Chromium complexes bidentate

Published data on the volatility of complexes of the transition metals including chromium with bidentate sulfur and sulfur-oxygen donor ligands have been summarized.1042... 

Neutral bidentate [N2] supporting ligands, chromium complexes, 5, 359... 

Thus five steps are involved in the reaction between a hexaaquachromium(III) ion and an o,o -dihydroxydiarylazo compound at low pH to form the 1 1 chromium complex dyestuff three ligand replacement reactions and two ionization stages. Studies with other ligands lead to the conclusion that the probable rate-determining step is replacement of the first of the six coordinated water molecules in the highly symmetrical hexaaquachromium(III) ion by one of the donor functions of the ligand. For example, it has been shown that the rate of reaction between the hexaaquachromium(III) ion and the bidentate oxalate or malonate ions to form monochelate... 

The [2.2]paracyclophanediene 42 with an enhanced electron density outside the aromatic rings has been used as a bidentate ligand for tricarbonylarenechro-mium complexes. The mono- and bis(tricarbonyl)chromium complexes 123 and 124 were obtained from the reaction of tris(propanenitrile)tricarbonylchro-mium with 42 and characterized by X-ray crystal structure analyses [83]. 

The major developments of catalytic enantioselective cycloaddition reactions of carbonyl compounds with conjugated dienes have been presented. A variety of chiral catalysts is available for the different types of carbonyl compound. For unactivated aldehydes chiral catalysts such as BINOL-aluminum(III), BINOL-tita-nium(IV), acyloxylborane(III), and tridentate Schiff base chromium(III) complexes can catalyze highly diastereo- and enantioselective cycloaddition reactions. The mechanism of these reactions can be a stepwise pathway via a Mukaiyama aldol intermediate or a concerted mechanism. For a-dicarbonyl compounds, which can coordinate to the chiral catalyst in a bidentate fashion, the chiral BOX-copper(II)... 

In a bidentate ligand system, three molecules of a dye containing either a terminal salicylic acid unit (as in 5.2) or an o-nitrosonaphthol residue are able to chelate simultaneously with a trivalent metal ion of CN6, such as chromium (III) or iron(III), to form a 1 3 metal-dye complex (as in 5.8). Historically, the most important bidentate ligand system was alizarin (5.1). It has been suggested that both hydroxy groups and the keto group in the peri position are all involved with the metal atom in the chelation mechanism. 

The mass spectra of several partially fluorinated P-diketonatochromium(iii) complexes have been determined and discussed. Hydroxyhexafluoro-isobutyric acid, H0C(CF3)2C02H (34), acts as a bidentate ligand and forms a tris-octahedral complex with chromium(iii). A new ligand, hydroxy-methylenenorcamphor (61) (HL) has been synthesized and CrL3 has been prepared and characterized. ... 

VC13 with primary amines gave similar derivatives containing one coordinated amide and one or more molecules of amine,64 but ethylenediamine186,187 and propylenediamine186 give [V(L)3]C13 (L = en, pn). These are isomorphous with the chromium(III) complexes the chlorine atoms are ionic, and the cations are tris-bidentate. 

Although earlier attempts to isolate chromium(II) complexes of various bidentate amines from aqueous solutions produced chromium(III) complexes and hydrogen, the predominantly non-aqueous methods outlined in Scheme 10 provide complexes of ethylenediamine (en), 1,2-diaminopropane (pn), 1,3-diaminopropane (tmd), l,2-diamino-2-methylpropane (dmp), jVjA-dimethylethylenediamine (NNdmn) and N, N -dimethylethylenediamine (NN dmn) (Table 11). In general, ethanol is a suitable solvent but with some amines it is necessary to dehydrate the halide with 2,2-dimethoxypropane (DMP) and dry the ethanol carefully to prevent hydrolysis and oxidation. 

Complexes of adenine (10 Ade) have been isolated by mixing the ligand in 2-methoxy-ethanol with chromium(II) halides in butanol. The low magnetic moments (Table 16)104 indicate dinuclear species [Cr2X2(Ade)4+] (Section 35.3.5.5), or polynuclear structures with bidentate adenine. 

In the complex tris(jV-benzoyl-jV-phenylhydroxylamine)chromium(III) the ligand acts as a bidentate two O donor.616... 

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