Chromium complexes 1,3-diketones

Chromium, (ri6-benzene)tricarbonyl-stereochemistry nomenclature, 1,131 Chromium complexes, 3,699-948 acetylacetone complex formation, 2,386 exchange reactions, 2,380 amidines, 2,276 bridging ligands, 2,198 chelating ligands, 2,203 anionic oxo halides, 3,944 applications, 6,1014 azo dyes, 6,41 biological effects, 3,947 carbamic acid, 2,450 paddlewheel structure, 2, 451 carboxylic acids, 2,438 trinuclear, 2, 441 carcinogenicity, 3, 947 corroles, 2, 874 crystal structures, 3, 702 cyanides, 3, 703 1,4-diaza-1,3-butadiene, 2,209 1,3-diketones... 

An alternative procedure starts from a metal complex of o-phenylenedi-amine. For example, the bis(o-phenylenediamine) complex of nickel(II) chloride reacts with acetylacetone to give a mixture of a nickel complex of the diamine and diketone together with 2,4-dimethylbenzodiazepinium chloride (76CPB1934 91JPR327). Chromium complexes have been used in the same way [91JCS(D)2045]. 

The octahedral complex Cr[CH3C(0)CHC(0)Fc]3 displays a single ferrocenyl oxidation at -1-0.58 V, vs. SCE (CH2CI2 solution), which is lower by about 60 mV than that of the free l-ferrocenyl-l,3-butanedionato ligand, thus suggesting that the chromium(III) diketonate donates electron density to the ferrocenyl appendices . As a consequence, the Cr(in) Cr(II) reduction, which is partially overlapped by the solvent discharge in Cr(acac)3, cannot be detected. The simultaneous oxidation of the three ferrocenyl units means that they are electronically isolated from each other. 

Another major contributor to this research area has been the ButenschSn laboratories, whose focus has been on the double addition of alkenyllithium reagents to benzocyclobutenedione chromium complex jg4 220,221 j ej-eas the addition of alkenyllithium reagents to the squarate esters used in the Paquette studies favor the tra 5-addition pathway, addition to 184 gives exclusively sy -addition products, enabling them to undergo facile dianionic oxy-Cope rearrangements. In a similar fashion, the diketones produced are well situated to undergo intramolecular aldol additions. 

Several unusual complexes containing neutral acetylacetonate have been reported.746 The complex [CrBr2(acac)(acacH)] was obtained from the reaction of HBr with [Cr(acac)3] [CrCl2(acac)(acacH)] was obtained from the reaction of CrCl3(THF)3 with acetylacetonate. Other unusual /3-diketonates include the tris(rhenaacetonates) (171).747,748 Two different forms of the tris complex of 2-nitroacetophenone with chromium(III) have been reported 749 these are probably geometric isomers. 

The Cotton effects in mixed amino acidate/acetylacetonate complexes [Cr(acac)2L] (L = l-alanine, L-valine or L-phenylalanine) have been studied 774 absolute configurations were assigned by reference to the parent tris(acetylacetonate) complexes. Synthesis was achieved by the photolysis of mixtures of the amino acid and [Cr(acac)3]. The partial photoresolution of both cis- and irans-(l,l,l-trifluoro-2,4-pentanedionato)chromium has been accomplished by irradiation with circularly polarized light (5461 A) in chlorobenzene solution.775 The results indicated that both bond rupture and twist mechanisms were important. A number of other jS-diketonates have also been investigated.776... 

The complexes of the monothio-/3-diketonate RC(SH)=CHCOR (R = R = phenyl R = phenyl, 2-thienyl, j8-naphthyl R = CF3), which are acetylacetonate analogues have been synthesized (242).1143 Dipole moment measurements are consistent with facial structures (243). Mass spectra indicate no metal-containing peaks for the complex [Cr(PhC(S)=CHCOPh)3)] however, for the fluorinated monothio-j8-diketonates, various metal-containing peaks, e.g. M—2b=F, were observed. Such ions involve fluoride migration. Monothiooxalate complexes of chromium(III) have been prepared fairly unusual complexes, exemplified by [Cr (C2S03)Cu(Ph3)2 3], were reported. On refluxing under chloroform (7h) reactions of the kind illustrated were alleged to occur (equation 55). 44... 

