A modular synthesis of tris(aryl)tren ligands: Synthesis, structure and lithiation chemistry

A modular synthesis of tris(aryl)tren ligands has been demonstrated via the condensation of nitrilotracetyl chloride with different anilines followed by reduction. Varying the aniline in the condensation step from 2-methylthioaniline, to 2-phenylthioaniline, to 2-chloroaniline, generates 2,2′,2″-nitrilotris(N-(2-(methylthio)phenyl)acetamide) (1), 2,2′,2″-nitrilotris(N-(2-(phenylthio)phenyl)acetamide) (2) and 2,2′,2″-nitrilotris(N-(2-chlorophenyl)acetamide) (3) respectively. The 2-chloroaniline synthesis is complicated by the production of N-(2-chlorophenyl)-3,5-dioxo-1-piperazine-N-(2-chlorophenyl)acetamide (4), but can be adjusted to produce only 3. The reduction of complexes 1–3 proceeds with lithium aluminum hydride for 1 and 2 and with borane for 3 to yield the tris(aryl)tren ligands tris-(2-(2-(methylthio)phenylamino)ethyl)amine (5), tris-(2-(2-(phenylthio)phenylamino)ethyl)amine (6), and tris-(2-(2-chlorophenylamino)ethyl)amine (7). All three of these ligands can be deprotonated with tert-butyllithium for 5 and 7, and n-butyllithium for 6 to generate their trilithium complexes, 8, 9 and 10 for 5, 6 and 7 respectively, with 10 forming two different solvates (10a and 10b). All complexes are characterized by 1H and 13C NMR and the solid state structures of complexes 2, 3, 4, 7, 8, 9, 10a and 10b are described.