Hatfield, William E., 1937- (The University of Arizona., 1961)
    • Characterization of the electronic structure of complexes containing metal-heteroatom multiple bonds.

      Lichtenberger, Dennis L.; Hoppe, Martin Louis.; Feltham, Robert; Kukolich, Steven; Forster, Leslie; Keller, Philip (The University of Arizona., 1988)
      The electronic structure of a variety of metal-heteroatom multiply bonded complexes, including some active alkyne metathesis catalysts, have been investigated using He(I) and He(II) ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and Fenske-Hall molecular orbital calculations. Utilizing this electronic structure information, confirmation of the proposed mechanism for the alkyne metathesis reaction which involves formation of a metallacyclobutdienyl intermediate was ascertained. Also, the important relationships between metallatetrahedral and metallacyclobutadienyl complexes, both of which have been mentioned as possible intermediates in the alkyne metathesis reaction and for which examples have been prepared and isolated, are discussed in significant detail. In the final chapters the electronic structure of some corresponding metal-nitrogen triply bonded complexes are discussed as well as the results probing the charge distribution in metal-heteroatom multiply bonded systems as determined by the XPS experiment.
    • Electronic structure and bond energy trends in silicon-hydrogen and germanium-hydrogen bond activation by transition metals.

      Lichtenberger, Dennis; Rai Chaudhuri, Anjana.; Feltham, Robert; Enemark, John; Bates, Robert; Salzman, Ron (The University of Arizona., 1989)
      The electronic structure factors that control Si-H and Ge-H bond activation by transition metals are investigated by means of photoelectron spectroscopy. Molecular orbital calculations are also used to gain additional insight into the orbital interactions involved in bond activation. The complexes studied have the general molecular formula (η⁵-C₅R'₅)Mn(CO)(L)HER₃, where R' is H or CH₃, L is CO or PMe₃, E is Si or Ge and R is Ph or Cl. These compounds are interesting models for catalysts in industrial processes like hydrosilation. The compounds display different stages of interaction and "activation" of the E-H bonds with the metal. One purpose is to measure the degree of Mn, Si, H 3-center-2-electron bonding in these complexes. The three-center interaction can be tuned by changing the substituents on Si, methylating the cyclopentadienyl ring, changing the ligand environment around the metal and substituting Si with Ge. The degree of activation is measured by observing the shifts in the metal and ligand ionizations relative to starting materials and free ligand in the photoelectron spectrum. Changing the substituent on Si extensively changes the degree of activation. Photoelectron spectral studies on (η⁵-C₅H₅)Mn(CO)₂HSiPh₃ show this to be a Mn(I) system. Progressive methylation of the cyclopentadienyl ring increases the electron richness at the metal center with no substantial effect on the degree of activation. Substitution on the metal (PMe₃ for CO) is less able to control the electronic structure factors of activation than the substitution on the Si atom. The magnitude of Ge-H bond activation is found to be of the same order as the Si-H bond activation for analogous compounds as found by studying (η⁵-C₅H₅)Mn(CO)₂HGePh₃, (η⁵-CH₃C₅H₄)Mn(CO)₂HGePh₃ and (η⁵- C₅(CH₃)₅)Mn(CO)₂HGePh₃ complexes by photoelectron spectroscopy. The photoelectron spectra of CpFe(CO)₂SiCl₃ and CpFe(CO)₂SiMe₃ were measured to study the electron charge shift from the metal to the ligand in these complexes as compared to CpMn(CO)₂HSiR₃ complexes. The photoelectron spectroscopic studies include numerous perturbations of the ligand and metal center to observe the extent of bond interaction and remain one of the best techniques to detect activation products.

