The reactions of 2-borane-1,3,4,5-tetramethylimidazoline (BH ₃·NHC^Me) with selected phosphane adducts of the Lewis acids B(C₆F₅)₃ and Ga(C₆F ₅)₃ are studied. Among others, adducts (C ₆F₅)₃Ga·PH₂Cp* (1a) and (C₆F₅)₃B·PH₂Cp* (2) are used as starting materials. When the (C₆F₅) ₃Ga-phosphane adducts 1a and (C₆F₅) ₃Ga·PPhH₂ are treated with BH₃· NHC^Me, the Lewis acid/base stabilised phosphanylboranes (C ₆F₅)₃Ga·P(Cp*)HBH ₂·NHC^Me (3a) and (C₆F₅) ₃Ga· P(Ph)HBH₂·NHC^Me (3b) are formed, respectively, by a hydrogen elimination reaction. In contrast, the reaction of BH₃·NHC^Me with the (C₆F ₅)₃B-phosphane adducts (C₆F₅) ₃B· PH₂R [R = H, R = Cp* (2) and R = Ph] in CH₂Cl₂ at room temperature leads to the formation of a salt with the general formula [(C₆F₅)₃BH] [RPH₂·BH₂·NHC^Me] (4a: R = H, 4b: R = Cp*, 4c: R = Ph). To synthesise the Lewis acid/base stabilised phosphanylborane with (C₆F₅)₃B as a Lewis acid and 1,3,4,5-tetramethylimidazolylidene (NHC^Me) as a Lewis base, a different synthetic pathway was applied: the replacement reaction of the Lewis base. At room temperature, NHC^Me displaced the amine in (C ₆F₅)₃B·P(Ph)HBH₂· NMe₃ to yield (C₆F₅)₃B·P(Ph) HBH₂·NHC^Me (5). All compounds were comprehensively characterised by spectroscopic methods. Compounds 1a, 1b, 2, 3a, 3b and 5 were additionally characterised by X-ray crystallographic analysis.