Silicon Carbamates by CO₂ Fixation: Brønsted Acid Labile Precursor of a Lewis Superacid

Abstract

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.

p-Block Element Catecholates: Lewis Superacidic, Constitutionally Dynamic, and Redox Active

“…Hence, another FLP approach was pursued by reacting a mixture of Si(cat Cl )2 and the Lewis base tetramethylpiperidine (TMP) or hexahydropyrimidopyrimidine (hppH) towards CO2 (Figure 7c/d). [64] Depending on the base, 4-membered ring κ Despite numerous attempts, we could not achieve FLP type dihydrogen activation with the class of bis(catecholato)silanes. This shortcoming can be traced back to several factors.…”

“…Consequently, another FLP approach was pursued by reacting a mixture of Si(cat Cl ) 2 and the Lewis base tetramethylpiperidine (TMP) or hexahydropyrimidopyrimidine (hppH) with CO 2 (Figures 7c and 7d). 64…”

“…Consequently, another FLP approach was pursued by reacting a mixture of Si(cat Cl ) 2 and the Lewis base tetramethylpiperidine (TMP) or hexahydropyrimidopyrimidine (hppH) with CO 2 (Figures 7c and 7d). 64 Depending on the base, a four-membered ring κ 2 O -adduct [H 2 TMP][ 1 -(κ 2 -CO 2 )-(TMP)] or a six-membered ring [hppH 2 ][ 1 -(κ 1 -CO 2 )-(hpp)] was formed with TMP and hppH, respectively. Interestingly, the structural differences cause differing behavior in subsequent reactivity toward an epoxide.…”

Molecular Structures and Intermolecular Hydrogen Bonding of Silylated 2-Aminopyrimidines

“…Furthermore, some guanidinates are also capable of bridging Si atoms with other metal atoms in heteronuclear complexes (e.g., XVII [25], XVIII [20], XIX [26], Figure 3). For some representatives of Si-guanidinates, it has also been shown that their Si-N bond may be prone to CO 2 insertion [22,27]. The silicon compounds of aromatic guanidines (2-aminopyrimidine derivatives), however, are scarcely explored.…”