Differently substituted 2-chloro-, 2-fluoro-, and 2-iodo-2,3-dihydro-1H-1,3,2-diazaboroles were prepd. by various methods. 1,3-Di-tert-butyl-2-fluoro-2,3-dihydro-1H-1,3,2-diazaborole (I), 1,3-di-tert-butyl-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (II), 1,3-bis(2,6-dimethylphenyl)-2-chloro-2,3-dihydro-1H-1,3,2-diazaborole (III), 2-chloro-4,5-dimethyl-1,3-dineopentyl-2,3-dihydro-1H-1,3,2-diazaborole, and 1,3-di-tert-butyl-2-iodo-2,3-dihydro-1H-1,3,2-diazaborole were formed from the corresponding lithiated Z-1,2-diaminoethenes, by treatment with BF3.OEt2, BCl3, or BI3 in n-hexane. I, II, and III are also available by Na amalgam redn. of the adduct (tBu)(BF3)N:CHCH:N(BF3)(tBu), and the borolium salts [RNa:CH-CH:Nb(R)BCl2]X (Na-B) (R = tBu, X = BCl4; R = 2,6-Me2C6H2, X = Cl). The iodo deriv. (2,6-Me2C6H2)-Na-CH:CH-Nb(2,6-Me2C6H2)BI (Na-B) (IV) was synthesized in a redox reaction between the corresponding 1,4-diazabutadiene and BI3. The novel compds. were characterized by 1H, 11B and 13C NMR spectroscopy, as well as by x-ray structure anal. of IV (monoclinic, space group C2/c, a 14.911(2), b 7.9706(8), c 16.9105(12) , b 114.360(6) Deg, V = 1830.9(3) .ANG.3, Z = 4, rc = 1.459 g/cm3, m(MoKa) = 1.747 mm-1, 1884 obsd. reflections with I > 2s(I), 102 refined parameters, R1 = 0.042, wR2 = 0.1043).