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Synthesis, Oxidation and Photophysics of Perfluoroborated Tetrakis(pyrophosphito)diplatinate (II) and Density Functional Theory (DFT) Study of Electrochemical CO2 Reduction by Mn Catalysts

Citation

Lam, Yan Choi (2015) Synthesis, Oxidation and Photophysics of Perfluoroborated Tetrakis(pyrophosphito)diplatinate (II) and Density Functional Theory (DFT) Study of Electrochemical CO2 Reduction by Mn Catalysts. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z94J0C2D. http://resolver.caltech.edu/CaltechTHESIS:05212015-155730829

Abstract

In the first part of this thesis (Chapters I and II), the synthesis, characterization, reactivity and photophysics of per(difluoroborated) tetrakis(pyrophosphito)diplatinate(II) (Pt(POPBF2)) are discussed. Pt(POP-BF2) was obtained by reaction of [Pt2(POP)4]4- with neat boron trifluoride diethyl etherate (BF3·Et2O). While Pt(POP-BF2) and [Pt2(POP)4]4- have similar structures and absorption spectra, they differ in significant ways. Firstly, as discussed in Chapter I, the former is less susceptible to oxidation, as evidenced by the reversibility of its oxidation by I2. Secondly, while the first excited triplet states (T1) of both Pt(POP-BF2) and [Pt2(POP)4]4- exhibit long lifetimes (ca. 0.01 ms at room temperature) and substantial zero-field splitting (40 cm-1), Pt(POP-BF2) also has a remarkably long-lived (1.6 ns at room temperature) singlet excited state (S1), indicating slow intersystem crossing (ISC). Fluorescence lifetime and quantum yield (QY) of Pt(POP-BF2) were measured over a range of temperatures, providing insight into the slow ISC process. The remarkable spectroscopic and photophysical properties of Pt(POP-BF2), both in solution and as a microcrystalline powder, form the theme of Chapter II.

In the second part of the thesis (Chapters III and IV), the electrochemical reduction of CO2 to CO by [(L)Mn(CO)3]- catalysts is investigated using density functional theory (DFT). As discussed in Chapter III, the turnover frequency (TOF)-limiting step is the dehydroxylation of [(bpy)Mn(CO)3(CO2H)]0/- (bpy = bipyridine) by trifluoroethanol (TFEH) to form [(bpy)Mn(CO)4]+/0. Because the dehydroxylation of [(bpy)Mn(CO)3(CO2H)]- is faster, maximum TOF (TOFmax) is achieved at potentials sufficient to completely reduce [(bpy)Mn(CO)3(CO2H)]0 to [(bpy)Mn(CO)3(CO2H)]-. Substitution of bipyridine with bipyrimidine reduces the overpotential needed, but at the expense of TOFmax. In Chapter IV, the decoration of the bipyrimidine ligand with a pendant alcohol is discussed as a strategy to increase CO2 reduction activity. Our calculations predict that the pendant alcohol acts in concert with an external TFEH molecule, the latter acidifying the former, resulting in a ~ 80,000-fold improvement in the rate of TOF-limiting dehydroxylation of [(L)Mn(CO)3(CO2H)]-.

An interesting strategy for the co-upgrading of light olefins and alkanes into heavier alkanes is the subject of Appendix B. The proposed scheme involves dimerization of the light olefin, operating in tandem with transfer hydrogenation between the olefin dimer and the light alkane. The work presented therein involved a Ta olefin dimerization catalyst and a silica-supported Ir transfer hydrogenation catalyst. Olefin dimer was formed under reaction conditions; however, this did not undergo transfer hydrogenation with the light alkane. A significant challenge is that the Ta catalyst selectively produces highly branched dimers, which are unable to undergo transfer hydrogenation.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Photophysics; d8-d8 complex; DFT; CO2 Reduction; Catalysis; Electrochemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Gray, Harry B. (advisor)
  • Goddard, William A., III (advisor)
Thesis Committee:
  • Okumura, Mitchio (chair)
  • Gray, Harry B.
  • Goddard, William A., III
  • Bercaw, John E.
  • Labinger, Jay A.
Defense Date:9 March 2015
Non-Caltech Author Email:yanchoi.lam (AT) gmail.com
Funders:
Funding AgencyGrant Number
NSF Center for Chemical InnovationCHE-0802907
NSF Center for Chemical Innovation in Solar FuelsCHE-1305124
Gordon and Betty Moore Foundation, Caltech Center for Sustainable Energy ResearchUNSPECIFIED
Czech Ministry of Education KONTAKTME10124
U.S. Department of EnergyDE-SC0004993
Record Number:CaltechTHESIS:05212015-155730829
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05212015-155730829
DOI:10.7907/Z94J0C2D
ORCID:
AuthorORCID
Lam, Yan Choi0000-0001-7809-4471
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8876
Collection:CaltechTHESIS
Deposited By: Yan Choi Lam
Deposited On:26 May 2015 21:19
Last Modified:20 Sep 2017 22:49

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