Chromium anionic complexes

Reaction of haloafene chromium tricarboriyl complexes [Cr(CO)3ArX] with alkoxide anions... 

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... 

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... 

The formation of chromium(II) complexes of many oxo anions, e.g. NOf, is precluded by the reducing ability of the metal ion. 

The chromium(V) complexes M3[Cr(02)4], obtained from alkaline solutions, contain dodecahedral anions (see Section 35.6.2). 

Stereospecific benzylic hydroxylation.5 The anion of the chromium tricarbonyl complex (1) of (+ )-N,N-dimethylamphetamine is hydroxylated by oxodi-peroxymolybdenum(pyridine)(hexamethylphosphoric triamide) to give the optically pure complex (2) of (+ )-N-methylpseudoephedrine (3). 

Aldol reactions.1 The anion generated (BuLi) from chromium carbene complexes undergoes aldol reactions with aldehydes or ketones activated by a Lewis acid. Best results are obtained with ketones in the presence of BF3 etherate, whereas TiCl4 is the preferred catalyst for aldehydes and acetals. 

A large number of commercially important plating processes occur from complex ion baths in which the metal is a constituent of an anionic complex, e.g. copper, zinc, cadmium, silver and gold are all commonly plated from cyanide baths, and tin plates from a stannate bath in which [SnIV(OH)6]2 is present. Chromium is commonly plated from a chromate bath although in this case the background medium is acid rather than alkaline. Thus the mechanism of deposition of metals from anionic complexes is of particular interest. It will be instructive to comment on two situations, one occurring in alkaline baths, the other in acidic baths. 

Once it is recognized that cyclohexadienyl anionic complexes of chromium (34) can be generated by addition of sufficiently reactive nucleophiles and that simple oxidizing techniques convert the anionic in-... 

The anionic complexes (50) are obtained from the group VI carbonyl and the dilithium derivatives of the hydroxyalkynes HC=CCR2(OH) subsequent protonation or acylation affords propadienylidene (51) or carbene (52) complexes by complex cyclization and addition reactions (Scheme 3) (28). Attempts to obtain the dimethyl complex by reaction of the chromium alkynolate dianion with COCl2 gave only polymeric material. More stable complexes were obtained with R = aryl (73). 

Anionic bidentate [P2] ligated derivatives chromium(II) complexes, 5, 365... 

Anionic tridentate [NP2] ligated derivatives chromium(II) complexes, 5, 368 chromium(III) complexes, 5, 370 Anionic tridentate [N3] supporting ligands chromium(II) derivatives, 5, 362 chromium(III) derivatives, 5, 363 Anion receptors... 

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