2,2'-Bipyridine

2,2'-Bipyridine

Names
IUPAC name 2,2′-Bipyridine
Other names Bipyridyl Dipyridyl Bipy Bpy Dipy
Identifiers
CAS Number	366-18-7
ChEBI	CHEBI:30351
ChEMBL	ChEMBL39879
ChemSpider	13867714
Jmol interactive 3D	Image
RTECS number	DW1750000
UNII	551W113ZEP
InChI InChI=1S/C10H8N2/c1-3-7-11-9(5-1)10-6-2-4-8-12-10/h1-8H Key: ROFVEXUMMXZLPA-UHFFFAOYSA-N InChI=1/C10H8N2/c1-3-7-11-9(5-1)10-6-2-4-8-12-10/h1-8H Key: ROFVEXUMMXZLPA-UHFFFAOYAP
SMILES c1ccnc(c1)c2ccccn2
Properties
Chemical formula	C10H8N2
Molar mass	156.19 g·mol^−1
Melting point	70 to 73 °C (158 to 163 °F; 343 to 346 K)
Boiling point	273 °C (523 °F; 546 K)
Structure
Dipole moment	0 D
Hazards
Main hazards	toxic
R-phrases	25
S-phrases	36/37-45
Related compounds
Related compounds	4,4′-Bipyridine Pyridine Phenanthroline 3-Pyridylnicotinamide Terpyridine Biphenyl
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

2,2′-Bipyridine (bipy or bpy, pronounced /ˈbɪpiː/) is an organic compound with the formula (C₁₀H₈N₂). This colorless solid is an important isomer of the bipyridine family. It is a bidentate chelating ligand, forming complexes with many transition metals. Ruthenium complex and platinum complexes of bipy exhibit intense luminescence, which may have practical applications.

Preparation and general properties

It is prepared by the dehydrogenation of pyridine using Raney nickel:^[1]

2C₅H₅N → (C₅H₄N)₂ + H₂

Although uncoordinated bipyridine is often drawn with its nitrogen atoms in cis conformation, the lowest energy conformation both in solid state and in solution is in fact coplanar, with nitrogen atoms in trans position.^[2] Protonated bipyridine adopts a cis conformation.^[3] Upon binding to metal ions the related N,N-heterocyclic ligand phenanthroline does not incur an enthalpic and entropic penalty, and thus its complexes tend to be more stable.

Reflecting the popularity of this ligand design, many substituted variants of bipy have been described.^[4][5]

Coordination chemistry

Illustrative complexes

• Mo(CO)₄(bipy), derived from Mo(CO)₆.
• RuCl₂(bipy)₂,^[6] a useful precursor to mixed ligand complexes.
• [Ru(bipy)₃]Cl₂, a well known luminophore.
• [Fe(bipy)₃]²⁺ is used for the colorimetric analysis of iron ions.

Tris-bipy complexes

Bipyridine complexes absorb intensely in the visible part of the spectrum. The electronic transitions are attributed to metal-to-ligand charge transfer (MLCT). In the "tris(bipy) complexes" three bipyridine molecules coordinate to a metal ion, written as [M(bipy)₃]ⁿ⁺ (M = metal ion; Cr, Fe, Co, Ru, Rh and so on; bipy = 2,2′-bipyridine). These complexes have six-coordinated, octahedral structures and two enantiomers as follows:

Three-dimensional view of the [Fe(bipy)₃]²⁺ complex.

These and other homoleptic tris-2,2′-bipy complexes of many transition metals are electroactive. Often, both the metal centred and ligand centred electrochemical reactions are reversible one-electron reactions that can be observed by cyclic voltammetry. Under strongly reducing conditions, most tris(bipy) complexes can be reduced to neutral derivatives containing bipy⁻ ligands. Examples include M(bipy)₃, where M = Al, Cr, Si.

References

1. Sasse, W. H. F. (1966). "2,2′-Bipyridine". Org. Synth. 46: 5.; Coll. Vol. 5, p. 102
2. Merritt, L. L.; Schroeder, E. (1956). "The Crystal Structure of 2,2′-Bipyridine". Acta Crystallographica 9 (10): 801–804. doi:10.1107/S0365110X56002175.
3. Göller, A.; Grummt, U.-W. (2000). "Torsional barriers in biphenyl, 2,2′-bipyridine and 2-phenylpyridine". Chemical Physics Letters 321 (5–6): 399–405. doi:10.1016/S0009-2614(00)00352-3.
4. Smith, A. P.; Lamba, J. J. S.; Fraser, C. L. (2002). "Efficient Synthesis of Halomethyl-2,2′-Bipyridines: 4,4′-Bis(chloromethyl)-2,2′-Bipyridine". Org. Synth. 78: 82.; Coll. Vol. 10, p. 107
5. Smith, A. P.; Savage, S. A.; Love, J.; Fraser, C. L. (2002). "Synthesis of 4-, 5-, and 6-Methyl-2,2′-Bipyridine by a Negishi Cross-Coupling Strategy". Org. Synth. 78: 51.; Coll. Vol. 10, p. 517
6. Lay, P. A.; Sargeson, A. M.; Taube, H.; Chou, M. H.; Creutz, C. (1986). "Cis-Bis(2,2′-Bipyridine-N,N′) Complexes of Ruthenium(III)/(II) and Osmium(III)/(II)". Inorganic Syntheses 24: 291–299. doi:10.1002/9780470132555.ch78.