On the Use of Triarylsilanols as Catalysts for Direct Amidation of Carboxylic Acids

Abstract

Triarylsilanols have been reported as the first silicon-centered molecular catalysts for direct amidation of carboxylic acids with amines as identified after a screen of silanols, silanediols, disiloxanediols, and incompletely condensed silsesquioxanes as potential homogeneous catalysts. Subsequent synthesis and testing of various electronically differentiated triarylsilanols have identified tris(p-haloaryl)silanols as more active than the parent triarylsilanol, where the bromide congener is found to be the most active. Catalyst decomposition can be observed by NMR methods, but RPKA methods reveal that product inhibition is operative, where tertiary amides are more inhibitory than secondary amides. Studies using an authentically synthesized triaryl silylester as a putative intermediate in the catalytic system enable a plausible mechanism to be proposed as supported by computationals.

Auto-VTNA: An Automatic VTNA platform for Determination of Global Rate Equations

“…1). 7,20,31 To develop a robust automated method, we began by emulating the manual routine within a Python script that calculates the transformed time axis for a chosen reaction species and corresponding order value(s) using a selected subset of the kinetic data, tested on literature examples (see section S8). 28 Subsequently, a robust automatic method of assessing the overlay of reaction progress profiles https://doi.org/10.26434/chemrxiv-2024-ck8c5 ORCID: https://orcid.org/0000-0001-9920-2793 Content not peer-reviewed by ChemRxiv.…”

“…1,2,3,4 Chemical kinetics is also utilized extensively to understand and optimize the behaviour of reaction systems, particularly complex catalytic reactions. [5][6][7][8][9] The global rate equation (a.k.a. the rate law) is a mathematical expression that correlates the rate of a reaction with the concentration of each reaction species, with the general form: A global rate equation can be constructed empirically from experimental data, without explicit considerations of the reaction mechanism or mass transfer effects.…”

Oligo‐Condensation Reactions of Silanediols with Conservation of Solid‐State‐Structural Features.

“…[19][20] Different stable monosilanols, silanediols and -triols are already described in literature, such as Ph 3 SiOH, [21] Et 3 SiOH, [21] (n-Bu) 3 SiOH, [21] (tert-BuO) 3 SiOH, [22] Me 2 Si(OH) 2 , [23] Ph 2 Si(OH) 2 , [24] (cis-C 6 H 11 ) 2 Si(OH) 2 , [25] (tert-Bu) 2 Si(OH) 2 , [10] (ortho-tolyl) 2 Si(OH) 2 , [26] (iso-propyl) 2 Si(OH) 2 [27] PhSi(OH) 3 , [28] c-C 6 H 11 Si(OH) 3 [29][30] and tert-BuSi(OH) 3 . [31] Silanediols have been already used, for example, in the synthesis of LED encapsulation resins and in pharmaceutical applications, [24,[32][33] monosilanols were applied as catalysts for various organic syntheses, such as cross coupling reactions [34][35][36] or direct amidation of carboxylic acid [37] and silanetriols have already been used for the synthesis of various metallasiloxanes [38][39] and POSS cages. [40][41][42] Many of the stable silanols are solid and crystalline at room temperature.…”

Hexylsilane-mediated direct amidation of amino acids with a catalytic amount of 1,2,4-triazole

“…In 2018, the ACS Green Chemistry Institute Pharmaceutical Roundtable identified sustainable (direct) amide or peptide formation as a “key green chemistry research area”. 2 Silyl-based coupling reagents have been recently developed on this background, 3 with amide bond formation using hydrosilanes attracting considerable attention. Hydrosilanes have low toxicity.…”

“…The previous report focusing on silicon-mediated amide bond synthesis suggested that the active intermediate was the silyl ester species. 3,5,6,11,18 We failed to separate any silyl ester species of amino acids but considered the mechanism of this reaction based on the abovementioned results (Scheme 5). First, the carboxy group of the amino acid was deprotonated by the amine, and the resulting carboxylate 5 attacked the silicon atom of hexylsilane, releasing hydrogen to form the silyl ester 6 .…”