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Topic

Generation and Reactivity of Transient Aminoboranes and Phosphinoboranes: Intermediates in the Formation of Inorganic Polymers

Department of Chemistry

Date & location

• Monday, November 25, 2024
• 2:00 P.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Ian Manners (deceased), Department of Chemistry, University of Victoria (Supervisor)
• Dr. Jeremy Wulff, Department of Chemistry, UVic (Supervisor)
• Dr. Lisa Rosenberg, Department of Chemistry, UVic (Member)
• Dr. Christopher Bose, Department of Mathematics and Statistics, UVic (Outside Member)

External Examiner

• Dr. Douglas Stephan, Department of Chemistry, University of Toronto

Chair of Oral Examination

• Dr. Raad Nashmi, Department of Biology, UVic

Abstract

Polymers are ubiquitous. From the infamous plastic water bottle, typically made of polyethylene terephthalate, to chitin, a polysaccharide, polymeric materials are produced on massive scales in both industry and the biosphere. Most known polymers consist of long chains containing C–C, C–O, or C–N bonds. However, inclusion of elements other than carbon, oxygen, or nitrogen, can introduce valuable properties into the resulting bulk material. For example, the first boot to make contact with the moon had a sole comprised of silicone rubber, a material that can remain rubbery at even lunar temperatures. The ability of this material remain pliable at such low temperatures is largely due to the inorganic Si–O bonds in its main-chain, which allow for greater conformational flexibility compared to polymers comprised primarily of C–C bonds.

The work described in this thesis focuses on a different class of inorganic polymers, polyaminoboranes and polyphosphinoboranes. These polymers feature mainchains of alternating nitrogen and boron or phosphorus and boron atoms.

• Chapter 1 provides a general introduction to inorganic polymers as well as a more detailed survey of polyaminoboranes and polyphosphinoboranes.
• Chapter 2 explores the synthesis of polyphosphinoboranes via the generation of transient phosphinoboranes (PhRP–BH₂; R = H, Ph, Et) through the deprotonation of PhRPH•BH₂(NTf₂). These transient phosphinoboranes then undergo an addition polymerization.
• Chapter 3 describes the solution generation, observation, and subsequent reactivity of primary aminoboranes (RNH=BH₂; R = tBu, Me, CPh₃), a class of species that has only otherwise been isolated on solid argon matrices or observed as a complex mixture of products by ¹¹B NMR spectroscopy. These aminoboranes were generated via the deprotonation of RNH₂•BH₂(NTf₂) and observed at –78 °C as the sole ¹¹B containing species, allowing for subsequent reactivity studies.
• Chapter 4 explores the role of catalysts in the catalytic dehydropolymerization of phosphine-borane adducts, where it is discovered that high molar mass, low dispersity polymers can be accessed using commercially available salts such as LiOTf or by adding catalytic amounts of BH₃•SMe₂. Further, a new potential mechanism for phosphine-borane dehydropolymerization is discussed.
• Chapter 5 ties together the themes of phosphinoboranes and aminoboranes, revealing that sterically unencumbered aminoboranes can accept hydrogen from phosphine-borane adducts, producing amine-borane adducts and phosphinoboranes. These transient phosphinoboranes then undergo subsequent reactivity to form dehydrocoupled products.
• Chapter 6 summarizes the findings of the research, discusses future research directions, and provides an overall outlook.