The synthesis and characterization of the unprecedented compounds IDipp.E ' H2AsH2 (E '=Al, Ga; IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) are reported, the first monomeric, parent representatives of an arsanylalane and arsanylgallane, respectively, stabilized only by a LB (LB=Lewis Base). They are prepared by a salt metathesis reaction of KAsH2 with IDipp.E ' H2Cl (E '=Al, Ga). The H-2-elimination pathway through the reaction of AsH3 with IDipp.E ' H-3 (E '=Al, Ga) was found to be a possible synthetic route with some disadvantages compared to the salt metathesis reaction. The corresponding organo-substituted compounds IDipp.GaH2AsPh2 (1) and IDipp.AlH2AsPh2 (2) were obtained by the reaction of KAsPh2 with IDipp.E ' H2Cl (E '=Al, Ga). The novel branched parent compounds IDipp.E ' H(EH2)(2) (E '=Al, Ga; E=P, As) were synthesized by salt metathesis reactions starting from IDipp.E ' HCl2 (E '=Al, Ga). Supporting DFT computations give insight into the different synthetic pathways and the stability of the products.