Abstract
Are (poly)amine ligands, added to a tetrahydrofuran solution of an organolithium compound, bonded to lithium, or not? This question is of relevance for physical organic studies as well as for the evaluation of the ground state of (stereoselective) reactions of organolithium species in the presence of such ligands. Therefore, we studied [ 6Li]- α-(phenylthio)benzyllithium 1- 6Li as a model compound in THF/[D 8]THF solution (1:1) in the presence of several acyclic and cyclic (poly)amine ligands by 1 H , 6Li-HOESY and 1 H and 13 C NMR spectroscopy. (Poly)amine complexes of 1- 6Li are obtained in most cases. Ligands with up to three N-atoms afford contact ion pairs (CIPs) while in complexes with tetradentate amines, CIPs are in temperature-dependent equilibrium with separated ion pairs (SIPs). Graphical analyses of the 1 H and 13 C NMR spectra of the (poly)amine complexes of 1- 6Li revealed that the chemical shifts of the para phenyl carbon C-5, the para phenyl proton H-5, the benzylic carbon C-1, and the proton-carbon coupling constant J(C-1,H-1) are proportional to each other. These NMR spectroscopic parameters can be used as probes for the charge distribution within the carbanionic moieties of 1- 6Li in the respective complexes, which is especially useful for a classification to CIPs and/or SIPs.
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