Highly regioselective [2 + 2 + 2] cycloaddition of terminal alkynes catalyzed by η6-arene complexes of titanium supported by dimethylsilyl- bridged p-tert-butyl calix[4]arene ligand

Oleg V. Ozerov, Brian O. Patrick, Folami T. Ladipo

Research output: Contribution to journalArticlepeer-review

130 Scopus citations

Abstract

Two new Ti-η6-arene complexes [(DMSC)Ti{η6-1,2,4- C6H3(SiMe3)3}] (6) and [(DMSC)Ti{η6-1,3,5-C6H3Bu(t)3}] (7) containing 1,2-alternate, Me2Si-bridged p-tert-butylcalix[4]arene (DMSC) ancillary ligand have been synthesized. The solid-state structure of 6 revealed a highly folded arene ligand [with a dihedral angle of 29.7(7)°] and suggests that 6 is better described as a 7-titananorbornadiene species. Both 6 and 7 are efficient catalysts for highly regioselective [2 + 2 + 2] cycloaddition of terminal alkynes to yield 1,2,4-substituted benzenes. Kinetic studies of the catalytic [2 + 2 + 2] cycloaddition of Me3SiC≡CH revealed first-order dependence on [6] and [Me3SiC≡CH]; and activation parameters, ΔH(+) = 14 kcal/mol, and ΔS(+) = -11 cal/mol K, that are consistent with an associative mechanism. The reaction rate is influenced by the steric requirements of both the alkyne and the η6-arene compound. The high selectivity for 1,2,4-substituted benzene may be understood in terms of the directing influence of the DMSC ligand.

Original languageEnglish
Pages (from-to)6423-6431
Number of pages9
JournalJournal of the American Chemical Society
Volume122
Issue number27
DOIs
StatePublished - Jul 12 2000

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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