The Li salts of variously substituted 1,2-azaboroles react with numerous haloboranes to give the corresponding mono(1,2-azaborol-3-yl)boranes I (R1 = CMe3, SiMe3; R2 = H, SiMe3; R3 = NMe2, N(SiMe3)2, NEt2, Me; R4 = NMe2, Cl, Br, F, Me). In the case of I (R1 = CMe3, R2 = SiMe3, R3 = NMe2, R4 = Cl), which is substituted by SiMe3 at C-3, 2,5-dihydro isomers can be obsd. as intermediates by NMR spectroscopy with a B(Cl)NMe2 group at C-5 and the SiMe3 substituent either at C-4 (11a) or at C-3 (11b). The thermodynamically stable final product (R1 = CMe3, R2 = SiMe3, R3 = NMe2, R4 = Cl) ia probably formed from 11b via an allylic transition state. The x-ray structure anal. of (R1 = CMe3, R2 = SiMe3, R3 = NMe2, R4 = Cl) at ca. 0 Deg proves the suggested structure. The first and only example of a bis(1,2-azaborol-3-yl)borane was realized by the reaction of I (R1 = CMe3, R2 = H, R3 = NMe2, R4 = Cl) with 1-tert-butyl-2-methyl-1,2-azaborolyllithium. The x-ray structure anal. of bis(1-tert-butyl-2,3-dihydro-2-methyl-1H-1,2-azaborol-3-yl)(dimethylamino)borane shows one of the two NMR-spectroscopically obsd. diastereoisomers with perpendicularly oriented azaborolyl rings. Two iron sandwich complexes were prepd. via 1-tert-butyl-3-[bis(dimethylamino)boryl]-2-methyl-1,2-azaborolyllithium with FeCl2.