Pyridine-derived tetrapodal ligands with NO4 and NN4 donor sets

摘要

The Mg2+ assisted synthesis of a pyridine-derived tetraalcohol ligand with an NO4 donor set is described. 2,6-Diethylpyridine reacts cleanly with aqueous formaldehyde solution in the presence of 1 equivalent of MgSO4 hydrate in a pressurised vessel to give the quadruply hydroxymethylated product 2,6-C5H3N[CMe(CH2OH)(2)](2) (1) as a crystalline solid. Two alkali/alkaline earth metal perchlorate adducts of 1 have been structurally characterised, viz. [(1)2 . LiClO4] (6) and [(1)(2) . Ba(ClO4)(2)] (7). The ligand adopts a bridging coordination mode in both 6 (distorted tetrahedral coordination of Li+) and 7 (square prismatic coordination of Ba2+). The further derivatization of 1 leads to the tetratosylate (2) and the tetraazide (3), both of which have been obtained in pure form for the first time. Reduction of 3 gives the pentaamine ligand 2,6-C5H3N[CMe(CH2NH2)(2)](2) (4), isolated as the tetrakis(hydrobromide) salt 4 . 4 HBr. The presence of four ammonio substituents and an unprotonated pyridine nitrogen atom in the solid state has been unequivocally established by an X-ray structural analysis. [References: 46]