Röntgenstrukturanalyse von 2,4,6‐Tri( tert ‐butyl)phenyl‐lithium · N , N , N ′, N ′‐Tetramethylpropan‐1,2‐diamin: Eine monomere Organolithium‐Verbindung

X‐Ray Crystal‐Structure Analysis of 2,4,6‐Tri( tert ‐butyl)phenyllithium · N , N , N ′, N ′‐Tetramethylpropane‐1,2‐diamine: a Monomeric Organolithium Compound Tri( tert ‐butyl)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 Et 2 O, 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 Et 2 O/hexane (disorder along the two‐fold crystallographic axis running through LiC(1) 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, (η 1 ‐Li on aromatic ring); ( ii ) it has the rare trigonal‐planar coordination of the Li‐atom; iii ) there are close contacts between the Li‐atom arid 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 ( Fig. 2 ).