•Synthesis of a sterically demanding TBS-substituted oligosilane.•Transformation of the silyl potassium compound to silyl Grignard compound.•Synthesis of dihalocyclopentasilanes successfully.•Analysis of molecular structures in the solid state.A sterically demanding TBS-substituted oligosilane (4, TBS = t-butyldimethylsilyl) was stepwisely formed by reactions of oligosilanyl potassium compound and the corresponding chlorosilane. Although a well-established method, the ring closure reaction of compound 4 in the presence of t-BuOK and 18-Cr-6 with SiX4 (X = Cl, Br) failed. The silyl potassium compound was then transformed to silyl Grignard compound 5, which can be used to react with SiX4 to give the dihalocyclopentasilanes (6, X = Cl; 7, X = Br) successfully. The molecular structures of 3–7 have been confirmed by X-ray single-crystal analyses.A sterically demanding TBS-substituted oligosilane was stepwisely formed by reactions of oligosilanyl potassium compound and the corresponding chlorosilane. However, the similar reaction using SiX4 (X = Cl, Br) could not afford the ring closure product. The silyl anion was then transformed to silyl Grignard compound 5, which can be used to react with SiX4 to give the dihalocyclopentasilanes (6, X = Cl 7, X = Br) successfully. The molecular structures of 3–7 have been confirmed by X-ray single-crystal analyses.