In the above examples, the nucleophilic role of the metal complex only comes after the formation of a suitable complex as a consequence of the electron-withdrawing effect of the metal. Perhaps the most impressive series of examples of nucleophilic behaviour of complexes is demonstrated by the p-diketone metal complexes. Such complexes undergo many reactions typical of the electrophilic substitution reactions of aromatic compounds. As a result of the lability of these complexes towards acids, care is required when selecting reaction conditions. Despite this restriction, a wide variety of reactions has been shown to occur with numerous p-diketone complexes, especially of chromium(III), cobalt(III) and rhodium(III), but also in certain cases with complexes of beryllium(II), copper(II), iron(III), aluminum(III) and europium(III). Most work has been carried out by Collman and his coworkers and the results have been reviewed.4-29 A brief summary of results is relevant here and the essential reaction is shown in equation (13). It has been clearly demonstrated that reaction does not involve any dissociation, by bromination of the chromium(III) complex in the presence of radioactive acetylacetone. Furthermore, reactions of optically active... 

The reaction, of metal carbonyls with 1,3-diketones generally results in a complete displacement of carbon monoxide accompanied by oxidation of the metal to yield 1,3-diketonato complexes. For example, iron pentacarbonyl, chromium hexa-carbonyl, and molybdenum hexacarbonyl afford FefCgHjOOs,1 Cr(CsHr02)8,2 and Mo(CgH702)s,2,s respectively, when allowed to react with 2,4-pentanedione. 

In general, it has been observed that mixed [Co(III)(dik)bis(ethylendiamine)] complexes of general formula 100 react with chromium(II) salts at least partially via inner-sphere attack of the reducing agent either at the coordinated oxygen of the S-diketonate or at the substituent X. In the case of [Co(acac)2(en)]+ both inner- and outer-sphere mechanisms are involved with formation of different chromium(III) compounds and the transition state 101 has been proposed . ... 

HPLC separation of geometrical isomers of / -diketonates was also described. The retention of the fac- and wter-isomers of chromium(in) and cobalt(III) complexes with eight asymmetric / -diketonates was studied iu the 0DS-(Me0H-H20) system. The reteutiou order for two geometrical isomers depends on the structure of the complexing S-diketonates. Thus, the retention order/ac < mer was found for complexes of the fi-diketonates which possess a fluorinated functional group in each molecule. The reverse... 

A simple and rapid method for the iodometric determination of microgram amounts of chromium(ni) in organic chelates is based on the oxidation of chromium(III) with periodate at pH 3.2, removal of the umeacted periodate by masking with molybdate and subsequent iodometric determination of the liberated iodate . Iodometric titration was also used for determination of the effective isoascorbate (see 2) concentration in fermentation processes . The content of calcium ascorbate can be determined with high sensitivity by complexometric titration with edta, which is superior to iodometry. The purity of /3 -diketonate complexes of Al, Ga, In and Ni was determined by complexometric titration with edta at pH 5.5-3, with RSD < 0.01 for determining 5-30% metal ion. Good analytical results were obtained by a similar procedure for the metal content of 15 lanthanide organic complexes. ... 

One of the most versatile classes of ligands in coordination chemistry is that of the /3-diketonates, of which the most common is the acetylacetonate, (acac), Figure 9.1. The coordination chemistry of this ligand first appears in the literature in work by Combes in 1887-1894. Alfred Werner also published on the chemistry of the acac ligand in 1901. The acac ligand is remarkable in that it forms complexes with virtually any metal, including beryllium, lead, aluminum, chromium, platinum, and gadolinium. 

It was found that octahedral iron(lll), manganese(III) or chromium(lll) ions produced mesomorphic complexes when complexed with three -diketonate ligands, presumably with the molecules associating as in Figure 88 [167],... 

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