Chromium, chelates

Certain other 1,3-dicarbonyl chelates were brominated with difficulty or not at all. For example, the trifluoro- and hexafluoroacetylacetonates (VI, R = CF3, R = CH3, and R = R = CF3) were not brominated under a variety of vigorous conditions. However, in the case of the chromium chelates of 1-phenyl-1,3-butanedione and dibenzoylmethane (VI, R = C( Hr), R = CH5, and R = R = C(iHr)), reaction with N-bromosuccinimide (NBS) was successful. That the electron density at the central carbon of the chelate ring is an important factor in the success or failure of these electrophilic substitutions is evident from the fact that the bis-(ethylenediamine)-2,4-pentanedionocobalt(III) cation cannot be brominated even under vigorous conditions. 

Treatment of chromium (III) acetylacetonate with acetic anhydride and boron trifluoride etherate yielded a complex mixture of acetylated chelates but very little starting material. Fractional crystallization and chromatographic purification of this mixture afforded the triacetylated chromium chelate (XVI), which was also prepared from pure triacetylmethane by a nonaqueous chelation reaction (8, 11). The enolic triacetylmethane was prepared by treating acetylacetone with ketene. The sharp contrast between the chemical properties of the coordinated and uncoordinated ligand is illustrated by the fact that chromium acetylacetonate does not react with ketene. 

Under the same conditions, cobalt acetylacetonate afforded a mixture of four products the mono-, di-, and triacetylated chelates (XVII, XVIII, and XIX), along with the starting material. In contrast to the chromium chelates, the mixture of cobalt complexes was cleanly separated by chromatography. The identity of each of these products was established by an NMR spectrum. The presence of uncoordinated carbonyl groups was revealed by infrared absorption at 1675 cm.-1... 

A GC-MS method was used in the study of the analytical characteristics of volatile Al(dik)3 and Cr(dik)3, dik = acac and tfac. Aluminum and chromium chelates were well separated on a fused silica capillary column of 25 m length and 0.20 mm i.d. with electron impact ionization MS detection, and yielded the unique base peak pattern corresponding to the loss of one ligand from the molecular ion. Cr(tfac)3 exhibited a pair of chromatographic peaks which were found to produce nearly identical mass spectra, pointing to the existence of two geometrical isomers. ... 

The chromium chelate of malonaldehyde is a red crystalline solid soluble in benzene and chloroform but insoluble in water. The chelate undergoes nitration and bromina-tion at the central carbon of each chelate ring in the manner of an aromatic system. The infrared spectrum of this substance exhibits major bands at 1600, 1490, 1445, 1375, and 1310 cm. . The complex undoubtedly exists as a diracemate, but its resolution has not been achieved. 

The following procedure is an adaptation of a recently devised method of preparing chromium chelates. - The... 

No chromium chelates of a,j8-unsaturated )3-keto amines ( 3-amino ketones) have been previously reported, although a wide variety of these ligands are known. The following procedure is representative of the preparation of a chro-mium(III) complex of a hydrolytically unstable ligand under completely anhydrous conditions.t This method is general and can be employed in the synthesis of a large number of analogous chromium(III) complexes. ... 

Alkyllithium addition to the (ti -arene) dicarbonylchromium imine chelates has been examined. Treatment of optically pure chelate (41) with methyllithium provides amine (42) with an enantiomeric excess of 94% (Scheme 5). No diastereoselectivity was reported for alkyllithium additions to (arene)tri-carbonylchromium complex (40). In the absence of additional examples, the generality of this chromium chelate methodology for asymmetric amine synthesis cannot be assessed. 

Scheme 58. Novel synthesis of centrosymmetric chrysenes (127) by dimerization of intramole-cularly stabilized alkyne-carbene chromium chelate complexes [160a, d]...

