Chromium complexes anilines

Trifluoroacetamide may be successfully employed as a nucleophile in the synthesis of aniline complexes. The formation of aniline derivatives 14g can be realized by adding the in situ generated trifluoroacetamide anion CF3CONH to the o-chlorotoluenetricarbonyl-chromium complex 14a followed by KOH treatment (Scheme 21) [31]. 

Pyrroles 531 are formed from the chromium complex 529 and alkynes 530 (R = H, Me or Ph = Me, Ph or NEt2). The dicobaltoctacarbonyl-catalysed reaction of cyanotrimethylsilane with a variety of acetylenes R C=CR (R R = alkyl or Ph) furnishes pyrroles 532, in which the bulkier of the two substituents of unsymmetrical internal acetylenes appears at the position marked with an asterisk . An indole synthesis from o-iodo-aniline and alkynes R C=CR (R R =alkyl or Ph) in the presence of palladium(II) acetate, triphenylphosphine, lithium chloride and potassium carbonate has been described (equation 56). In the case of unsymmetrical alkynes, the bulkier substituent tends to be in position 2 of the indole. ... 

It has been observed that in basic media aromatic hydrocarbons and benzylmethyl ethers bound to -Cr(CO)3 are easily nitrosated at the benzylic position. A review type article discusses the stereoselective manipulation of acetals derived from o-substituted benzaldehyde chromium tricarbonyls. The diastereoselective synthesis of a range of substituted cyclohexadienes has been reported from enandomerically pure (2-phenyl-4,S-dibydroxazole)chromium tiicaibonyl complexes. Aromatic nucleophilic substitution on halaogenoarene tricarbonylchromium complexes gives rise to a series of complexed aniline derivatives. The diastereoselective 1,4-addition of organocuprates to o-substituted-phenyI-(E)-enone chromium carbonyl conq)lexes provides a new method for remote stereocontrol at the 1,3, and S-positimis of the side chains. ... 

Lithiation. With anisole, fluorobenzene, and chlorobenzene chromium complexes, lithiation always occurs at an ortho position of the substituents under mild conditions (eqs 14 and 15). Protected phenol or aniline chromium complexes with sterically bulky substituents produce meta lithiation exculsively. The lithi-ated position of some (arene)chromium complexes (3) differs from that of the corresponding chromium-free compounds (4). ... 

This complex, formerly called pyridine perchromate and now finding application as a powerful and selective oxidant, is violently explosive when dry [1], Use while moist on the day of preparation and destroy any surplus with dilute alkali [2], Preparation and use of the reagent have been detailed further [3], The analogous complexes with aniline, piperidine and quinoline may be similarly hazardous [4], The damage caused by a 1 g sample of the pyridine complex exploding during desiccation on a warm day was extensive. Desiccation of the aniline complex had to be at ice temperature to avoid violent explosion [4]. Pyridinium chlorochromate is commercially available as a safer alternative oxidant of alcohols to aldehydes [5], See Chromium trioxide Pyridine Dipyridinium dichromate See Other AMMINECHROMIUM PEROXOCOMPLEXES... 

The coupling of Naphtol AS or its phenyl-substituted derivatives with diazonium salts from variously substituted anilines in aqueous alkaline solution (section 4-11) gave incomplete reactions and impure products in some instances, probably because these coupling components have inadequate solubility in aqueous media. Pure dyes in ca. 90% yields were obtained by reaction in dimethylformamide in the presence of sodium acetate. Metallisation of these o,o -dihydroxyazo ligands with sodium chromium salicylate or a cobalt(II) salt gave metal-complex dyes in 80-100% yields [22]. Specific structural isomers of these complexes were identified by i.r., n.m.r., Raman and UV/visible spectroscopy [23]. 

Another common approach consists of the comparison between the experimental rate constants and theoretical values calculated by the procedure developed by Marcus (1956), Marcus and Sutin (1985) as well as Hush (1958). This classical procedure is used widely. Premsingh et al. (2004) gave the relevant references and described a detailed procedure to analyze the ion-radical reaction between anilines and chromium (V) complexes of azomethyne derivatives. Lepage et al. (2003) studied transformation of para-substituted thioanisoles to corresponding methylarylsulfoxides... 

