The first x-ray anal. of a 1,2-azaborolyllithium salt proves the lithium atom, stabilized by tetramethylethylenediamine (TMEDA), to be h5 coordinated. The solvate-free 2-methylbis(trimethylsilyl)-1H-1,2-azaborolyllithium (I) shows a temp. dependent dynamic behavior in soln. At -100 Deg three states can be frozen in which the C bonded SiMe3 group is fixed in the positions 3, 4, and 5. Reaction of I with Me3SiCl gave 1,3,3- and 1,3,5-tris(trimethylsilyl) derivs. II and III. III isomerizes to II by a 5,3-SiMe3 shift within 24 h. Reaction of I with SiCl4 (2:1) leads to the 2,3- (IV) as well as to the mixed 2,3- and 2,5-dihydro-1,2-azaborole (V). Both contain chiral rings; other possible isomers are not obsd. V isomerizes to IV within 3 wk. The structure of IV has been investigated by an x-ray structure anal., showing the two rings with oppositely directed at. sequences. N-SiMe3 and N-CMe3 substituted Li salts treated with different element chlorides [E]Cl ([E] = SiMe3, GeMe3, SnMe3, PbMe3, H) led to substitution in the 3-position to give 2,3-dihydro-1,2-azaboroles. They all are nondynamic systems with fixed substituents in the 3-position.