UC Berkeley

The following dissertation discusses the development of tandem catalytic processes involving olefins. These processes include the hydroaminomethylation of α-olefins, the contra-thermodynamic isomerization of internal olefins to terminal olefins, and the chemical recycling of polyolefins by dehydrogenation in concert with isomerizing ethenolysis. Chapter 1 surveys the chemistry of olefins and the tandem catalytic processes that involve olefins.

Chapter 2 describes the development of a multi-catalytic approach to the hydroaminomethylation of α-olefins. We report an approach to conducting the hydroaminomethylation of diverse α-olefins with a wide range of alkyl, aryl, and heteroarylamines at low temperatures (70-80 °C) and pressures (1.0-3.4 bar) of synthesis gas. This approach is based on simultaneously using two distinct catalysts that are mutually compatible. The hydroformylation step is catalyzed by a rhodium diphosphine complex, and the reductive amination step, which is conducted as a transfer hydrogenation with aqueous, buffered sodium formate as the reducing agent, is catalyzed by a cyclometallated iridium complex. By adjusting the ratio of CO to H2, we conducted the reaction at one atmosphere of gas with little change in yield. A diverse array of olefins and amines, including hetreroarylamines that do not react under more conventional conditions with a single catalyst, underwent hydroaminomethylation with this new system, and the pharmaceutical ibutilide was prepared in higher yield and under milder conditions than those reported with a single catalyst.

Chapter 3 describes the development of a contra-thermodynamic, positional isomerization of internal olefins to terminal olefins by chain-walking hydrosilylation in concert with dehydrosilylation. We report a contra-thermodynamic isomerization of internal olefins to terminal olefins driven by redox reactions and formation of Si–F bonds. This process involves chain-walking hydrosilylation of internal olefins and subsequent formal retro-hydrosilylation. The process rests upon the high activities of platinum hydrosilylation catalysts for isomerization of metal alkyl intermediates and a new, metal-free process for the conversion of alkylsilanes to alkenes. By this approach, 1,2-disubstituted and trisubstituted olefins are converted to terminal olefins.

Chapter 4 describes the development of a contra-thermodynamic, positional isomerization of internal olefins to terminal olefins by chain-walking hydrosilylation in concert with a catalytic dehydrosilylation. We report a newly developed, palladium-catalyzed dehydrosilylation of terminal alkylsilanes that combines with chain-walking hydrosilylation to create a one-pot isomerization of internal olefins to terminal olefins. This catalytic dehydrosilylation is one of the few examples of thermal catalytic functionalizations of unactivated alkylsilanes. The reaction involves transmetalation of an alkylsilane, β-hydride elimination, release of the terminal olefin, and reoxidation of the palladium catalyst. A variety of linear internal olefins underwent the overall isomerization to terminal olefins in good yields and in good regioselectivities. Particularly noteworthy, isomerizations occurring over seven carbon units proceeded in yields that are comparable to those of isomerizations occurring over one carbon unit.

Chapter 5 describes the development of a contra-thermodynamic, positional isomerization of internal olefins to terminal olefins by chain-walking hydroboration in concert with dehydroboration. We report a newly developed dehydroboration reaction that can be coupled to chain-walking hydroboration to create a one-pot, contra-thermodynamic isomerization of internal olefins to terminal olefins. This dehydroboration reaction is the first dehydroboration of unactivated boronic esters. The reaction involves activation of the boronic acid, followed by iodination and base-promoted elimination. A variety of linear and branched internal olefins underwent the isomerization in good yields and with excellent regioselectivities.

Chapter 6 describes the chemical recycling of polyethylene by dehydrogenation and isomerizing ethenolysis. We converted polyethylene to olefins by either catalytic cracking or dehydrogenation, and we converted these olefins to propene by a highly selective isomerizing ethenolysis. Up to 33% yield of propene was obtained from dehydrogenated polyethylene and up to 72% yield of propene was obtained from octadecene, a model long-chain alkene.