A series of new ligands with three pyridines linked into a macrocycle by various CH2, CMe2, and CH2CH2 groups at all sites ortho to the pyridine nitrogen have been synthesized and attached to PdCl2 or PtMe2. The ligands bind to them through only two nitrogens, and the third pyridine is constrained in close proximity to the planar complex with a filled d(z2) orbital. Rapid reversible migration of PdCl2 or PtMe2 to the unused pyridine nitrogen is observed at 20 degreesC in the case of the CH2-bridged macrocycle and does not occur in the case of the CMe2-bridged analogue, and the mechanism of this fluxionality has been established by NMR and computational techniques.