The syntheses and characterizations of the first bismuthanylborane monomers stabilized only by a donor in D$BH2Bi(SiMe3)2 (D = DMAP 1a, IDipp 1b, IMe4 1c; DMAP = 4-dimethylaminopyridine, IDipp = 1,3-bis(2,6diisopropylphenyl)-imidazolin-2-ylidene, IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) are presented. All compounds were synthesized by salt metathesis reactions between D$BH2I and KBi(SiMe3)2(THF)0.3 and represent some of the extremely rare compounds featuring a 2c–2e B–Bi bond in a molecular compound. The products display high sensitivity towards air and light and slowly decompose in solution even at −80 °C. By the reaction of IDipp$GaH2(SO3CF3) with KBi(SiMe3)2(THF)0.3, the synthesis of the first bismuthanylgallane IDipp$GaH2Bi(SiMe3)2 (2) stabilized only by a 2-electron donor was possible, as evident from single crystal X-ray structure determination, NMR spectroscopy and mass spectrometry. Computational studies shed light on the stability of the products and the electronic nature of the compounds.