STEREOISOMERS OF A MACROCYCLIC NICKEL(2) COMPLEX CONTAINING 6 ASYMMETRIC CENTERS . FACTORS DETERMINING STABILITIES OF CONFIGURATIONS AND CONFIGURATIONS AND CONFORMATIONS

The complex ion Ni(1,7-CTH)2+ (structure I) can exist in 20 theoretically possible isomeric forms, depending on the configurations of the two asymmetric carbon centers and the four asymmetric nitrogen centers. Three isomers have been characterized. Thorough stereochemical analysis combined with pmr and infrared spectral data permit assignments of structures to these species. From the structures that exist and the analysis presented, it may be inferred that (a) the stabilities of the definable conformations for six-membered chelate rings vary in the sequence chair > twist > boat; (b) when either of two linked five-membered and six-membered chelate rings must exist in an unfavorable conformation in order for the other to exist in a favorable conformation, the six-membered ring will have the stable form; and (c) the selection of the equatorial over the axial site for such bulky groups as CH3 is at least as large for six-membered chelate rings as for five-membered chelate rings. © 1969, American Chemical Society. All rights reserved.