1,2-CF bond activation of perfluoroarenes and alkylidene isomers of titanium. DFT analysis of the C-F bond activation pathway and rotation of the titanium alkylidene moiety

José G. Andino, Hongjun Fan, Alison R. Fout, Brad C. Bailey, Mu Hyun Baik, Daniel J. Mindiola

Research output: Contribution to journalArticle

Abstract

Isomeric alkylidene complexes syn- and anti-(PNP)Ti[CtBu(C 6F5)](F) (1) and (PNP)Ti[CtBu(C 7F7)](F) (2) have been generated from C-F bond addition of hexafluorobenzene (C6F6) and octafluorotoluene (C 7F8) across the alkylidyne ligand of transient (PNP)Ti≡CtBu (A) (PNP-N[2-P(CHMe2) 2-4-methylphenyl]2), which was generated from the precursor (PNP)TiCHtBu(CH2tBu). Two mechanistic scenarios for the activation of the C-F bond by A are considered: 1,2-CF addition and [2 + 2]-cycloaddition/β-fluoride elimination. Upon formation of the alkylidenes 1 and 2, the kinetic and thermodynamic alkylidene product is the syn isomer, which gradually isomerizes to the corresponding anti isomer to ultimately establish an equilibrium mixture (when using 1, 65/35) if the solution is heated in benzene to 105 °C for 1 h. Single crystal X-Ray crystallographic data obtained for the two isomers of 2 (and syn isomer of 1) are in good agreement with computed DFT-optimized models. Our calculations suggest convincingly that the isomerization process proceeds via a concerted rotation involving a heterolytic bond cleavage about the alkylidene bond. The two rotamers are thermodynamically very close in energy and interconvert with an estimated barrier of ∼26 kcal/mol. The electronic reason for this unexpectedly low barrier is investigated.

Original languageEnglish (US)
Pages (from-to)4138-4146
Number of pages9
JournalJournal of Organometallic Chemistry
Volume696
Issue number25
DOIs
StatePublished - Dec 15 2011

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Keywords

  • 1,2-CF bond addition
  • Alkylidene
  • C-F bond activation
  • Rotation
  • Titanium

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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