Oxygen atom transfer with manganese-exchanged metal-organic frameworks
Name
1142099807-MIT.pdf
Size
9.02 MB
Format
Adobe PDF
Checksum (MD5)
00ee42b92880962083db0d45a27c0ed8
Author(s)
Stubbs, Amanda Walcott.
Advisor(s)
Mircea Dincă.
Date Issued
2019
Publisher
Massachusetts Institute of Technology
Abstract
Oxygenates represent some of the most versatile commodity chemicals, justifying continued interest in the discovery of new selective oxidation catalysts from both a fundamental and applied perspective. Metal-organic frameworks (MOFs) are an attractive platform for catalysis because they enable access to unique coordination environments and reactivities; this is due in part to their tunability combined with the site isolation offered by their solid state. In one example, partial substitution of Zn[superscript II] by Mn[superscript II] in Zn₄O(terephthalate)₃ (MOF-5) leads to a distorted all-oxygen ligand field supporting a single Mn[superscript II] site, whose structure was confirmed by Mn K-edge X-ray absorption spectroscopy. Upon exposure to [superscript t]BuSO₂PhIO, Mn-MOF-5 produces a putative Mn[superscript IV]-oxo intermediate, which upon further reaction with adventitious hydrogen is trapped as a Mn[superscript III]-OH species.
Most intriguingly, the intermediacy of the high-spin Mn[superscript IV]-oxo species is likely responsible for catalytic activity of the Mn[superscript II]-MOF-5 precatalyst, which in the presence of [superscript t]BuSO₂PhIO catalyzes oxygen atom transfer reactivity to selectively form epoxides from cyclic alkenes. In a second study, partial substitution of Zn[superscript II] by Mn[superscript II] in Zn₅(OAc)₄(bibenzotriazolate)₃ (CFA-1) yields a material in which manganese is supported by a ligand environment reminiscent of that found in molecular scorpionates. Unlike molecular analogs, Mn-CFA-1 is capable of activating molecular oxygen to convert substrates with sufficiently weak C-H bonds, such as cyclohexene, to alcohol and ketone products. In-situ spectroscopies including Mn K-edge X-ray absorption, DRIFTS, and Diffuse Reflectance UV-vis indicate that reactivity proceeds through a high valent Mn-peroxo species.
These results demonstrate that MOF secondary building units serve as competent platforms for accessing high-valent metal-oxygen species that consequently engage in catalytic oxygen atom transfer chemistry owing to the ligand fields and site isolation provided by the material.
Description
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019
"September 2019." Cataloged from PDF version of thesis.
Includes bibliographical references (pages 93-105).
Subjects
Chemistry.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
Terms of Use
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