      Lichtenberger, Dennis; HUBBARD, JOHN LEE. (The University of Arizona., 1982)
      Transition metal-ligand interactions in several groups of closely related organometallic complexes are discussed from the results of both valence and core photoelectron experiments. Particular attention is given to the novel experimental aspects, including a charged particle oscillator He II source, sample introduction and containment, and data collection and spectral analysis procedures not normally associated with gas phase photo-electron spectroscopy. The application of the ionization experiments begins with a reassessment of the bonding in the group VIb metal hexacarbonyls. He I ionization data of unprecedented quality for the predominantly metal d t₂g level of Cr(CO)₆ and W(CO)₆ reveals for the first time the presence of metal-carbon vibrational fine structure. These positive ion M-C stretching frequencies are significantly reduced from neutral ground state values, giving direct evidence of the pi back-bonding nature of the t₂g level. The next chapter focuses on the comparison of the metal-nitrosyl interactions in the trans-X-W(CO)₄NO complexes to the isoelectronic/isostructural metal-carbonyl interactions in the X-Re(CO)₅ complexes (X = Cl,Br,I). A further comparison of carbonyl and nitrosyl bonding, as well as the first photoelectron assessment of metal-thionitrosyl bonding, is addressed in the next chapter by comparing the valence and core ionization data for CpCr(CO)₂NO and CpCr(CO)₂NS (Sp = η⁵-C₅H₅) to the data reported earlier for CpMn(CO)₃ and CpMn(CO)₂CS. The final chapter of the dissertation compares the electronic structure of the CpFe(CO)₂X complexes to their CpCr(NO)₂X analogs (X = Cl,Br,I,CH₃,CN). The essence of this work fully contrasts the Fe(CO)₂ and Cr(NO)₂ functional groups.
    • Ionization-structure relationships of thin film and gas phase group VI metal-metal quadruple-bonded complexes.

      Kristofzski, John Gregory; Feltham, Robert; Pemberton, Jeanne; Armstrong, Neal R.; Rund, John; Wigley, David (The University of Arizona., 1988)
      Principles involving the electronic structure of group VI metal-metal multiple bonded complexes are examined in order to provide insights into the intramolecular and intermolecular interactions of these systems. Examination of chromium, molybdenum and tungsten tetracarboxylate thin films by ultraviolet photoelectron spectroscopy has provided the first experimental evidence for the location of the σ ionization in dimolybdenum tetracarboxylate quadruple bonded complexes. These compounds have significant intermolecular interactions as thin films which destabilizes ionization of the valence σ state, allowing it to be experimentally observed. This is supported by the observed destabilization of the σ ionization feature of the ditungsten analogue in going to the thin film. The Cr₂(O₂CCH₃)₄ comparison shows a destabilization of the leading predominantly metal ionizations consistent with the broad range of M-M bond lengths observed for Cr₂ complexes. The Group VI M₂(mhp)₄ and M₂(chp)₄ [mhp=6-methyl-2-oxo-pyridine and chp=6-chloro-2-oxo-pyridine] complexes are also examined. The geometric constraints imposed on the compounds by the ligand effectively block intermolecular interaction axial to the metal-metal bond in the solid state. Comparison of the two ligand spectra, Hmhp and Hchp, has provided a unique opportunity to assign ionizations previously attributed to the keto form of the Hmhp tautomers. The spectra of the complexes exhibit minimal relative shifting of ionization features in going to the thin films because of this constraint. A band previously believed to be due to spin orbit coupling is assigned to the σ ionization in the ditungsten complex. The overall ionization band profiles of the two series correlate well, metal by metal, with the expected shifting due to substitution of the more electronegative chlorine atoms for a methyl group. The synthesis and characterization of Mo₂(N-t-butyl-acetamide)₄, the first tetraamidodimetal compound without large rings with delocalized pi structure, is described. The single crystal X-ray structure is presented, revealing the novel (one of three examples) cis configuration of the MoN₂O₂ ligand set. The Mo-Mo bond length of 2.063 Å is one of the shortest seen to date. A preliminary gas phase He I valence spectrum is reported.
    • The kinetics and equilibria of reactions of Toluene-3,4-dithiol with selected metal ions

      Brinkman, William John, 1947- (The University of Arizona., 1973)

      Hilliard, Harold Marcus, 1928- (The University of Arizona., 1965)

      Angel, Armando Carlos, 1940- (The University of Arizona., 1972)