Silicon Carbamates by CO 2 Fixation: Brønsted Acid Labile Precursor of a Lewis Superacid.

Treatment of Lewis superacidic Si(cat Cl ) 2 (MeCN) 2 and tetramethylpiperidine (TMP) or hexahydropyrimidopyrimidine (hppH) with CO 2 leads to an FLP-type formation of silicon carbamates. The employed Lewis base determines the hapticity at silicon and the reactivity of the carbamates in subsequent transformations. Upon treatment with a Brønsted acid, the carbamates liberate CO 2 and reactivate the Lewis superacidic behavior of 1 . Hence, the CO 2 fixation products serve as valuable surrogates for Si(cat Cl ) 2 that circumvent its insolubility in organic solvents. Quantum chemical computations support all of the experimental observations.