Arene tricarbonyl chromium complexes

Chung et al. [179] demonstrated that carbohydrate auxiliaries can also be employed for the preparation of chiral (arene)tricarbonyl complexes, which are useful intermediates in organic synthesis. The D-glucose-derived benzylidene acetal 284 was reacted with hexacarbonyl chromium... 

Not all carbon nucleophiles will add to arene chromium tricarbonyl complexes. For example, alkyllithium reagents and simple ketone enolates do not give adducts.325... 

We have shown that the result of replacing stepwise bond dissociation enthalpies by mean bond dissociation enthalpies and transferring bond dissociation enthalpies from one molecule to another can be deceptive The assumption that in Cr(CO)3 (C6H6), DH° (Cr-CO) + DH° Cr-CO) + DH° Cr-CO) 3 (DH°)( Cr CO) led to an error of 72 kJ mol-1 in DH°[(CObCr-CeHe]. Yet this error cancels out if the same procedure is applied to derive relative Cr-arene bond dissociation enthalpies in a series of ( r 6-arcnc)chromium tricarbonyl complexes. 

The Dotz benzannulation reaction yields either arene chromium tricarbonyl complexes or the decomplexed phenols, depending on the work-up conditions. Because of the instability of hydroxy-substituted arene chromium tricarbonyl complexes, yields of the latter tend to be low. High yields of arene complexes can, however, be obtained by in situ silylation of the crude product of the benzannulation reaction [336]. Oxidative work-up yields either decomplexed phenols or the corresponding quinones. Treatment of the benzannulation products with phosphines also leads to decomplexed phenols [272]. 

Chromium tricarbonyl complexes with arenes bonded to rigid polynorbornyl-type... 

Aromatic organosilicon compounds react with chromium hexacar-bonyl on prolonged heating to give the corresponding silylated rjfi-arene chromium tricarbonyl complexes (57, 150). The trimethylsilyl derivative, obtained in 20% yield, is air-stable as a solid ... 

Some novel silicon-containing arene-chromium tricarbonyl complexes (IV-VII), derived from phenyl-substituted silacyclobutanes (118), 1,1-dimethylsilaindane (120) and alkynylarenes (45), have been prepared by essentially identical methods. It is worth mentioning here that the organosilicon complex (VI) is somewhat more thermally stable than the silicon-free 1,1-dimethylindane complex (120). 

The XH and 13C NMR spectra of (i76-C6H5SiMe3)Cr(CO)3 have been analyzed in detail and compared with those of other arene-chromium tricarbonyl complexes (48, 125). 

Arene-chromium tricarbonyl complexes. Seinmelhack and Yamashita have used (he activating and meta-directing effect of the CKCO)3 group to obtain the spiro-[4.5]decenone system of acorenone (3) and acorenone B (4) from anisole. Treatment... 

The carbonyl complexes listed in Table V are of two types tricarbonyl-chromium rj6-arene 77-complexes, and pentacarbonyltungsten <7-pyridine complexes, with both complex types having relatively low y. Nonlinearities increase on arene or pyridine 77-system lengthening, and on proceeding from acceptor to donor substituent on the tricarbonylchromium-coordinated arene ring. Relative magnitudes and trends thus mirror those observed with quadratic nonlinearities of these complexes (see Ref. 1)... 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

Substitution reactions at aromatic carbon (see also Reduction reactions, Ullmann ether coupling, specific reactions such as Nitration) Arene(tricarbonyl)chromium complexes, 19... 

Hydrogenation catalysts Arene(tricarbonyl)chromium complexes, 19... 

Hydrogenation by (7r-arene)chromium tricarbonyl complexes has also been shown to convert dienes to c/s-monoenes, but these catalysts appear to add to conjugated dienes in a 1,4 manner (73, 74). 

Arene(chromium tricarbonyl complexes, preparation and properties, 5, 258 (Arene(chromium tricarbonyls... 

Complexes of Cr, W, Mo, Fe, Ru, V, Mn and Rh form stable, isolable arene if -complexes. Among them, arene complexes of Cr(CO)3 have high synthetic uses. When benzene is refluxed with Cr(CO)6 in a mixture of dibutyl ether and THF, three coordinated CO molecules are displaced with six-7r-electrons of benzene to form the stable i/fi-benzene chromium tricarbonyl complex (170) which satisfies the 18-electron rule (6 from benzene + 6 from Cr(0) + 6 from 3 CO = 18). Complex formation is facilitated by electron-donating groups on benzene, and no complex of nitrobenzene is formed. Complex formation has a profound effect on reactivity of arenes, and the resulting complexes are used in synthetic reactions. The metal-free reaction products can be isolated easily after decomplexation by mild oxidation using low-valent Cr. Cycloheptatriene also forms a stable complex with Cr(CO)3 and its synthetic applications are discussed below. 

An enantioselective approach to cytotoxic nor-calamenenes via electron-transfer-driven benzylic umpolung of an arene tricarbonyl chromium complex. Synthesis 2003, 1851-1855. 

In arene complexes, for example in (q6-arene)chromium tricarbonyl derivatives, the arene ring C — H bonds have enhanced acidity. These complexes, similarly to Cp complexes (see above), are treated with BuLi, and the resulting lithio (q6-arene)chromium tricarbonyl complexes react with a variety of electrophiles. For instance, reacting with BuLi, (C6H5Y)Cr(CO)3 (Y = H, OMe, F, Cl) forms (C6H5Li)Cr(CO)3, and further reaction with C02, MeX, PhCHO, MeCOMe, etc. gives o-products (o-C6H4YR)Cr(CO)3 [74c]. 

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