Of bipyridines

Rapoport s findings have been confirmed in the authors laboratory where the actions of carbon-supported catalysts (5% metal) derived from ruthenium, rhodium, palladium, osmium, iridium, and platinum, on pyridine, have been examined. At atmospheric pressure, at the boiling point of pyridine, and at a pyridine-to-catalyst ratio of 8 1, only palladium was active in bringing about the formation of 2,2 -bipyridine. It w as also found that different preparations of palladium-on-carbon varied widely in efficiency (yield 0.05-0.39 gm of 2,2 -bipyridine per gram of catalyst), but the factors responsible for this variation are not knowm. Palladium-on-alumina was found to be inferior to the carbon-supported preparations and gave only traces of bipyridine,... 

Treatment of bipyridine-dicarboxylic acid 191 in alcohols with thionyl chloride and gaseous chlorine furnished the corresponding trichloroindolizines 193 through the intermediary of diesters 192 (Scheme 6) <2002J(P 1) 1688, 2002MI1, 2002MOL628>. 

The ground state spectrum in Figure 5 exhibits the typical features of the Raman spectrum of a bipyridine complex (40,51,52). Seven relatively intense peaks dominate the spectrum. These may be approximately described as the seven symmetric C-C and C-N stretches expected of bipyridine in any point group wherein the two pyridine rings are related by a symmetry element. 

Figure 6. Comparison of the TR3 spectrum of Ru(bpy)s2 (top) to the c.w. resonance Raman spectrum of bipyridine radical anion (lithium reduction) (bottom), (Reproduced from Ref. 19c. Copyright 1981, American Chemical Society.)...

Replacement of both pyridine rings of bipyridine by imidazole has a much greater effect than replacement by thiazole and the [Fe N6]2+ derivative of 2,2 -biimidazole 34 (Dq(Ni2+)=1080 cm-1) is purely high spin [41]. The spin-crossover behaviour of tris(2,2/-bi-imidazoline)iron(II) salts seems somewhat unexpected in light of this and the relatively low a-donor power as indicated by the small Dq(Ni2+) value (1030 cm-1) for 36. 

In order to gain more insight into this proposed mechanism, Montgomery and co-workers tried to isolate the intermediate metallacycle. This effort has also led to the development of a new [2 + 2 + 2]-reaction.226 It has been found that the presence of bipyridine (bpy) or tetramethylethylenediamine (TMEDA) makes the isolation of the desired metallacycles possible, and these metallacycles are characterized by X-ray analysis (Scheme 56).227 Besides important mechanistic implications for enyne isomerizations or intramolecular [4 + 2]-cycloadditions,228 the TMEDA-stabilized seven-membered nickel enolates 224 have been further trapped in aldol reactions, opening an access to complex polycyclic compounds and notably triquinanes. Thus, up to three rings can be generated in the intramolecular version of the reaction, for example, spirocycle 223 was obtained in 49% yield as a single diastereomer from dialdehyde 222 (Scheme 56).229... 

Pyridine-pyridine connections via a Stille reaction have been well precedented for the syntheses of bipyridine, terpyridine, tetrapyridine and other oligomers of pyridine [73-75]. These reactions are exemplified by the synthesis of tetrapyridine 84 [75] from terpyridyl chloride 83 and 2-tributylstannylpyridine. 

Kwong et al. (57) examined the use of bipyridines containing chiral carbinol stereocenters in the 2,9 positions. Interestingly, reduction of 84 with diazoester occurred at ambient temperature unlike every other catalyst reported to date. The resulting complex efficiently mediates the cyclopropanation of styrene. 

The discovery of the positive inotropic and systemic vasodilator activities of bipyridine-derived compounds, like amrinone (7) and milrinone (8), has markedly stimulated research aimed at the development of structurally related non-steroidal, non-catecholamine cardiotonics. In this context, a wide variety of pyridazinone derivatives have been prepared and investigated in search for novel agents useful for the chronic management of congestive heart failure. 

Scheme 4.2 Self-recognition within mixtnres of bipyridine-based Cn+ donble helicates.

Fig. 1 (a) Single molecule conductance experiments of bipyridine. (Reprinted with permission from [5], (b, c) Single molecule transistor experiments using an organic molecule. (Reprinted with permission from [6])... 

The organic chemistry of the bipyridines has not previously been reviewed, although short sections devoted to aspects of bipyridines are included in treatises on pyridine chemistry. A booklet on some aspects of bipyridines has appeared in Russian. This review provides a thorough coverage of the chemistry of the bipyridines to the end of 1981 and includes work reported in most chemical journals to mid-1982. The early chemistry of the bipyridines, which has received some discussion in the reviews of pyridine chemistry, is mentioned briefly to provide continuity. The review excludes the extensive metal and nonmetal coordination chemistry of the bipyridines... 

