Diketones complex formation

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... 

A key step proposed in the radical chain mechanism for the formation of the formyl complex is the coordination of CO to the Rh(OEP)- monomer, to give an intermediate carbonyl complex, Rh(OEP)(CO)- which then abstracts hydride from Rh(OEP)H to give the formyl product.This mechanism was proposed without direct evidence for the CO complex, and since then, again from the research group of Wayland, various Rh(fl) porphyrin CO complexes, Rh(Por)(CO), have been observed spectroscopically along with further reaction products which include bridging carbonyl and diketonate complexes. 

Zinc complex formation with 1,3-diketones in aqueous solution has been investigated with pentane-2,4-dione, l,l,l-trifluoropentane-2,4-dione, and 4,4,4-trifluoro-l-(2-thienyl)butane-l, 3-dione. The buffer dimethylarsinic acid was shown to have a catalytic effect on complex formation with pentane-2,4-dione and the proton transfer reactions were affected.471,472 High-resolution solid state 13C NMR studies of bis(2,4-pentanedionato) zinc complexes have been carried out.473... 

Table 19 Equilibrium Constants for Formation of Mono-fi-diketone Complexes of V02+ in Aqueous Solution at 25 °C...

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 1,3-diketonate anions which are formed are excellent didentate chelating ligands for transition metals. In general, the formation of a diketonate complex is so favourable that simply treating a metal salt with the 1,3-diketone in the presence of a mild base results in the formation of a complex of the deprotonated ligand. In some cases, it is not necessary to add an external base - another ligand co-ordinated to the metal centre may be capable of acting as the base (Fig. 5-3). 

The formation of luminescent lanthanide complexes relies on a number of factors. The choice of coordinating ligand and the method by which the antenna chromophore is attached to it, as well as the physical properties of the antenna, are important. In order to fully coordinate a lanthanide ion, either a high-level polydentate ligand such as a cryptate 1 or a number of smaller ligands (such as 1,3-diketones, 2) working in cooperation are required. Both 1 and 2 are two of the simplest coordination complexes possible for lanthanide ions. In both cases there are no antennae present. However, the number of bound solvent molecules is decreased considerably from nine (for lanthanide ions in solution) to one to two for the cryptate and three for the 1,3-diketone complexes. 

A detailed study of the acid-base properties of /3-diketones of the selenophene series made it possible to evaluate their utility in complex formation and to establish how the dissociation constant of a /3-diketone varies with its structure.126-128... 

It is well known that ir-allylpalladium complexes (86) are easily formed by the reaction of PdCb with P. y-unsaturated esters or ketones (85). An attempted oxidation of. y-unsaturated esters and ketones with the PdCl2/CuCl/02 catalyst system in aqueous DMF led to ir-allylpalladium complex formation as the main reaction, and the oxidation of the alkenic bond was hardly observed to a significant extent. However, in aqueous dioxane or THF, the oxidation became the main reaction, giving y-keto esters and 1,4-diketones (87), respectively, with high regioselectivity (Scheme 26).Some results are shown in Table 2. In all cases, no P-keto ester or 1,3-diketone was detected. At the end of the reaction, formation of a considerable amount of the ir-allylpalladium complex (86) was observed. y-Keto esters and 1,4-diketones are useful intermediates for Ae preparation of cyclopentanedione and cyclopentenone, respectively, by base-catalyzed cyclization. Tliis regioselective oxidation provides a unique and efficient synthetic method for y-keto ester and 1,4-diketone synthesis. 

Terbium complexes reported for electroluminescence can be separated mainly into two classes terbium carboxylates and P-diketone complexes. Terbium carboxylates have good luminescence but they are difficult to use as efficient emission materials in OLEDs due to their multi-coordination mode and consequent formation of inorganic polymers with poor solubility or volatility. For these reasons, in this section we will focus on use of the newly developed f)-diketonate terbium complexes in OLEDs. 

