Pyridines metallic derivatives

Several side reactions have also been observed, and, for the present purpose, all reactions leading to products other than 2,2 -bipyridines will be considered under this heading. Some of these undoubtedly involve hydrogen derived from the catalyst, but no attempt will be made adequately to review the field of reactions involving pyridines, metal catalysts, and hydrogen. 

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,... 

In contrast to the large number of chiral pyridine derivatives used as ligands of metal complexes in asymmetric catalysis, only a few examples of chiral sulfur-containing pyridine ligands have so far been reported, such as pyridine thioethers derived from ( + )-camphor depicted in Scheme 1.33, which were assessed in the test reaction providing enantioselectivities of up to 76% ee. The related 2,2 -bipyridine thioethers were also prepared but showed a lower stereodilferentiating capability in the test reaction. 

Transition metal derivatives have been less extensively investigated. /i-2,3,5,6-Tetrafluorophenylenedisilver (I) was generated in pyridine solutions of silver tetrafluoroterephthalate [Eq. (97)] (69). Decomposition of... 

Silver 2,4,6-tris(dioxoselena)perhydrotriazine-l,3,5-triide, 0039 Silver trisulfurpentanitridate, 0024 Tetrasilver diimidodioxosulfate, 0043 Tetrasilver diimidotriphosphate, 0042 Tetrasilver orthodiamidophosphate, 0041 Tetrasulfurtetraimide-silver perchlorate, 0029 1,2,4-Triazolo 14.3 -a pyridine - silver nitrate Trisilver tetranitride, 0040 See other heavy metal derivatives... 

During a discussion with G Pannetier (Universite Paris VI) in Paris, he mentioned that he thought he had seen evidence for mixed pyridine-phosphine derivatives of the type [(cod)Rh(PPh3)(C5H5N)]BF4 in the Rh series. On returning to Gif, I confirmed this result by isolating the compound and mentioned it to Morris, who tried to obtain the iridium complex. Our initial idea was that a 1 1 phosphine to metal catalyst might be even more active than the 2 1 species. 

Mossbauer spectroscopy features relating to pyridine and derivatives complexed with Fe or certain other metallic ions in crystalline state1 ... 

The addition product of sodium and pyridine (or its 2-methyl derivative) ignites in air. See related N-METAL DERIVATIVES... 

It explodes fairly violently above 250°C, as does the pyridine analogue. See other N-METAL DERIVATIVES, PLATINUM COMPOUNDS... 

H. Complexes of Pyridines with Late Transition and Rare Earth Metal Derivatives... 

Similarly to the analogous reaction with furo[2,3-Z>]pyridines, metallation of compound (20) with n-butyllithium in TMEDA followed by the addition of DMF afforded the 2-formyl derivative in 66% yield. Likewise, metallation of the isomer (22) under the same conditions afforded the 2-formyl derivative in comparable yield <84JHC785>. Introduction of a carbonyl group at C-3 of compound (20) was accomplished by halogen-metal exchange between 3-bromothieno[2,3-6]pyridine and n-butyllithium. Table 45 lists some of the thieno[2,3-Z>]pyridine derivatives formed by this method <74JHC355>. 

The hexacarbonylniobate(—1) and hexacarbonyltanta-late(—1) anions are well established. The [Nb(CO)6] anion can be prepared at atmospheric pressure of CO from NbCls by using a prereduction step with alkali metal/naphthalene at low temperature, followed by carbonylation of the intermediate at low temperature in DME as solvent. Another method of preparation, also operating at atmospheric pressure of CO, uses the reduction of NbCls with Mg/Zn/pyridine at room temperature and gives yields as high as 48% of recrystallized Na(THF)[Nb(CO)6]. The alkali metal derivatives of [M(CO)6] , M = Nb, Ta, are rapidly oxidized by air the PPN derivatives are stable in air for short periods of time. PPN[Nb(CO)6] and PPN[Ta(CO)6] are isostructural the hexacarbonyl anions possess an almost exact octahedral geometry with the following bond distances Nb-CO, 2.089A Ta-CO, 2.083 A. 

The chemistry of tris(2-pyridyl) tripod ligands such as (107)-(113) and their metal derivatives has been recently reviewed.160 These ligands are neutral donors, coordinating in a facial manner to a single metal center through the pyridyl nitrogens. Tris(2-pyridyl)amine (107), which is a pyridine analogue of triphenylamine, and its monosubstituted derivatives can be prepared by sequential condensation of 2-halopyridine with 2-aminopyridine.160... 

N2S2- and N3S-donor ligands containing thioether and pyridine moieties, such as (112) and (113), have been developed because of the potential relevance of their metal derivatives as model systems for metal sites in metalloenzymes.173,174... 

Thiophenes furans and pyridines are in general the most readily available of the various hetero-aromatic systems and therefore we have carried out a great deal of metallation and derivatization reactions with these compounds. Furan and thiophene are cheap starting compounds and the stability of their easily obtainable 2-lithio derivatives permits reactions with a variety of electrophilic reagents. Hetero-aromatics with two or more hetero atoms (e.g. thiazoles, pyrazoles, oxazoles) are less readily available, and some of their metal derivatives have a low thermostability (cyclofragmentations). For these reasons their metallation and functionalization reactions have been studied less extensively [1]. 

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