Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

George G. Stanley

Abstract

The fundamental purpose of this project was to expand the knowledge of the et,ph-P4 ligand system, $\rm Et\sb2PCH\sb2CH\sb2P(Ph)CH\sb2P(Ph)CH\sb2CH\sb2PEt\sb2$, used to make the very active bimetallic catalyst racemic- ($\rm Rh\sb2(NBD)\sb2(et,ph$-P4)) (BF$\sb4)\sb2$. The ligand was designed to both bridge and chelate two metal centers to allow the metals to remain in close proximity. This is the key to the bimetallic cooperativity concept involved in the hydroformylation of olefin substrates, where an intramolecular hydride transfer has been proposed to occur from one rhodium center to another during the catalytic cycle. This project involved the study of a variety of olefin substrates to probe their activity and behavior with our catalyst system. The addition of several non-nucleophilic basels to the catalytic solution to hinder the production of undesirable isomerization by-products in the reaction showed a strong correlation between the pK$\rm\sb{b}$ of the base and the initial turnover frequency, but with no correlation with the steric bulk of the base used. A neutral catalyst precursor, racemic-$\rm Rh\sb2(\eta\sp3$-allyl)$\sb2$(et,ph-P4), was synthesized and is a terrible catalyst precursor for the hydroformylation of 1-hexene. The addition of 2 equivalents of HBF$\sb4$ to this system generates a highly active and regioselective bimetallic catalyst. In situ FT-IR mechanistic studies on several bimetallic hydroformylation catalysts are reported and new proposed mechanisms for bimetallic hydroformylation involving bimetallic cooperativity are presented. These bimetallic mechanisms incorporate both monocationic and dicationic catalytic species in the catalytic cycles.

Pages

175

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