AbstractThe formation and properties of silicon‐phosphorus and aluminum‐phosphorus compounds are described. Silylphosphines are decomposed solvolytically by H2O, C2H5OH, NH3, hydrogen halides, C2H5I, and boron halides at the SiP bond; decomposition may be preceded by formation of an addition compound. Extensive side reactions during the reaction of halogenosilanes with LiPEt2The following abbreviations are used in this paper: Et = C2H5; Me = CH3; M = alkali metal(formation of Et2PPEt2, HPEt2, Si‐rich residues) are due to an excess of LiPEt2in the reaction mixture. The reaction of LiPEt2with AlCl3, AlHCl2, and AlH2Cl leads to definite aluminum‐phosphorus compounds if only one PEt2group is present per Al atom, e.g. in (Cl2Al–PEt2)3, or if salts such as Li[Al(PEt2)4] and Li[AlH2(PEt2)2] can be formed with an exc