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Development of Bulky Dipyrromethene Complexes of Aluminum, Zinc, and Rhodium

Gianopoulos, Christopher G
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418317025

Abstract Details

2014, Doctor of Philosophy, University of Toledo, Chemistry.
The chemistry of dipyrromethene ligands is dominated by boron difluoride luminophores (BODIPY), which are commercially important laser dye materials and have also found application to imaging/staining biological samples. Despite the importance of BODIPY complexes, dipyrromethene complexes of the heavier group 13 elements are scarce. Our interest in bulky dipyrromethene ligands is based on analogy to popular ß-diketiminate ligands that have found use in stabilizing unusual metal complexes on the basis of steric protection. The preparation and characterization of aluminum, zinc and rhodium complexes of bulky dipyrromethene ligands is the subject of the following discourse. The preparation and characterization of aluminum alkyl, aryl and hydride complexes of 1,9-dimesityl-5-phenyldipyrromethene is reported in chapter two. The synthesis and characterization of a bimetallic aluminoxane with terminal hydride coligands is also reported. The preparation and characterization of dimethylaluminum complexes of 1,9-dimesityl-5-pentafluorophenyldipyrromethene and 1,9-dimesityl-5-(2’-pyridyl)dipyrromethene are also reported. These compounds have been characterized by NMR spectroscopy and X-ray crystallography. The structural data clearly demonstrate similarities and differences of the steric environment of dipyrromethene and ß-diketiminate ligands. The alkyl and aryl aluminum complexes are surprisingly robust and tolerate exposure to air, moisture and even silica gel chromatography. We have proposed that the stability of these compounds is due to kinetic stabilization afforded by the steric environment of the bulky dipyrromethene ligand. The preparation of aluminum complexes of 1,9-dimesityl-5-phenyldipyrromethene is extended in chapter 3. In this chapter, the preparation of aluminum complexes with halide, alkoxide and amido coligands is reported. These complexes were characterized by NMR spectroscopy and X-ray crystallography. The alkoxide and amido complexes were also evaluated for their ability to initiate the polymerization of e-caprolactone and preliminary results are discussed. Unfortunately, these aluminum complexes are poor catalysts for caprolactone polymerization, which only proceeds at elevated temperature. Furthermore, the aluminum catalysts are sensitive to impurities in the lactone monomer and catalysis was often found to halt after long reaction times. As mentioned previously, we became interested in the chemistry of aluminum complexes of dipyrromethene ligands based on analogy to ß-diketiminate ligands. ß-Diketiminate ligands have found use in stabilizing rare metal complexes, such as terminal imido complexes of aluminum. A major aim of our work with dipyrromethenes is to identify a system capable of stabilizing aluminum complexes with terminal divalent coligands such as imido or alkylidene ligands. In chapter 4, theoretical calculations performed at the DFT level are presented. The electronic structure of dipyrromethene aluminum complexes with terminal imido and alkylidene coligands was calculated as well as the thermochemical parameters of reactions to prepare such complexes. Synthetically viable substitutions were made in order to determine the effect of electronic perturbations (to the dipyrromethene or alkylidene coligand) on the stability of terminal alkylidene complexes of aluminum. The results of this chapter show that a terminal alkylidene of aluminum must be formed from an Al(I) precursor, rather than Al(III), and also that modification of the electronics of these systems has little effect on the stability of the resulting complexes. These results indicate that isolation of a stable, terminal alkylidene complex of aluminum will likely require kinetic stabilization of the reactive alkylidene moiety by use of steric bulk rather than stabilization through electronic modification to the system. Chapter 5 concerns the preparation and characterization of zinc halide, alkyl and alkoxide complexes of 1,9-dimesityl-5-phenyldipyrromethene. These compounds have been characterized by NMR spectroscopy and X-ray crystallography. The preparation of monomeric zinc alkoxides has been challenging and results to this aim are discussed at length. As an extension of the work reported in chapter 3, we have also explored the polymerization of e-caprolactone initiated by zinc alkoxide complexes and preliminary results will be discussed. In chapter 6 the preparation and characterization of rhodium(I) 1,5-cyclooctadiene (COD), carbon monoxide (CO) and arene complexes of 1,9-dimesityl-5-pentafluorophenyldipyrromethene are reported. These complexes were characterized by NMR spectroscopy and X-ray crystallography. Results from this chapter demonstrate the flexibility of the dipyrromethene ligand to accommodate square-planar coordination to rhodium(I). The preparation of low-coordinate rhodium complexes is also discussed. Chapter 7 reports the synthesis of Cr(TPP)Cl(THF), a component of the Coates system for carbonylation of epoxides, by a previously unreported method. Traditionally, Cr(TPP)Cl(THF) is prepared from divalent or zero-valent chromium precursors that are expensive, air-sensitive materials. Our method involves the use of inexpensive, air-stable trivalent chromium. Appendix 1 reports the synthesis and characterization of three compounds which were prepared as parts of side projects. The experimental details and crystal structures are reported, discussion is however kept to a minimum. The compounds presented in the appendix include nickel bromide and chromium chloride complexes of 1,9-dimesityl-5-phenyldipyrromethene and also a pseudo-octahedral homoleptic aluminum complex ligated by 2-(2’-pyridyl)pyrrole.
Mark Mason (Advisor)
Jon Kirchhoff (Committee Member)
Joseph Schmidt (Committee Member)
Kana Yamamoto (Committee Member)
Maria Coleman (Committee Member)
219 p.
Chemistry; Inorganic Chemistry
Dipyrromethene; aluminum complexes; zinc complexes; polymerization of caprolactone; rhodium complexes; bulky ligands; alkylidene complexes of aluminum; DFT calculations;

Recommended Citations

Citations

  • Gianopoulos, C. G. (2014). Development of Bulky Dipyrromethene Complexes of Aluminum, Zinc, and Rhodium [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418317025

    APA Style (7th edition)

  • Gianopoulos, Christopher. Development of Bulky Dipyrromethene Complexes of Aluminum, Zinc, and Rhodium. 2014. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418317025.

    MLA Style (8th edition)

  • Gianopoulos, Christopher. "Development of Bulky Dipyrromethene Complexes of Aluminum, Zinc, and Rhodium." Doctoral dissertation, University of Toledo, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1418317025

    Chicago Manual of Style (17th edition)

toledo1418317025
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This open access ETD is published by University of Toledo and OhioLINK.