Structural investigations of aryllithium clusters in solution II. A. 13C and 7Li NMR study of substituted phenyllithium compounds containing ortho-directing NME 2 and CH 2NMe 2 groups

Abstract

7Li and 13C NMR spectroscopic studies have been made on the behaviour of several aryllithium compounds containing a N, N-dimethylamino substituent suitably positioned for intramolecular coordination to lithium in the presence of accurately known quantities of coordinating solvents (diethyl ether, THF) and ligand (TMEDA). The solvent molecules compete with the internal nitrogen coordination, and if their donor strength is sufficient and the steric situation is favourable they can fully replace intramolecular N-coordination. In the presence of more than one equivalent of the solvent, the aryllithium cluster can be broken down to afford solvent coordinated dimeric species. This change is reflected in an upfield shift of ca. 10 ppm for the 13C NMR C- ipso signal, with a concomitant change of 1 J( 7Li, 13C) from ca. 11 to 20 Hz, and by an upfield shift of the 7Li NMR signal by ca. 1 ppm.