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.