4,4″-Disubstituted Terpyridines and Their Homoleptic FeII Complexes

A novel synthetic route to 4,4″-disubstituted-2,2′:6′,2″-terpyridine ligands by Suzuki–Miyaura cross-coupling was elaborated by synthesizing compounds 4a–5c. The considerable stability of 4-substituted lithium triisopropyl 2-pyridylborates 2a–c, which are less prone to protodeboronation than similarly functionalized neutral boronic acid derivatives, enabled this synthetic route. The terpyridine core structure was further functionalized by exposing 4,4″-dichloroterpyridine (4b) to Suzuki coupling conditions to yield 4,4″-diarylterpyridines 5a–c. Homoleptic FeII complexes 8a–f of the reported terpyridine ligands were formed quantitatively, which demonstrates the lack of steric repulsion of substituents at the 4- and 4″-positions during complexation. The solid-state structures of particular ligands and FeII complexes were analyzed by single-crystal X-ray crystallography. UV/Vis absorption data for the FeII complexes are also provided to complement the results reported here.