Synthesis and characterization of bifunctional oligo-α-aminopyridines and their copper(II) complexes

The synthesis of two new bifunctional oligo-α-aminopyridine ligands, N-(6-{6-[3-(6-amino-pyridin-2-ylamino)-phenylamino]-pyridin-2-ylamino}-pyridin-2-yl)-4-methylbenzenesulfonamide (apppm) and N-(6-{6-[3-(6-bromo-pyridin-2-ylamino)-phenylamino-pyridin-2-yl-amino]-pyridin-2-yl)-4-methylbenzenesulfonamide (bpppm), by double aminated couplings and Pd-catalization is presented in this paper. NaNH2 was used as a critical base in the first step of the aminated coupling for synthesizing the key building block N-(6-bromo-pyridin-2-yl)-pyridine-2,6-diamine (bppd) in 96% yield. Pyridine was then used in the second step of the aminated coupling for 4-toluenesulphonyl chloride and bppd. Finally, the monoamination was facilitated by the palladium-catalyzed Buchwaldʹs coupling reaction, and subsequently the corresponding metal complexes of these bifunctional ligands were constructed. The single-crystal X-ray crystallographic data of the complex [Cu(apppm)(ClO4)(H2O)](ClO4)·2THF (1), [Cu(bpppm)](ClO4)2·(H2O)5/3·(CH3CN)1/3 (3), and the related salt [H(appm)](ClO4)·THF (2), were prepared and characterized. In complex 1, Cu(II) coordinates with the three nitrogen atoms of the pyridine rings, with the oxygen atom of the p-toluenesulphonyl group, strongly with the oxygen of the water molecule, and weakly with the oxygen atom of the perchlorate anion, and shows a distorted octahedral geometry. However, in the complex 3, Cu(II) bonds to N(1), N(3), N(5), and N(7) of the ligand bpppm toughly and exhibits a twisted square planar geometry.