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Review
. 2019 Oct 31;24(21):3951.
doi: 10.3390/molecules24213951.

The Early Years of 2,2'-Bipyridine-A Ligand in Its Own Lifetime

Edwin C Constable  1 , Catherine E Housecroft  2
Affiliations
Review

The Early Years of 2,2'-Bipyridine-A Ligand in Its Own Lifetime

Edwin C Constable et al. Molecules. .

Abstract

The first fifty years of the chemistry of 2,2'-bipyridine are reviewed from its first discovery in 1888 to the outbreak of the second global conflict in 1939. The coordination chemistry and analytical applications are described and placed in the context of the increasingly sophisticated methods of characterization which became available to the chemist in this time period. Many of the "simple" complexes of 2,2'-bipyridine reported in the early literature have been subsequently shown to have more complex structures.

Keywords: 2,2’-bipyridine; coordination chemistry; history; supramolecular chemistry; synthesis.

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Conflict of interest statement

The authors declare that there are no conflicts of interest.

Figures

Figure 1
Figure 1
The structures of 2,2′-bipyridine (1) and some related compounds. The numbering scheme for the parent compound, 2,2′-bipyridine is shown. The coordination chemistry of 1,10-phenanthroline (2) is very similar to that of 1. The compounds 3, 4 and 5 are the isomers 4,4′-bipyridine, 3,4-bipyridine and 3,3’-bipyridine. Compound 6, 2,2′-bipiperidine, is one of the reduction products of 1. Also shown is the next higher oligopyridine 2,2′:6’,2”-terpyridine, 7, which Blau described in 1889.
Figure 2
Figure 2
Fritz Blau first prepared 2,2′-bipyridine by the dry distillation of copper(II) pyridine-2-carboxylate [16].
Figure 3
Figure 3
(a) The structures proposed by Fritz Blau for [Fe(phen)3]2+ and [Fe(phen)3]3+ [29]. The diagrams indicate that Blau had not fully understood Werner’s concepts of primary and secondary valence. The bonding to the iron(II) and iron(III) centres are based upon valency of two and three respectively (rather than an oxidation state). The bonding of the chloride to the nitrogen was relatively common in the depiction of ammonium and pyridinium salts at this period in time. (Reprinted from reference 29 by permission from Springer). (b) The bright red colour of the [Fe(bpy)3]2+ is familiar to all scientists who work with 2,2′-bipyridines.
Figure 4
Figure 4
(a) The solid-state crystal structure of 1 shows that the molecules of 2,2′-bipyridine are planar and possess a trans-conformation; (b) molecules of 1 exhibit face-to-face stacking in the crystal lattice. Graphics generated from data from reference [42].
Figure 5
Figure 5
What a difference a century makes! (a) The first reported absorption spectrum of 2,2′-bipyridine from 1913 (Reproduced from reference 46 by permission of The Royal Society of Chemistry); (b) a modern absorption spectrum of the same compound (courtesy of Ms. Dalila Rocco, University of Basel). Both spectra are recorded in ethanol as solvent.
Figure 6
Figure 6
The structures of bioactive materials related to the bipyridines, the herbicides paraquat (8) and diquat (9), the alkaloid nicotine (10) and neonicotine (11). The latter compound was responsible for the reported toxicity of crude bipyridine preparations [52].
Figure 7
Figure 7
The preparation of 2,2′-bipyridine utilizing the Ullmann reaction was introduced by Wibaut in 1928 (Hal = Br or Cl) [72].
Figure 8
Figure 8
The structures of the earliest derivatives of 2,2′-bipyridine to be described; compound 12 was obtained from the pyrolysis of 2-methylpyridine [73].
