The one‐pot reaction of L1SiCl (L1=PhC(NtBu)2) with MesPX2/IsPX2 (X=Cl, Br; Is=2,4,6‐iPr3C6H2, Mes=2,4,6‐Me3C6H2) in the presence of KC8 yielded two phosphasilene compounds L1Si(Cl)=PIs (1) and L1Si(Cl)=PMes (2) with interesting Cl−Si=P characteristics. The introduction of Cl−Si=P moiety improved the reactivity of phosphasilene. Furthermore, phosphasilenes 1 and 2 with LSi as well as Si=P building units are sensitive to moisture with distinct differences. The hydrolysis of 2 resulted in two products [L1(PHMes)Si]2(μ‐O)2 (3) and L1Cl (4), respectively, due to the amount of water, while the hydrolysis of 1 afforded L1Cl (4). In addition to the silylene L1SiCl, different types of aluminum compounds were studied to react with IsPX2/MesPX2 in the presence of KC8 in THF at low temperature. However, we failed to isolate the desired compounds due to the formation of numerous by‐products.