2,2′-Bipyridine

2,2'-Bipyridine
Names
	Preferred IUPAC name 2,2'-Bipyridine
	Other names Bipyridyl; Dipyridyl; Bipy; Bpy; Dipy
Identifiers
CAS Number	366-18-7 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	113089
ChEBI	CHEBI:30351 ;
ChEMBL	ChEMBL39879 ;
ChemSpider	13867714 ;
ECHA InfoCard	100.006.069
EC Number	206-674-4 923-456-0;
Gmelin Reference	3720 936807
PubChem CID	1474;
RTECS number	DW1750000;
UNII	551W113ZEP ;
CompTox Dashboard (EPA)	DTXSID9040635 ;
	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 n1ccccc1-c2ccccn2;
Properties
Chemical formula	C10H8N2
Molar mass	156.188 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
	Occupational safety and health (OHS/OSH):
Main hazards	toxic
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). verify (what is ?) 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

^ Sasse, W. H. F. (1966). "2,2′-Bipyridine". Organic Syntheses. 46: 5; Collected Volumes, vol. 5, p. 102.
^ Merritt, L. L.; Schroeder, E. (1956). "The Crystal Structure of 2,2′-Bipyridine". Acta Crystallographica. 9 (10): 801–804. doi:10.1107/S0365110X56002175.
^ 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.
^ 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". Organic Syntheses. 78: 82; Collected Volumes, vol. 10, p. 107.
^ 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". Organic Syntheses. 78: 51; Collected Volumes, vol. 10, p. 517.
^ 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.

[1] Sasse, W. H. F. (1966). "2,2′-Bipyridine". Organic Syntheses. 46: 5; Collected Volumes, 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". Organic Syntheses. 78: 82; Collected Volumes, 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". Organic Syntheses. 78: 51; Collected Volumes, 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.

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