Part I. Mechanism Of Chromium-Salen Catalyzed Oxidative Cross-Coupling Of Phenols Part Ii. Chromium-Salen Catalyzed Oxidative Cross-Coupling Of N,n-Disubstituted Anilines And Aminonaphthalenes With Phenols And Naphthols Part Iii. Hydrogen Bond Strength Determination Using Colorimetric Sensor Of Wea
Date of Award
Doctor of Philosophy (PhD)
Marisa C. Kozlowski
Gary A. Molander
Part I: A highly selective oxidative coupling of phenols using a chromium-salen catalyst was developed. To probe the selectivity of the process, the mechanism and origin of selectivity was investigated through various mechanistic experiments. Using an oxo-Cr(V) species to conduct stoichiometric single-turnover experiments to probe the mechanism after the rate-determining step, the Cr(V) species was found to be the active catalyst of the process. Additionally, oxidation of the phenol occurred via an inner-sphere electron transfer, which was coupled with a proton transfer from the more acidic phenol. Selectivity was determined during the carbon-carbon bond-forming step. Site nucleophilicity calculations provided insight into the regioselectivity of the more nucleophilic phenol. Steric hinderance explained regioselectivity of the more oxidizable phenol, with reaction occurring at the least hindered ortho- or para- site. Although certain limitations exist with the process, the understanding of the mechanism allowed for the development of a model used predict cross-coupled products.
Part II: The development of a selective cross-coupling of N,N-disubstituted anilines and aminonaphthalenes with phenols and naphthols using a chromium-salen catalyst under aerobic conditions was achieved. The reaction was effectively catalyzed using air as the oxidant. Single products were observed in most cases, but mixtures of C-C and C-O coupled products were obtained when using N,N-dimethylaminonaphthalene with sterically unencumbered phenols. Initial mechanistic studies give support for the oxo-Cr(V) species acting as the active catalyst and oxidizing the aniline/aminonaphthalene coupling partner. The oxidization proceeds through an outer-sphere electron transfer, followed by nucleophilic attack by the phenol/naphthol partner.
Part III: Methods of quantifying hydrogen bond strengths of weak hydrogen bond donors are limited. The use of a colorimetric sensor, 7-methyl-2-phenylimidazo[1,2-a]pyrazine-3-(7H)-one, was found to assess hydrogen bond strengths of weak donors using UV/Vis spectroscopy. Upon compilation of all hydrogen bond data obtained by our laboratory, a simplification of the method was achieved by obtaining accurate estimates of hydrogen bond strengths from single, double, or triple measurements instead of full titrations. The most accurate data was obtained from triple point measurements at 100, 1000, and 10000 equivalents of donor. Single point measurements at 1000 equivalents provided sufficient estimates when limited donor was available for titration. Single point measurements can differentiate between slight electronic and structural effects.
Paniak, Thomas John, "Part I. Mechanism Of Chromium-Salen Catalyzed Oxidative Cross-Coupling Of Phenols Part Ii. Chromium-Salen Catalyzed Oxidative Cross-Coupling Of N,n-Disubstituted Anilines And Aminonaphthalenes With Phenols And Naphthols Part Iii. Hydrogen Bond Strength Determination Using Colorimetric Sensor Of Wea" (2020). Publicly Accessible Penn Dissertations. 3930.