69. Roentgenstrukturanalyse von 2,4,6-Tri(tert-butyl)phenyllithium*N,N,N',N'-Tetramethylpropan-1,2-diamin: eine monomere Organolithium-Verbindung

Article abstract of DOI:10.1002/hlca.19890720321

Tri(tert-buty)phenyllithium is an important reagent for the preparation of derivatives of main-group elements with low coordination state as well as a highly hindered base for the generation of amine-free Li-enolates.Its monomeric nature in solution was previously deduced from NMR measurements.While Et2O, THF, and N,N,N',N'-tetramethylethylene-1,2-diamine (tmen) led to crystalline samples which were not suitable for structure analysis, the N,N,N',N'-tetramethylpropane-1,2-diamine (tmpn) gave good single crystals of the title compound from Et2O/hexane (disorder along the two-fold crystallographic axis running through Li-C(2) and C(4) of the Ph ring).The structure (Fig. 1, Table 1) has some remarkable features: i) it is one of the very few monomeric organolithium compounds so far, (ν¹-Li on aromatic ring): ii) it has the rare trigonal-planar coordiantion of the Li-atom; iii) there are close contacts between the Li-atom and one of the Me groups in each ortho-position (Fig. 3).The internal angle on the Ph-ring ipso-C-atom is 114.This angle as well as those of the other known phenyllithium (Table 2), -magnesium, and -aluminum structures are included in a plot of ipso-angles against Pauling electronegativities.