Arenetricarbonylchromium complexes

Two synthetic approaches on intact indoles are notable. In one, the indole substrate is converted into the /6-arenetricarbonylchromium complex. The -acetyl and 1 -ethoxy-carbonyl derivatives are cleaved to indoles, whereas the... 

G. Al-Takhin, J. A. Connor, H. A. Skinner, M. T. Zafarani-Moattar. Thermochemistry of Arenetricarbonylchromium Complexes Containing Toluene, Anisole, N,N-Dimethylaniline, Acetophenone and Methyl benzoate. J. Organometal. Chem. 1984, 260, 189-197. 

Arenetricarbonylchromium Complexes Ipso, Cine, Tele Nucleophilic Aromatic Substitutions... 

Tab. 1. Ipso nucleophilic aromatic substitution of arenetricarbonylchromium complexes C-O, C-S and C-Se bond formation.

Other approaches to Cr-mediated aromatic thiation have been studied [24], and quenching of lithiated arenetricarbonylchromium complexes by electrophilic sulfur has been compared to halogen displacement by nucleophilic sulfur. 

Metal-based nucleophiles may react with activated haloarenechromium complexes leading to substitution of the halides. The reaction of Collmarfs reagent Na2[Fe(CO)4] with chloro-arenetricarbonylchromium complexes in THF/N-methylpyrrolidinone produces the yellow anionic dinuclear complexes 91a in 45 % yield (Scheme 40) as a result of an ipso SNAr [64]. Spectroscopic data suggest that complex 91a adopts the rj6 structure as opposed to the alternative //5 -cyclohexadieny 1 carbene structure 92. Similarly, it has been reported by the same group that the potassium salt of [CpFe(CO)2] participates in ipso nucleophilic attack on chloroarenechromium substrates, producing dinuclear complexes 91b in 92 % yield (Scheme 40) [65]. 

The addition to an arenetricarbonylchromium complex can be considered as a Michael-type reaction. In the case of (l-methoxynaphthalene)tricarbonylchromium an addition of the anion 496 took place to C5, whereas tris(phenylsulfanyl)methyllithium (497) failed249. 

It has been reported that addition of 2-lithioisobutyronitrile to p-chlorotoluenetricarbonylchromium followed by protonation leads to the production of m-2-cyanopropan-2-yltoluenetricarbonylchromium (Scheme 24). This represents the first example of cine-substituion of arenetricarbonylchromium complexes. 

Schlogl K (1989) Stereochemistry of arenetricarbonylchromium complexes—useful intermediates for stereoselective synthesis. In Werner H, Erker G (eds) Organometal-lics in organic synthesis 2. Springer, Berlin Heidelberg New York, p 63 Solladi -Cavallo A (1989) Chiral arene-chromium-carbonyl complexes in asymmetric synthesis. In Liebeskind LS (ed) Advances in metal organic chemistry, vol 1. Jai Press, London, p 99... 

The chemistry of arenetricarbonylchromium complexes has been extensively studied and reviewed. Compared to the uncomplexed arenes they show greatly enhanced reactivity towards nucleophiles. ... 

While arenetricarbonylchromium complexes are deactivated to electrophilic substitution with respect to the free arene, their susceptibility to nucleophilic substitution is enhanced. The chlorobenzene complex, for example, undergoes ready substitution by sodium methoxide. In this way it resembles l-chloro-4-nitrobenzene. 

The complex tm 5,/ra 5-hexa-2,4-dienetetracarbonylchromium has been shown to be an intermediate in the photocatalytic hydrogenation of tram,rra/zj-hexa-2,4-diene with [Cr(CO)8]. The complexes [Cr(CO)3(L)] (L=phenanthrene, naphthalene, or anthracene) are much more active in the catalysis of diene hydrogenation than typical arenetricarbonylchromium complexes in addition to which induction times are significantly lower. This can be correlated with the asymmetry of the Cr—arene bonding which may facilitate formation of an intermediate (47) during the induction period. ... 

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