Abstract
New macrocyclic imidazolylboranes [imidazolylB(R 1) 2] n , where selected carbon atoms of imidazolyl rings may bear substituents other than hydrogen, and where n=4 or 5, are obtained from 1-trimethysilylimidazoles and haloboranes XB(R 1) 2 by boron/silicon exchange using 2-bromoimidazole and benzimidazole. These macrocycles are formally zwitterionic and contain imidazolyl rings linked through their nitrogen atoms by BH 2, B(R 1) 2 or BR 1X units. Despite the sterical demand of these derivatives tetrameric macrocycles are formed. A new synthetic strategy to macrocyclic imidazolylboranes includes the preparation and cyclization of bis(imidazolyl)boronium chlorides. In addition dihaloboranes have been tested for cyclization to yield halogen-containing macrocycles. The new compounds are spectroscopically characterized and X-ray structure analyses of tetrameric- ( 2a) and pentameric 1-imidazolylborane ( 2a′), tetrameric 1-imidazolyldimethylborane ( 2b), tetrameric 1-(2-bromo)imidazolylborane ( 2d) and bis(2-bromoimidazolyl)boronium chloride ( 3d) are reported.
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