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Synthesis and Characterization of Platinum and Palladium Complexes with NCN Pincer Ligands

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2014, PhD, University of Cincinnati, Arts and Sciences: Chemistry.
A series of platinum(II) complexes with the formulae Pt(phebox)(L)+ (phebox- = 1,3-bis(4,4'-dimethyl-2'-oxazolinyl)phenyl anion) (L = pyridine (py), 4-phenylpyridine (phpy), quinoline (quin), acridine(ac)) and Pt2(phebox)2(&micro-L')2+ (L'= pyrazine (pyz), 4,4'-bipyridine (bpy), 1,2-bis(4-pyridyl)ethane (bpa)) was prepared by the treatment of Pt(phebox)Cl with a silver(I) salt followed by the addition of the pyridyl ligand. The complexes have been characterized by 1H NMR, X-ray crystallography and elemental analysis. Crystallographic data establish that the metal center is bonded to the tridentate phebox and monodentate pyridyl ligand. The most distorted 5-membered oxazoline rings adopt a CH2-CMe2 twist conformation. The structures of the oxazoline groups do not lie on a single pseudorotation pathway with a unique puckering amplitude. The electronic structures were investigated using cyclic voltammetry, UV-Visible and emission spectroscopies. Pt(phebox)Cl and Pt(phebox)(py)+ undergo a ligand-based chemically reversible redox reaction, whereas, the electrochemistry of the other complexes is chemically and electrochemically less reversible. In contrast to complexes with the 1,3-bis(piperdylmethyl)phenyl anion ligand or related pincer ligands, each of the phebox- complexes described here exhibits intense emission in room-temperature methylene chloride solution, which is assigned as originating from a lowest, predominantly phebox- ligand-centered excited state. In coordinating solvents, the complexes undergo solvolysis resulting in displacement of the pyridyl ligands. Six cyclometalated platinum(II) complexes Pt(phebox)(&eta1-L")+ (L" = 2,2'-bipyridine (2,2'-bpy), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), 6-phenyl-2,2'-bipyridine (phbpy), 1,10-phenanthroline (phen), 2-phenyl-1,10-phenanthroline (pnp), 2,2':6',2''-terpyridine (tpy)) were prepared by the reaction of Pt(phebox)Cl with a silver(I) salt followed by the addition of the pyridyl ligand at room temperature under an inert atmosphere. In contrast to previously reported reactions involving pyridine, following this procedure in air also yielded platinum(IV) products with chelating pyridyl ligands, such as Pt(phebox)(&eta2-2,2'-bpy)(OH)2+, Pt(phebox)(&eta2-tpy)(OH)2+, and Pt(phebox)(&eta2-2,2'-bpy)(Cl)2+. Crystallographic data for the platinum(II) complexes establish that 2,2'-bpy, Me2bpy, phbpy, phen, pnp and tpy are each monodentate, but there is a tendency for a second pyridyl group to be directed toward the Pt(II) center. The most distorted 5-membered oxazoline rings preferentially adopt a CH2-CMe2 twist conformation, but the structures of the oxazoline groups do not lie on a single pseudorotation pathway with a common puckering amplitude. In room temperature solution and 77K glassy solution, the complexes exhibit intense emission that is tentatively attributed to a lowest excited state with mainly phebox- ligand character and some metal-to-ligand (phebox-) charge-transfer character. 1H NMR spectra of samples dissolved in CD3CN solution indicate that each Pt(phebox)(L)+ complex (except L = pnp) undergoes solvolysis to form Pt(phebox)(solvent)+ in acetonitrile. However, Pt(phebox)(phen)+ undergoes comparatively slow pyridyl ligand dissociation, and Pt(phebox)(pnp)+ is stable to dissociation. Taken together, these data suggest that the presence of a formally non-bonding pyridyl group capable of interacting with the Pt(II) center has a significant impact on the spectroscopy and reactivity of the Pt(phebox)(&eta1-L)+ complexes.
William Connick, Ph.D. (Committee Chair)
Thomas Beck, Ph.D. (Committee Member)
Hairong Guan, Ph.D. (Committee Member)
140 p.

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Citations

  • Zhao, D. (2014). Synthesis and Characterization of Platinum and Palladium Complexes with NCN Pincer Ligands [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1399623983

    APA Style (7th edition)

  • Zhao, Daoli. Synthesis and Characterization of Platinum and Palladium Complexes with NCN Pincer Ligands. 2014. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1399623983.

    MLA Style (8th edition)

  • Zhao, Daoli. "Synthesis and Characterization of Platinum and Palladium Complexes with NCN Pincer Ligands." Doctoral dissertation, University of Cincinnati, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1399623983

    Chicago Manual of Style (17th edition)