Investigations of group IVA transition metal mediated carbon-carbon bond forming reactions

Chemistry, Investigations, IVA transition, carbon-carbon bond, metal mediated

Wysong, Ernest Byron ; Grubbs, Robert H.

University:California Institute of Technology

Department:Chemistry and Chemical Engineering

关键词: Chemistry, Investigations, IVA transition, carbon-carbon bond, metal mediated;   

Others  :  https://thesis.library.caltech.edu/8788/1/Wysong-eb-1990.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

Zirconocene aldehyde and ketone complexes were synthesized in high yield by treatment of zirconocene acyl complexes with trimethylaluminum or diisobutylaluminum hydride. These complexes, which are activated by dialkylaluminum chloride ligands, inserted unsaturated substrates such as alkynes, allenes, ethylene, nitriles, ketenes, aldehydes, ketones, lactones, and acid chlorides with moderate to high conversion. Insertion of aldehyde substrates yielded zirconocene diolate complexes with up to 20:1 (anti:syn) diastereoselectivity. The zirconocene diolates were hydrolyzed to afford unsymmetrical 1,2-diols in 40-80% isolated yield. Unsymmetrical ketones gave similar insertion yields with little or no diastereoselectivity. A high yielding one-pot method was developed that coupled carbonyl substrates with zirconocene aldehyde complexes that were derived from olefins by hydrozirconation and carbonylation. The zirconocene aldehyde complexes also inserted carbon monoxide and gave acyloins in 50% yield after hydrolysis.

The insertion reaction of aryl epoxides with the trimethylphoshine adduct of titanocene methylidene was examined. The resulting oxytitanacyclopentanes were carbonylated and oxidatively cleaved with dioxygen to afford y-lactones in moderate yields. Due to the instability and difficult isolation of titanocene methylidene trimethylphoshine adducts, a one-pot method involving the addition of catalytic amounts oftrimethylphosphine to β,β-dimethyltitanacyclobutane was developed. A series of disubstituted aryl epoxides were examined which gave mixtures of diastereomeric insertion products. Based on these results, as well as earlier Hammett studies and labeling experiments, a biradical transition state intermediate is proposed. The method is limited to aryl substitutedepoxide substrates with aliphatic examples showing no insertion reactivity.

The third study involved the use of magnesium chloride supportedtitanium catalysts for the Lewis acid catalyzed silyl group transfercondensation of enol silanes with aldehydes. The reaction resulted insilylated aldol products with as many as 140 catalytic turnovers beforecatalyst inactivation. Low diastereoselectivities favoring the anti-isomerwere consistent with an open transition state involving a titanium atombound to the catalyst surface. The catalysts were also used for the aldolgroup transfer polymerization of t-butyldimethylsilyloxy-1-ethene resulting in polymers with molecular weights of 5000-31,000 and molar massdispersities of 1.5-2.8. Attempts to polymerize methylmethacrylate usingGTP proved unsuccessful with these catalysts.