4,4’- and 6,6’-substituted bipyridines
2,2’-Bipyridine and its substituted analogues, such as our extensive range shown in Scheme 1, are of significant interest in coordination chemistry, due to their ability to act as bidentate chelating ligands, forming complexes with a range of transition metals.
1,2
Scheme 1
The broad interest in the chelating properties of bipyridines has its origins in the pioneering work of Blau, who prepared 2,2’-bipyridine (bpy) and described the first transition metal complex of the ligand in 1888.
3
The ligands find frequent use in catalytic organic synthesis. For example, 4,4'-di-
tert-butyl-2,2'-bipyridine (dtbpy, product code FD07160) is used as a ligand in combination with the iridium catalyst bis(η
4-1,5-cyclooctadiene)-di-μ-methoxy-diiridium [Ir(OMe)(COD)]
2 for the C-H borylation of arenes and heteroarenes, Scheme 2.
4 This catalytic C-H borylation, first described by Smith in 1999,
5 provides a useful alternative to the traditional methods of forming aryl- and heteroaryl-boron derivatives; reaction of trialkylborates with magnesium or lithium reagents, or Pd-catalysed cross-coupling of halides with di(alkoxo)boranes.
Scheme 2
2,2’-Bipyridine-6,6’-dicarboxylic acid is used as a starting material for the synthesis of the chiral bipyridine ligand bis(oxazolinyl)bipyridine, also known as bipymox (
1), Scheme 3.
6
Scheme 3
After pre-formation of a rhodium-bipymox catalyst {RhCl
3(bipymox)}, the system can be used for the asymmetric hydrosilylation of ketones with high enantioselectivity, as shown in Scheme 4 for the reduction of acetophenone.
6
Scheme 4
Since the late 1970’s there has been a significant increase in research into the properties of substituted bipyridines, much of which has been stimulated by interest in the Ru(bpy)
32+ cation, which has useful and intriguing redox and photocatalytic properties, an area which can been extensively reviewed.
7. Substitution within the pyridine rings can have a profound modifying effect on physical and chemical properties, such as the stability, redox potentials and colour intensities of transition metal complexes containing the ligands. The 4,4’-disubstitution pattern is particularly useful for moderating properties, as it does not present a steric complication upon chelation of the metal.
8
In addition to their roles in coordination chemistry and organic synthesis, substituted 2,2’-bipyridines have diverse roles in fields such as supramolecular chemistry, non-linear optical materials, artificial photosynthesis systems, solar cells and luminescent sensor materials.
9-13
References:
1. Constable, E. C.; Steel, P. J.
Coord. Chem. Rev.
1989,
93, 205.
2. Kaes, C.; Katz, A.; Hosseini, M. W.
Chem. Rev.
2000,
100, 3553.
3. Blau, F.
Ber. Dtsch. Chem. Ges. 1888,
27, 1077.
4. Ishiyama, T.; Takagi, J.; Nobuta, Y.; Miyaura, N.
Org. Synth.
2005,
82, 126.
5. Iverson, C. N.; Smith, M. R., III.
J. Am. Chem. Soc. 1999,
121, 7696.
6. Nishiyama, H.; Yamaguchi, S.; Park, S.-B.; Itoh, K.
Tetrahedron: Asymmetry 1993,
4, 143.
7. Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.; van Zelewsky, A.
Coord. Chem. Rev.
1988,
84, 85.
8. Kavanagh, P.; Leech, D.
Tetrahedron Lett. 2004,
45, 121.
9. Tamminen, J. T.; Kolehmainen, E. T.; Haapala, M. H.; Salo, H. T.; Linnanto, J. M.
Arkivoc 2000, 80.
10. Sun, X.; Yang, Y.-K.; Lu, F.
Macromol. Chem. Phys.
1997,
198, 833.
11. Fujihara, T.; Kobayashi, A.; Iwai, M.; Nagasawa, A.
Acta Crystallogr., Sect. E 2004,
60, m1172.
12. Sengul, A.; Arslan, H.
Turk. J. Chem.
2008, 32, 355.
13. Altuna-Urquijo, M. et al
Tetrahedron 2009, 65, and references therein.