Synthetic and theoretical MO calculational studies of lithiotriazine intermediates produced during alkyllithium-induced cyclotrimerisation reactions of organic nitriles, and comparison of their structures with that of a methylmagnesiotriazine derivative

D.R. Armstrong, Kenneth. W. Henderson, M. MacGregor, Robert Mulvey, M.J Ross, W. Clegg, P.A. O'Neil

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27 Citations (Scopus)

Abstract

Benzonitrile can be readily cyclotrimerised by treatment with a suitable alkyllithium to give a simple triazine, or to a solvated lithiodihydrotriazine derivative. Which cyclic product dominates depends mainly on the source of the active Li+ cation (n-butyllithium, t-butyllithium and tetramethylguanidinolithium are considered here), and on the solvent employed. X-ray crystallographic studies on a representative compound show that the lithio species exists as a mononuclear, contact ion pair structure, with the triazine ring in a 1,4-dihydro state. On reaction with the Grignard reagent, MeMgCl, this compound gives a methylmagnesiodihydrotriazine, which has also been crystallographically characterised and found to closely resemble its lithio precursor. Ab initio MO calculations on model systems reveal that the 1,4-dihydrotriazine arrangement is energetically preferred to the 1,2-dihydro alternative irrespective of the counterion (Li+ or H+) present. A theoretical investigation of the methanolysis of the lithio species indicates that the formation of an intermediate MeOH complex, with the alcohol attached to a ring N atom and not to Li+, directs the reaction towards ultimate formation of a 1,2-dihydrotriazine.

Original languageEnglish
Pages (from-to)79-93
Number of pages15
JournalJournal of Organometallic Chemistry
Volume486
Issue number1-2
DOIs
Publication statusPublished - 25 Jan 1995

Keywords

  • triazine
  • lithium
  • magnesium
  • Ab initio
  • crystal structure
  • organomagnesium compounds
  • lithium compunds
  • ring stacking

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