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Title: Pore Environment Effects on Catalytic Cyclohexane Oxidation in Expanded Fe 2 (dobdc) Analogues

Abstract

Here, metal–organic frameworks are a new class of heterogeneous catalysts in which molecular-level control over both the immediate and long-range chemical environment surrounding a catalytic center can be readily achieved. Here, the oxidation of cyclohexane to cyclohexanol and cyclohexanone is used as a model reaction to investigate the effect of a hydrophobic pore environment on product selectivity and catalyst stability in a series of iron-based frameworks. Specifically, expanded analogues of Fe 2(dobdc) (dobdc 4– = 2,5-dioxido-1,4-benzenedicarboxylate) were synthesized and evaluated, including the biphenyl derivative Fe 2(dobpdc) (H 4dobpdc = 4,4¢-dihydroxy-[1,1¢-biphenyl]-3,3¢-dicarboxylic acid), the terphenyl derivative Fe 2(dotpdc) (H 4dotpdc = 4,4¢¢-dihydroxy-[1,1¢:4¢,1¢¢-terphenyl]-3,3¢¢-dicarboxylic acid), and three modified terphenyl derivatives in which the central ring is replaced with tetrafluoro-, tetramethyl-, or di- tert-butylaryl groups. Within these five materials, a remarkable three-fold enhancement of the alcohol:ketone (A:K) ratio and an order of magnitude increase in turnover number is achieved by simply altering the framework pore diameter and installing nonpolar functional groups near the iron site. Mössbauer spectroscopy, kinetic isotope effect, and gas adsorption measurements reveal that variations in the A:K selectivities arise from differences in the cyclohexane adsorption enthalpies of these frameworks, which become more favorable as the number of hydrophobic residues and thus vanmore » der Waals interactions increases.« less

Authors:
 [1];  [1];  [1];  [2]
  1. Univ. of California, Berkeley, CA (United States)
  2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Research Org.:
Univ. of Minnesota, Minneapolis, MN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1458984
Grant/Contract Number:  
FG02-12ER16362; SC0008688
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 138; Journal Issue: 43; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Xiao, Dianne J., Oktawiec, Julia, Milner, Phillip J., and Long, Jeffrey R. Pore Environment Effects on Catalytic Cyclohexane Oxidation in Expanded Fe2 (dobdc) Analogues. United States: N. p., 2016. Web. doi:10.1021/jacs.6b08417.
Xiao, Dianne J., Oktawiec, Julia, Milner, Phillip J., & Long, Jeffrey R. Pore Environment Effects on Catalytic Cyclohexane Oxidation in Expanded Fe2 (dobdc) Analogues. United States. doi:10.1021/jacs.6b08417.
Xiao, Dianne J., Oktawiec, Julia, Milner, Phillip J., and Long, Jeffrey R. Wed . "Pore Environment Effects on Catalytic Cyclohexane Oxidation in Expanded Fe2 (dobdc) Analogues". United States. doi:10.1021/jacs.6b08417. https://www.osti.gov/servlets/purl/1458984.
@article{osti_1458984,
title = {Pore Environment Effects on Catalytic Cyclohexane Oxidation in Expanded Fe2 (dobdc) Analogues},
author = {Xiao, Dianne J. and Oktawiec, Julia and Milner, Phillip J. and Long, Jeffrey R.},
abstractNote = {Here, metal–organic frameworks are a new class of heterogeneous catalysts in which molecular-level control over both the immediate and long-range chemical environment surrounding a catalytic center can be readily achieved. Here, the oxidation of cyclohexane to cyclohexanol and cyclohexanone is used as a model reaction to investigate the effect of a hydrophobic pore environment on product selectivity and catalyst stability in a series of iron-based frameworks. Specifically, expanded analogues of Fe2(dobdc) (dobdc4– = 2,5-dioxido-1,4-benzenedicarboxylate) were synthesized and evaluated, including the biphenyl derivative Fe2(dobpdc) (H4dobpdc = 4,4¢-dihydroxy-[1,1¢-biphenyl]-3,3¢-dicarboxylic acid), the terphenyl derivative Fe2(dotpdc) (H4dotpdc = 4,4¢¢-dihydroxy-[1,1¢:4¢,1¢¢-terphenyl]-3,3¢¢-dicarboxylic acid), and three modified terphenyl derivatives in which the central ring is replaced with tetrafluoro-, tetramethyl-, or di-tert-butylaryl groups. Within these five materials, a remarkable three-fold enhancement of the alcohol:ketone (A:K) ratio and an order of magnitude increase in turnover number is achieved by simply altering the framework pore diameter and installing nonpolar functional groups near the iron site. Mössbauer spectroscopy, kinetic isotope effect, and gas adsorption measurements reveal that variations in the A:K selectivities arise from differences in the cyclohexane adsorption enthalpies of these frameworks, which become more favorable as the number of hydrophobic residues and thus van der Waals interactions increases.},
doi = {10.1021/jacs.6b08417},
journal = {Journal of the American Chemical Society},
number = 43,
volume = 138,
place = {United States},
year = {2016},
month = {10}
}

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Cited by: 47 works
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Figures / Tables:

Figure 1. Figure 1.: Portions of the crystal structures of Fe2(dobdc), Fe2(dobpdc), Fe2(dotpdc) and their corresponding ligands. (a) View of the one-dimensional hexagonal pores of Fe2(dobdc), with an inset showing the local coordination environment around each coordinatively unsaturated iron(II) site. The pore sizes indicated here were calculated from experimental 77-K N2 adsorptionmore » isotherm data using DFT methods.« less

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