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 H₂-elimination pathway through the reaction of AsH₃ with IDipp⋅E′H₃ (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.