The reactivities of o-carborane-fused silylenes toward molecules with C≡E (E = C, P) bonds are reported. The reactions of bis(silylene) [(LSi:)C]2B10H10 (1a, L = PhC(NtBu)2) with arylalkynes afforded bis(silylium) carborane adducts 2 and 3, showing a Si(μ-C2)Si structure with an open-cage nido-carborane backbone. In contrast, the reaction of 1a with a phosphaalkyne AdC≡P (Ad = 1-adamantyl) smoothly furnished compound 4, comprising fused CPSi rings with a C=Si double bond and Si-Si single bond, and the related formation mechanism was investigated by DFT calculations. Furthermore, when monosilylene [(LSi:)C]CHB10H10 (1b) was employed to react with AdC≡P, compound 5 was isolated. The structure of 5 features a 1,2,3-triphosphetene core. All products were characterized by NMR spectroscopy and/or X-ray crystallography.