Reaction Progress Kinetics Analysis of 1,3-Disiloxanediols as Hydrogen-Bonding Catalysts

Abstract

1,3-Disiloxanediols are effective hydrogen-bonding catalysts that exhibit enhanced activity relative to silanediols and triarylsilanols. The catalytic activity for a series of 1,3-disiloxanediols, including naphthyl-substituted and unsymmetrical siloxanes, has been quantified and compared relative to other silanol and thiourea catalysts using the Friedel Crafts addition of indole to trans-β-nitrostyrene. An in-depth kinetic study using reaction progress kinetic analysis (RPKA) has been performed to probe the catalyst behavior of 1,3-disiloxanediols. The data confirm that the disiloxanediol-catalyzed addition reaction is first order in catalyst over all concentrations studied with no evidence of catalyst self-association. 1,3-Disiloxanediols proved to be robust and recoverable catalysts with no deactivation under reaction conditions. No product inhibition is observed, and competitive binding studies with nitro-containing additives suggest that 1,3-disiloxanediols bind weakly to nitro groups but are strongly activating for catalysis.

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

“…POSS 2 was found to provide poor yield, suggesting that intramolecular H‐bonding occurs in 1 a for catalysis. Disiloxanediols 6 a and 6 b were observed to provide greater yield in the reaction under these conditions in addition to accelerating rate, as seen previously . When studying relative rates (Table , Column 4), POSS 1 a surprisingly afforded the highest rate enhancement despite poor catalytic activity.…”

“…Given our previous work with disiloxanediols as H-bond donor [43] and anion-binding catalysts, [35] we evaluated the catalytic activity of POSS triol 1a for the addition of indole( 8a)t o trans-b-nitrostyrene(7a)( Table 2, Column3). Despite enhanced H-bonding activity based on TEPO data, POSS 1a was found to yield comparable to silanediol 5 in o-DCB.…”

“…Disiloxanediols 6a and 6b were observed to provide greater yield in the reaction under these conditions in addition to accelerating rate, as seen previous- ly. [39,43] When studying relative rates (Table2,C olumn4), POSS 1a surprisingly afforded the highest rate enhancement despite poor catalytic activity.O verall the data suggests the presence of some inhibitory mechanism.P OSS diol 2 afforded no rate enhancement and POSS 1b provedi nsoluble under these conditions. We next conducted ak inetic investigation of POSS triol 1a as aH BD catalyst to identify the cause of poor catalysis despite high rate, and to determine if POSS-triols can be homogeneous model compounds for silica gel catalysis.…”

The Influence of Weakly Coordinating Cations on the O−H⋅⋅⋅O− Hydrogen Bond of Silanol‐Silanolate Anions

“…The obtained structures are strongly affected by the presence of solvent molecules capable of hydrogen bonding. Silanols have also found application as catalysts in silanol‐hydrogen‐bond‐assisted coupling reactions [10, 11] and CO 2 fixation strategies [16, 18] …”

Understanding the Mechanism of Nitrobenzene Nitration with Nitronium Ion: A Molecular Electron Density Theory Study

“…[16][17][18][19][20][21][22][23][24][25][26] However, nitration reactions are very polluting processes as they require an excess of concentrated nitric acid and the aid of a strong acid, like concentrated sulfuric acid, thus generating pollutants such as vapours, oxides of nitrogen, NO x , and large quantities of acid waste. [27][28][29][30][31] In order to rationalize the experimental outcomes and the mechanism of this important reaction, theoretical chemists have been working on this reaction for several decades trying to explain the mechanism through three competitive reaction paths, i. e. ortho, meta and para, according to the regioselective attack of the nitronium ion on monosubstituted aromatic compounds.…”