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New bis(amidate) Titanium-bis(amido) complexes as hydroamination precatalysts : synthetic and mechanistic investigations Li, Chunyu

Abstract

This thesis focuses on the exploration of a new titanium complex for the hydroamination of alkynes/alkenes. A new pentafluoro amide proligand, [HNC4H9CO( CeF5)] 5, and two related bis(amidate)titanium-bis(amido) complexes (8 and 9) were designed, prepared and fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analysis and X-ray crystallography. Both intramolecular and intermolecular hydroamination of alkynes were investigated using the bis(amidate)titanium-bis(amido) complexes as catalysts. Preliminary results were obtained from NMR tube scale reaction monitored by ' H NMR spectroscopy using an internal standard. Larger scale intermolecular hydroamination reactions followed by LAH/THF reduction were carried out to give corresponding isolated amines in yields comparable to that of the NMR tube scale reaction. Hydroamination of.alkenes using these precatalysts was unsuccessful. Compared with other reported titanium complexes, our precatalysts demonstrated better or comparable hydroamination reactivity. Based on literature reports, a mechanism was proposed for the bis(amidate)titanium complex-catalyzed hydroamination which was further verified by preparation of catalytically active intermediates. Stoichiometric reactions of precatalysts with bulky primary amines indicated formation of a titanium imido complex, the active species for hydroamination. Titanium imido complexes or pyridine-trapped imido complexes were isolated and characterized by multinuclear NMR spectroscopy and mass spectrometry. In one case a pyridine-trapped imido complex shows higher reactivity than the corresponding bis(amidate) precatalyst. However, the stoichiometric reaction between precatalysts and less bulky amines form titanium imido dimers, explaining This thesis focuses on the exploration of a new titanium complex for the hydroamination of alkynes/alkenes. A new pentafluoro amide proligand, [HNC4H9CO( CeF5)] 5, and two related bis(amidate)titanium-bis(amido) complexes (8 and 9) were designed, prepared and fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analysis and X-ray crystallography. Both intramolecular and intermolecular hydroamination of alkynes were investigated using the bis(amidate)titanium-bis(amido) complexes as catalysts. Preliminary results were obtained from NMR tube scale reaction monitored by ' H NMR spectroscopy using an internal standard. Larger scale intermolecular hydroamination reactions followed by LAH/THF reduction were carried out to give corresponding isolated amines in yields comparable to that of the NMR tube scale reaction. Hydroamination of.alkenes using these precatalysts was unsuccessful. Compared with other reported titanium complexes, our precatalysts demonstrated better or comparable hydroamination reactivity. Based on literature reports, a mechanism was proposed for the bis(amidate)titanium complex-catalyzed hydroamination which was further verified by preparation of catalytically active intermediates. Stoichiometric reactions of precatalysts with bulky primary amines indicated formation of a titanium imido complex, the active species for hydroamination. Titanium imido complexes or pyridine-trapped imido complexes were isolated and characterized by multinuclear NMR spectroscopy and mass spectrometry. In one case a pyridine-trapped imido complex shows higher reactivity than the corresponding bis(amidate) precatalyst. However, the stoichiometric reaction between precatalysts and less bulky amines form titanium imido dimers, explaining

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