Part I. Synthesis and thermolysis of cyclopentadienyl and pentamethylcyclopentadienyl molybdenum dioxo alkoxides. Part II. Structural characterization of polysilicate intermediates formed during sol-gel polymerization

Rosenberg, Frank Stewart

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https://hdl.handle.net/2142/18981 Copy

Description

Title

Part I. Synthesis and thermolysis of cyclopentadienyl and pentamethylcyclopentadienyl molybdenum dioxo alkoxides. Part II. Structural characterization of polysilicate intermediates formed during sol-gel polymerization

Author(s)

Rosenberg, Frank Stewart

Issue Date

1990

Doctoral Committee Chair(s)

Klemperer, Walter G.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Chemistry, Analytical
• Chemistry, Inorganic
• Engineering, Chemical

Language

eng

Abstract

• Part I. The molybdenum(VI) dioxo alkoxides ($\eta\sp5$-$C\sb5$H$\sb5$)MoO$\sb2$(OR) (R=CH$\sb2$CH$\sb3$, CH(CH$\sb3)\sb2$) and ($\eta\sp5$-C$\sb5$(CH$\sb3)\sb5$) MoO$\sb2$(OR) (R=CH$\sb3$, CH$\sb2$CH$\sb3$, CH(CH$\sb3)\sb2$) have been prepared and characterized. Single crystal X-ray diffraction studies showed that CpMoO$\sb2$(OCH$\sb2$CH$\sb3$) and Cp$\sp{*}$MoO$\sb2$(OCH$\sb2$CH$\sb3$) adopt the expected piano stool geometry. Oxygen-17 NMR chemical shifts of the terminal oxygens showed that Cp$\sp{*}$ is a better electron donor to the metal center than Cp. Oxygen-17 NMR also showed that for a series of compounds, CpMoO$\sb2$(OR) (R=Me, Et, i-Pr and t-Bu), electron donation increased in the order methoxide $<$ ethoxide $<$ 2-propoxide $<$ t-butoxide. Thermolysis of CpMoO$\sb2$ (OCH$\sb2$(CH$\sb3)\sb2$)) at 55$\sp\circ$C in CD$\sb3$CN produced, after a ten minute induction period in which no organic products were observed, equal amounts of acetone and 2-propanol. Thermolysis of CpMoO$\sb2$(OCH$\sb2$CH$\sb3$) produced ethanol and very small amounts of acetaldehyde. Acetaldehyde was found to react readily with CpMoO$\sb2$(OCH$\sb2$CH$\sb3$) to produce acetal and (CpMoO$\sb2)\sb2$O. Thermolysis of Cp$\sp{*}$MoO$\sb2$(OCH$\sb2$CH$\sb3$) at 80$\sp\circ$C in CD$\sb3$CN resulted in the formation of half an equivalent of ethanol, half an equivalent of tetramethylfulvene and 1/4 equivalent of (Cp$\sp{*}$Mo$\sb2$O$\sb4$(OCH$\sb2$CH$\sb3$)) $\sb2$. Single crystal X-ray structural analysis revealed that the latter complex was comprised of two Mo$\sb2$O$\sb4$ units linked by bridging alkoxide ligands and capped on each end by an $\eta\sp5$-C$\sb5$Me$\sb5$ ligand. The thermal behavior of the title compounds stands in contrast to the thermal decomposition of ((P$\sb3$O$\sb9$)MoO$\sb2$(OCH$\sb2$CH$\sb3$)) $\sp{2-}$, a model compound for alkoxides on a MoO$\sb3$ surface, which at 180$\sp\circ$C in CD$\sb3$CN produced, with no induction period, half an equivalent of acetaldehyde and half an equivalent of ethanol (Wang, R. C. Ph.D. Thesis, University of Illinois, 1988).
• Part II. The principle mono- through hexasilicate structural isomers formed by hydrolysis of methanolic tetramethylorthosilicate in the presence of HCl have been structurally assigned and quantitatively determined. Complex silica sol-gel mixtures were separated into several simpler samples which were characterized by gas chromatography and mass spectrometry (Ramamurthi, S. D. Ph.D. Thesis, University of Illinois, 1988). The contents of each sample were structurally characterized and quantified by $\rm \sp{29}Si\{\sp1H\}$ NMR techniques (1-pulse, 1D-INADEQUATE and 2D-INADEQUATE). By comparing the NMR data with the gas chromatographic data, structural assignments were made and response factors were calculated for each of the components separated by gas chromatography.

Type of Resource

text

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Copyright 1990 Rosenberg, Frank Stewart

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