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Title: Inter- and Intramolecular Cooperativity Effects in Alkanolamine-Based Acid–Base Heterogeneous Organocatalysts

Abstract

Intramolecular cooperativity in heterogeneous organocatalysts is investigated using alkanolamine-functionalized silica acid–base catalysts for the aldol condensation reaction of 4-nitrobenzaldehyde and acetone. Two series of catalysts, one with and one without silanol-capping, are synthesized with varied alkyl linker lengths (two to five) connecting secondary amine and terminal hydroxyl functionalities. The reactivity of these catalysts is assessed to determine the relative potential for intermolecular (silane amine–surface silanol) vs intramolecular (amine–hydroxyl within a single silane) cooperativity, the impact of inhibitory surface–silane interactions, and the role of alkyl linker length and flexibility. For the array of catalysts tested, those with longer linker lengths generally give increased catalytic activity, although the turnover frequency trends differ between catalysts with and without surface silanol capping. Catalysts with alkyl-substituted amines lacking a terminal hydroxyl demonstrate an adverse effect of chain length, where the larger alkyl substituent on the amine provides steric hindrance depressing catalytic activity, while giving additional evidence for improved rates afforded by intramolecular cooperativity in the alkanolamine materials. The silanol-capped alkanolamine catalyst with the longest alkyl linker is found to be the most active alkanolamine catalyst due to its hydrophobized surface, which removes hypothesized silanol–alkanolamine inhibitory interactions, with the sufficient length and flexibility of its amine–hydroxylmore » linker allowing for favorable conformations for cooperativity. This study demonstrates the feasibility of and important factors affecting intramolecular cooperative activity in acid–base heterogeneous organocatalysis.« less

Authors:
 [1];  [1]; ORCiD logo [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States)
Publication Date:
Research Org.:
Georgia Inst. of Technology, Atlanta, GA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1490772
Alternate Identifier(s):
OSTI ID: 1508824
Grant/Contract Number:  
FG02-03ER15459
Resource Type:
Journal Article: Published Article
Journal Name:
ACS Omega
Additional Journal Information:
Journal Volume: 4; Journal Issue: 1; Journal ID: ISSN 2470-1343
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; ldol condensation; Catalysis; Catalysts; Mechanical properties; Organic compounds and Functional groups; Reaction kinetics; Reaction mechanism; Surface treatment

Citation Formats

Xie, Jingwei, Ellebracht, Nathan C., and Jones, Christopher W. Inter- and Intramolecular Cooperativity Effects in Alkanolamine-Based Acid–Base Heterogeneous Organocatalysts. United States: N. p., 2019. Web. doi:10.1021/acsomega.8b02690.
Xie, Jingwei, Ellebracht, Nathan C., & Jones, Christopher W. Inter- and Intramolecular Cooperativity Effects in Alkanolamine-Based Acid–Base Heterogeneous Organocatalysts. United States. doi:10.1021/acsomega.8b02690.
Xie, Jingwei, Ellebracht, Nathan C., and Jones, Christopher W. Mon . "Inter- and Intramolecular Cooperativity Effects in Alkanolamine-Based Acid–Base Heterogeneous Organocatalysts". United States. doi:10.1021/acsomega.8b02690.
@article{osti_1490772,
title = {Inter- and Intramolecular Cooperativity Effects in Alkanolamine-Based Acid–Base Heterogeneous Organocatalysts},
author = {Xie, Jingwei and Ellebracht, Nathan C. and Jones, Christopher W.},
abstractNote = {Intramolecular cooperativity in heterogeneous organocatalysts is investigated using alkanolamine-functionalized silica acid–base catalysts for the aldol condensation reaction of 4-nitrobenzaldehyde and acetone. Two series of catalysts, one with and one without silanol-capping, are synthesized with varied alkyl linker lengths (two to five) connecting secondary amine and terminal hydroxyl functionalities. The reactivity of these catalysts is assessed to determine the relative potential for intermolecular (silane amine–surface silanol) vs intramolecular (amine–hydroxyl within a single silane) cooperativity, the impact of inhibitory surface–silane interactions, and the role of alkyl linker length and flexibility. For the array of catalysts tested, those with longer linker lengths generally give increased catalytic activity, although the turnover frequency trends differ between catalysts with and without surface silanol capping. Catalysts with alkyl-substituted amines lacking a terminal hydroxyl demonstrate an adverse effect of chain length, where the larger alkyl substituent on the amine provides steric hindrance depressing catalytic activity, while giving additional evidence for improved rates afforded by intramolecular cooperativity in the alkanolamine materials. The silanol-capped alkanolamine catalyst with the longest alkyl linker is found to be the most active alkanolamine catalyst due to its hydrophobized surface, which removes hypothesized silanol–alkanolamine inhibitory interactions, with the sufficient length and flexibility of its amine–hydroxyl linker allowing for favorable conformations for cooperativity. This study demonstrates the feasibility of and important factors affecting intramolecular cooperative activity in acid–base heterogeneous organocatalysis.},
doi = {10.1021/acsomega.8b02690},
journal = {ACS Omega},
issn = {2470-1343},
number = 1,
volume = 4,
place = {United States},
year = {2019},
month = {1}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1021/acsomega.8b02690

Figures / Tables:

Figure 1 Figure 1: Chemical structure and naming convention of synthesized alkanolamine (AA) bifunctional catalysts grafted on SBA-15 with (b) and without (a) HMDS-capping of surface silanols. Catalytically active basic species (secondary amines) are shown in blue and weakly acidic species (surface silanols, terminal hydroxyls) in red.

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