Design and Synthesis of Tridentate Facially Chelating Ligands of the [2.<i>n</i>.1]-(2,6)-Pyridinophane Family

Syntheses are reported for tripyridine macrocycles 2 and 3 and some of their alkyl derivatives. The macrocycles are designed to stabilize to various extents coordinated d8 metal precursors and d6 alkane oxidative addition products (PtIV), therefore allowing favorable kinetics and thermodynamics of (e.g., PtII) the cleavage of substrate H−C(sp3) bonds. Both the Chichibabin protocol and oxidative coupling of carbanions by copper(I) iodide were used for the macrocyclization step. Crystal structures of singly and doubly protonated 2 establish atom connectivity in the macrocycle, and reveal structural features which are obscured in solution NMR by rapid proton migration.