Overcrowded silanedichalcogenols Tbt(Mes)Si(EH)(E′H), such as silanedithiol (E = E′ = S), hydroxysilanethiol (E = O, E′ = S) and hydroxysilaneselenol (E = O, E′ = Se), bearing an efficient combination of steric protection groups, Tbt and Mes (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes = 2,4,6-trimethylphenyl), were synthesized and isolated as air- and moisture-stable crystals, and their structures were fully characterized by spectroscopic and elemental analyses together with X-ray crystallographic analyses. The results of IR spectroscopy and the X-ray structural analyses suggested that these compounds exist as monomers without any intra- and intermolecular interactions such as hydrogen bonds even in the solid state and in solution. Novel four-membered-ring compounds, such as Tbt(Mes)Si(μ-S) 2PnBbt and [Tbt(Mes)Si(μ-E)(μ-E′)ML n ] [E, E′ = O, S, Se; Pn = Sb, Bi; Bbt = 2,6 -bis[bis(trimethylsilyl)methyl] -4 -[tris(trimethylsilyl)methyl]phenyl; ML n = Pd(PPh 3) 2, Pt(PPh 3) 2, Ru(η 6-benzene)] were synthesized by utilizing the silanedichalcogenols as key building blocks. The molecular structures of these newly isolated compounds were determined by NMR spectroscopic data together with X-ray crystallographic analyses.