Synthesis, Characterization, and Catalytic Activity of Cationic Co(II) Pre-Catalysts and Cooperative Germylene–Metal Complexes

Author

David R. Holzknecht, Louisiana State University at Baton RougeFollow

Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

The conversion of olefins to aldehydes represents an important chemical transformation that can be exploited to generate a wide range of products from the hydroformylation process. The aldehydes produced via hydroformylation are often converted to additional value-added products. This process is typically catalyzed by monovalent rhodium or cobalt complexes. Industrially, rhodium complexes have become increasingly popular due to their high activity and tolerance to bidentate phosphine and phosphite ligands. Developing a competitive cobalt catalyst is of interest to drive down the cost of the catalytic system.

Recently, a cationic Co(II) precatalyst was reported to perform hydroformylation with activity within an order of magnitude of Rh(I) systems. This report, however, would later be contested as Zhang et al. could not replicate the results. The [Co(acac)(dppBz)]BF₄ precatalyst in question was investigated further. First, the characterization of the complex was more thoroughly investigated by ESI-TOF mass spectrometry. The previously unappreciated impurity, Co(acac)₂(dppBz), was identified and quantified by ESI-TOF MS, and subsequently removed via synthetic modification. Pure [Co(acac)(dppBz)]BF₄ was shown to be an effective hydroformylation precatalyst. Adding Co(acac)₂(dppBz) impurities to [Co(acac)(dppBz)]BF₄ in situ resulted in less hydroformylation activity. In addition, the hydroformylation activity of [Co(acac)(dioxane)₄]BF₄ was studied and determined to be a more flexible platform exhibiting enhanced activity with substoichiometric equivalents of dppBz. [Co(acac)(dppBz)]BF₄ was also iterated on further by attempting to replace the acac with a monodentate alkoxide to promote the activation of the precatalyst. Co(OⁱPr*)₂(dppBz) was synthesized, but the protonolysis to generate the desired precatalyst [Co(OⁱPr*)(dppBz)]BF₄ remains a challenge.

Traditionally, CO/ethylene copolymerization proceeds via a near perfect alternation of CO and ethylene catalyzed by a cationic Pd, Rh, or Ni catalyst. Disrupting this perfect alternation is an area of active interest due to the high melting of polyketones (257 ^oC), which is driven by the strong interchain interactions of the polar carbonyls. Disrupting this interaction by the double insertion of CO has remained elusive in the literature. Introducing germylene ligands could promote this by trapping the metal–acyl intermediate through π-activation of the carbonyl. A PGeP-typepincer ligand was synthesized and coordinated to Pd through treatment of PGeP with Pd(PPh₃)₄.

Date

4-11-2024

Recommended Citation

Holzknecht, David R., "Synthesis, Characterization, and Catalytic Activity of Cationic Co(II) Pre-Catalysts and Cooperative Germylene–Metal Complexes" (2024). LSU Doctoral Dissertations. 6401.
https://repository.lsu.edu/gradschool_dissertations/6401

Committee Chair

Chambers, Matthew B.