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]

Hydroalumination of 1-aza-but-1-en-ynes 1 provides facile access to propargylamines 4 by reduction of the CN bonds or alternatively to 1-aza-buta-1,3-dienes 6 by reduction of the triple bond. The chemoselectivity depends not only on the steric properties of both the hydroalumination agent (di-iso-butylaluminum (DIBAL-H, iBu 2 AlH) versus ditert-butylaluminum hydride (tBu 2 AlH)) and the substrates but also on the reaction temperatures. In several cases, initial aluminum species of 5-aluminazole type 5 could be isolated and characterized by X-ray diffraction, indicating an "anti-Michael" addition of the hydride to the triple bond. Aqueous workup of those species led to 1-azabutadiene derivatives 6. High-level DFT calculations indicate that the observed chemoselectivity is only compatible with a dimeric nature of the hydroaluminating agent. Using such a dimer, the imine reduction corresponds to the kinetically controlled pathway, whereas the triple bond reduction leads to the thermodynamically much more stable 5-aluminazoles, 5.

Hydrometallation of the alkynylelement hydrides iPr2E(H)–C≡C‐tBu (1; E = Si, Ge) with R2M–H [M = Al, Ga; R = tBu, CH(SiMe3)2] afforded in moderate yields the Al and Ga functionalized alkenylsilanes and ‐germanes iPr2E(H)C(MR2)=CH‐tBu (2). The air and moisture sensitive Al compounds reacted with CO2 under mild conditions (room temperature, 1 bar) to yield the formates [iPr2EC(AlR2)=C(H)–tBu]O2CH (3) by C=O insertion into the E–H bond and coordination of the second O atom to aluminum. The acetal MeAl[C(SiiPr2)=CH‐tBu]2O2CH2 (4a) was obtained as a unique side‐product. The less Lewis acidic Ga compound 2c did not react with CO2 even at higher temperature and pressure. Reaction with CS2 yielded the dithioacetals [iPr2EC(MtBu2)=CH‐tBuS]2CH2 (6) by reduction of both C=S bonds. Compounds 6 have two ECMS heterocycles bridged by a CH2 group. The reaction of the Ga compound 2c required elevated temperature (40 °C). At 70 °C the formal elimination of H2C=CMe2 and “CH4” afforded the unusual gallium sulfide {iPr2SiC[Ga(tBu)(µ‐S)]=CH‐tBu}2 (7c) which crystallized as a dimer with a central Ga2S2 heterocycle that is joined via its Ga–S edges to two four‐membered GaSCSi heterocycles.

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