Dissertation
Bio-inspired modulation of tris(triazolyl)borate's electronic properties resulting in enhanced reactivity of Cu(I/II) and other transition metal complexes
Doctor of Philosophy (Ph.D.), Drexel University
Nov 2013
DOI:
https://doi.org/10.17918/etd-4365
Abstract
The natural design of enzymes and proteins inspires synthetic strategies for designing more efficient transition metal catalysts for achieving similar organic transformations. Novel tris(triazolyl)borate ligands with intermediate steric bulk, tris(3-isopropyl,5-methyl,1,2,4-triazolyl)hydroborate (Ttz^[iPr,Me]), tris(3,5-diisopropyl,1,2,4-triazolyl)hydroborate (Ttz^[iPr2]), and tris(3,5-diisopropyl,1,2,4-triazolyl)methane (Ttzm^[iPr2]), were synthesized and characterized. These ligands were used to support transition metal complexes: (Ttz^[iPr, Me])NiCl, (Ttz^[iPr, Me])CuCl, (Ttz^[iPr, Me])ZnCl, (Ttz^[iPr, Me])ZnOAc, (Ttz^[iPr, Me])NiCl, (Ttz^[iPr2]CuCl)₂, (Ttz^[iPr2]CuOH)₂, (Ttz^[iPr2])CuOAc, (Ttz^[iPr2])CuCO, (Ttz^[iPr2])CuNO₂, (Ttz^[iPr2])CuNO₃, (Ttz^[iPr2])ZnCl, (Ttz^[iPr2])ZnCH₂CH₃, and (Ttzm^[iPr2])Cu(NO₃)₂. These complexes either serve as models of the active-site of metallo-enzymes or as precursors used to achieve the desired mimic. The modulation of a metallo-enzyme's electronic properties by a network of hydrogen-bonds or protonation/deprotonation events is an important feature regarding its reactivity towards an organic substrate. The Ttz is a unique ligand such that it can model this feature and thus we studied the effects protonation of the Ttz-ligand has on the electronic density of (Ttz^[R1,R2])Cu(I)CO centers, where the stretching mode of the CO ligand determined by IR was used to assess the change in the electronic properties of the Cu(I)-center upon protonation. Four protonated-states were characterized by deconvolution of the CO spectral features and by DFT calculations. This concept was applied to studying the reactivity of (Ttz^[R1,R2])Cu(I/II) complexes towards various organic substrates. (Ttz^[R1,R2])CuNO₂ complexes were synthesized as models for the copper nitrite reductase enzyme. The stoichiometric reduction of nitrite to form NO_(g) was studied. [(Ttz^[tBu,Me])Cu^[I]NO₂]⁻ facilitated the stoichiometric reduction of nitrite to generate NO_(g) in yields of up to 93% determined by UV-Vis. (Ttz^[tBu,Me])Cu^[II]NO₂ and (Ttz^[tBu,Me])Cu^[II]NO₂ in the presence of HBF₄ generated NO_(g) in yields of 75% and 90% determined by UV-vis. Additionally, (Ttz^[R1,R2])CuNCCH₃ complexes were synthesized as catalysts for C-H activation of cyclohexanes, hexanes, dimethylbutane, and tetrahydrofuran, and % product conversion and TON values increased under acidic conditions determined by ¹H-NMR and GC-MS. Furthermore, the steric environment around the Cu-center was determined to influence the catalyst's reactivity towards C-H bonds. Attempts at synthesizing Ttz^[iPr2]ZnOH and Ttz^[Ph,Me]MoO₂Cl as models for carbonic anhydrase and molybdenum-containing enzymes were also made.
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Details
- Title
- Bio-inspired modulation of tris(triazolyl)borate's electronic properties resulting in enhanced reactivity of Cu(I/II) and other transition metal complexes
- Creators
- Natalie Anne Dixon - DU
- Contributors
- Elizabeth T. Papish (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Arts and Sciences; Chemistry; Drexel University
- Other Identifier
- 4365; 991014632949504721