2,2'-Bipyridine

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2,2'-Bipyridine
Bipy molecule
Identifiers
CAS number 366-18-7
ChemSpider 13867714 YesY
UNII 551W113ZEP
ChEBI CHEBI:30351
ChEMBL CHEMBL39879 YesY
RTECS number DW1750000
Jmol-3D images Image 1
Properties
Molecular formula C10H8N2
Molar mass 156.18 g mol−1
Melting point 70-73 °C
Boiling point 273 °C
Structure
Dipole moment 0 D
Hazards
R-phrases 25
S-phrases 36/37-45
Main hazards toxic
Related compounds
Related compounds 4,4'-Bipyridine
Pyridine
Phenanthroline
3-Pyridylnicotinamide
Terpyridine
Biphenyl
Except where noted otherwise, 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 "bip-ee")) 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[edit]

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

C5H5N → (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[edit]

Illustrative complexes[edit]

Tris-bipy complexes[edit]

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:

Bpycomp.png
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[edit]

  1. ^ Sasse, W. H. F. (1966), 2,2’-Bipyridine, Org. Synth. 46: 5 ; Coll. Vol. 5: 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: 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: 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.