Figure 9
Figure 9
The preparation of 2,2′-bipyridine by the reaction of pyridine with FeCl3 at elevated temperatures provided a convenient access to the ligand in 52% yield, although the work-up was sometimes challenging because of the large amounts of metal salts [77].
Figure 10
Figure 10
The Λ and Δ enantiomers of the [Fe(bpy)3]2+ cation resolved by Werner in 1912 [78].
Figure 11
Figure 11
The structures of some early derivatives of 2,2′-bipyridine.
Figure 12
Figure 12
The solid-state structure of [W(bpy)(CO)4] (structural data taken from reference [102].
Figure 13
Figure 13
The solid-state structure of [Fe(24)(H2O)4](SO4) (structural data taken from reference 117) and the structure of 5,5′-dimethyl-2,2′-bipyridine, 24.
Figure 14
Figure 14
The solid-state structure of structure of {Fe(bpy)Cl3}, which was shown to be [Fe(bpy)2Cl2][FeCl4] (structural data taken from reference 129).
Figure 15
Figure 15
(a) mer-[Ru(bpy)Cl3(NO)] [134] (b) fac-[Ru(bpy)Cl3(NO)] [134] (c) the cis-[Ru(bpy)2Cl(NO)]2+ cation in [Ru(bpy)2Cl(NO)](ClO4)2 [135] (d) the trans-[Ru(bpy)2Cl(NO)]2+ cation in [Ru(bpy)2Cl(NO)](ClO4)2 [136].
Figure 16
Figure 16
(a) The structure of the [Ru(bpy)Cl4]– anion in K[Ru(bpy)Cl4] [138] and (b) the (H5O2)+ cation present in [(H5O2)Ru(25)Cl4].2H2O (25 = 2,2′-bipyridine-4,4′-dicarboxylic acid) [139].
Figure 17
Figure 17
(a) The neutral cobalt(II) coordination entity present in [Co(bpy)2Cl2].3H2O [141] (b) the [Co(bpy)2(H2O)2]2+ cation present in [Co(bpy)2(H2O)2][{N(CH2CO2)3}Cr(μ-OH)Cr{N(CH2CO2)3] [143].
Figure 18
Figure 18
(a) The one-dimensional coordination polymer present in {Ni(bpy)(H2O)2(SO4)}.nH2O [153] and (b) the dimer [(bpy)Cl(H2O)Ni(μ-Cl)2Ni(bpy)Cl(OH2)] [160].
Figure 19
Figure 19
The [Pt(bpy)2]2+ is distorted from the idealized square-planar geometry with the bpy ligands lying in the square-plane because of unfavourable steric interactions between H6 protons of the bpy ligands. The complexes are either distorted to (a) tetrahedral arrangement of the nitrogen donors about the platinum or (b) the ligands are riffled about a square-planar metal centre [179].
Figure 20
Figure 20
(a) The yellow polymorph [Pt(bpy)Cl2] contains zig-zag chains of Pt centres while (b) in the red polymorph the metal centres are closer and the propagation along the Pt...Pt...Pt vector is closer to linear.
Figure 21
Figure 21
The structure of the dimer [(bpy)(Cu(μ-I)2Cu(bpy)] (data taken from reference [207]).
Figure 22
Figure 22
The structure of the one-dimensional coordination polymer [{Cu(bpy)(H2O)2(μ-SO4)}n] (data taken from reference [211]).
Figure 23
Figure 23
Two polymorphs of {Cu(bpy)Cl2}. Although both are one-dimensional coordination polymers, the coordination number of the copper varies. (a) [{Cu(bpy)Cl(μ-Cl)}n] [217], (b) [{Cu(bpy)(μ-Cl)2}n] [218].
Figure 24
Figure 24
(a) The dimeric structure of [(AcO)(bpy)Cu(μ-OAc)2Cu(AcO)(bpy)].2H2O [240] and (b) the dimer present in anhydrous [Cu(bpy)(OAc)2] [241].
Figure 25
Figure 25
The solid-state structure of [Ag(bpy)2]2+ cation in [Ag(bipy)2](ClO4)2 [245].
Figure 26
Figure 26
(a) The compound initially formulated K[Au(bpy)(CN)2] was subsequently shown to have no bpy-Au bonding (data taken from reference 253. Colour code: K purple; Au, yellow. (b) The proposed structure of [Et2AuBr(μ-bpy)AuBrEt2] [255].
Figure 27
Figure 27
The one dimensional coordination polymers (a) [{Zn(bpy)(H2O)2(μ-SO4)}n] (data taken from reference [260]) and (b) [{Cd(bpy)(H2O)(O2NO)(μ-NO3)}n] [269].
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