UVM Theses and Dissertations
Format:
Print
Author:
Ghebreab, Michael Berhane
Dept./Program:
Chemistry
Year:
2013
Degree:
PhD
Abstract:
Metal catalyzed reactions have a greater role in element-element bond formation affecting preparation of small molecules in organic synthesis, polymers, hydrogen storage, and materials science. In this dissertation, some of the exploratory work done in zirconium catalyzed dehydrocoupling and hydrophosphination reactions with primary and secondary phosphines to form P-P and P-C[sigma] bonds, respectively, is described.
A triamidoamine-supported zirconium complex [K⁵-N, N, N, N, C(Me₃SiNCH₂CH₂)₂NCH₂CH₂NSiMe₂CH₂]Zr (1) has been applied in phosphine dehydrocoupling, an atom-economic transformation for P-P[sigma] bond formation. A number of stoichiometric reactions of 1 with bisphosphine compounds formed zirconium-phosphorus complexes that were isolated and characterized. Thermal decomposition experiments on these phosphide complexes provided some insight towards a 'chain growth' mechanism for P-P [sigma] bond formation in complex molecules.
Further study done on the selectivity of 1 in the dehydrocoupling and heterodehydrocoupling of primary and secondary phosphines suggest sterics and electronics, play a greater role in the reactions. Investigation of 1 in catalytic dehydrocoupling reactions with a variety of bisphosphines compounds were applied towards formation of organophosphorus [pi]-conjugated dimers, oligomers, and polymers. Some bisphosphine compounds containing [pi]-conjugated linkers formed dimeric phosphine products while others formed insoluble hyper-branched polymeric products. A variety of new alkylated bisphosphine compounds with [pi]-conjugated linkers were prepared to avert from the formation of hyper-branched P-P [sigma] bonds and increase the solubility of the phosphine polymers. In an attempt to improve the catalytic dehydrocoupling reactions using 1 with primary phosphines, an alkene trapping regent was added to, reaction that resulted in catalytic hydrophosphination.
The hydrophosphination of alkenes was observed to proceed at a relatively faster rate as compared to that of dehydrocoupling of phosphines. Hydrophosphination reaction of carbon multiple bonds with primary phosphine are described. A series of alkenes, dienes, and imines substrates were investigated to form functionalized secondary phosphine products with high selectivity. Additionally, competition experiments were performed on the catalytic hydrophosphination of styrene with el~ctron-withdrawing and -donating functional groups using 1 and phosphine. Finally, the utility of these secondary phosphines is illustrated by asymmetric alkylation using known late metal catalyzed reactions to form new enantiomeric enriched tertiary phosphine products.
A triamidoamine-supported zirconium complex [K⁵-N, N, N, N, C(Me₃SiNCH₂CH₂)₂NCH₂CH₂NSiMe₂CH₂]Zr (1) has been applied in phosphine dehydrocoupling, an atom-economic transformation for P-P[sigma] bond formation. A number of stoichiometric reactions of 1 with bisphosphine compounds formed zirconium-phosphorus complexes that were isolated and characterized. Thermal decomposition experiments on these phosphide complexes provided some insight towards a 'chain growth' mechanism for P-P [sigma] bond formation in complex molecules.
Further study done on the selectivity of 1 in the dehydrocoupling and heterodehydrocoupling of primary and secondary phosphines suggest sterics and electronics, play a greater role in the reactions. Investigation of 1 in catalytic dehydrocoupling reactions with a variety of bisphosphines compounds were applied towards formation of organophosphorus [pi]-conjugated dimers, oligomers, and polymers. Some bisphosphine compounds containing [pi]-conjugated linkers formed dimeric phosphine products while others formed insoluble hyper-branched polymeric products. A variety of new alkylated bisphosphine compounds with [pi]-conjugated linkers were prepared to avert from the formation of hyper-branched P-P [sigma] bonds and increase the solubility of the phosphine polymers. In an attempt to improve the catalytic dehydrocoupling reactions using 1 with primary phosphines, an alkene trapping regent was added to, reaction that resulted in catalytic hydrophosphination.
The hydrophosphination of alkenes was observed to proceed at a relatively faster rate as compared to that of dehydrocoupling of phosphines. Hydrophosphination reaction of carbon multiple bonds with primary phosphine are described. A series of alkenes, dienes, and imines substrates were investigated to form functionalized secondary phosphine products with high selectivity. Additionally, competition experiments were performed on the catalytic hydrophosphination of styrene with el~ctron-withdrawing and -donating functional groups using 1 and phosphine. Finally, the utility of these secondary phosphines is illustrated by asymmetric alkylation using known late metal catalyzed reactions to form new enantiomeric enriched tertiary phosphine products.