Synthesis and Characterization of New Mono-N-functionalized Tetraaza Macrocyclic Nickel(II) and Copper(II) Complexes

The reaction of bromoacetonitrile with 3,14-dimethyl-2,6,13,17-tetraazatetracyclo[16.4.1^2.6.0^1.18.0^7.12]tricosane (L¹⁰) containing a N-CH₂-N linkage produces 17-cyanomethyl-3,14-dimethyl-2,6,13,17-tetraazatetracyclo- [16.4.1^2.6.0^1.18.0^7.12]tricosane (L¹¹). The mono-N-functionalized macrocyclic complexes [ML²]²⁺ (M = Ni(II) or Cu(II): L² = 2-cyanomethyl-5,16-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0^7.12]docosane) can be prepared by the reaction of L¹¹ with nickel(II) or copper(II) ion in acetonitrile. The N-CH₂CN group attached to [ML²]²⁺ readily reacts with water or methanol to yield the corresponding complexes of HL³ bearing one N-CH₂CONH₂ pendant arm or L⁴ bearing one N-CH₂C(=NH)OCH₃ group. The N-CH₂CONH₂ or N-CH₂C(=NH)OCH₃ group of each complex is coordinated to the central metal ion. Both [NiL⁴(H₂O)]²⁺ and [CuL⁴]²⁺ are quite stable in acidic aqueous solutions, but undergo hydrolysis to yield [Ni(HL³)(H₂O)]²⁺ or [Cu(HL³)]²⁺ in basic aqueous solutions. In contrast to [Cu(HL³)]²⁺, [Ni(HL³) (H₂O)]²⁺ is readily deprotonated to form [NiL³ (H₂O)]⁺ (L³ = a deprotonated form of HL³) in basic aqueous solutions