The Quest for Stable Silaaldehydes: Synthesis and Reactivity of a Masked Silacarbonyl

The first donor–acceptor complex of a silaaldehyde, with the general formula (NHC)(Ar)Si(H)OGaCl3 (NHC=N‐heterocyclic carbene), was synthesized using the reaction of silyliumylidene–NHC complex [(NHC)2(Ar)Si]Cl with water in the presence of GaCl3. Conversion of this complex to the corresponding silacarboxylate dimer [(NHC)(Ar)SiO2GaCl2]2, free silaacetal ArSi(H)(OR)2, silaacyl chloride (NHC)(Ar)Si(Cl)OGaCl3, and phosphasilene–NHC adduct (NHC)(Ar)Si(H)PTMS unveil its true potential as a synthon in silacarbonyl chemistry. The first silicon analogue of an aldehyde stabilized with an external Lewis base and Lewis acid was successfully isolated and characterized. It shows unique reactivity mimicking the behavior of carbonyl congeners and provides access to various classes of silacarbonyl derivatives.