Magnesium and zinc complexes of the monoanionic ligands N,N'-bis(2,6-di-isopropylphenyl)triazenide, L-1, N,N'-bis(2,6-di-isopropylphenyl)acetamidin ate, L-2, and N,N'-bis(2,6-di-isopropylphenyl)tert-butylamidinate, L-3, have been synthesized, but only L-3 possesses sufficient steric bulk to prevent bis-chelation. Hence, the reaction of (LH)-H-1 with excess ZnEt2 leads to the isolation of (L-1)(2)Zn, 1; (LH)-H-1 also reacts with BU2Mg in Et2O to afford (L-1)(2)Mg(Et2O), 2. Similar reactivity is observed for (LH)-H-2, leading to the formation of (L-2)(2)Zn, 3, and (L-2)(2)Mg, 4. The reaction of (LH)-H-2 with ZnR2 may also afford the tetranuclear aggregates {(L-2)Zn2R2}(2)O, 5 (R = Me) and 6 (R = Et). By contrast, the tert-butylamidinate ligand was found to exclusively promote mono-chelation, allowing (L-3)ZnCl(THF), 7, [(L-3)Zn(mu-Cl)](2), 8, (L-3)ZnN(SiMe3)(2), 9, (L-3)(MgPr)-Pr-i(Et2O), 10, and (L-3)(MgPr)-Pr-i(THF), 11, to be isolated. X-ray crystallographic analyses of 1, 2, 3, 4, 5, 6, 8, and 10 indicate that the capacity of L-3 to resist bis-chelation is due to greater occupation of the metal coordination sphere by the N-aryl substituents.