Abstract
A three-step synthetic route giving access to nonsymmetrical bisazolyl 2,4,6-trisubstituted pyridines with different substituents on the pyrazole, indazole, and pyridine heterocycles is described. From the readily available 4-bromo-2,6-difluoropyridine, both fluorine atoms allow for easy selective stepwise substitution, and the bromine atom provides easy access to additional functionalities through both Suzuki and Sonogashira Pd(0) cross-coupling reactions. These synthons represent optimal structures as building blocks in complexation and metalloorganic structures for the tuning of their chelating and photophysical properties.
Highlights
Galán-Fernández, L.; Martínez-Poly-N-heterocyclic frameworks with extended electronic delocalization have been traditionally used as effective and stable ligands for the complexation of transition metal ions.These metal ion complexes, in particular polypyridine ligands such as 2,20 :6,200 -terpyridine [1–3], have been used in the design of luminescent devices or as sensitizers for light-to-electricity conversion due to their rich photophysical, photochemical [4–6], and electrochemical properties [7].The use of 2,20 :60,200 -terpyridines in a wide range of applications and in a variety of research areas has created a sizeable “pool” of different functionalized terpyridines
Combination with side-by-side azole rings such as pyrazole, indazole, oxazole, triazole, and tetrazole, and flanking to pyridine rings is of great interest [9,10]
Based on the pioneering work of Schlosser regarding the reactivity of polyfluoropyridines [24–26], the 4-bromo-2,6-difluoropyridine molecule has been described as a good alternative for accessing 2,6-dipyrazole and 2,6-diindazolepyridine derivatives [13,14,27]
Summary
Galán-Fernández, L.; Martínez-Poly-N-heterocyclic frameworks with extended electronic delocalization have been traditionally used as effective and stable ligands for the complexation of transition metal ions.These metal ion complexes, in particular polypyridine ligands such as 2,20 :6,200 -terpyridine (tpy) [1–3], have been used in the design of luminescent devices or as sensitizers for light-to-electricity conversion due to their rich photophysical, photochemical [4–6], and electrochemical properties [7].The use of 2,20 :60 ,200 -terpyridines in a wide range of applications and in a variety of research areas has created a sizeable “pool” of different functionalized terpyridines. Poly-N-heterocyclic frameworks with extended electronic delocalization have been traditionally used as effective and stable ligands for the complexation of transition metal ions. These metal ion complexes, in particular polypyridine ligands such as 2,20 :6,200 -terpyridine (tpy) [1–3], have been used in the design of luminescent devices or as sensitizers for light-to-electricity conversion due to their rich photophysical, photochemical [4–6], and electrochemical properties [7]. While the number of publications concerning applications with terpyridine complexes has increased enormously, comparably the number of reported functionalized 2,20 :60 ,200 -terpyridine derivatives is much lower [1,8], as many of the synthetic methods involve ring assembly reactions, which shorten and hinder access to these interesting tridentate pincer ligands. The compound 2,6-bis(pyrazol-1-yl)pyridine (bppy) has been used as a versatile analogue to the 2,20 :60 ,200 -terpyridine
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