Synthesis of Structurally Varied 1,3‐Disiloxanediols and Their Activity as Anion‐Binding Catalysts

Abstract

A series of new 1,3-disiloxanediols has been synthesized, including naphthyl-substituted and unsymmetrical siloxanes, and demonstrated as a new class of anion-binding catalysts. In the absence of anions, diffusion-ordered spectroscopy (DOSY) displays self-association of 1,3-disiloxanediols through hydrogen-bonding interactions. Binding constants determined for 1,3-disiloxanediol catalysts indicate strong hydrogen-bonding and anion-binding abilities with unsymmetrical siloxanes displaying different hydrogen-bonding abilities for each silanol group.

Reactivity of the Sterically Demanding Siloxanediol Mes2Si(OH)(μ‐O)Si(OH)Mes2 Towards Water and Ether Molecules

“…Most likely, a fast conformational equilibrium as well as intramolecular dynamics associated with the hydrogen bridge in a cis conformer are responsible for proton exchange. However, intermolecular hydrogen bonding of 3 d is rather unlikely, since the self‐association of the comparable tetraphenyl‐1,3‐disiloxanediol was only observed at high concentrations or in the solid state . The 17 O{ 1 H} NMR spectrum of 3 d in C 6 D 6 changes negligibly when compared to the spectra in [D 8 ]THF.…”

“…Organosilanols show interesting properties, as their ability for hydrogen bonding can be associated, for example, with condensation reactions and applications in catalysis or drug design . Recently, Franz and co‐workers reported the hydrogen bonding driven self‐association and anion binding of various 1,3‐disiloxanediols . Organosilanols and siloxanediols in particular, can be regarded as models for surface‐bound silanol groups, which are abundant structural motifs in silicates and silica materials.…”

Kinetic and Binding Studies Reveal Cooperativity and Off‐Cycle Competition for H‐Bonding Catalysis with Silsesquioxane Silanols

“…Given our previous work with disiloxanediols as H‐bond donor and anion‐binding catalysts, we evaluated the catalytic activity of POSS triol 1 a for the addition of indole ( 8 a ) to trans ‐β‐nitrostyrene ( 7 a ) (Table , Column 3). Despite enhanced H‐bonding activity based on TEPO data, POSS 1 a was found to yield comparable to silanediol 5 in o ‐DCB.…”

“…Our group and others have demonstrated that activity of organic, silanol‐containing hydrogen‐bond donor (HBD) catalysts can be tuned by silanol arrangement and acidity (e.g. 4 – 6 , Figure ) . Silanols display higher acidities compared with alcohols, which is attributed to hyperconjugation effects between the oxygen and silicon .…”

“…4-6, Figure 1). [31][32][33][34][35] Silanols display higher acidities compared with alcohols, which is attributed to hyperconjugation effectsb etween the oxygen and silicon. [36,37] Of the silanol scaffolds studied (e.g.…”