1,2‐Azaborolyl‐Komplexe, XXIX. Synthese und Eigenschaften von 1,2‐Azaborolylboranen

Abstract

1,2‐Azaborolyl Complexes, XXIX[1]. — Synthesis and Properties of 1,2‐AzaborolylboranesThe 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 SiMe3 at C‐3, 2,5‐dihydro isomers can be observed 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 11 is probably formed from 11b via an allylic transition state. The X‐ray structure analysis of 11 at ca. 0°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 (1a). 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 sandwich complexes were synthesized; 15 is formed via 1‐tert‐butyl‐3‐[bis(dimethylamino)boryl]‐2‐methyl‐1,2‐azaborolyllithium (14) and FeCl2, whereas the ClB‐substituted sandwich complex 16 results from the reaction of 15 with BCl3.