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Homo- and Heteronuclear Transition Metal Complexes Supported by Multinucleating Ligands


Suseno, Sandy (2015) Homo- and Heteronuclear Transition Metal Complexes Supported by Multinucleating Ligands. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9668B43.


This dissertation is mainly divided into two sub-parts: organometallic and bioinorganic/materials projects. The approach for the projects involves the use of two different multinucleating ligands to synthesize mono- and multinuclear complexes. Chapter 2 describes the synthesis of a multinucleating tris(phosphinoaryl)benzene ligand used to support mono-nickel and palladium complexes. The isolated mononuclear complexes were observed to undergo intramolecular arene C¬–H to C–P functionalization. The transformation was studied by nuclear magnetic resonance spectroscopy and X-ray crystallography, and represents a rare type of C–H functionalization mechanism, facilitated by the interactions of the group 10 metal with the arene π–system.

Chapter 3 describes the construction of multinickel complexes supported by the same triphosphine ligand from Chapter 2. This chapter shows how the central arene in the ligand’s triarylbenzene framework can interact with dinickel and trinickel moieties in various binding modes. X-ray diffraction studies indicated that all compounds display strong metal–arene interactions. A cofacial triangulo nickel(0) complex supported by this ligand scaffold was also isolated and characterized. This chapter demonstrates the use of an arene as versatile ligand design element for small molecular clusters.

Chapter 4 presents the syntheses of a series of discrete mixed transition metal Mn oxido clusters and their characterization. The synthesis of these oxide clusters displaying two types of transition metals were targeted for systematic metal composition-property studies relevant to mixed transition metal oxides employed in electrocatalysis. A series of heterometallic trimanganese tetraoxido cubanes capped with a redox-active metal [MMn3O4] (M = Fe, Co, Ni, Cu) was synthesized starting from a [CaMn3O4] precursor and structurally characterized by X-ray crystallography and anomalous diffraction to conclusively determine that M is incorporated at a single position in the cluster. The electrochemical properties of these complexes were studied via cyclic voltammetry. The redox chemistry of the series of complexes was investigated by the addition of a reductant and oxidant. X-ray absorption and electron paramagnetic resonance spectroscopies were also employed to evaluate the product of the oxidation/reduction reaction to determine the site of electron transfer given the presence of two types of redox-active metals. Additional studies on oxygen atom transfer reactivities of [MMn3O4] and [MMn3O2] series were performed to investigate the effect of the heterometal M in the reaction rates.

Chapter 5 focuses on the use of [CoMn3O4] and [NiMn3O4] cubane complexes discussed in Chapter 4 as precursors to heterogeneous oxygen evolution reaction (OER) electrocatalysts. These well-defined complexes were dropcasted on electrodes with/without heat treatment, and the OER activities of the resulting films were evaluated. Multiple spectroscopic techniques were performed on the surface of the electrocatalysts to gain insight into the structure-function relationships based on the heterometallic composition. Depending on film preparation, the Co-Mn-oxide was found to change metal composition during catalysis, while the Ni-Mn oxide maintained the NiMn3 ratio. These studies represent the use of discrete heterometallic-oxide clusters as precursors for heterogeneous water oxidation catalysts.

Appendix A describes the ongoing effort to synthesize a series of heteromultimetallic [MMn3X] clusters (X = O, S, F). Complexes such as [ZnMn3O], [CoMn3O], [Mn3S], and [Mn4F] have been synthesized and structurally characterized. An amino-bis-oxime ligand (PRABO) has been installed on the [ZnMn3O] cluster. Upon the addition of O2, the desymmetrized [ZnMn3O] cluster only underwent an outer-sphere, one-electron oxidation. Efforts to build and manipulate other heterometallic [MMn3X] clusters are still ongoing, targeting O2 binding and reduction. Appendix B summarizes the multiple synthetic approaches to build a [Co4O4]-cubane complex relevant to heterogeneous OER electrocatalysis. Starting with the tricobalt cluster [LCo3(O2CR)3] and treatment various strong oxidants that can serve as oxygen atom source in the presence Co2+ salt only yielded tricobalt mono–oxo complexes. Appendix C presents the efforts to model the H-cluster framework of [FeFe]-hydrogenase by incorporating a synthetic diiron complex onto a protein-supported or a synthetic ligand-supported [Fe4S4]-cluster. The mutant ferredoxin with a [Fe4S4]-cluster and triscarbene ligand have been characterized by multiple spectroscopic techniques. The reconstruction of an H-cluster mimic has not yet been achieved, due to the difficulty of obtaining crystallographic evidence and the ambiguity of the EPR results.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:homometallic, heterometallic, multinucleating ligands
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Agapie, Theodor
Thesis Committee:
  • Peters, Jonas C. (chair)
  • Agapie, Theodor
  • Bercaw, John E.
  • Rees, Douglas C.
Defense Date:29 October 2014
Record Number:CaltechTHESIS:11202014-184045649
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2 adapted for ch. 3
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8728
Deposited By: Sandy Suseno
Deposited On:24 Nov 2014 23:51
Last Modified:04 Oct 2019 00:07

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