Chromium tricarbonyl, complexation

The possibility of activating the indole nucleus to nucleophilic substitution has been realized by formation of chromium tricarbonyl complexes. For example, the complex from TV-methylindole (215) undergoes nucleophilic substitution with 2-lithio-l,3-dithiane to give a product (216) which can be transformed into l-methylindole-7-carbaldehyde (217) (78CC1076). 

The coupling reaction of an a ,/3-unsaturated chromium carbene complex, e.g. 1, and an alkyne 2, through coordination to the chromium center, is called the Dotz reaction. The initial product is the chromium tricarbonyl complex of a hydroquinone derivative 3, which can easily be converted to a free hydroquinone or quinone. 

Complete diastereoselection is observed in the HDA reaction of Danishefsky s diene with o-substituted benzaldehyde chromium tricarbonyl complexes. Decomplexation is facile and good yields of 2-aryl-2,3-dihydropyran-4-ones result <96SL258>. Cis-2,3-disubstituted pyranones are accessible from the Lewis-acid catalysed HDA reaction between (triisopropylsilyloxy) dienes and aldehydes and dehydrogenation of the resulting dihydropyrans <96JOC7600>. 

One of the most useful types of it complexes of aromatic compounds from the synthetic point of view are chromium tricarbonyl complexes obtained by heating benzene or other aromatics with Cr(CO)6. 

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

Treatment of a polyfunctional chromium-tricarbonyl-complexed hydroxy aldehyde with an excess of Et3SiFFTFA for 4.5 hours gives an 82% yield of fully reduced product with both the formyl and hydroxy groups completely and selectively reduced (Eq. 193).352... 

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. 

Aryl ethers from haloarene chromium tricarbonyl complexes (Table 2.4)... 

Haloarene chromium tricarbonyl complexes are activated to nucleophilic attack by thiolate anions [58, 59]. High yields of the thioethers are obtained under liquiddiquid two-phase conditions, but optimum yields are achieved under soliddiquid conditions. In many cases the thioether is produced directly but, where the reaction mixture contains thioether and its chromium complex, the thioether can be isolated by degradation of the complex with iodine or an excess of the thiol. Both 1,2- and 1,4-dichlorobenzenes yield only monothioethers, even when an excess of thiolate anion is used. In contrast, 1,3-dichlorobenzenes produce a mixture of the mono- and dithioethers [59]. Aryl allyl thioethers have been produced under catalysed Heck reaction conditions from S-allyl thiocarbamates and iodobenzene [60]. 

Selected examples of the reaction of haloarene chromium tricarbonyl complexes [Cr(CO)jArX] with thiolate anions... 

Jaouen, G. and Meyer, A., Facile syntheses of optically active 2-substituted indanones, indanols, tetralones, and tetralols via their chromium tricarbonyl complexes. J. Am. Chem. Soc., 1975, 97, 4667. 

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]. 

An interesting picture was revealed by Gouverd et al. (2006) as a result of comparison between the neutral chromium tricarbonyl complex of C,P-diaryl phosphaalkene [(CO)3Cr<—PhCH=PMes ] and its anion-radical [(CO)3Cr <— PhCH=PMes ] (Mes is 2,4,6-tris(tert-butyl)phenyl). According to the ESR and DFT data for the anion-radical, about 40% of the negative charge is localized on Cr(CO)3 moiety. This is understandable if one takes into account the known electron-acceptor... 

No significant pseudo-contact shifts could be induced in the spectra of dibenzothiophene, its sulfoxide, or its sulfone, with Eu(dpm)3 although a marked shielding of the protons of one ring was observed in the spectrum of the chromium tricarbonyl complex of dibenzothiophene,presumably due to a contact shift mechanism. 

Dibenzothiophene 5-oxide reacts with triaryltin chlorides to give complexes which show bacteriostatic and fungistatic properties, and a chromium tricarbonyl complex of dibenzothiophene has been described. ... 

The crystal structures of (3a,4-8,8a-f/)-[5.7,8-trimethyl-8H-cyclohepta-(fe)-thiophen]- and (1—3,3a.8a-f7)-[5,7-dimethyl-4//-cyclohepta-(c)-thiophen]-chromium tricarbonyl complexes, (55) and (56). respectively, have been determined. ... 

The chromium tricarbonyl complex 429 of triphenylphosphine oxide is hthiated and silylated (in situ quench) by 360 and McsSiCl to give 430 (X = Si) in 90% yield and 73% ee (Scheme 175) °. Interestingly, the sense of asymmetric induction is reversed from the anisole result. With two equivalents of chiral base, bis-sUyl compounds 432 could be formed. 

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

The reaction of iminium ions with dihydropyridines is a method, suggested from biosynthetic studies, for the formation of carbon-carbon bonds to these six-membered heterocycles. The 1,4-dihydropyridine (8), a presumed intermediate from the reaction of ammonia with glutaraldehyde, reacts with the cyclic iminium ion (159) to give, after oxidation, nicotine (160) (72CC1091). Another example of this reaction has provided a total synthesis of olivacine (163). The 1,2-dihydropyridine ring system in (161), generated from its chromium tricarbonyl complex, was observed to undergo an intramolecular cyclization... 

The crystal structure determination by Vahrenkamp and Noth proves the assumed structure of this new and interesting chromium-tricarbonyl complex 56 (Fig. 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). 

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