Synthesis, Chemistry, and Spectroscopy of Some Tris(pentahaptocycioentadienyl)uranium( IV) Alkyl and Aryl Compounds

Tobin J. Marks*, Afif M. Seyam, John R. Kolb

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

168 Scopus citations

Abstract

The systematic high yield syntheses of a number of (h5-C5H5)3UR compounds from (h5-C5H5)3UCl and the corresponding RLi or RMgX reagents are reported. The new compounds have been characterized by chemical and magnetochemical means and by vibrational and nmr spectroscopy. The allyl compound has a ground state monohaptoa geometry and is fluxional. In the isopropyl compound restricted rotation is observed about the U-R bond, indicating considerable crowding of ligands around the central metal. Analysis of the isotropic nmr chemical shifts indicates the contribution of large contact shifts; the mechanism of spin distribution involves negative spin density at the a-carbon atom of the alkyl or aryl group and is qualitatively in accord with SCF INDO molecular orbital calculations. The U-C bond is susceptible to attack by protonic solvents and, hence, is somewhat ionic. Most of the new compounds exhibit surprisingly high thermal stability, the general order of stability determined by kinetic studies in toluene solution being primary > secondary > tertiary. In the thermolysis, β elimination of olefin does not occur to any major extent, but intramolecular abstraction of hydrogen from a cyclopentadienyl ring occurs yielding RH ; this takes place with essentially complete retention of stereochemical configuration at the a carbon atom of R. A homolytic U-C bond scission producing a highly constrained caged radical pair, or a concerted elimination of RH, explains these observations.

Original languageEnglish (US)
Pages (from-to)5529-5539
Number of pages11
JournalJournal of the American Chemical Society
Volume95
Issue number17
DOIs
StatePublished - Aug 1 1973

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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