5,5″-Disubstituted 2,2′:6′,2″-Terpyridines through and for Metal-Mediated Cross-Coupling Chemistry

Abstract

The 0.3 ± 5 g scale syntheses of the 2,2':6',2''-terpyridines 3, 6, 9, and 10 are described. The pyridine units are connected to one another by Pd-catalyzed crosscoupling reactions. This method allows the easy introduction of halogen, stannyl, and boronic ester functionalities at positions C-5 and C-5''; this results in a novel functionality pattern for terpyridines that considerably widens the applicability of this class of tridentate ligands for supra-and macromolecular applications. The feasibility of growth reactions with these novel terpyridines was demonstrated by the synthesis of compounds 12 a ± c.

A Shape-Persistent Macrocycle With Two Opposing 2,2′:6′,2"-Terpyridine Units

“…Scheme 1 The synthesis of cycle 9 is shown in Schemes 1 to 3. It is constructed from the two symmetrical half-cycles 7 and 8, [1] whose tpy units were obtained using different strategies. Whereas unit 7 was built from the central pyridine 6 and the terminal phenylpyridine 5, the half-cycle 8 was obtained using an already preformed tpy building block from our construction set.…”

“…Whereas unit 7 was built from the central pyridine 6 and the terminal phenylpyridine 5, the half-cycle 8 was obtained using an already preformed tpy building block from our construction set. [1] Changing the coupling functionalities from halo to boronic acid, in the dihalo ''half-cycles'' of type 8 was not feasible. [9] For the synthesis of the terminal phenylpyridine 5, the suitably functionalized benzene derivative 3 was obtained according to the sequence in Scheme 1.…”

“…[1] It utilizes iodobromopyridine 4, which was easily obtained by reacting compound 10 with hydroiodic acid on the 14 g scale. Stille cross-coupling of 11 with 6 gave 12 in a yield of 50%.…”

“…Purification by preparative GPC gave 9 (132 mg, 20.5%) as a white solid. 1 5-Bromo-2-iodopyridine (11): 2,5-Dibromopyridine 10 (14.4 g, 60.8 mmol) in 67% HI (48 mL) was heated at 100°C for 12 h, and then at 170°C for 4 h. After cooling to room temp. the mixture was poured into 40% NaOH (50 mL) and ice, and extracted with Et 2 O (2 ϫ 100 mL).…”

“…Parallel to this work we have been investigating related cycles with terpyridine (tpy) units located at a hexagonЈs corners. [1,4] Here the chelating moiety can only lead to endo complexation. The present contribution describes the synthesis of a macrocycle that has two opposing tpy units, and is decorated with four flexible chains for solubility reasons.…”