Steric and electronic effects of 1,3-disubstituted cyclopentadienyl ligands on metallocene derivatives of Cerium, Titanium, Manganese, and Iron

Thesis/Dissertation · Mon May 01 00:00:00 EDT 2000

DOI:https://doi.org/10.2172/764394· OSTI ID:764394

Sofield, Chadwick Dean ^[1]

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1. Univ. of California, Berkeley, CA (United States)

Sterically demanding 1,3-disubstituted cyclopentadienyl ligands were used to modify the physical properties of the corresponding metallocenes. Sterically demanding ligands provided kinetic stabilization for trivalent cerium compounds. Tris(di-t-butylcyclopentadienyl)cerium was prepared and anion competition between halides and cyclopentadienyl groups which had complicated synthesis of the tris(cyclopentadienyl)compound was qualitatively examined. Bis(di-t-butylcyclopentadienyl)cerium methyl was prepared and its rate of decomposition, by ligand redistribution, to tris(di-t-butylcyclopentadienyl)cerium was shown to be slower than the corresponding rate for less sterically demanding ligands. Asymmetrically substituted ligands provided a symmetry label for examination of chemical exchange processes. Tris[trimethylsilyl(t-butyl)cyclopentadienyl]cerium was prepared and the rate of interconversion between the C1 and C3 isomers was examined. The enthalpy difference between the two distereomers is 7.0 kJ/mol. The sterically demanding cyclopentadienyl ligands ansa-di-t-butylcyclopentadiene (Me₂Si[(Me₃C)₂C₅H₃]₂), ansa-bis(trimethylsilyl)cyclopentadiene (Me₂Si[(Me₃Si)₂C₅H₃]₂) and tetra-t-butylfulvalene and metallocene derivatives of the ligands were prepared and their structures were examined by single crystal X-ray crystallography. The effect that substituents on the cyclopentadienyl ring have on the pi-electron system of the ligand was examined through interaction between ligand and metal orbitals. A series of 1,3-disubstituted manganocenes was prepared and their electronic states were determined by solid-state magnetic susceptibility, electron paramagnetic resonance, X-ray crystallography, and variable temperature UV-vis spectroscopy. Spin-equilibria in [(Me₃C)₂C₅H₃]₂Mn and [(Me₃C)(Me₃Si)C₅H₃]₂Mn were examined and indicate an enthalpy difference of 15 kJ/mol between the high-spin and low-spin forms. Cyclopentadienyl groups resistant to intramolecular oxidative addition allowed isolation of compounds susceptible to intramolecular decomposition. A kinetically stable, base-free titanocene was prepared using di-t-butylcyclopentadienyl ligands and the reactivity of the compound toward small molecules was investigated. The titanocene reacts reversibly with hydrogen to form the titanocene dihydride and the equilibrium in solution between titanocene dihydride, and titanocene and hydrogen, was examined.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 764394
• Report Number(s): LBNL-45881; R&D Project: 403003; TRN: AH200102%%141
• Resource Relation: Other Information: TH: Thesis (Ph.D.); Submitted to Dept. of Chemistry, Univ. of California, Berkeley, CA (US); PBD: 19 May 2000
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CERIUM COMPOUNDS
ELECTRON SPIN RESONANCE
IRON COMPOUNDS
MAGNETIC SUSCEPTIBILITY
MANGANESE COMPOUNDS
PHYSICAL PROPERTIES
TITANIUM COMPOUNDS
ORGANOMETALLIC COMPOUNDS
LIGANDS
STEREOCHEMISTRY
METALLOCENE TITANOCENE MANGANOCENE ORGANOMETALLIC SYNTHESIS