The novel tridentate azaoxa macrocycle [O(NH)(2)], 3,3-dimethyl-1,5-diaza-8-oxacyclodecane, can be singly or doubly lithiated with (BuLi)-Bu-n at the secondary amine N atoms, giving [O(NH)N]Li and [O(N)(2)]Li-2, respectively, and further elaborated with introduction of TMS substituents via reaction with (TMS) Cl. Aminolysis of [Ti(NMe2)(2)Cl-2] or [Zr(NR2)(2)Cl-2(THF)(2)] with [O(NH)(2)] in toluene gave the distorted octahedral M[O(NH) N](NR2) Cl-2 (M) Ti, R) Me; M) Zr, R) Me or Et), in which the macrocycle functions as a monoanionic ligand via an amido, an amine, and an ether functionality. Salt metathesis of [Zr(NEt2)(2)Cl-2(THF)(2)] with [O(NH)N] Li in toluene afforded Zr[(O(NH) N)](NEt2)(2)Cl, the structure of which also confirms tridentate macrocycle coordination via one amido, one amine, and one ether group; in contrast, analogous salt metathesis involving [Zr(NEt2)(2)Cl-2(THF)(2)] and [O(N)(2)Li-2] gave the "sandwich" complex [(ON2)(2)Zr], with the macrocycle behaving as a dianionic ligand (Porter, R. M.; et al. Dalton Trans. 2005, 427). Finally, treatment of [O(NH)(2)] with AlMe3 gave the simple donor-acceptor adduct [O(NH)(2)]AlMe3, which resisted alkanolysis by prolonged heating. In the presence of MAO the new zirconium, titanium, and aluminum complexes show low activity in the polymerization of ethylene.