The ring-chain tautomerism of a 2-aryl-1,2,3,4-tetrahydroquinazo-line has been exploited to induce reversible changes in the aminal-imine equilibrium, as desired, by coordination of a suitable metal ion. This process was studied by NMR and UV-vis spectroscopies, X-ray crystallography, and molecular modeling approach. The results obtained show that the imine H2Li undergoes a selective ring-closing reaction upon complexation with Ni2+. As a result, complexes of the type Ni(HLa)(2) are obtained, whose chirality arises from the chiral ligand H2La and the helicity of the structure. Hence, helical enantiomers form the following racemates: [Delta-C(R,R)N(S,S),Lambda-C(S,S)N(R,R)]-Ni(HLa)(2)center dot 2HOAc and [Delta,Lambda-C(S,R)N(R,S)]-Ni(HLa)(2)center dot 4MeOH. In contrast to the situation observed for Ni2+, the cyclic tautomer of the ligand, H2La, undergoes a selective ring-opening reaction upon complex formation with Pd2+, ultimately yielding Pd(HLi)(2)center dot MeOH, in which the open-chain imine ligand is bidentate through the N,O donor set of the quinoline residue. Density functional theory calculations were conducted to provide insight into the different behavior of both coordinated metals (Ni2+ and Pd2+) and to propose a mechanism for the metal-assisted opening/closing reaction of the tetrahydroquinazoline ring.