The coordination chemistry of macrocyclic diamides. Transition metal complexes of 5,7-dioxo-1,4,8,11-tetraazacyclotetradecane

Summary A convenient preparation of the 14-membered macrocyclic diamide 5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (LH₂) is described. The pK _NH ⁺ values of the ligand are pK₁ = 5.76 and pK₂ = 9.63 at 25° and I = 0.1 mol dm^–3 (KNO₃). With metal ions able to ionise amide hydrogens, the ligand acts as a planar quadridentate, L^2–. Thus copper(II) and nickel(II) give the neutral complexes ML, and conductivity measurements confirm that they are nonelectrolytes in aqueous solution. Both the nickel(II) and copper(II) complexes are acid labile unlike the analogues of 1,4,8,11-tetraazacyclotetradecane (cyclam).The cobalt(III) complex CoL(NH₃)₂]Cl has been characterised and¹H n.m.r. measurements established the N-meso stereochemistry at the chiral nitrogen centres.