Reversible Covalent Chemistry of CO2: An Opportunity for Nano-Structured Hybrid Organic–Inorganic Materials

Abstract

A new approach to get ordered and highly amine-functionalized organosilicas is described. The method consisted of using the reversible reaction between CO2 and amines giving rise to ammonium carbamate salts. Four amine containing precursors were selected for this study: 3-aminopropyltrimethoxysilane (1), 11-amino-undecyltrimethoxysilane (2), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (3), and N-(6-aminohexyl)-3-aminopropyltrimethoxysilane (4). CO2 reacted with 1 and 2 affording bis-silylated organosilica precursors containing ammonium carbamate salts in the core while the reaction between CO2 and 3 or 4 led to a supramolecular network of silylated ammonium carbamate salts. The hydrolytic polycondensation of these carbamate derivatives by using the sol–gel process provided hybrid materials with lamellar structure containing ammonium carbamate salts. Subsequent elimination of CO2 upon heating generated materials with free amino groups in which the long-range order was maintained. The structuration was found to be highly dependent on van der Waals interactions between the long alkylene chains. Some complexation reactions and chemical transformations were achieved to investigate the accessibility of the amino groups as well as the chelating capability of the materials.