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Unique Reactivity Patterns of Enhanced Urea Catalysts

Nickerson, David M
http://rave.ohiolink.edu/etdc/view?acc_num=osu1395859006

Abstract Details

2014, Doctor of Philosophy, Ohio State University, Chemistry.
Strategic enhancement of urea organocatalysts using internally coordinated Lewis acids has allowed for the discovery of new and useful reactions. Specifically, the incorporation of transition metals onto urea scaffolds has been shown to improve catalytic activity when compared to traditional urea and thiourea catalysts. An example of this enhancement has been demonstrated in the development of hybrid urea palladacycles that have been shown to be highly active, hydrogen bond donor catalysts in the activation of substrates not amenable to traditional urea catalysis, such as alkylidene malonates. Other internal Lewis acids such as platinum, silicon and boron have also been incorporated onto urea scaffolds, and the new catalysts have been compared in their abilities to activate new substrates such as nitrocyclopropane carboxylates and nitrodiazoesters. Correlations between catalyst structure and activity show that increased acidity due to internally coordinated Lewis acids is one of the important factors in urea catalyst design. To compare the internal Lewis acids’ effects on acidity and on catalyst activity, the pKas of differently internally-coordinated catalysts have been determined and found to range from a highly acidic 6.8 for a coordinated palladium to a weakly acidic 16.0 for a silicate urea. Boronate ureas surveyed had intermediate pKas of 7.5 and 9.5. The different catalysts’ abilities to activate both nitrocyclopropanes and nitrodiazoesters by coordination to the nitro group have also been investigated by studying the rates of these reactions. An internally coordinated difluoroboronate urea has been determined to be the best catalyst for both reaction systems. Using urea catalysts, a new organocatalytic coupling strategy has also been discovered. Specifically, nitroamines and nitrimines have been identified as urea-activated handles allowing for useful carbon–heteroatom and carbon–carbon coupling reactions. This reaction mode has been shown to be broadly useful in its ability to form enamines by coupling nitrimines to a wide variety of secondary amines including hindered, N-aryl amines. These sterically hindered, N-aryl enamines are not readily accessible either by traditional enamine forming methods or by more recently developed organometallic methods using vinyl triflates or vinyl bromides in traditional palladium catalyzed cross couplings. The ability to form enamine atropisomers with restricted nitrogen–carbon bond rotation has emphasized the powerful coupling ability of the new method. Additionally, using nitroamines, initial results have shown promise in metal-free, biaryl carbon–carbon coupling reactions under mild, urea catalyzed conditions.
Anita Mattson (Advisor)
179 p.
Chemistry; Organic Chemistry
Organocatalysis; Organocatalyst; Urea Catalysis; Thiourea Catalysis; Urea Catalyst; Thiourea Catalyst; Palladacycle; Nitroimine; Nitrimine; Nitroenamine; Nitroamine; Internal Lewis Acid; Alkylidene Malonate; Biaryl Coupling

Recommended Citations

Citations

  • Nickerson, D. M. (2014). Unique Reactivity Patterns of Enhanced Urea Catalysts [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1395859006

    APA Style (7th edition)

  • Nickerson, David. Unique Reactivity Patterns of Enhanced Urea Catalysts. 2014. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1395859006.

    MLA Style (8th edition)

  • Nickerson, David. "Unique Reactivity Patterns of Enhanced Urea Catalysts." Doctoral dissertation, Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1395859006

    Chicago Manual of Style (17th edition)

osu1395859006
1,193
© 2014, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.