Shape‐Complementary Dimers of Simple Mononuclear Cobalt(III) Complexes Formed Through Eightfold Hydrogen Bonding

ABSTRACT Here we report the synthesis and dimerization behavior of a series of mononuclear cobalt(III) saloph complexes [LCoA 2 ](OTf) bearing primary amines (A) as axial ligands. Complexes ( 1–5 ) incorporating the 3‐MeOsaloph ligand and the corresponding methoxy‐free analogue ( 6 ) were prepared to clarify the roles of the axial amines (A) and the methoxy substituents in dimer formation. The 1 H NMR spectra exhibited clear concentration‐dependent changes, indicating reversible dimerization in solution. Quantitative analysis showed that both the stability of the dimers ( K dim ) and the monomer–dimer exchange kinetics ( k a , k d ) depend strongly on the nature of the coordinated primary amine ligands. Comparison of the methoxy‐substituted complexes and the corresponding methoxy‐free analogue further demonstrated an important contribution of the methoxy groups to dimer stability. X‐ray crystallography revealed that, despite their different solution behaviors, all complexes adopt similar hydrogen‐bonded dimeric structures in the crystalline state. In the dimers of the 3‐MeOsaloph complexes ( 1–5 ), two mononuclear units are arranged in a slipped, parallel fashion and are held together by eight complementary N─H···O hydrogen bonds involving both phenoxo and methoxy oxygen atoms. The combination of the 3‐MeOsaloph framework and axial primary amine ligands provide a modular platform for constructing shape‐complementary hydrogen‐bonded dimers of mononuclear metal complexes with tunable thermodynamic and kinetic properties.