The syntheses of novel N-heterocyclic carbene (NHC) adducts of group 13, 14 and 15 element hydrides are reported. Salt metathesis reactions between NaPH2 and IDipp ⋅ GeH2BH2OTf (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) led to mixtures of the two isomers IDipp ⋅ GeH2BH2PH2 (2 a) and IDipp ⋅ BH2GeH2PH2 (2 b); by altering the reaction conditions an almost exclusive formation of 2 b was achieved. Attempts to purify mixtures of 2 a and 2 b by re-crystallization from THF afforded a salt [IDipp ⋅ GeH2BH2 ⋅ IDipp][PHGeH2BH2PH2BH2GeH2] (4) that contains the novel anionic cyclohexyl-like inorganic heterocycle [PHGeH2BH2PH2BH2GeH2]−. In addition, the borane adducts IDipp ⋅ GeH2BH2PH2BH3 (3 a) and IDipp ⋅ BH2GeH2PH2BH3 (3 b) as even longer chain compounds were obtained from reactions of 2 a/2 b with H3B ⋅ SMe2 and were studied by NMR spectroscopy. Accompanying DFT computations give insight into the mechanism and energetics associated with 2 a/2 b isomerization as well as their decomposition pathways.