1,2-AZABOROLYL COMPLEXES .XXIX. SYNTHESIS AND PROPERTIES OF 1,2-AZABOROLYLBORANES

The Li salts of variously substituted 1,2-azaboroles 1a-1c react with numerous halogenoboranes to give the corresponding mono(1,2-azaborol-3-yl)boranes 2-12. In the case of 11, which is substituted by SiMe(3) at C-3, 2,5-dihydro isomers can be observed as intermediates by NMR spectroscopy with a B(C1)NMe2 group at C-5 and the SiMe3 substituent either at C-4 (11a) or at C-3 (11b). The thermodynamically stable final product 11 is probably formed from 11b via an allylic transition state. The X-ray structure analysis of 11 at ca. 0 degrees C proves the suggested structure. The first and only example of a bis(1,2-azaborol-3-yl)borane 13 was realized by the reaction of (1-tert-butyl-2,3-dihydro-2-methyl-1H-1,2-azaborol-3-yl)chloro (dimethylamino)borane (3) with 1-tert-butyl-2-methyl-1,2-azaborolyllithium (la). The X-ray structure analysis of bis(1-tert-butyl-2,3-dihydro-2-methyl-1H-1,2-azaborol-3-yl)(dimethylamino)borane (13) shows one of the two NMR-spectroscopically observed diastereoisomers with perpendicularly oriented azaborolyl rings. Two iron sandswich complexes were synthesized; 15 is formed via 1-tert-butyl-3-[bis(dimethylamino)boryl]-2-methyl-1,2-azaborolyllithium (14) and FeCl2, whereas the CIB-substituted sandwich complex 16 results from the reaction of 15 with BCl3.,.