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)2·6H2O, Co(ClO4)2·6H2O, 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 = NiII, CoII), 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 Λ absolute configuration of the metal center
is favored in both cases. 1H NMR spectroscopy suggests that the high diastereoselectivity of Λ-[Co((R)-4)2](ClO4)2
is maintained in solution. The reaction of (R)-2 with CuCl2 leads to the dinuclear complex [Cu2((R)-2)Cl4], which
has a [Cu2(μ2-Cl2)] core. The reaction of CuSO4 with (R)-2 gives a dimeric complex, {Cu((R)-4)SO4}2, which
features a [Cu2(μ2-(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
[Cu2((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)2·6H2O 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 [Cu2((R)-2)Cl4], [Cu((R)-4)(μ2-SO4)]2, and [Cu2((R)-4)((S)-4)(μ2-SO4)2] all show weak antiferromagnetic coupling with J = −1.0, −0.40, and −0.67 cm-1, respectively.