Structural investigations of aryllithium clusters in solution II. A. ¹³C and ⁷Li NMR study of substituted phenyllithium compounds containing ortho-directing NME₂ and CH₂NMe₂ groups

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 ¹J(⁷Li,¹³C) from ca. 11 to 20 Hz, and by an upfield shift of the ⁷Li NMR signal by ca. 1 ppm.