Mono- and dinuclear complexes of chiral tri- and tetradentate Schiff-base ligands derived from 1,1′-binaphthyl-2,2′-diamine

The synthesis and characterization of the bis(bidentate) Schiff-base ligand [(R)-2] formed by the condensation reaction of (R)-1,1'-binaphthyl-2,2'-diamine [(R)-BINAM] with pyridine-2-carboxaldehyde is presented. The coordination chemistry of (R)-2 with Ni(ClO4)(2)(.)6H(2)O, Co(ClO4)(2)(.)6H(2)O, CuCl2, and CuSO4 has been investigated. Reaction of (R)-2 with the first two metal salts leads to complexes of the type [M((R)-4)(2)](ClO4)(2) (M = Ni-II, Co-II), where (R)-4 is a tridentate ligand resulting from the hydrolytic cleavage of one of the pyridyl groups from (R)-2. Both complexes were characterized by X-ray crystallography, which showed that the A absolute configuration of the metal center is favored in both cases. H-1 NMR spectroscopy suggests that the high diastereoselectivity of Lambda-[Co((R)-4)(2)](ClO4)(2) is maintained in solution. The reaction of (R)-2 with CuCl2 leads to the dinuclear complex [Cu-2((R)-2)Cl-4], which has a [Cu-2(mu(2)-Cl-2)] core. The reaction of CuSO4 with (R)-2 gives a dimeric complex, {Cu((R)-4)SO4}(2), which features a [Cu-2(mu(2)-(SO4)(2))] core. This complex can be prepared directly by the reaction of (R)-BINAM with pyridine-2-carboxaldehyde and CuSO4. The use of rac-BINAM in this synthetic procedure leads to the heterochiral dimer [Cu-2((R)-4)((S)-4)(SO4)(2)]; that is, the ligands undergo a self-sorting (self/nonself discrimination) process based on chirality. The reaction of rac-BINAM, pyridine-2-carboxaldehyde, and Co(ClO4)(2)(.)6H(2)O proceeds via a homochiral self-sorting pathway to produce a racemic mixture of [Co((R)-4)(2)](2+) and [Co((S)-4)(2)](2+). The variable-temperature magnetic susceptibilities of the bimetallic complexes [Cu-2((R)-2)Cl-4], [Cu((R)-4)(mu(2)-SO4)](2), and [Cu-2((R)-4)((S)-4)(mu(2)-SO4)(2)] all show weak antiferromagnetic coupling with J = -1.0, -0.40, and -0.67 cm(-1), respectively.