Synthesis, crystal structures, and deprotonation of cis- and trans-octahedral nickel(II) complexes with a 14-membered tetraaza macrocycle bearing two N-phenacyl pendant arms

摘要

The di-N-functionalized macrocycle 2,13-bis(2-phenacyl)-5,16-dimethyl-2,6, 13,17-tetraazatricyclo[16.4.0. ~(1.18)0 ~(7.12)]docosane (H _2L ~2) bearing two N-CH _2COC _6H _5 groups has been prepared by the reaction of 3,14-dimethyl-2,6,13, 17-tetraazatricyclo[16.4.0.0 ~(7.12)]docosane (L ~1) with phenacyl bromide. Interestingly, H _2L ~2 reacts with Ni ~(2+) ion to form two geometric isomers, trans-[Ni(H _2L ~2)] ~(2+) and cis-[Ni(H _2L _2)] ~(2+). The axial Ni-O (N-CH _2COC _6H _5 group) bond distance (2.080(2)) of trans-[Ni(H _2L ~2)] (ClO _4) _2·2DMSO is shorter than the in-plane Ni-N distances (2.096(2) and 2.100(2)). However, the Ni-O distances (2.105(2) and 2.124(2)) of cis-[Ni(H _2L ~2)](ClO _4) _2·H _2O are considerably longer than the Ni-N distances (2.053(2)-2.086(2)). Each N-CH _2COC _6H _5 group of trans-[Ni(H _2L ~2)] ~(2+) and cis-[Ni(H _2L ~2)] ~(2+) exists as its keto form in the solid state and in various solvents. Two N-CH _2COC _6H _5 groups of trans-[Ni(H _2L ~2)] ~(2+) are readily deprotonated in basic aqueous solutions, producing the enolate form trans-[Ni(L ~2)]. On the other hand, cis-[Ni(H _2L ~2)] ~(2+) undergoes deprotonation to yield cis-[Ni(HL _2)] ~+, in which one N-CH _2COC _6H _5 group is not deprotonated, under similar conditions.