2,2'-Bipyridine

2,2'-Bipyridine is a chemical compound with the formula (C₅H₄N)₂. This colorless solid, commonly abbreviated bipy (pronounced "bip-ee"), is a widely used isomer of bipyridine. 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.

Additional recommended knowledge

Guide to balance cleaning: 8 simple steps

Recognize and detect the effects of electrostatic charges on your balance

Don't let static charges disrupt your weighing accuracy

Preparation and general properties

It is prepared by the dehydrogenation of pyridine using Raney nickel.^[1] Reflecting the popularity of this ligand design, many substituted variants of bipy have been described.^[2][3]

Bipyridine complexes absorb intensely in the visible part of the spectrum. The electronic transitions are attributed to metal-to-ligand charge transfer (MLCT).

Illustrative bipy complexes

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

Tris-bipy complexes

Tris(bipy) complexes have three bipyridine molecules are coordinated to a metal ion, written as [M(bipy)₃]ⁿ⁺ (M = metal ion; Cr, Fe, Co, Ru, Rh and so on; bpy = 2,2'-bipyridine). These complexes have six-coordinated, octahedral structures and two enantiomers as follows:

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. “2,2’-Bipyridine” Organic Syntheses, Collected Volume 5, p.102 (1973).
2. ^ Smith, A. P.;Lamba, J. J. S.; Fraser, C. L. “Efficient Synthesis of Halomethyl-2,2'-Bipyridines: 4,4'-Bis(chloromethyl)-2,2'-Bipyridine” Organic Syntheses, Collected Volume 10, p.107 (2004).
3. ^ Smith, A. P.; Savage, S. A.; Love, J.; Fraser, C. L. “Synthesis of 4-, 5-, and 6-Methyl-2,2'-Bipyridine by a Negishi Cross-Coupling Strategy” Organic Syntheses, Collected Volume 10, p.517 (2004).
4. ^ Lay, P. A.; Sargeson, A. M.; Taube, H.”cisBis(2,2’-Bipyridine-N,N’) Complexes of Ruthenium(III)/(II) and Osmium(III)/(II)” Inorganic Syntheses, 1986, volume 24, 291-299. ISBN 0-471-83441-6