Comparative Studies of Kinetics of Ene-yne Metathesis Catalyzed by Two Different Ruthenium Carbenes
Marshall, Jennifer E.
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In Chapter One of the dissertation the development of ene-yne metathesis catalysts will be summarized. The development and uses of the Grubbs second generation catalyst will be highlighted. The first examples of ene-yne metathesis and the early mechanistic studies will be highlighted as well. The development of the kinetic studies done on intermolecular ene-yne metathesis catalyzed by the Grubbs second generation catalyst will be discussed and a mechanism is developed. In Chapter Two the mechanistic work done in olefin metathesis, primarily catalyzed by the Grubbs first generation catalyst will be discussed in order to compare similarities to the mechanistic work done on ene-yne metathesis catalyzed by the Grubbs first generation catalyst. In this chapter the kinetics of intermolecular ene-yne metathesis were developed which resulted in a rate law first order dependent in alkyne and half order dependent on catalyst concentration. The rate law was compared to the rate law derived from the mechanistic work done on intermolecular ene-yne metathesis catalyzed by the Grubbs second generation catalyst. The effects of ethylene were also explored and it was found to slow the rate of metathesis. Chapter Three of this dissertation highlights the background on the development of the phosphine-free Hoveyda catalyst. The development of the phosphine-free catalyst explores the steric and electronic effects of the chelating ligand. The kinetics of intermolecular ene-yne metathesis were developed by use of a ReactIR which took IR scans every 10-30 seconds. It was proposed that the rate is first order dependent on alkene concentration and first order dependent on catalyst concentration. However, at high concentrations of alkene the rate determining step shifts to an alkene independent state, possibly a resting state. When linear alkynes were tested, the reaction failed to show reactivity. Two decomposition pathways were proposed: alkyne oligomerization and η 3 -chelation to the metal. The kinetics of the Hoveyda catalyst are compared to the Grubbs type catalyst to illucidate the three catalysts' reactivity. Chapter Four of this dissertation explores the Buchner Insertion of ruthenium carbenes in the metathesis catalyst and the ability to identify them by Electrospray-Mass Spectrometry. This chapter explored identifying the insertion products of metathesis catalyst by ESI-MS as well as the decomposition pathway for linear alkynes that failed in the previous chapter. The insertion/ESI-MS method was also employed to identify the initiation pathway for intermolecular ene-yne metathesis catalyzed by the Hoveyda catalyst.