Structure of a Reduced Nickel(II) Tetradentate Macrocycle

THE Ni(II) complex of the macrocycle ligand I (CR) can be reduced catalytically with hydrogen to the system shown in II (reduced ligand, CRH)1. We were interested in determining the structure of this reduced nickel macrocycle because of the various possible isomers that can exist for the reduced macrocycle. The isomers originate from both the positions of the methyl groups arid the positions of the three hydrogens of the NH system. The various isomers are stable species because the lone pairs of the nitrogen atoms are used in bonding with the nickel atom. The fourteen possible geometric isomers of Ni(CRH)2+ are schematically shown in Fig. 1.