Homoleptic allyl complexes of chromium with trimethylsilylated ligands

Christin N. Carlson, J. Dominic Smith, Timothy P. Hanusa, William W. Brennessel, Victor G. Young

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20 Scopus citations

Abstract

Reaction of two equivalents of K[1-(SiMe3)C3 H4], K[1,3-(SiMe3)2C3 H3], or K[1,1′,3-(SiMe3)3 C3H2] with CrCl2 in THF at -78 °C produces the red complexes {[1-(SiMe3)C3 H4]2Cr}2 (1), [1,3-(SiMe3) 2C3H3]2Cr (2) and [1,1′,3-(SiMe3)3C3H2] 2Cr (3), respectively. They are thermally stable compounds, remarkably so for the monomeric 2 and 3, which possess formal 12-electron counts. Single crystal X-ray structures confirm the dimeric nature of {[1-(SiMe3)C3H4]2Cr} 2, which is constructed around a Cr2 core with Cr-Cr′=1.9784(7) Å. In the monomeric complexes, the allyl ligands are bound in a trihapto manner to the metals, with Cr-C distances of 2.193(2)-2.257(2) Å in 2 and 2.223(5)-2.319(5) Å in 3. The allyl ligands adopt staggered conformations, with a 10.4° angle between the C3 planes in (2) and parallel ligands in (3). The trimethylsilyl groups in both complexes are in a syn, anti conformation. The monomeric complexes are high-spin, with four unpaired electrons. The steric shielding provided to the metal by the trimethylsilyl groups is probably responsible for the lack of reactivity of 2 with bulky donors such as PPh3, although it forms a monoadduct with the more sterically compact PMe3. Density functional theory calculations were performed on (C3H5)2Cr, and comparisons made with the structures of the trimethylsilylated derivatives.

Original languageEnglish (US)
Pages (from-to)191-199
Number of pages9
JournalJournal of Organometallic Chemistry
Volume683
Issue number1
DOIs
StatePublished - Oct 7 2003

Keywords

  • Allyl
  • Bulky ligands
  • Chromium
  • Crystal structure
  • Trimethylsilyl group

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