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Transition Metal Clusters Supported by Multinucleating Ligand Frameworks as Models of Biological Active Sites


Tsui, Emily Yuan (2014) Transition Metal Clusters Supported by Multinucleating Ligand Frameworks as Models of Biological Active Sites. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/CWJ4-QQ41.


This dissertation describes efforts to model biological active sites with small molecule clusters. The approach used took advantage of a multinucleating ligand to control the structure and nuclearity of the product complexes, allowing the study of many different homo- and heterometallic clusters. Chapter 2 describes the synthesis of the multinucleating hexapyridyl trialkoxy ligand used throughout this thesis and the synthesis of trinuclear first row transition metal complexes supported by this framework, with an emphasis on tricopper systems as models of biological multicopper oxidases. The magnetic susceptibility of these complexes were studied, and a linear relation was found between the Cu-O(alkoxide)-Cu angles and the antiferromagnetic coupling between copper centers. The triiron(II) and trizinc(II) complexes of the ligand were also isolated and structurally characterized.

Chapter 3 describes the synthesis of a series of heterometallic tetranuclear manganese dioxido complexes with various incorporated apical redox-inactive metal cations (M = Na+, Ca2+, Sr2+, Zn2+, Y3+). Chapter 4 presents the synthesis of heterometallic trimanganese(IV) tetraoxido complexes structurally related to the CaMn3 subsite of the oxygen-evolving complex (OEC) of Photosystem II. The reduction potentials of these complexes were studied, and it was found that each isostructural series displays a linear correlation between the reduction potentials and the Lewis acidities of the incorporated redox-inactive metals. The slopes of the plotted lines for both the dioxido and tetraoxido clusters are the same, suggesting a more general relationship between the electrochemical potentials of heterometallic manganese oxido clusters and their "spectator" cations. Additionally, these studies suggest that Ca2+ plays a role in modulating the redox potential of the OEC for water oxidation.

Chapter 5 presents studies of the effects of the redox-inactive metals on the reactivities of the heterometallic manganese complexes discussed in Chapters 3 and 4. Oxygen atom transfer from the clusters to phosphines is studied; although the reactivity is kinetically controlled in the tetraoxido clusters, the dioxido clusters with more Lewis acidic metal ions (Y3+ vs. Ca2+) appear to be more reactive. Investigations of hydrogen atom transfer and electron transfer rates are also discussed.

Appendix A describes the synthesis, and metallation reactions of a new dinucleating bis(N-heterocyclic carbene)ligand framework. Dicopper(I) and dicobalt(II) complexes of this ligand were prepared and structurally characterized. A dinickel(I) dichloride complex was synthesized, reduced, and found to activate carbon dioxide. Appendix B describes preliminary efforts to desymmetrize the manganese oxido clusters via functionalization of the basal multinucleating ligand used in the preceding sections of this dissertation. Finally, Appendix C presents some partially characterized side products and unexpected structures that were isolated throughout the course of these studies.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Biomimetic complexes; Lewis acids; redox-inactive metals; synthetic clusters
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Awards:The Herbert Newby McCoy Award, 2014
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Agapie, Theodor
Thesis Committee:
  • Lewis, Nathan Saul (chair)
  • Agapie, Theodor
  • Heath, James R.
  • Peters, Jonas C.
Defense Date:18 February 2014
Record Number:CaltechTHESIS:04302014-134133118
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 1 adapted for ch. 2 DOIArticle adapted for ch. 2 adapted for ch. 3 DOIArticle adapted for ch. 4 DOIArticle adapted for ch. 4 adapted for ch. 5
Tsui, Emily Yuan0000-0001-6419-3954
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8207
Deposited By: Emily Tsui
Deposited On:07 May 2014 17:13
Last Modified:04 Oct 2019 00:04

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