Novel carbometallation and hydrometallation reactions catalyzed by transition metal complexes
Abstract
The ethylzincation of monosubstituted alkenes can be achieved cleanly and in high yields with diethylzinc and a catalyst generated in situ by treatment of zirconocene dichloride with two molar equivalents of ethylmagnesium bromide. The resulting diisoalkylzinc can be cross-coupled in high yields with a variety of organyl halides in the presence of palladium catalysts. Mechanistic studies were performed. Alkynes can also be ethylzincated using this procedure. A hydrogen transfer hydroalumination of monosubstituted alkenes can be achieved cleanly, in high yields and wide scope with triisobutylaluminum and catalytic amounts of palladium and other late transition metal complexes. The most efficient catalyst is bis(triphenylphosphine) palladium dichloride. Hydroalumination of α,ω-dienes shed some light on the mechanism of this novel hydroalumination. Mono- and disubstituted alkynes and conjugated dienes can be hydrosilated in high yields and high regio and stereoselectivity with diphenylsilane and a catalyst generated in situ by treatement of titanocene dichloride with two molar equivalents of isobutylmagnesium chloride. The reaction produces vinylsilanes from alkynes and allylsilanes from conjugated dienes. Some insights into the mechanism were obtained. Zipper- and Dumbbell-mode cyclizations via carbonylative cascade carbopalladation can be achieved when the first relay functional group is an internal alkyne and can be terminated by nucleophilic trapping with an internal C-enolate. Two substrates were cyclized and confirmed earlier observations on carbopalladation versus acylpalladation after CO insertion. Results also show that the latter can happen under high CO pressures and when there is a significant driving force such as aromatization. The zirconium-catalyzed carboalumination and the Negishi's hydrozirconation of metallated terminal alkynes containing a hydroxyl group can be achieved when this metal is aluminum and lead to the formation of 1,1-dimetallo-alkenoxide intermediates.
Degree
Ph.D.
Advisors
Negishi, Purdue University.
Subject Area
Organic chemistry
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