Methyl benzoate, anisole, and diphenyl ether each give sandwich compounds with chromium vapor, although in rather low yield (32, 55, 110). Chromium appears to attack alkyl ethers and this deoxygenation probably competes with complexation with the aromatic oxygen compounds. No simple product has been isolated from chromium atoms and aniline, but bis(7V,7V-dimethylaniline)chromium has been prepared (32). The behavior of molybdenum and tungsten vapors closely resembles that of chromium in reactions with oxygen- and nitrogen-substituted arenes (113). 

Transition metal complexes such as Fe(CO)5, in the presence of alcohols, cause a trichloromethyl compound to be selectively reduced to the corresponding dichloromethyl compound. This reaction has been reviewed elsewhere and is a very useful means of generating a dihalomethyl group130. Also chromium(II) complexes have been used to reduce aryl bromides131,132. Aromatic compounds such as benzene, aniline and pyridine have been used as hydrogen donors for the hydrodehalogenation of a-haloketones in the presence of tin(II) and iron(II) salts133. 

Richard followed the course of the reactions of Cr(CO)6 and Mo(CO)6 with hexamethylborazine by UV-vis spectroscopy but although he observed that the intensity of the absorption maximum of the hexacarbonyls at around 290 nm decreased and a new band at around 350 nm appeared, he was unable to identify the new product. Experiments with other starting materials such as norborna-diene chromium and molybdenum tetracarbonyl or tris(aniline) molybdenum tricarbonyl which readily react with arenes by ligand exchange, also failed. The key to success was to use tris(acetonitrile) chromium tricarbonyl as the precursor, which in dioxan under reduced pressure afforded the desired hexamethylborazine chromium tricarbonyl as a stable crystalline solid in 90% yield. This was the breakthrough and, after we had communicated the synthesis and spectroscopic data of the complex in the January issue 1967 of Angewandte Chemie, Richard finished his work and defended his Ph.D. thesis in June 1967. Six months before, in December 1966,1 defended my Habilitation thesis in front of the faculty and became Privatdozent (lecturer) on the 1st of January 1967. 

In some cases, aniline or indole derivatives can be substituted meta to the nitrogen by lithiadon of the appropriate chromium tricarbonyl complexes. °" Examples are given in Scheme 3. One of the Cr—C=0 bonds eclipses the C—N bond, and therefore the other carbonyls eclipse the meta C—H bonds. Two suggestions have been offered for the meta selectivity (i) the butyllithium coordinates the chromium carbonyl oxygen and then removes the proximate proton (a kinetic effect) (ii) the eclipsed conformation produces a lower electron density at the meta position, which in turn renders the meta protons more acidic (a thermodynamic effect). ... 

Aniline complexes of Cofll), Ni(II), Cu(II) Bis-bipyridine-silver Bipyridine complexes of osmium and chromium... 

The direct synthesis of (arene)Mo(CO)3 complexes from arene and Mo(CO)g is much more limited than for chromium (Scheme 4) [11,51]. The long reaction times at elevated temperature (e.g., ten days for (benzene)Mo(CO)3) and the high sensitivity to oxygen often results in low yields for substituted arenes. While (benzene)Mo(CO)3 (40) has been reportedly obtained in near quantitative yield, the yield was based on liberated CO rather than isolated complex [11]. In the author s laboratory, an isolated yield of 50% is more realistic for this procedure. The reaction time can be shortened by reacting Mo(CO)g in benzene in the presence of pyridine in an autoclave [52]. Toma and coworkers have described a different procedure that uses a double condenser system, and decalin plus ethylformate as solvent [53]. With a bath temperature of 240 °C this cuts the preparation time of the aniline complex 42 to 1 h (55% yield) (Scheme 4). In the authors laboratory the method is used routinely for the synthesis of complex 40 (18 h, 60% yield). 

Beyond numerous studies of soluble reaction intermediates and products (as an example see a study of electroreduction of nitrosobenzene [23] or investigations of chromium aryl complexes [24]) this design has also been employed successfully in studies of polymer films deposited onto these electrodes. Films showing redox activity and, in many cases, intrinsic electronic conductivity [intrinsically conducting polymers (ICPs)] have been studied for an overview see [25, 26]. In a typical set of spectra (Fig. 5.5) obtained with a film of poly aniline, optical absorptions corresponding to the 7T 7T transition (around 330 nm) and to further transitions involving species like radical cations (polarons) and dications (bipolarons) formed in the sequence of electrooxidation of the film are observed. 

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