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Browsing by Author "Liu, Shih-Yuan"

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    Boron-Substituted 1,3-Dihydro-1,3-azaborines: Synthesis, Structure, and Evaluation of Aromaticity
    (Wiley-VCH, 2013) Xu, Senmiao; Mikulas, Tanya C.; Zakharov, Lev N.; Dixon, David A.; Liu, Shih-Yuan; University of Oregon; University of Alabama Tuscaloosa
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    A comparison of hydrogen release kinetics from 5-and 6-membered 1,2-BN-cycloalkanes
    (Royal Society of Chemistry, 2021) Giustra, Zachary X.; Chen, Gang; Vasiliu, Monica; Karkamkar, Abhijeet; Autrey, Tom; Dixon, David A.; Liu, Shih-Yuan; Boston College; University of Alabama Tuscaloosa; United States Department of Energy (DOE); Pacific Northwest National Laboratory
    The reaction order and Arrhenius activation parameters for spontaneous hydrogen release from cyclic amine boranes, i.e., BN-cycloalkanes, were determined for 1,2-BN-cyclohexane (1) and 3-methyl-1,2-BN-cyclopentane (2) in tetraglyme. Computational analysis identified a mechanism involving catalytic substrate activation by a ring-opened form of 1 or 2 as being consistent with experimental observations.
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    Rhodium-Catalyzed B-H Activation of 1,2-Azaborines: Synthesis and Characterization of BN Isosteres of Stilbenes
    (American Chemical Society, 2014) Brown, Alec N.; Zakharov, Lev N.; Mikulas, Tanya; Dixon, David A.; Liu, Shih-Yuan; Boston College; University of Oregon; University of Alabama Tuscaloosa
    The first example of catalytic B-H activation of azaborines leading to a new family of stilbene derivatives through dehydrogenative borylation is reported. Ten 1,2-azaborine-based BN isosteres of stilbenes have been synthesized using this method, including a BN isostere of a biologically active stilbene. It is demonstrated that BN/CC isosterism in the context of stilbenes can lead to significant changes in the observed photophysical properties such as higher quantum yield and a larger Stokes shift. Direct comparative analysis of BN stilbene 3g and its carbonaceous counterpart 6g is consistent with a stronger charge-transfer character of the excited state exhibited by 3g in which the 1,2-azaborine heterocycle serves as a better electron donor than the corresponding arene.
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    The Synthesis, Characterization and Dehydrogenation of Sigma-Complexes of BN-Cyclohexanes
    (Wiley-VCH, 2016) Kumar, Amit; Ishibashi, Jacob S. A.; Hooper, Thomas N.; Mikulas, Tanya C.; Dixon, David A.; Liu, Shih-Yuan; Weller, Andrew S.; University of Oxford; Boston College; University of Alabama Tuscaloosa
    The coordination chemistry of the 1,2-BN-cyclohexanes 2,2-R-2-1,2-B,N-C4H10 (R-2=HH, MeH, Me-2) with Ir and Rh metal fragments has been studied. This led to the solution (NMR spectroscopy) and solid-state (X-ray diffraction) characterization of [Ir(PCy3)(2)(H)(2)(eta(2)eta(2)-H2BNR2C4H8)][BAr4F] (NR2=NH2, NMeH) and [Rh(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))(eta(2)eta(2)-H2BNR2C4H8)][ BAr4F] (NR2=NH2, NMeH, NMe2). For NR2=NH2 subsequent metal-promoted, dehydrocoupling shows the eventual formation of the cyclic tricyclic borazine [BNC4H8](3), via amino-borane and, tentatively characterized using DFT/GIAO chemical shift calculations, cycloborazane intermediates. For NR2=NMeH the final product is the cyclic amino-borane HBNMeC4H8. The mechanism of dehydrogenation of 2,2-H,Me-1,2-B,N-C4H10 using the {Rh(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))}+ catalyst has been probed. Catalytic experiments indicate the rapid formation of a dimeric species, [Rh-2(iPr(2)PCH(2)CH(2)CH(2)PiPr(2))(2)H-5][BAr4F]. Using the initial rate method starting from this dimer, a first-order relationship to [amine-borane], but half-order to [Rh] is established, which is suggested to be due to a rapid dimer-monomer equilibrium operating.