1,3,2-diazaborole (4a) and Similarly, 1,3-di-tert-butyl-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8a) and 1,3-bis(2,6-dimethylphenyl)-2-1,3-bis(2,6-dimethylphenyl)-2,3-dihydro-1H-1,3,2-diazaborole (4b) were formed by the reaction of the corresponding trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8b) were accessible from 1a or 2b and trimethylstannyllithium. In the 2-bromo or 2-iodo derivatives 1a and 2b with LiAlH 4 . Treatment of 1a with n-butyllithium afforded 2-n-butyl-1,3-complex 9a the compound 3a serves as an η 1 ligand towards the [Cr(CO) 5 ] unit via the cyano group. These novel di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (5a), whereas 1,3-di-tert-butyl-2-cyano-2,3-dihydro-1H-1,3,2-diazaborole compounds were characterized by 1 H-, 11 B-, 13 C-, and 119 Sn-NMR spectroscopy, as well as by X-ray structure analyses of (3a) was converted into the 2-tert-butyl derivative 6a or the 2-ethynyl-1,3,2-diazaborole 7a by means of tert-butyllithium 4b, 8a, and 9a. or by the ethylenediamine adduct of lithium acetylide.
Results and Discussion
One general route to 2,3-dihydro-1H-1,3,2-diazaboroles Scheme 1. Chemical transformations of II involves the formation of borolium salts from suitable 1,4diazabutadienes and organoboron halides prior to reduction with sodium amalgam. [2,3,7,8] Accordingly, in the the desired diazaborole 4a and the corresponding saturated early attempts to synthezise 2,3-dihydro-1H-1,3,2-diazabor-2-bora-1,3-diazacyclopentane VI. [9] oles a 1,4-diazabutadiene derivative was treated with However, the availability of 2-halo-functionalized 2,3-di-Me 2 NH • BH 3 , which led to an inseparable 1:4 mixture of hydro-1H-1,3,2-diazaboroles provides an alternative approach to 2,3-dihydro-1H-1,3,2-diazaboroles. Thus, the [a]