Study of the lithiated phenylacetonitrile monoanions and dianions formed according to the lithiated base used (LHMDS, LDA, or n-BuLi). 1. Evidence of heterodimer ("Quadac") or dianion formation by vibrational spectroscopy

Jacques Corset; Martine Castellà-Ventura; Françoise Froment; Tekla Strzalko; Lya Wartski

doi:10.1021/jo020492t

Study of the lithiated phenylacetonitrile monoanions and dianions formed according to the lithiated base used (LHMDS, LDA, or n-BuLi). 1. Evidence of heterodimer ("Quadac") or dianion formation by vibrational spectroscopy

J Org Chem. 2003 May 16;68(10):3902-11. doi: 10.1021/jo020492t.

Authors

Jacques Corset¹, Martine Castellà-Ventura, Françoise Froment, Tekla Strzalko, Lya Wartski

Affiliation

¹ LADIR - CNRS (UMR 7075), 2 Rue Henri Dunant, BP 28, 94320 Thiais, France.

PMID: 12737570
DOI: 10.1021/jo020492t

Abstract

It is evidenced through vibrational spectroscopy that a heterodimer or "Quadac" is formed when an excess of base (LHMDS, LDA, or n-BuLi) is added to PhCH(2)CN in THF, THF-hexane, or THF-toluene solution. The amount of heterodimer increases with the pK(H)(a) of the lithiated base. A dianionic species may be formed through decomposition of this heterodimer if the pK(H)(a) of the base is sufficiently high, as in the case of n-BuLi. With LDA, only a very small amount of dianion is observed, and with LHMDS, no dianion is detected. The predominant dianionic species observed are the linear and bridged separated ion pairs of the dilithiated dianion. The presence of the amine in the medium is of paramount importance. The PhCHCNLi monomer-dimer equilibrium is entropy driven toward the dimer solvated by the amine.