Anion Recognition and the Application by Silanol Derivatives

Anions are fundamental species in the environment and in living cells; therefore, the recognition of anions is important. We found that silanol derivatives, including silanediols, silanetriol, 1,3-disiloxane-1,3-diol, and 1,3-disiloxane-1,1,3,3-tetraol, form multiple hydrogen bonds with anions in organic solvents. The X-ray single crystal structure of di(1-naphthyl)silanediol and Cl− revealed that the two hydroxy groups formed cooperatively hydrogen bonds to Cl−. The association constants of the silanol derivatives for anions were comparable to those of the corresponding urea derivatives. In addition, silanediols bearing pyrenyl and substituted naphthyl groups slowly react in the presence of a base to form the corresponding cyclotri- and cyclotetrasiloxanes, respectively under mild conditions without cleaving the Si-C bonds. The structures and the photophysical properties are also presented. Notably, silanol derivatives can be utilized as organocatalyst, similar to thiourea and squaramide derivatives. The addition of indole to β-nitrostyrene catalyzed by silanetriol was faster than that with silanediol indicating that three hydroxy groups cooperatively stabilize the transition state of the reaction.