Beryllium chemistry includes its S-diketonate complexes formed from dimedone (9), acetylacetone and some other S-diketones such as a,a,a-trifluoroacetylacetone. However, unlike the monomeric chelate products from acetylacetone and its fluorinated derivative, the enolate species of dimedone (9) cannot form chelates and as the complex is polymeric, it cannot be distilled and is more labile to hydrolysis, as might be expected for an unstabilized alkoxide. However, dimedone has a gas phase deprotonation enthalpy of 1418 9 kJmoD while acetylacetone enol (the more stable tautomer) is somewhat less acidic with a deprotonation enthalpy of 1438 10 klmoD Accordingly, had beryllium acetylacetonate not been a chelate, this species would have been more, not less, susceptible to hydrolysis. There is a formal similarity (roughly 7r-isoelectronic structures) between cyclic S-diketonates and complexes of dimedone with benzene and poly acetylene (10). The difference between the enthalpies of formation of these hydrocarbons is ca... 

When CVD with copper(I) /3-diketonate complexes containing a Lewis base is carried out in the presence of hydrogen, deposition of metallic copper occurs by direct reduction with liberation of the Lewis-base ligand and formation of the corresponding -diketone, as was demonstrated for 10c (equation 6). In contrast, it is found that Cu(hfac)(l,3-butadiene) (lOg) deposits copper via disproportionation even in the presence of hydrogen . 

Calcium, strontium and barium form some poorly characterised /9-diketone complexes and rather unstable ammines tendency to covalence, even as indicated by hydration of the ions, has decreased with cation size. The determination of magnesium and calcium with sodium ethylenediamine tetra-acetate, e.d.t.a., probably involves the formation of a chelate complex whose stability is enhanced by the presence of 5-membered rings. 

Compounds such as fluorinated /3-ketones have been used mainly for the extraction of lanthanides and actinides, as more effective ligands than fluorinated dithiocarbamates for complexation with f-block elements. In addition to complex formation, some analytes (e.g. tervalent lanthanides) require the presence of a small amount of water containing 5% methanol — which act as matrix and solvent modifier, respectively — for quantitative extraction [89]. Also, a synergistic effect on the SFE of actinides [90,91] and of lanthanides from cellulose [92] and acid solutions [93] was observed when using a mixture of tributylphosphate (TBT) and a fluorinated /3-diketone. The effect was ascribed to competition of TBT with the matrix for the unoccupied coordination sites of lanthanides and actinides. Thus, the formation of adducts with the complexes of these analytes with fluorinated /3-ketones in supercritical COj facilitates their removal from the solid matrix. 

The inherent steric bulk of the porphyrin directly affects the amount of the bridging a-diketone complex that is formed. At pco = 1 atm and T = 298K, formation of the dimer is favored in all but the bulkiest system (TTiPP). In the case of the least sterically demanding porphyrin, (OEP)Rh, reaction with CO produces the dimetal ketone, (OEP)Rh-C(0)-Rh(OEP).98... 

In an interesting paper, Sutin and co-workers [97] have reported a detailed investigation of the kinetics and mechanism of the formation of the monothenoyltrifluoroacetone complex of Ni(II) (and Co(II) and Cu(II)) by stopped-flow spectrophotometry. The major species present in aqueous solution of the 3-diketone is the keto hydrate although this form is not reactive towards the metal ion. Complex formation occurs exclusively via the enol form, the rate law indicating parallel acid-independent and inverse-acid routes as shown in the scheme... 

In a subsequent paper, Cowie et al. (1986 b) reported on the formation of interesting and unexpected products obtained from this chelate complex 10.52. When the latter was refluxed in toluene, dediazoniation and ortho metalation of one of the phosphine groups took place leading to the yff-diketonate complex shown in Fig. 10-1. The diketonate group chelates through both O-atoms and is formed by hydride transfer from the metal to the carbene C-atom that is generated by the dediazoniation. 

Gas phase reduction of the hydrated hexafluoroacetylacetonates of Cu and Ni and of the trifluoroacetylacetonates of Cu" and Rh leads to deposition of thin films of the respective metals. Reduction can be carried out at as low as 250 °C and the diketone byproduct can, in principle, be recycled. The facile reduction by hydrogen or hydrocarbons of Pd(CF3COCHCOCF3)2 and its Lewis base complexes provides thin palladium films useful as catalysts or primers for electroless plating. In this case, reduction is facilitated by complex formation since, in the complexes, palladium has a formal positive charge and thus an increased electron aflSnity. Use instead olF hydrogen sulfide allows chemical vapor deposition of metal sulfides such as CdS. ... 

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