Of 3-diketonate complexes

The coordination of /3-diketonates and related species to alkali and alkaline earth cations has long been recognized. Combes first prepared Be(acac)2 in 1887,255 and the contribution of Sidgwick and Brewer concerning the nature of dihydrated alkali metal /3-diketonates plays a seminal role in the development of this area of coordination chemistry.19 A review concerning the structure and reactivity of alkali metal enolates has been written, 6 and sections on alkali and alkaline earth /3-diketonates can be found within more generalized accounts of /3-diketone complexes.257,258... 

The main problem here is to obtain suitable coordination compounds that can be vaporized at reasonably low temperatures at which they are thermally stable. To this end a great deal of work has been published on the gas chromatography of (3-diketone complexes such as (61 R2 = H) 93 Volatile complexes of the rare earths with dipivaloylmethane (61 R1 = R3 = CMe3 R2 = H) were first prepared in 1965 but while the separation of pairs of neighbouring metals (e.g. Eu and Sm) has been reported, the complete separation of the whole group has not been successfully achieved. Attempts to use columns longer than 70-75 cm result in peak-broadening and inefficient separation.94... 

It is less well known that the synthetic methods of (3-diketonate complexes have been elaborated, where ligands of the type discussed are bound with the metal through a C-donor atom 850 [6,11,12,14,85 88], Such mercury complexes, for example 851, were obtained as a result of transformation (4.20) [89] ... 

Thus if one wants to improve the overall quantum yield of /3-diketonate complexes, removal of coordinated water molecules is absolutely necessary. By means of the estimated nonradiative deactivation rate constants, calculations showed that removal of these water molecules allows one to reach a maximum quantum yield of 2.6% in toluene for the Ybm-tta complex. However, water molecules are usually replaced with a coordinating secondary ligand, such as phenanthroline, which also contributes to the nonradiative deactivation ( Phen 3.6 x 104 s-1), but to a much lesser extent than water molecules. Further improvement can be reached by deuteration of the central C-H group in the /i-dikctonatc in Yb(ttax/i )3(phcn) for instance, deactivation due to C-H oscillators occurs eight times faster when compared to C-D oscillators. 

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. ... 

An important use of /3-diketonate complexes that are soluble in organic solvents, such as those derived from l,l,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione, especially of Eu and Pr, is for shift reagents in nmr spectrometry. The paramagnetic complex deshields the protons of complicated molecules, and vastly improved separation of the resonance lines may be obtained.266... 

The electrophilic substitution of (3-diketonate complexes appears to occur as for arenes, and a process involving initial coordination of the electrophile, followed by an intramolecular group transfer, has not been observed, although it has been postulated for the reaction of copper(II) acetylacetonate with thioacetals (equation 14). ... 

Intramolecular rearrangements of /3-diketone complexes, which are degenerate in the sense that compositional integrity is maintained, have received considerable attention in the literature. Rearrangements of materials containing an MOg coordination core are particularly important as they involve fundamental questions about reaction mechanisms of inorganic compounds. 

Another reaction shown to lead to active catalysts is the combination of (DAB)Ni(COD) with MAO under reaction conditions.although there is some indication that oxygen promotes this activity. - The use of /3-diketonate complexes of nickel as catalyst precursors leads to a halide-free system, and the MAO is proposed to participate in the ligand-exchange process. The order of mixing is important addition of MAO to a solution of Ni(acac)2 and DAB yields an active system, while addition of Ni(acac)2 to a solution of DAB/MAO is far less active. In addition, other routes to in situ catalyst formation have been reported. 

Dithiolium salts and dithio- 3-diketone complexes of the transition metals. T. N. Lockyer and R. L. Martin, Prog. Inorg. Chem., 1980, 27, 223-324 (198). 

Casey et al. have studied the decarbonylation reactions of [cis-(OC)4M(MeCO)(PhCO)], in which M is Mn or Re (16,17). These complexes lose a carbonyl ligand to form five-coordinate intermediates of the type [(OC)3M(MeCO)(PhCO)]. Reversible methyl migration proceeds much more rapidly than does phenyl migration. In the course of these studies, a phosphine substituted rhena-/3-diketonate complex, [fac-(OC)3(Et3P)Re(MeCO) (PhCO)], was prepared. 

Because the interligand C—C coupling of the acyl carbon donor atoms in metalla-/3-diketonate complexes [Eq. (8)] is such a general (though unusual) reaction that occurs very facilely, we have proposed (without proof) a formal description of how this type of coupling might take place (44,50). This formalism has been adopted by others to explain the C—C coupling shown in Eq. (10) (47). 

