The azadiboriridine [±BR±NR±BR±] (1; R = tBu) is bromoborated at the B±B bond by alkyldibromoboranes R'BBr 2 to give the products Br±BR±NR=BR±BR'±Br (8 a±g: R' = Me, Bu, iBu, Bzl, CH 2 CHEt 2 , CH 2 Cy, CH 2 (4-C 6 H 4 tBu)). Two isomers of each of the products 8 a±g are formed and attributed to a cis/trans isomerism at the BN double bond; the isomerization is followed thermodynamically and kinetically by NMR methods with 8 a±d. The analogous chloroboration of 1 with BCl 3 yields Cl±BR±NR=BR±BCl 2 (8 h), which at ambient temperature undergoes a degenerate exchange of the ligands Cl and BCl 2 along the B±N±B skeleton. At room temperature, the isomer Cl±BR±NR=BCl±BR±Cl (8 h') is slowly formed by an irreversible exchange of R and Cl along the B±B bond of 8 h. Different from BCl 3 , the chloroborane BH 2 Cl is simply added to the B±B bond of 1 under formation of the azanido-tetraborane NB 3 R 3 H 2 Cl (2 b). The chloroborane BHCl 2 gives a mixture of 8 h' and 2 b upon addition to 1, apparently according to a preceding dismutation into BCl 3 and BH 2 Cl. The configuration at the B3 atom of the nido-clusters NB 3 R 3 H 2 X (X = H, Cl) is discussed on the basis of the corresponding model molecules NB 3 Me 3 H 2 X, whose structure and NMR signals are computed by the B3LYP method. The boranes 8 b±g can be debrominated with Li in the presence of tmen on applying ultrasound. The products are found to be the B-borylated azadiboriridines [±BR±NR±B(BRR')±] (9 b±g). The 2-borylazadiboriridines NB 3 H 4 (9 h) and NB 3 Me 4 (9 i) were found as local minima on the energy hyperface by the B3LYP method, but minima for structural isomers with lower energy were also found; the tetrahedral clusters NB 3 R 4 give high-energy minima with triplet ground states. Computations of the 11 B NMR shifts of 9 h and 9 i support the proposed structures of 9 b±g.