Pyridine dipyridine complex

Perchlorates are unusual in that most are either extremely soluble or only sparingly soluble in water. Silver (I) perchlorate is one of the most soluble salts known, while its coordination compound with pyridine is so insoluble that pyridine can be precipitated quantitatively from aqueous solution by treatment with silver (I) perchlorate.1 Although several complexes of pyridine and silver (I) perchlorate have been described,1,2 the one in which silver(I) exhibits its common coordination number of two is the most stable. This compound provides a stable, nondeli-quescent starting material for synthesizing the perchlorates of the dipyridine complexes of unipositive bromine3 and iodine.4... 

Dipyridiue-chromium(VI) oxide2 was introduced as an oxidant for the conversion of acid-sensitive alcohols to carbonyl compounds by Poos, Arth, Beyler, and Sarett.3 The complex, dispersed in pyridine, smoothly converts secondary alcohols to ketones, but oxidations of primary alcohols to aldehydes are capricious.4 In 1968, Collins, Hess, and Frank found that anhydrous dipyridine-chromium(VI) oxide is moderately soluble in chlorinated hydrocarbons and chose dichloro-methane as the solvent.5 By this modification, primary and secondary alcohols were oxidized to aldehydes and ketones in yields of 87-98%. Subsequently Dauben, Lorber, and Fullerton showed that dichloro-methane solutions of the complex are also useful for accomplishing allylic oxidations.6... 

B. General Oxidation Procedure for Alcohols. A sufficient quantity of a 5% solution of dipyridine chromium (VI) oxide (Note 1) in anhydrous dichloromethane (Note 7) is prepared to provide a sixfold molar ratio of complex to alcohol. This excess is usually required for complete oxidation to the aldehyde. The freshly prepared, pure complex dissolves completely in dichloromethane at 25° at 5% concentration to give a deep red solution, but solutions usually contain small amounts of brown, insoluble material when prepared from crude complex (Note 8). The alcohol, either pure or as a solution in anhydrous methylene chloride, is added to the red solution in one portion with stirring at room temperature or lower. The oxidation of unhindered primary (and secondary) alcohols proceeds to completion within 5 minutes to 15 minutes at 25° with deposition of brownish-black, polymeric, reduced chromium-pyridine products (Note 9). When deposition of reduced chromium compounds is complete (monitoring the reaction by gas chromatography or thin-layer chromatography analysis is helpful), the supernatant liquid is decanted from the (usually tarry) precipitate and the precipitate is rinsed thoroughly with dichloromethane (Note 10). 

From 1995 to 2000, catalyst profiles of several ruthenium catalysts bearing pyridine-diimide 1 [13], diiminocarbene 2 [14], diamine-arene 3 [15],phos-phino-arene 4 [16], and substituted cyclopentadienyl 5 and 6 [17, 18] were shown to have good activity for the cydopropanation (Fig. 1). At the relatively high reaction temperature of 60-100 °C,they also gave moderate-to-high yields over 90%. It is interesting in that the dipyridine-diimide complex 1 and the p-cymene-carbene complex 2 show high trans selectivity, 86 14 and 82 18, respectively. 

The only other example of a Schiff base condensation with dipyridine to form a macrocyclic complex has been reported by Tasker et al.112) in which 2,6-diformyl-pyridine or 2,6-diacetylpyridine is condensed with 6,6 -dihydrazmo-2,2 -dipyridine (132) in the presence of zinc(II) to afford a pentagonal bipyramidal complex 133. The rigidity of the system results in an equatorial Ns donor set that is essentially planar water molecules occupy the axial positions. 

Among complex mercury(II) azides a colorless, explosive dipyridine diazido-mercury(II) of the possible structure [Hg (Py)2(N3)2] is precipitated when water is added to a solution of mercury(II) nitrate in pyridine [138]. A triazidomercurate(II), [Hg (N3)3] , is obtained from mercury(II) nitrate and excess sodium azide in acid media and isolated as the tetraphenylphosphonium salt [139,222,238]. 

Porphyrin-based molecular capsules 38 were obtained from two moles of respective tetra-pyridylporphyrin derivatives and four moles of cfs-Pd(II) dppp complexes through pyridine-Pd(II) coordinative interaction [95]. The structures of 38 were confirmed by H NMR and CSI-MS. NMR studies revealed that the capsules 38 have a highly symmetrical 4 structure with a large vacant cavity. The zinc porphyrin assemblies are able to accommodate large dipyridine guests such as 4,4 -trimethylenedipyridine with high affinity = 2.6 x 10 by a two-point simvdtaneous pyridine-zinc(II) interaction. 

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