enantioselectivity compared to the corresponding 2-H derivative, probably due to disfavor-able coordination with the organolithium complex. In contrast, alkyl groups show the reverse effect along with increased bulkiness (e.g., Tabic 1, entries l-3a) but 2,6-dimethyl substitution provides lower ee values. Furthermore, the 4-substituent of the TV-aryl moiety is of minor importance for the stereoselectivity of the reaction [the Ar-phcnyl and the /V-(4-methoxyphenyl) derivatives give similar results], whereas a substituent in the 3-position results in lower stereoselectivities (e.g., Et, Cl, OCHj)41. 

Investigations by various experimental techniques have been prompted by the structural diversity of organolithium complexes. The methods used range from... 

TABLE 2. Li chemical shifts, in ppm", of some selected delocalized organolithium complexes in various solvents ... 

TABLE 8. "Li quardupolar coupling constants of delocalized organolithium complexes ... 

In conclusion, the investigations presented show that the Li- C REDOR technique can be a valuable tool for the structural characterization of organolithium complexes. Contrary to X-ray, there is no need for single crystals. Although the carbon-lithium distances are to some extent overestimated by the REDOR technique, the precision is sufficient to discriminate between various possible lithium positions in the complexes. 

One problem with the REDOR method and other similar solid state NMR techniques is that unambiguous results only can be obtained when the spin system is based on isolated spin pairs, as shown in a recent publication . This means that the prevalent aggregates found in organolithium complexes cannot be studied by these methods. However, a recent 3D TEDOR study of uniformly labelled peptides gives some hope, provided that... 

The dynamic behavior of various solid organolithium complexes with TMEDA was investigated by variable-temperature and CP/MAS and Li MAS NMR spectroscopies. Detailed analysis of the spectra of the complexes led to proposals of various dynamic processes, such as inversion of the five-membered TMEDA-Li rings and complete rotation of the TMEDA ligands in their complex with the PhLi dimer (81), fast rotation of the ligands in the complex with cyclopentadienyllithium (82) and 180° ring flips in the complex with dilithium naphthalene (83) °. The significance of the structure of lithium naphthalene, dilithium naphthalene and their TMEDA solvation coiMlexes, in the function of naphthalene as catalyst for lithiation reactions, was discussed . ... 

There are reports that other HMPA-organolithium complexes have a dramatic effect on lithiation regioselectivity away from coordination-favoured sites . ... 

The configuration of the organolithium complex (S,S)-9 has been confirmed by X-ray crystallography". 

Crystal Structures of Lithium Halide and Mixed Lithium Halide -Organolithium Complexes... 

Fig. 25. Structures of selected lithium halide and lithium halide-organolithium complexes.

In contrast, 46 demonstrates divergent behaviour with different electrophiles (scheme 6.1.10).43 The situation here is complicated by the fact that the stereochemical outcome is the result of a dynamic kinetic resolution of two interconverting diastereoisomeric organolithium complexes 46a and 46b (see section 6.2). It is not possible to be sure whether the different stereochemical outcomes represent retentive/invertive reactions or whether they represent halides and tosylates reacting at different rates with diastereoisomeric substrates. 

In order to get an indication about the accuracy of REDOR, the TMEDA complex of indenyllithium (69), a complex whose structure has been established by X-ray diffraction176, was studied128. It was found that the REDOR method systematically overestimates the Li—C distances by ca 0.2-0.15 A (depending on the optimization method), and that the error becomes larger for longer distances. These studies have shown that the REDOR method is a valuable tool for the structural characterization of organolithium complexes and for correlating their solid state and solution structures. 

Miscellaneous Mixed-Metal Organolithium Complexes Structures of Lithium Compounds without Lithium-Carbon Bonds... 

Where does one draw the line of demarcation between inorganic and organic chemistry Is modeling of an organolithium complex an inorganic... 

In 1962 and 1963 the chelated organolithium complexes and their application in ethylene telomerization were discovered independently of each other by Eberhardt (12) at Sun Oil Co. This research led to two patents (13, 14) in which the claims involving chelated catalysts were... 

X-ray structures for various crystalline organolithium complexes are covered in Chapter 3 which provides proof for chelate ring structures as opposed to open chain polymeric structures. It also supports the NMR finding of increased ionic character in the Li-C bond upon solvation of the lithium (10). 

Reactivity of Various Tertiary Diamines in the Preparation of Tertiary Diamine Organolithium Complexes by Metalation. Previous work has shown that the reactivity and the rate of metalation for Reaction 2 of the tertiary diamine organolithium complexes is a function of the tertiary diamine in the complex (1,9). In the specific case of the metala-... 

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