Synthetic studies of sodium aminodiboranate salts with electronwithdrawing substituents

Daly, Connor I.

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https://hdl.handle.net/2142/108071 Copy

Description

Title

Synthetic studies of sodium aminodiboranate salts with electronwithdrawing substituents

Author(s)

Daly, Connor I.

Issue Date

2020-05-15

Director of Research (if dissertation) or Advisor (if thesis)

Girolami, Gregory

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Sodium Aminodiboranates
• Electron-Withdrawing Substituents

Abstract

Magnesium diboride, MgB2, has the highest superconducting critical temperature of all traditional superconductors and is being considered for the fabrication of superconducting integrated circuits that can operate at higher temperatures than analogous niobium alloy circuits. A significant barrier to preparing superconducting MgB2 thin films, however, is that the films must be deposited below 300 C to prevent Mg from subliming out of the film and causing loss of the superconducting properties. One approach to solve this problem is to prepare low-temperature chemical vapor deposition (CVD) precursors which would enable deposition of MgB2 at temperatures low enough to prevent loss of Mg from the thin film. In chapter 1, we describe the synthesis of three new sodium aminodiboranate salts, Na(BH3)2NRR′, with trimethylsilyl groups on nitrogen. These compounds – sodium N,N-bis-(trimethylsilyl)¬aminodiboranate, sodium N-trimethylsilylamino¬diboranate, and sodium N-methyl-N-trimethylsilylaminodiboranate – were prepared by the reaction of μ-aminodiborane(6) species with sodium hydride. IR, 1H NMR, 13C NMR, and 11B NMR spectra are reported for all of these compounds, along with the crystal structures of N-trimethylsilyl¬amino¬diboranate and N-methyl-N-trimethylsilylaminodiboranate. Comparisons of 11B NMR chemical shifts suggest that steric, inductive, and hyperconjugative effects of the substituents on nitrogen are all in competition in these systems. In chapter 2 we describe the preparation of fluorinated aminodiborantes, although here the longer reaction times required for their synthesis lead to undesirable production of butoxyborate species through the ring-opening reaction of thf with BH3. To circumvent this problem, we employed non-cyclic ethers such as diglyme and cyclopentyl(methyl)ether to investigate the preparation of μ-aminodiborane(6) species from the fluorinated amines N,N-bis(2,2,2-trifluoroethyl)¬amine, N-(2,2,2-trifluoroethyl)amine, and N-methyl-N-(2,2,2-trifluoro¬ethyl)¬amine. We find that there is a correlation between the pKa of the ammonium form of the amine with the relative stabilities of the μ-aminodiborane(6) and aminoborane: N,N-bis(2,2,2-trifluoroethyl)amine forms the aminoborane preferentially, whereas both N-(2,2,2-trifluoroethyl)amine and N-methyl-N-(2,2,2-trifluoroethyl)¬amine form the -aminodiborane(6) in good yields. Sodium N-methyl-N-(2,2,2-trifluoroethyl)¬aminodiboranate was prepared and characterized by 11B NMR spectroscopy, although efforts to isolate it were unsuccessful.

Graduation Semester

2020-05

Type of Resource

Thesis

Permalink

http://hdl.handle.net/2142/108071

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Copyright 2020 Connor Daly

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