Hydrosilylation and Hydrogermylation of CO(2)and CS(2)by Al and Ga Functionalized Silanes and Germanes - Cooperative Reactivity with Formation of Silyl Formates and Disilylacetals

Hepp, A; Layh, M; Uhl, W.

Abstract

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.