Effects of Substituent Substitution on a Bimetallic Hydroformylation Catalyst Based on a Tetraphosphine Ligand.
Date of Award
Doctor of Philosophy (PhD)
George G. Stanley
The main concentration of this work was to further study the unusual catalytic activity and selectivity of the bimetallic hydroformylation catalyst based on the tetraphosphine ligand, et,ph-P4. This activity and selectivity are a product of both the rigid steric environment and the cooperativity between the two Rh metal centers. This project focused on probing both the mechanism employed by this system, and studying the effect of manipulation on the steric environment at the binding site. In situ spectroscopic methods have led to the formulation of a dicationic catalytic system. This is highly unusual in that all monometallic rhodium or cobalt hydroformylation catalysts operate via neutral hydrido-carbonyl metal complexes. However, a neutral catalyst precursor based on this ligand is a terrible hydroformylation catalyst. Spectroscopic studies have shown that the two systems are very different under hydroformylation conditions. Assignment of various catalytic species present in both systems are discussed. Variations to the tetraphosphine ligand have allowed for study of the importance of the rigid steric environment present in this catalyst. In particular, the relative size and shape of the substituents on the terminal phosphines have been shown to play an important role in determining both the activity and selectivity of the catalyst. Three new catalyst systems were synthesized and tested for catalytic activity. All three new systems negatively effected both the activity and regioselectivity of the catalyst for hydroformylation of alpha-olefins. Initial studies on the catalyst based on me,ph-P4, however, have shown it to be effective for the asymmetric hydroformylation of vinyl esters. Initial results with chiral 1-[Rh2(nbd)2(me,ph-P4)] 2+ are reported here.
Howell, Donna Kae, "Effects of Substituent Substitution on a Bimetallic Hydroformylation Catalyst Based on a Tetraphosphine Ligand." (1999). LSU Historical Dissertations and Theses. 6995.