Backbone structure pyridine ligands

The piperidone precursor of 57 (see Chart 6) is a possible starting material for the synthesis of 2,6-substituted chiral, tetradentate bispidine ligands. The copper(II) complex of 57 is chiral [see Fig. 2(d) for a plot of the experimental structure] and has an interesting set of bond distances. Quite unexpectedly on the basis of the chelate ring sizes, the 2-pyridine substituent of the bispidine backbone is the axial donor (2.25 A), while N3 (2.08 A), N7 (2.05 A), the N7-pendant pyridine (2.01 A) and the chloride (2.28 A) are the in-plane donors (80). 

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