Lewis acidic titanium species: The synthesis, structure, bonding and molecular modelling considerations of the complexes Ti(NR2)3CI (R = Me, Et)

David G. Dick, Roger Rousseau, Douglas W. Stephan

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Abstract

Reaction of simple amides with TiCl4 affords mixed amido-chloride species Ti(NR2)4-nCln The trisamide-chloride species Ti(NR2)3Cl can be prepared directly employing three equivalents of amide or by reaction Ti(NR2)4 with TiCl4. The compound Ti(NMe2)3Cl, 1, crystallizes in the trigonal space group Ric, with a = 11.525(5), c = 14.939(3) A, Z = 6, and V = 1718(1) Å;3. The compound Ti(NEt2)3Cl, 2, crystallizes in the monoclinic space group P21/c, with a = 8.385(2) Å, b = 15.958(2) Å, c = 14.230(4) Å, β= 107.79(1)°, Z = 4, and V = 1813(1) Å;3. The geometry of the Ti coordination sphere in these complexes is best described as pseudo-tetrahedral. The structural data are consistent with Ti-N multiple bonding. Preliminary results of EHMO calculations are consistent with dπ-pπ Ti-N bonding. Attempts to replace thehalides with phosphides (LiPR2, R = Me, Et, Ph) led not to the Ti(IV) phosphido species, but rather to redox chemistry yielding Ti(III) amides and P2R4. The barrier to rotation about the Ti-N bonds has been considered. Variable temperature 'H NMR studies reveal that the barrier is small. Extended Hiickel total energy minimization calculations have been performed. In addition, MMX calculations of the barrier to Ti-N rotation are reported. The results of these calculations imply that the rotational barrier is dominated by steric effects.

Original languageEnglish
Pages (from-to)357-362
Number of pages6
JournalCanadian Journal of Chemistry
Volume69
Issue number2
DOIs
Publication statusPublished - Jan 1 1991

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Keywords

  • Structures
  • Ti-N bonding
  • Titanium amides

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Organic Chemistry

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