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

Abstract

}7{Li and }1{}3{C 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 }1{}3{C NMR C-ipso signal, with a concomitant change of }1{J(}7{Li,}1{}3{C) from ca. 11 to 20 Hz, and by an upfield shift of the }7{Li NMR signal by ca. 1 ppm.