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Oxidative Aliphatic Carbon-Carbon Bond Cleavage Reactions Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 5-2013 Oxidative Aliphatic Carbon-Carbon Bond Cleavage Reactions Caleb J. Allpress Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Chemistry Commons Recommended Citation Allpress, Caleb J., "Oxidative Aliphatic Carbon-Carbon Bond Cleavage Reactions" (2013). All Graduate Theses and Dissertations. 2003. https://digitalcommons.usu.edu/etd/2003 This Dissertation is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. OXIDATIVE ALIPHATIC CARBON-CARBON BOND CLEAVAGE REACTIONS by Caleb J. Allpress A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Chemistry Approved: Lisa M. Berreau, Ph.D. Alvan C. Hengge, Ph.D. Major Professor Committee Member John L. Hubbard, Ph.D. Paul R. Grossl, Ph.D. Committee Member Committee Member Bradley S. Davidson, Ph.D. Mark R. McLellan, Ph.D. Committee Member Vice President for Research and Dean of the School of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2013 ii Copyright © Caleb Allpress 2013 All Rights Reserved iii ABSTRACT Oxidative Aliphatic Carbon-Carbon Bond Cleavage Reactions by Caleb J. Allpress, Doctor of Philosophy Utah State University, 2013 Major Professor: Dr. Lisa M. Berreau Department: Chemistry and Biochemistry The work presented in this dissertation has focused on synthesizing complexes of relevance to dioxygenase enzymes that oxidatively cleave aliphatic carbon-carbon bonds. The goal of this research was to elucidate mechanistic aspects of the activation of aliphatic carbon-carbon bonds towards cleavage by reaction with oxygen, and also investigate the regioselectivity of these reactions. The oxidative cleavage of a variety of enolizable substrates has been explored by utilizing several transition metal complexes supported by an aryl-appended tris(pyridylmethyl)amine ligand. In order to probe the widely-accepted “chelate hypothesis” for how changes in regiospecificity are achieved as a function of metal ion, we synthesized the compound [(6-Ph2TPA)Fe(PhC(O)COHC(O)Ph)]OTf. Based on UV-vis and IR spectroscopy, the acireductone enolate was found to bind via a six-membered chelate ring. By comparison with the reactivity of [(6-Ph2TPA)Ni(PhC(O)COHC(O)Ph)]ClO4, we determined that the chelate hypothesis was an insufficient explanation of the observed regioselectivity. iv Rather, ferrous ion-mediated hydration of a vicinal triketone intermediate was the key factor in determining the regioselectivity of the C-C cleavage reaction. We have developed a high-yielding synthetic route to protected precursors of C(1)H acireductones. Preparation of the complexes [(6- Ph2TPA)M(PhC(O)COCHOC(O)CH3)]ClO4 (M = Fe, Ni) followed by judicious choice of deprotecting conditions allowed us to investigate the oxygen reactivity of a mono- nuclear complex with a dianionic acireductone substrate for the first time. This provides a promising strategy to continue investigations of complexes of relevance to the enzyme- substrate adduct of the acireductone dioxygenases. Divalent late first-row transition metal complexes have been used to investigate some new strategies for the activation of dioxygen and subsequent cleavage of C-C bonds. We have utilized photoreduction of a Ni(II) center to generate a highly O2-reactive Ni(I) fragment that leads to cleavage of a chloro-diketonate substrate. Additionally, we have found a Cu(II)-mediated thermal cleavage of chloro-diketonate substrates at room temperature. This reaction is interestingly accelerated by the addition of a catalytic amount of chloride ion. (315 pages) v PUBLIC ABSTRACT Oxidative Aliphatic Carbon-Carbon Bond Cleavage Reactions by Caleb J. Allpress, Doctor of Philosophy Utah State University, 2013 Major Professor: Dr. Lisa M. Berreau Department: Chemistry and Biochemistry The work presented in this dissertation has focused on the activation and cleavage of chemical bonds between two carbon atoms. The selective oxidative activation of carbon-carbon bonds is important due to potential applications in the utilization of biomass for fuel production, applications in wastewater treatment and bioremediation, and in developing new reactions for organic synthesis of fine chemicals including pharmaceuticals. Ideally these reactions would be carried out with high atom economy at low temperatures and pressures, and using earth-abundant elements as reagents and catalysts. With these points in mind, nature provides an ideal model framework, carrying out its chemistry at ambient temperature and pressure. Enzymes that cleave C-C bonds by a dioxygenolytic pathway have been our focus as