Macrocycles Having Two cis-1,2-Diaminocyclohexane Subunits: Crystal Structure and Coordination Behaviors of the Saturated Complex

There has been considerable interest in the preparation of various types of C- and/or N-configurational isomers of polyaza macrocyclic complexes.1-11 In particular, 14-membered macrocyclic complexes having one or two 1,2-diamino-cyclohexane subunit(s) theoretically occur as various C-configurational isomers because the diaminocyclohexane subunit exists as either cis- or trans-isomer. Although both [Ni(3t)](ClO4)2 and [Ni(3c)](ClO4)2 have a square-planar coordination geometry, reports indicate tat their chemical properties and stereochemistry vary with the isomeric structure of the 1,2-diaminocyclohexane subunit (Chart 1).8 Furthermore, the chemical properties of [Ni(4s)]2+ are differ-ent from those of [Ni(4a)]2+, even though both of them contain cis-1,2-diaminocyclohexane subunits.10 C-methylat-ed complexes, [Ni(1t)]2+ and [Ni(2t)]2+, containing two trans-1,2-diaminocyclohexane subunits have been also reported.11-13 However, relatively few isomers of such compounds have been prepared,7-13 and discussions of their chemical proper-ties are not sufficient.8-10 To gain further insight into the chemistry of such macro-cyclic compounds, we prepared the nickel(II) complexes of 1c and 2c, having two cis-1,2-diaminocyclohexane subunits. It was found that the axial coordination of a solvent mole-cule, such as MeCN or DMF, is much easier to [Ni(2c)]2+ than to [Ni(2t)]2+. The coordination behavior of [Ni(2c)]2+ is also considerably different from that of [Ni(3c)]2+. To investigate the differences, the crystal structure of [Ni(2c)] (ClO4)2 was determined. The structure and chemical proper-ties of [Ni(2c)](ClO4)2 were compared with those of [Ni(2t)]2+, [Ni(3c)]2+, and other related nickel(II) complexes