Arene chromium tricarbonyl

Photolysis of several arene chromium tricarbonyls (Ar Cr ( 0)3) (Ar = benzene, toluene, or xylene) and... 

Alkyl radical addition reactions to styrene chromium tricarbonyl can be accomplished using alkyl halides (10 equiv) and (TMSlsSiH (5 equiv) in the presence of AIBN in refluxing benzene, for 18 h (Reaction 66). " These reactions are believed to proceed through intermediates in which the unpaired electron is interacting with the adjacent arene chromium tricarbonyl moiety since the analogous reaction with styrene affords only traces of addition products. 

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

Salzer et al. prepared a set of planar-chiral diphosphine ligands based on the arene chromium tricarbonyl backbone (Fig. 36.3) [21]. The straightforward four-step synthetic route allowed the preparation of 20 ligands of this family. These ligands were tested in Ru- and Rh-catalyzed enantioselective hydrogenation of various substrates, including the standard C=C substrates (dimethyl itaconate, methyl-2-acetamidocinnamate, methyl-2-acetamidoacrylate) as well as MEA-imine (l-(methoxymethyl)ethylidene-methylethylaniline) and ethyl pyruvate. Moderate conversions and ee-values were obtained. 

Scheme 12 Synthesis of (R)-phoracantholide using a chiral arene chromium tricarbonyl catalyst...

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]. 

In a further development of the norbornene/anihne OHA reaction, Salzer and coworkers used planar chiral arene-chromium-tricarbonyl-based diphosphines for the in situ formation of cis-trans mixtures of complexes 9 and 10 that gave enanti-oselectivities of 51% and 70%, respectively, at 333 K and with a 40-fold excess of naked fluoride , but activities were very low. In the same paper complex 6 was shown to be superior in both activity and enantioselectivity (64% ee) to the corresponding Josiphos compound 5 [15]. The activated N-H bond of benzamide was also stereoselectively added across the double bond of norbornene to afford N-benzoyl-e%o-aminonorbornane in up to 50% yield and 73% ee in the presence of 0.5mol% [IrCl((R)-MeO-bipheb)]2 at 373 K [16]. 

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... 

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