Silanediol Hydrogen Bonding Activation of Carbonyl Compounds

Abstract

Silicon is the second most abundant element on the earths surface, whereby inorganic silanols (SiOH) make up the reactive hydroxyl groups on the surface of minerals, zeolites, and silica gel. The acidic silanol groups [1] are known to be capable of hydrogen bonding to small molecules for heterogeneous catalysis and separation chemistry, but the discrete surface-molecule interactions are not well understood.[2] Silanediols R 2 Si(OH) 2 are of particular interest as they contain a geminal diol bonding motif that is not commonly accessible for carbon analogues, but they represent a synthetic challenge due to their rapid rates of self-condensation. While condensation is advantageous for the synthesis of siloxane polymers, metallosiloxanes, and silesquioxanes, [3] it creates a barrier that may hinder researchers from exploring the properties and applications of discrete silanediols. [4] Recent studies demonstrate that silanols can function as isosteres and transition-state analogues in drug design, in which the enhanced acidity of the silanol can improve binding to a receptor.[5] Small molecules containing silanol and silanediol groups may be useful as models to understand local surface sites and reactivity of silica materials for catalysis, and also to design new homogeneous small-molecule catalysts.We seek to understand the hydrogen bonding patterns and interactions between organic silanediols with carbonyls for applications to catalysis and molecular recognition. Hydrogen bonding interactions play an important role in molecular recognition and metal-free catalysis, and are frequently used in nature for structural organization and enzyme activity.[6] Previous structural studies have demonstrated the hydrogen bonding networks that silanediols can attain through dual donor and acceptor interactions, [4, 7] and also the ability to hydrogen bond with chloride anions for molecular recognition.[8] Studies of silanetriols have shown that amines can complex with and stabilize silanetriols.[9]Here we describe the synthesis and structural studies of organic silanediols for small-molecule hydrogen bonding activation of carbonyl compounds.[10] We are particularly interested in studying bulky silanediols that do not readily undergo condensation reactions.[11] We have performed crystallization and NMR-binding experiments to investigate the hydrogen bonding interactions in both solid-state and solution for molecular recognition and the design of new catalysts. This is the first study of neutral Lewis basic carbonyl compounds with silanediols.We have synthesized a series of bulky silanediols 2-4 that incorporate electron-withdrawing groups to enhance acidity while incorporating steric effects to overcome condensation reactions. Due to the synthetic challenge, the chemical space for silanediols is largely unexplored, and silanediols 2-4 represent new structures.[4] The mesityl group (Mes) was incorporated to prevent formation of disiloxanediols and higher order siloxanes.[12] Incorporating a mesityl group also provides enhanced so...

A Versatile Precursor System for Supercritical Fluid Electrodeposition of Main‐Group Materials

“…In the 1 H NMR spectra of 4 , the signal of the Si–OH protons is shifted to lower field and broadened as compared with 3 [δ( 3 ) = 5.49 ppm, δ( 4 ) = 5.82 ppm, [D 8 ]THF]. This observation may be attributed to increased polarization of the O–H bond in the presence of Bpy, similar to the interpretation in related cases 10,18. Furthermore, the signals for the protons of the Dmp substituent are slightly shifted as well.…”

Discovery of a Highly Selective PLD2 Inhibitor (ML395): A New Probe with Improved Physiochemical Properties and Broad‐Spectrum Antiviral Activity against Influenza Strains

“…Since Kondo's demonstration of silanediol anion recognition abilities, the Franz and Mattson laboratories have independently advanced their own silanediol catalyst designs. The Franz group developed a family of mesityl‐derived silanediols and first demonstrated their catalytic potential in the hetero‐Diels–Alder reaction between methacrolein and Rawal's diene 100 (Scheme ) 54. The mesityl group was strategically incorporated into their catalyst design in order to overcome undesired condensation reactions, as well as to increase the solubility of the catalysts relative to diphenylsilanediol.…”

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

“…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.…”