Not surprisingly, therefore, 2,3 -bipyridine is an ingredient of tobacco smoke and is a constituent of tobacco liquors. " An alkaloid named iso-nicoteine, which was isolated from Turkish tobacco liquors and was thought to be a pyridylpyrrole derivative, was subsequently shown to be identical to 2,3 -bipyridine. 5-Methyl-2,3 -bipyridine, 2,2 -bipyridine, and 4,4 -bipyridine are also found in tobacco smoke. The range of bipyridines found in tobacco smoke condensate has been considerably extended with the identification of several alkyl substituted 2,2 -, 2,3 -, and 3,3 -bipyri-... 

An important method for the synthesis of bipyridines involves reaction of an alkali metal, such as sodium or magnesium, with pyridine. This process results in the formation of several isomeric bipyridines, including 2,2 -bipyridine, but the predominant isomer formed is usually 4,4 -bipyridine. This method is covered in the section devoted to the synthesis of 4,4 -bipyr-idine (Section 4-Substituted pyridines, however, readily give 4,4 -... 

The most important synthesis of 4,4 -bipyridine involves the reaction of sodium on pyridine. This reaction was discovered as long ago as 1870, although the product was not deduced to be 4,4 -bipyridine until later. " 4,4 -Bipyridine is the predominant isomer formed, although varying amounts of other isomeric bipyridines, especially 2,2 -bipyridine and 2,4 -bipyridine, may be formed, depending on the reaction conditions. The reaction involves formation of the sodium derivative of pyridine, which is formulated as the radical 67. It then couples predominantly in the 4 positions to afford 68, which with water hydrolyzes to l,T,4,4 -tetrahydro-4,4 -bipyridine. Facile oxidation then gives 4,4 -bipyridine. ° If the reaction is carried out at the temperature of boiling pyridine (IIS C) instead of at lower temperatures, the proportion of bipyridines other than 4,4 -bipyridine increases, and some terpyridines may be formed as vvell. Oxidants... 

Electroreduction of the cobalt(II) salt in a mixture of either dimethylform-amide-pyridine or acetonitrile-pyridine as solvent, often in the presence of bipyridine, produces a catalytically active cobalt(I) complex which is believed to be cobalt(I) bromide with attached bipyridine ligands (or pyridine moieties in the absence of bipyridine). As quickly as it is electrogenerated, the active catalyst reduces an aryl halide, after which the resulting aryl radical can undergo coupling with an acrylate ester [141], a different aryl halide (to form a biaryl compound) [142], an activated olefin [143], an allylic carbonate [144], an allylic acetate [144, 145], or a... 

The addition of one molar equivalent of bipyridine with respect to ZnBr2 leads to a positive shift of the original reduction process located at —1.4 V/SCE and, more importantly, the signal intensity increases. Under these conditions, indeed, half of the zinc(II) species becomes electroactive and exists under bipyridine complexes9 13, 14, 15, 16 and 17. 

Of special interest is the comparison of the inactivity of bipyridine-Cu(II) as a catalyst in salicyl phosphate hydrolysis, with its strong catalytic effect on the hydrolysis of dicarboxyphenyl-2-phosphate. A comparison of formulas XXVII with XXXIV and XXXVI shows that mixed complex formation of Cu+2 with salicyl phosphate and bipyridine would prevent attack of the phosphate group via the proposed mechanism. The formation of the analogous mixed chelate with DCPP (XXXIV and XXXVI) would produce a reaction intermediate for the reaction, since the metal ion would tie up one of the carboxylate ions but leave... 

A series of l,T-difluorobipyridinium salts [l.T-difluoro-4,4 -bipyridinium, -2,2 -bipyridinium, -2,4 -bipyridinium ditriflate or bis(tetrafluoroborate)] have been synthesized in high yield by direct fluorination of salts or complexes of bipyridines with Bronstcd or Lewis acids with fluorine diluted with nitrogen (10% F2/N2).67,68... 

The attachment of bipyridine moieties also enables the synthesis of homo- and heteroleptic ruthenium(II)trisbipyridyl complexes with interesting photochemical properties [56]. 

Unusual rate laws involving higher orders are known, e.g. k0bs = (a + Z>[H+])[Br ] + c [H+][Br ]3 for the displacement of bipyridine from [Au(bipy)Br2]+ by Br in acid aqueous solution,444 and are frequently associated with the displacement of a multidentate ligand. However, the kobs = fej0 + /ca[OH ] + fcb[OH ]2 rate law observed in the displacement of NH3 from m-[Pt(NH3)2-(Me2S)2]+ by hydroxide445 offers no such explanation. 

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