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Synthesis and Reactivity of Nickel POCOP Pincer Complexes for the Reduction of Carbon Dioxide and Related Compounds

Eberhardt, Nathan A
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511864001952451

Abstract Details

2017, PhD, University of Cincinnati, Arts and Sciences: Chemistry.
The development of new catalysts for the reduction of carbon dioxide is of utmost importance to both limit the harmful greenhouse gas as well as to provide usable C1 feedstock chemicals. One method to reduce this CO2 is through the use of a metal hydride complex. Of these metal complexes, nickel POCOP pincer hydride complexes have been highly successful at catalyzing the reduction of carbonyl functionalities. Although these catalysts are effective at catalyzing this reduction, there are few processes to make these hydrides. Additionally, not much is known about which factors will improve catalytic reduction or what other reactions they can catalyze. Nickel chloride complexes bearing POCOP pincer ligands were easily synthesized using a microwave reactor. Through this methodology nickel POCOP pincer chloride complexes can be made in as little as 5 minutes in very high purities and yields. Nickel complexes with iPr, cPe, Cy, Ph, and tBu substituents on the phosphorous atoms can all be synthesized using this method. Additionally, palladium chloride complexes bearing isopropyl substituted POCOP ligands can be made. This method was also found to greatly limit the solvent needed to make these complexes. Alternative routes to synthesize nickel hydride complexes is an important problem due to the harsh methods used to synthesize them. To explore an additional method for hydride synthesis, nickel fluoride complexes bearing POCOP pincer ligands were synthesized. These complexes can be easily converted to hydride complexes using silanes or boranes. The factors that influence a metal hydrides ability to reduce CO2 were investigated. To determine which factors had an impact on the reduction of CO2 to formate complex, a series of nickel hydride and formate complexes were synthesized. The complexes were tested to determine the relative thermodynamic favorability for the reduction of CO2 to formate. Complexes bearing more electron donating ligands were found to be better at reducing CO2 to formate. Additionally, complexes with more sterically accessible nickel centers were found to be far better at reducing CO2. Also, nickel was found to be better than palladium for this reduction. Nickel hydride complexes were also found catalyze the oxidative esterification of aldehydes and alcohols. The process was found to be very efficient at this process with a number of alcohols and aldehydes. The mechanism proceeds through a reduction of an aldehyde to form an alkoxide complex followed by an exchange with an alcohol. The nickel alkoxide then reacts with an additional aldehyde to form a hemiacetal complex. Beta hydride elimination then forms the ester product. Alternative entry into the catalytic cycle using benchtop stable nickel chloride complex and nucleophilic base was achieved. Water, oxidation, and protonation of nickel hydride were identified as deactivation pathways. The products of deactivation were independently synthesized.
Hairong Guan, Ph.D. (Committee Chair)
William Connick, Ph.D. (Committee Member)
Allan Pinhas, Ph.D. (Committee Member)
100 p.
Chemistry
Nickel Hydride; CO2 Reduction; Oxidative Esterification; Nickel Fluoride

Recommended Citations

Citations

  • Eberhardt, N. A. (2017). Synthesis and Reactivity of Nickel POCOP Pincer Complexes for the Reduction of Carbon Dioxide and Related Compounds [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511864001952451

    APA Style (7th edition)

  • Eberhardt, Nathan. Synthesis and Reactivity of Nickel POCOP Pincer Complexes for the Reduction of Carbon Dioxide and Related Compounds. 2017. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511864001952451.

    MLA Style (8th edition)

  • Eberhardt, Nathan. "Synthesis and Reactivity of Nickel POCOP Pincer Complexes for the Reduction of Carbon Dioxide and Related Compounds." Doctoral dissertation, University of Cincinnati, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511864001952451

    Chicago Manual of Style (17th edition)

ucin1511864001952451
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This open access ETD is published by University of Cincinnati and OhioLINK.