Date of Award

2001

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

George G. Stanley

Abstract

Dicationic bimetallic rhodium complexes based on the novel binucleating tetraphosphine ligand system racemic-Et2PCH2CH 2P(Ph)CH2P(Ph) CH2CH2PEt2, et,ph-P4, are highly active and selective hydroformylation catalysts that make use of bimetallic cooperativity to operate. In situ FT-IR and NMR studies indicate that the most active catalyst is the unique dinuclear dicationic hydrido-carbonyl Rh(+2) oxidation state complex, [racemic-Rh 2H2(mu-CO)2(CO)2(et,ph-P4) 2+]. A kinetic study was performed to determine the rate orders of the dinuclear dicationic catalyst, and the substrate (1-hexene). The rate orders were found to be one for both components. The study was also performed to test the hypothesis of a bis-acyl species, which was not observed. The addition of 25--50% water to the acetone solvent caused a dramatic improvement in the hydroformylation catalysis with a 40% increase in the initial turnover frequency and a reduction in alkene isomerization and hydrogenation side reactions to less than 1%. The presence of water coupled with H 2 poor reaction conditions initiates a new catalytic reaction---an aldehyde-water shift process that takes aldehyde and water and produces carboxylic acid and H2. Too much H2 strongly inhibits this aldehyde-water shift reaction, which is why it is not observed under normal hydroformylation catalysis conditions. The carboxylic acid products have very high linear/branched selectivities. These pieces of evidence continue to support our theory of bimetallic cooperativity.

ISBN

9780493271613

Pages

110

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