Synthesis and hydrolysis of cis-octahedral nickel(II) complexes with C-racemic tetraaza macrocycles bearing two imidate ester pendant arms

Two di-N-functionalized macrocyclic complexes, [Ni(C-racemic-L-3)](2+) bearing two N-CH2CH2 C(=NH)OCH3 pendant arms and [Ni(C-racemic-L-8)](2+) bearing two N-CH2C(=NH)OCH3 pendant arms, have been prepared by the reaction of methanol with [Ni(C-racemic-L-2)(OAc)](+) (L-2 = 1,8-bis(N-cyanoethyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) or [Ni(C-racemic-L-7)(OAc)](+) (L-7 = 1,8-bis(N-cyanomethyl)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Both complexes have somewhat distorted cis-octahedral coordination geometry. Their hydrolysis has been investigated under various experimental conditions. The complex [Ni(C-racemic-L-3)](2+) is hydrolyzed to [Ni(C-racemic-L-4)](2+) bearing two N-CH2CH2COOCH3 groups in acidic aqueous solutions (pH <= 6), but to [Ni(C-racemic-L-5)](2+) bearing two N-(CH2)(2)CONH2 pendant arms in basic aqueous solutions (pH >= 9). Very interestingly, two N-(CH2)(2)C(=NH) OMe groups in [Ni(C-racemic-L-3)](2+) undergo different reactions at pH 7 to yield [Ni(C-racemic-L-6)](2+) bearing one N-(CH2)(2)CONH2 and one N-(CH2)(2)CN pendant arms. Although the N-CH2C(=NH)OCH3 groups in [Ni(C-racemic-L-8)](2+) undergo hydrolysis to form [Ni(C-racemic-L-9)](2+) bearing two N-CH2CONH2 pendant arms in basic aqueous solutions (pH >= 9), they are quite inert against hydrolysis in neutral and acidic aqueous solutions (pH <= 7). (C) 2012 Elsevier B. V. All rights reserved.