they utilize dioxygen as a terminal oxidant and also do not require any coreductants, maximizing atom economy. Our strategy has been to use small molecular models to study complex biological systems or, conversely, to take inspiration from highly active biological systems to design new ways to activate small molecules. We have focused on exploring the reaction vi pathways of several dioxygenase enzymes that cleave aliphatic C-C bonds, with the goal of understanding fundamental factors involved in the activation and direction of cleavage of these bonds. These efforts have led to several important advances in understanding of the cleavage of C-C bonds. Additionally, the work presented here has thus far led to five peer-reviewed publications and five presentations at scientific conferences across the country. vii ACKNOWLEDGMENTS I would firstly like to extend special thanks to my doctoral advisor and mentor, Dr. Lisa Berreau, for her continued advice and support, and for putting up with me telling her she was wrong (even when she was right). I’m especially grateful for the freedom she has given me in pursuing chemistry that is inherently interesting, even if it was not always the chemistry we had originally intended to investigate. I also thank the other members of my doctoral supervisory committee, Dr. John Hubbard, Dr. Alvan Hengge, Dr. Bradley Davidson, and Dr. Paul Grossl, as well as other faculty in the Department of Chemistry, for their support and allowing me to sound ideas off them throughout the years. I would also like to thank all the members of the Berreau group during my time here for their mentorship, support and friendship, with special thanks to fellow grad students from the Berreau lab, Kasia, James, Stacey and Sushma, as well as honorary members Danyal and Angeline. I am grateful to the various coauthors and collaborators: Dr. Ewa Szajna-Fuller and Dr. Katarzyna Grubel for providing characterization of two ferrous compounds, Dr. Atta Arif for performing all the X-ray crystallography, Dr. Dylan Houghton for performing electrochemistry, Dr. Dale Gardner for assistance with LC-MS experiments, Dr. Mark Mehn for providing the initial supply of Fe(OTf)2•2CH3CN, Jami Bennett and Dr. David Tierney for their EPR expertise, and Ana Miłaczewska and Dr. Tomasz Borowski for all the computations. Without their support and expertise, much of the work presented here would not have been possible. viii Finally, I would like to thank my family for their support, especially my wonderful wife, Teresa. Without her support I would have been unable to accomplish all that I have. And, although she is late to the picture, I would like to thank my beautiful daughter Nova for her small contribution to typing up the final chapter of this dissertation. Caleb J. Allpress ix CONTENTS Page ABSTRACT ………………………………………………………………………… iii PUBLIC ABSTRACT ……………………………………………………………… v ACKNOWLEDGMENTS ………………………………………………………….. vii LIST OF TABLES ………………………………………………………………….. x LIST OF FIGURES …………………………………………………………………. xi LIST OF SCHEMES ………………………………………………………………… xv CHAPTER 1. OXIDATIVE ALIPHATIC CARBON-CARBON BOND CLEAVAGE REACTIONS IN ENZYMATIC SYSTEMS AND RELATED MODEL SYSTEMS …………………………………………………………………… 1 2. REGIOSELECTIVE ALIPHATIC CARBON-CARBON BOND CLEAVAGE BY A MODEL SYSTEM OF RELEVANCE TO IRON- CONTAINING ACIREDUCTONE DIOXYGENASE ……………………. 73 3. IRON- AND NICKEL-CONTAINING MODEL SYSTEMS OF ACIREDUCTONE DIOXYGENASE THAT UTILIZE A C(1)H ACIREDUCTONE SUBSTRATE ………………………………………….. 120 4. PHOTOCHEMICALLY-INITIATED OXIDATIVE CARBON- CARBON BOND CLEAVAGE REACTIVITY IN CHLORO- DIKETONATE DIVALENT NICKEL COMPLEXES ……………………. 163 5. DIOXYGENASE-TYPE CARBON-CARBON BOND CLEAVAGE IN A MONONUCLEAR COPPER(II) CHLORO-DIKETONATE COMPLEX ………………………………………………………………….. 208 6. CONCLUSIONS ……………………………………………………………. 255 APPENDIX ... ………………………………………………………………………. 278 CURRICULUM VITAE ……………………………………………………………. 292 x LIST OF TABLES Table Page 1-1. Aliphatic carbon-carbon bond cleaving dioxygenase enzymes, active site metal ions, and metal coordination environment ………………………….. 4 1-2. Structural, spectroscopic, and redox properties of Fe(II) diketonate complexes of relevance to the enzyme/substrate adduct in Dke1 …………. 15 1-3. UV-vis spectroscopic properties of acireductone monoanion complexes …. 50 1-4. Level of 18O incorporation in benzoic acid/benzoate products ……………. 51 2-1. Summary of X-ray data collection and refinement ……………………… 89 2-2. Selected bond distances (Å) and angles (°) for 2-ClO4 and 4·0.5CH3CN … 90 2-3. 1H NMR shifts for selected paramagnetic compounds (ppm) ……………… 92 2-4. Summary of production of
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