Alkenylchlorosilanes functionalized by coordinatively unsaturated Al atoms, R′′(R′)Si(Cl)C(AltBu 2 )=C(H)R 5 [R = tBu, cHex, 1-Ad, Ph, 3,5-(F 3 C) 2 C 6 H 3 ; R′ = Mes, Ph, 4-tBuC 6 H 4 , 4-tBuOC 6 H 4 , 4-Et 2 NC 6 H 4 , tBu; R′′ = Mes, CH(SiMe 3 ) 2 , tBu], were obtained in good yields by hydroalumination of the respective alkynylchlorosilanes R′′(R′)Si(Cl)C≡C-R 3 with t Bu 2 Al-H. They feature four-membered, close to planar SiCAlCl heterocycles by intramolecular Al-Cl interactions. The activation of the Si-Cl bonds results in bond lengthening from about 209 pm in 3 to 220 to 225 pm in compounds 5. The 29 Si NMR resonances show an increasing shift to a lower field and range from δ = 24.0 for 5a [R = tBu, R′ = R′′ = Mes] to δ = 68.1 for 5j [R = R′ = R′′ = [a]