2,2 -Bipyridines, formation from

Four 2-substituted pyridines were found to give the expected 6,6 -disubstituted 2,2 -bipyridines in yields corresponding to only about 3% of the amount of 2,2 -bipyridine formed from pyridine itself under comparable conditions. It is also of interest that with three 2-methyl-pyridines the expected 6,6 -dimethyl-2,2 -bipyridines were accompanied by smaller amounts of 2,2 -bipyridines having no methyl groups in the 6,6 -positions. Moreover, a very small amount of 5,5 -dimethyl-2,2 -bipyridine (8) was isolated following reaction with 2,5-lutidine (6) but no 3,3 -dimethyl-2,2 -bipyridine could be detected. The absence of this compound suggests that 3,3, 6,6 -tetramethyl-2,2 -bipyri-dine (9) is not an intermediate, but that the 2-methyl group is lost before the formation of the 2,2 -bipyridine (6—>8). 

It would be expected that the stabilization of the adsorbed species by an extended conjugated system should increase with the number of aromatic rings in the adsorbed azahydrocarbon. However, data suitable for comparison are available only for phenanthridine, benzo-[/]quinoline, and benzo[h] quinoline. The large difference in the yields of biaryl obtained from the last two bases could be caused by steric interaction of the 7,8-benz-ring with the catalyst, which would lower the concentration of the adsorbed species relative to that with benzo[/]quinoline. The failure of phenanthridine to yield any biaryl is also noteworthy since some 5,6-dihydrophenanthridine was formed. This suggests that adsorption on the catalyst via the nitrogen atom is possible, but that steric inhibition to the combination of the activated species is involved. The same effect could be responsible for the exclusive formation of 5,5 -disubstituted 2,2 -dipyridines from 3-substi-tuted pyridines, as well as for the low yields of 3,3, 5,5 -tetramethyl-2,2 -bipyridines obtained from 3,5-lutidine and of 3,3 -dimethyl-2,2 -... 

Von Zelewsky has published many examples of the stereoselective synthesis of metal complexes using what he refers to as chiragen ligands. These are enantiopure natural compounds synthesized from the natural product (—)-a-pinene, which is combined with species such as bipyridine units to provide impressive control of metal-centered chirality.159-161 In this section, we will focus on the determination of absolute configurations in terms of stereospecific formation from different points of view in connection with absolute conformations in the ligands. 

The pale blue tris(2,2 -bipyridine)iron(3+) ion [18661-69-3] [Fe(bipy)2], can be obtained by oxidation of [Fe(bipy)2]. It cannot be prepared directiy from iron(III) salts. Addition of 2,2 -bipyridine to aqueous iron(III) chloride solutions precipitates the doubly hydroxy-bridged species [(bipy)2Fe(. t-OH)2Fe(bipy)2]Cl4 [74930-87-3]. [Fe(bipy)2] has an absorption maximum at 610 nm, an absorptivity of 330 (Mem), and a formation constant of 10. In mildly acidic to alkaline aqueous solutions the ion is reduced to the iron(II) complex. [Fe(bipy)2] is frequentiy used in studies of electron-transfer mechanisms. The triperchlorate salt [15388-50-8] is isolated most commonly. 

The formation of trace amounts of 2,2 -bipyridine following reaction between pyridine and ammonia in the presence of a variety of catalysts led Wibaut and Willink to develop a method for the preparation of 2,2 -bipyridine from pyridine under the influence of a nickel-alumina catalyst. Using a pyridine-to-catalyst ratio of 10 1, temperatures between 320° and 325°C, and pressures between 42 and 44 atm, 2,2 -bipyridine was formed in yields of 0.30-0.67 gm per gram of catalyst. This method w as later applied to -picoline, to quino-line, - and to some of its derivatives, ... 

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,... 

Rhodium-on-carbon has also been found to bring about the formation of 2,2 -biquinoline from quinoline, the yield and the percentage conversion being similar to that obtained with palladium-on-carbon. On the other hand, rhodium-on-carbon failed to produce 2,2 -bipyridine from pyridine, and it has not yet been tried with other bases. Experiments with carbon-supported catalysts prepared from ruthenium, osmium, iridium, and platinum have shown that none of these metals is capable of bringing about the formation of 2,2 -biquinoline from quinoline under the conditions used with palladium and rhodium. ... 

Several products other than 2,2 -biaryls have been isolated following reaction of pyridines with metal catalysts. From the reaction of a-picoline with nickel-alumina, Willink and Wibaut isolated three dimethylbipyridines in addition to the 6,6 -dimethyl-2,2 -bipyridine but their structures have not been elucidated. From the reaction of quinaldine with palladium-on-carbon, Rapoport and his co-workers " obtained a by-product which they regarded as l,2-di(2-quinolyl)-ethane. From the reactions of pyridines and quinolines with degassed Raney nickel several different types of by-product have been identified. The structures and modes of formation of these compounds are of interest as they lead to a better insight into the processes occurring when pyridines interact with metal catalysts. 

If it is assumed that 2,2 -bipyridine is bonded to the catalyst by both nitrogen atoms, then the position of the chemisorbed molecule on the metal is rigidly fixed. Unless two molecules of this base can be adsorbed at the required distance from each other and in an arrangement which is close to linear, overlap of the uncoupled electrons at the a-position cannot occur. The failure to detect any quaterpyridine would then indicate that nickel atoms of the required orientation are rarely, if ever, available. Clearly the probability of carbon-carbon bond formation is greater between one chemisorbed molecule of 2,2 -bipyridine and one of pyridine, as the latter can correct its orientation relative to the fixed 2,2 -bipyridine by rotation around the nitrogen-nickel bond, at least within certain limits. 

From the dimensions of the lattice of W-6 Raney nickel, it seems that the formation of 2,2 6, 2"-terpyridine would be expected when one molecule of 2,2 -bipyridine and one molecule of pyridine are... 

Homolytic aromatic substitution often requires high temperatures, high concentrations of initiator, long reaction times and typically occurs in moderate yields.Such reactions are often conducted under reducing conditions with (TMSlsSiH, even though the reactions are not reductions and often finish with oxidative rearomatization. Reaction (68) shows an example where a solution containing silane (2 equiv) and AIBN (2 equiv) is slowly added (8h) in heated pyridine containing 2-bromopyridine (1 equiv) The synthesis of 2,3 -bipyridine 75 presumably occurs via the formation of cyclohexadienyl radicals 74 and its rearomatization by disproportionation with the alkyl radical from AIBN. ... 

The presence of zinc with bidentate nitrogen donor ligands in the formation of novel composite materials by hydrothermal reactions has been studied. A zinc-containing one-dimensional material, [Zn(phenanthroline)Mo04] was isolated from molybdate, and from vanadium oxide in the presence of zinc 2,2 -bipyridine [Zn(2,2,-bipyridine)2V40i2] was obtained.212,213... 

Spontaneous self assembly of a dinuclear triple helical complex is observed with linked bis-[4,5]-pineno-2,2 -bipyridines. Studies by electrospray mass spectrometry, CD and NMR determined that the major species in solution was a complex of Zn L = 2 3 stoichiometry with a triple helical structure and an enantiomerically pure homochiral configuration at the metal centers. The preference for the formation of one of the possible stereoisomers over the other is of interest.265 Another binuclear triple helical complex is formed from zinc addition to bis[5-(l-methyl-2-(6-methyl-2 -pyridyl)benzimidazolyl)]methane. Spectrophotometric titrations with a zinc solution... 

---