By means of the above1 procedures, a variety of (3-dicarbonyl metal chelates have been halogenated. For example, the chromium chelates of formylacetone (52), l-phenyl-l,3-butanedione and dibenzoylmethane (67), ethylenediaminebis(2,4-pentanediono)copper(II) and the nickel(II) chelate of. TV-tt-butylsalicylaldimine (112) have been brominated in chloroform solution with Ar-bromosuccinimide. The chromium chelates of a number of... 

The ease of bromination of the metal chelates of /3-diketones varies greatly and in some instances bromination does not take place even under vigorous conditions. For example, the chromium chelates of trifluoro- and hexafluoroacetylacetone (structures IV and V) and bis(ethylenediamine)-2,4-pentanedionocobalt(III) cation (structure VI) cannot be brominated (48). This inertness undoubtedly reflects the effect of substituents on the /3-diketones themselves. 

The ligand acetylacetone was also successfully nitrated by the mixture of copper(II) nitrate trihydrate and acetic anhydride or by a mixture of chromium(III) nitrate trihydrate and acetic anhydride. In the former case, bis(3-nitro-2,4-pentanediono)copper(II) precipitated and was thereby protected from cleavage of the chelate rings. In the latter case, a mixture of products was formed, presumably the mono-, di-, and trinitrated chromium chelates (54). 

Tris(3-bromoacetylacetonato)chromium(III) is a dark red-brown crystalline material, which dissolves in benzene to form a green solution. The infrared spectrum of this chelate exhibits a characteristic strong singlet at 1540 cm. i, whereas chromium(III) acetylacetonate exhibits two peaks in this region, at 1560 and 1520 cm. b The ultraviolet spectrum of the brominated chromium chelate in chloroform exhibits a Xmax at 358 m/i(e = 13,070). The brominated chelate is reported to form a stable clathrate complex with chloroform (m.p. 240 to 241°). ... 

The reaction of superoxotitanium(IV) with a number of substrates has been monitored by stopped-flow techniques/ In 1 M perchloric acid, the oxidation of iodide and bromide proceeded with second-order ratde constants of 1.1 x 10 M s and 2M s respectively. It is proposed that the reduction of superoxotitanium(IV) proceeds by a one-electron mechanism. Based on proton dependences, the species TiO " is more reactive than the protonated form Ti02(0H)2. The chromium chelate, bis(2-ethyl-2-hydroxybutyrato)oxochro-mate(V), is reduced by iodide, generating a Cr(IV) intermediate. The reaction is considered to proceed through formation of an iodine atom (T) for which both Cr(V) and Cr(IV) compete. In aqueous solution, [Co(EDTA)] forms a tight ion pair with I . Upon irradiation of this ion pair at 313 nm, reduction of [Co(EDTA)] to [Co(EDTA)] occurs with oxidation of 1 to IJ. The results may be interpreted on the basis of a mechanism in which [Co(EDTA)] and V are the primary photoproducts where the latter subsequently disproportionate to I3 and 1 . The kinetics and mechanism of the oxidation of 1 by a number of tetraaza macrocyclic complexes of Ni(III) have been reported. Variations in rate constants and reaction pathways are attributable to structural differences in the macrocyclic ligands. Of interest is the fact that with some of the Ni(III) complexes, spectrophotometric evidence has been obtained for an inner-sphere process with characterization of the transient [Ni(III) L(I)] intermediates. Iodide has also been used as a reductant for a nickel(III) complex of R-2-methyl-1,4,7-triazacylononane. In contrast to the square-planar macrocycles, the octahedral... 

No chromium chelates of CKj/S-unsaturatcd /3-keto amines (j8-amino ketones) have been previously reported, although a wide variety of these ligands are known. The following... 

Kosyanchuk, L. E, Babkina, N. V., Yarovaya, N. V, Kozak, N. V, and Lipatov, Y. S., 2008. Phase separation in semi-interpenetrating polymer networks based on crosslinked poly(urethane) and linear p>oly(methyl methacrylate) containing iron, copper, and chromium chelates. Polymer Science Series A 50(4) 434-433. 

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