Date of Award
Doctor of Philosophy
Lee K. Woo
In response to current environmental issues and concerns, an abundance of chemical literature focuses upon green, benign methodologies. Considering these issues, work presented within this thesis focuses upon development of greener synthetic techniques that are robust and versatile in both and Pd-catalyzed cross-coupling reactions and alkoxycarbonylation.
Sonogashira coupling between terminal alkynes and aryl bromides or iodides was high yielding with Pd(PPh3)2Cl2 in water at 40 oC using commercially available surfactants such as SDS and CTAB. An iodide and Cu(I) inhibition was observed under these micellar conditions with aryl bromide substrates, leading to development of Cu(I)-free conditions. Studies under Cu(I)-free conditions suggest two competing mechanistic cycles. Both cycles (deprotonation and carbopalladation) lead to traditional Sonogashira products, but the carbopalladation cycle also produces an enyne product. The surfactant solution (either 2 wt% SDS or CTAB) can be recycled up to 3 times without reduction in yield when coupling 1-iodoanpthalene with 1-octyne in the presence of excess piperidine, 5 mol% CuI, and 2 mol% Pd(PPh3)2Cl2.
The effect of the phosphine ligand structure was evaluated in aqueous phase Heck cross-coupling reactions. A methyl cholate derivative was modified with a tri-aryl phosphine moiety, creating a novel ligand that effectively coordinated to Pd(OAc)2 when dissolved in methanol. The cholate-Pd complex proved to be an efficient catalyst for Heck cross-coupling between various olefins and aryl iodide substrates under basic aqueous conditions with mild heating. The cholate ligand appears to enhance reaction yields by creating a localized hydrophobic environment around the Pd center, which attracts and increases the local concentration of nonpolar coupling reagents near the active catalytic site. Homogeneity studies show that the catalytically active Pd species remains heterogeneous throughout the reaction duration.
Finally, palladium catalysts can also be effective in the conversion of olefinic molecules to aliphatic esters. Palladium complexes, generated from Pd(OAc)2 and benzimidazolium salts were developed as effective catalysts for the alkoxycarbonylation of olefins in high yields (>88%). Alkoxycarbonylation of 1-hexene in dimethylacetamide was achieved within 24 h at 110 oC using 1 mol % catalyst, 1000 psi CO, and ethanol. Reactions can be prepared in air, without auxiliary acid additives, to produce ethyl 2-methylhexanoate and ethyl heptanoate in approximately a 2:1 ratio. This method was also applied to unsaturated fatty acid esters to form &alpha:,ω-bifunctional molecules such as ethyl adipate, demonstrating potential as a novel methodology for making bioderrived monomers for polymer synthesis.
Gina M. Roberts
Roberts, Gina M., "Greener and renewable methods for Pd-catalyzed cross-coupling and alkoxycarbonylation reactions" (2014). Graduate Theses and Dissertations. 13808.