Arene ligand reactivity oxidation

The isolation of the first halobenzene complex, (q6-chlorobenzene)tricarbonylchromium(0), allowed a test for a direct analog of classical SNAr reactivity.15 The activating effect of the Cr(CO>3 unit was found to be comparable to a single p-nitro substituent in reaction with methoxide in methanol and the substituted arene ligand was detached with mild oxidation (equation 2). 

The complexes are air stable indeed, a limitation is the need for powerful oxidizing agents, such as Jones reagent CrVI, to detach the arene ligand.38 They are highly reactive toward nucleophiles. This limits the number of compatible synthesis manipulations that can be carried on in the presence of the [(arene)Mn(CO)3] unit but broadens the scope of effective nucleophiles. 

T/6-Arene ruthenium and osmium offer specific properties for the reactivity of arene ligand. The activation toward nucleophiles or electrophiles is controlled mainly by the oxidation state of the metal (II or 0). Recently, from classic organometallic arene ruthenium and osmium chemistry has grown an area making significant contributions to the chemistry of cyclo-phanes. These compounds are potential precursors of organometallic polymers which show interesting electrical properties and conductivity. 

The intermediate cyclooctene complex appears to be more reactive with respect to CS coordination and more sensitive to oxidation when the arene ring bears electron-withdrawing groups (e.g., C02CH3). Dicarbonyl(methyl rj6-benzoate)-thiocarbonyl)chromium is air stable in the solid state and reasonably stable in solution.9 The infrared spectrum exhibits metal carbonyl absorptions at 1980 and 1935 cm"1 and a metal thiocarbonyl stretch at 1215 cm"1 (Nujol) (these occur at 1978, 1932, and 1912 cm"1 in CH2C12 solution).10 Irradiation of the compound in the presence of phosphite or phosphine leads to slow substitution of CO by these ligands, whereas the CS ligand remains inert to substitution. The crystal structure has been published."... 

Petzold H, Xu J, Sadler PJ (2008) Metal and ligand control of sulfenate reactivity arene ruthenium thiolato-mono-S-oxides. Angew Chem Int Ed 47 3008-3011... 

The chromium analogue of 16, [(mesitylene)Cr(CO)3] (17) also undergoes a net two-electron oxidation in MeCN, but the chemistry involved is entirely different for the two complexes. With 17+, attack by solvent leads to rapid loss of arene and CO ligands, accompanied by further oxidation. (At fast scan rates, the 17+/17 couple becomes a reversible one-electron process.) A comparison of the relative reactivity of the 17-electron complexes 16+ and 17+ toward associative attack by MeCN led to the rate order W > Cr (ratio of ca. 104 1). It was suggested that this reactivity order reflects less steric congestion for nucleophilic attack at the... 

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