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Mechanistic Investigation of Biomime...

Piquette, Marc C.

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Mechanistic Investigation of Biomimetic Non-Heme Iron Complexes for Oxidation Catalysis.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Mechanistic Investigation of Biomimetic Non-Heme Iron Complexes for Oxidation Catalysis./
作者:	Piquette, Marc C.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
面頁冊數:	176 p.
附註:	Source: Dissertations Abstracts International, Volume: 81-09, Section: B.
Contained By:	Dissertations Abstracts International81-09B.
標題:	Inorganic chemistry. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27545278
ISBN:	9781658413916

Mechanistic Investigation of Biomimetic Non-Heme Iron Complexes for Oxidation Catalysis.
Piquette, Marc C.

Mechanistic Investigation of Biomimetic Non-Heme Iron Complexes for Oxidation Catalysis. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 176 p.

Source: Dissertations Abstracts International, Volume: 81-09, Section: B.

Thesis (Ph.D.)--Tufts University, 2020.

This item must not be sold to any third party vendors.

This work details mechanistic studies of non-heme iron complexes used in selective oxidation of unactivated hydrocarbons. We aim to mimic the potent oxidative ability seen in nature by enzymes such as Cytochrome P450 or the Rieske Dioxygenases. Developing these biomimetic models would contribute to the chemist's toolbox for predictable olefin epoxidation, and aromatic and aliphatic hydroxylation. However, these biomimetic catalysts exhibit high reactivity, which makes mechanistic elucidation challenging due to the short life of active intermediates, and unproductive reactions that occur. Further understanding their mechanisms and decay pathways will allow for fine tuning of catalyst reactivity, selectivity, and scope.The work herein focuses on complex [(PDP*)FeII](ClO4)2 (PDP* = bis(3,5-dimethyl-4-methoxy-pyridylmethyl)-(R,R)-2,2'-bipyrrolidine), a highly reactive non-heme iron-oxidation catalyst, which reacts with H2O2 to form peroxoiron(III), which undergoes O-O heterolysis to afford the putative oxoiron(V) active species. Homolysis, yielding oxoiron(IV), has also been observed, although its reactivity was unstudied. Detailed kinetic studies were conducted by direct generation of [(PDP*)FeIV]=O with two-electron oxidant IBXiPr (isopropyl 2-iodoxybenzoate). Reactivity towards organic substrates was greatly diminished compared to the oxoiron(V) pathway, but oxidations of cyclooctene, cyclohexane, and benzene were still observed. [(PDP*)FeIV]=O rapidly oxidized H2O2, reverting to a hydroxyiron(III) state and was then able to re-enter the FeIII/V catalytic cycle, though with somewhat diminished activity due to loss of active iron during the reduction process. This represents an unstudied pathway of H2O2 consumption in catalysis which deserves more attention, and may lend favor towards the use of peracids (mCPBA, peracetic acid), which were not oxidized by [(PDP*)FeIV]=O.The second focus was on catalysis with [(PDP*)FeII](ClO4)2 paired with H2O2 and AcOH or with peracids as oxidant. Carboxylic acid co-catalysts are known to greatly enhance catalytic yields and enantioselectivity, but mechanism and active species (either oxoiron(V) or an oxoiron(IV) radical species) remains unclear. Peracids show similar promise as a hybrid of oxidant and co-catalyst, but the details of its mechanism are unclear. We provide evidence of a common oxoiron(V) species with H2O2/AcOH and peracetic acid (AcOOH), but this could not be verified with mCPBA, likely due to rapid intramolecular oxidation of the bound aromatic moiety. High alcohol/ketone ratios in cyclohexane oxidation were observed with all three oxidants, supporting a common, selective active species regardless of oxidant used. In epoxidation catalysis, rates and yields were fastest with AcOOH, which may lend favor to this oxidant in synthetic applications. Yields were low with mCPBA, owing to unproductive hydroxylation of its aromatic ring intramolecularly. However, even challenging substrates such as chlorobenzene could be oxidized intermolecularly competitively with the intramolecular process, highlighting the selectivity of this catalyst.

ISBN: 9781658413916Subjects--Topical Terms:

3173556
Inorganic chemistry.
Subjects--Index Terms:

Biomimetic

Mechanistic Investigation of Biomimetic Non-Heme Iron Complexes for Oxidation Catalysis.
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500 $a Source: Dissertations Abstracts International, Volume: 81-09, Section: B.
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506 $a This item must not be sold to any third party vendors.
520 $a This work details mechanistic studies of non-heme iron complexes used in selective oxidation of unactivated hydrocarbons. We aim to mimic the potent oxidative ability seen in nature by enzymes such as Cytochrome P450 or the Rieske Dioxygenases. Developing these biomimetic models would contribute to the chemist's toolbox for predictable olefin epoxidation, and aromatic and aliphatic hydroxylation. However, these biomimetic catalysts exhibit high reactivity, which makes mechanistic elucidation challenging due to the short life of active intermediates, and unproductive reactions that occur. Further understanding their mechanisms and decay pathways will allow for fine tuning of catalyst reactivity, selectivity, and scope.The work herein focuses on complex [(PDP*)FeII](ClO4)2 (PDP* = bis(3,5-dimethyl-4-methoxy-pyridylmethyl)-(R,R)-2,2'-bipyrrolidine), a highly reactive non-heme iron-oxidation catalyst, which reacts with H2O2 to form peroxoiron(III), which undergoes O-O heterolysis to afford the putative oxoiron(V) active species. Homolysis, yielding oxoiron(IV), has also been observed, although its reactivity was unstudied. Detailed kinetic studies were conducted by direct generation of [(PDP*)FeIV]=O with two-electron oxidant IBXiPr (isopropyl 2-iodoxybenzoate). Reactivity towards organic substrates was greatly diminished compared to the oxoiron(V) pathway, but oxidations of cyclooctene, cyclohexane, and benzene were still observed. [(PDP*)FeIV]=O rapidly oxidized H2O2, reverting to a hydroxyiron(III) state and was then able to re-enter the FeIII/V catalytic cycle, though with somewhat diminished activity due to loss of active iron during the reduction process. This represents an unstudied pathway of H2O2 consumption in catalysis which deserves more attention, and may lend favor towards the use of peracids (mCPBA, peracetic acid), which were not oxidized by [(PDP*)FeIV]=O.The second focus was on catalysis with [(PDP*)FeII](ClO4)2 paired with H2O2 and AcOH or with peracids as oxidant. Carboxylic acid co-catalysts are known to greatly enhance catalytic yields and enantioselectivity, but mechanism and active species (either oxoiron(V) or an oxoiron(IV) radical species) remains unclear. Peracids show similar promise as a hybrid of oxidant and co-catalyst, but the details of its mechanism are unclear. We provide evidence of a common oxoiron(V) species with H2O2/AcOH and peracetic acid (AcOOH), but this could not be verified with mCPBA, likely due to rapid intramolecular oxidation of the bound aromatic moiety. High alcohol/ketone ratios in cyclohexane oxidation were observed with all three oxidants, supporting a common, selective active species regardless of oxidant used. In epoxidation catalysis, rates and yields were fastest with AcOOH, which may lend favor to this oxidant in synthetic applications. Yields were low with mCPBA, owing to unproductive hydroxylation of its aromatic ring intramolecularly. However, even challenging substrates such as chlorobenzene could be oxidized intermolecularly competitively with the intramolecular process, highlighting the selectivity of this catalyst.
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