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

Abstract

The reaction of bromoacetonitrile with 3,14-dimethyl-2,6,13,17-tetraazatetracyclo[<TEX>$16.4.1^{2.6}.0^{1.18}.0^{7.12}$</TEX>]tricosane (<TEX>$L^{10}$</TEX>) containing a N-<TEX>$CH_2$</TEX>-N linkage produces 17-cyanomethyl-3,14-dimethyl-2,6,13,17-tetraazatetracyclo-[<TEX>$16.4.1^{2.6}.0^{1.18}.0^{7.12}$</TEX>]tricosane (<TEX>$L^{11}$</TEX>). The mono-N-functionalized macrocyclic complexes <TEX>$[ML^2]^{2+}$</TEX> (M = Ni(II) or Cu(II); <TEX>$L^2$</TEX> = 2-cyanomethyl-5,16-dimethyl-2,6,13,17-tetraazatricyclo[<TEX>$16.4.0.0^{7.12}$</TEX>]docosane) can be prepared by the reaction of <TEX>$L^{11}$</TEX> with nickel(II) or copper(II) ion in acetonitrile. The N-<TEX>$CH_2CN$</TEX> group attached to <TEX>$[ML^2]^{2+}$</TEX> readily reacts with water or methanol to yield the corresponding complexes of <TEX>$HL^3$</TEX> bearing one N-<TEX>$CH_2CONH_2$</TEX> pendant arm or <TEX>$L^4$</TEX> bearing one <TEX>$N-CH_2C(=NH)OCH_3$</TEX> group. The <TEX>$N-CH_2CONH_2$</TEX> or <TEX>$N-CH_2C(=NH)OCH_3$</TEX> group of each complex is coordinated to the central metal ion. Both <TEX>$[NiL^4(H_2O)]^{2+}$</TEX> and <TEX>$[CuL^4]^{2+}$</TEX> are quite stable in acidic aqueous solutions, but undergo hydrolysis to yield <TEX>$[Ni(HL^3)(H_2O)]^{2+}$</TEX> or <TEX>$[Cu(HL^3)]^{2+}$</TEX> in basic aqueous solutions. In contrast to <TEX>$[Cu(HL^3)]^{2+}$</TEX>, <TEX>$[Ni(HL^3) (H_2O)]^{2+}$</TEX> is readily deprotonated to form <TEX>$[NiL^3 (H_2O)]^+$</TEX> (<TEX>$L^3$</TEX> = a deprotonated form of <TEX>$HL^3$</TEX>) in basic aqueous solutions.