1,3-Di-tert-butyl- and 1,3-bis(2,6-dimethylphenyl)-2,3-dihydro-1H-1,3,2-diazaborole (I) were formed by the reaction of the corresponding 2-bromo or 2-iodo derivs. with LiAlH4. Treatment of 2-bromo-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole with BuLi afforded 2-butyl-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole, whereas 1,3-di-tert-butyl-2-cyano-2,3-dihydro-1H-1,3,2-diazaborole (II) was converted into the 2-tert-Bu deriv. or the 2-ethynyl-1,3,2-diazaborole by Me3CLi or by the H2N(CH2)2NH2 adduct of LiC.tplbond.CH. Similarly, 1,3-di-tert-butyl-2-trimethylstannyl- (III) and 1,3-bis(2,6-dimethylphenyl)-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole were accessible. In II.Cr(CO)5, II serves as an h1-ligand towards the Cr(CO)5 unit via the cyano group. These novel compds. were characterized by 1H, 11B, 13C, and 119Sn NMR as well as by x-ray structure anal. of I, II.Cr(CO)5, and III.