The synthesis and characterization of the first parent phosphanylalane and phosphanylgallane stabilized only by a Lewis base (LB) are reported. The corresponding substituted compounds, such as IDipp.GaH2PCy2 (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) were obtained by the reaction of LiPCy2 with IDipp.GaH2Cl. However, the LB-stabilized parent compounds IDipp.GaH2PH2 (3) and IDipp.AlH2PH2 (4) were prepared via a salt metathesis of LiPH2.DME with IDipp.E ' H2Cl (E '=Ga, Al) or by H-2-elimination reactions of IDipp.E ' H-3 (E '=Ga, Al) and PH3, respectively. The compounds could be isolated as crystalline solids and completely characterized. Supporting DFT computations gave insight into the reaction pathways as well as into the stability of these compounds with respect to their decomposition behavior.