A helical arrangement within columns was also found for other metal 3-diketonate complexes provided with chiral side chains (32) by Serrano and co-workers.35,36 These compounds form rectangular columnar mesophases with helical order within the columns. A spin-coated sample of 32 showed a positive exciton-splitted signal in the CD spectra, which was interpreted as a left-handed (M) helix. Annealing of the film resulted in much higher optical activities and a shift of the absorption maxima. The observed optical changes clearly point to a chiral organization of the columns in the mesophase. 

The synthesis of a variety of /3-diketonato complexes of Tc has been described. None of these compounds has been structurally described, but they are formulated as [TcO(/3-diketonate)2-Clj. A further variant of purely oxygen-coordinated Tc results from use of the Klaui-ligand (IS). Yellow-green complexes of composition [(Lor)TcOC12] were prepared by reaction of [TcOJ in the presence of cone. HCl with the ligand (18). 

PPhs, the active oxidant being probably a Os =0 species. trani-Dioxoosmium(VI) complexes of Schiff base ligands obtained from the condensation of /3-diketones and 1,2-diaminoethane are also known. The X-ray structure of tra 5-[0s (0)2 (BA)2en ] has been determined. The 0s=0 distances are 1.753 A and 1.736 A (average) for the two crystallographically independent... 

For the deposition reactions carried out under an Ar atmosphere, up to 41% of the dark red tris-/3-diketonate complex Ru(hfac)3 is observed as a volatile byproduct. This finding suggests that the operation of a parallel pathway, which involves self-disproportionation of the source reagent, is necessary to account for the observed film growth ... 

By far the greatest number of reports have been on the /3-diketonate (LH = /3-diketone) complexes, and these provide a large series of types TiX3L, TDCtfLH), TiX2L2, [TiL3]+, TiOXL, [TiOL]2 (see Table 5 and structures 11-15). 

A series of [M(02)F3(diket)] complexes has been prepared by the reaction of /3-diketones with [M(02)F4(H20)] . 3H and 19FNMR spectra indicate that the products exist as a mixture of geometrical isomers in MeCN. The reaction of oxalic acid with [Nb(02)F4(H20)] yielded [Nb2(02)2F6(C204)]z. A bridging oxalato group and a coordination number of seven for the metal were proposed. [M(02)F3(phen)], [M20(02)F4(bipy)2] and [M(02)F3(0AsPh3)2] were obtained when the neutral ligands were allowed to react with [M(02)F4(H20)] . 

Several /3-diketonate complexes of the type [W(L-L)X2] (X = Cl, Br L = acac, 6-methyl-2,4-heptanedione, dibenzoylmethane) have been prepared from reaction of the j8-diketone ligands with WX5. The suggested cis stereochemistry, based on IR measurements, must be considered tentative. 

Under this section are considered lanthanide complexes of /3-diketones and their adducts, but work specifically in the area of lanthanide shift reagents is dealt with in Section 39.2.9. Of course, the majority of lanthanide shift reagents are lanthanide /3-diketonates, and when they function as shift reagents they do so by forming adducts in solution. Furthermore, interest in shift reagents has directly stimulated a considerable amount of fundamental research on lanthanide /3-diketonates and their adducts. Much of this fundamental work was, therefore, carried out in the early 1970s. AH this means that the division between this section and Section 39.2.9 is not entirely clear cut. 

Some articles review the coordination chemistry of /3-diketones1529,1530 and, specifically, isomerism1531 and Lewis acid behaviour of the complexes.1532 Amongst the carbon-bonded /3-diketone complexes, those of nickel(II) have not been reported.1533... 

The stability of some silver /3-diketone complexes has been determined by pH titrations at 30 °C in 75% dioxane.231 For most of the complexes studied, a linear relationship existed between the dissociation constant of the /3-diketone (pATd) and the stability constant (log KJ (Table 32). 

These occur particularly in solution, but in the solid state also coexistence of the different stereochemistries is possible in either case, complicated magnetic behaviours as functions of concentration, preparative details and temperature arise. Complexes of (3-diketones, substituted alkylenediamines and salicylaldiamines are characteristic sources of these phenomena. 

The chemistry of 1,3-diketone complexes of nonmetallic elements (B, Si, Ge, Sb, Te) has been reviewed.68 Condensation of acetylacetone with TeCl4 yields Te(CH2COCH2COCH2)Cl2 (8a), which may be reduced to Te(CH2COCH2COCFI2) (8b). The crystal structures of these compounds demonstrate an unusual coordination of tellurium to the terminal carbons of the diketonate.61 72 In the dichloride complex, Teiv exhibits a distorted trigonal bipyramidal geometry with a stereochemi-cally active lone electron pair in the equatorial plane. In S2(MeCOCHCOMe)2 the acetylacetonate methine carbons are bonded to a disulfur unit.73... 

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