Heptanedione complexes

Europium, tris(2,2,6,6-tetramethyl-3,5-heptanedione-quinuclidine)-stereochemistry, 1, 81 Europium complexes... 

Terbium, tris(2,2,6,6-tetramethyf-3,5-heptanedione)-photosubstitution, 1,408 Terbium complexes f5-diketones, 3, 1081... 

The aldol reaction can be applied to dicarbonyl compounds in which the two groups are favorably disposed for intramolecular reaction. Kinetic studies on cyclization of 5-oxohexanal, 2,5-hexanedione, and 2,6-heptanedione indicate that formation of five-membered rings is thermodynamically somewhat more favorable than formation of six-membered rings, but that the latter is several thousand times faster.170 A catalytic amount of acid or base is frequently satisfactory for formation of five- and six-membered rings, but with more complex structures, the techniques required for directed aldol condensations are used. 

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. 

A few observations of photosubstitution in lanthanide complexes have been reported. Irradiation into the f—f bands of [Pr(thd)3], [Eu(thd)3] and [Ho(thd)3] (thd is the anion of 2,2,6,6-tetramethyl-3,5-heptanedione) results in substitution of thd by solvent.153 The proposed mechanism involves intramolecular energy transfer from an f—f excited state to a reactive IL excited state which is responsible for the observed ligand loss. Photosubstitution has also been observed upon direct excitation into the ligand absorption bands of [Tb(thd)3].154... 

Extraction of the rare earths with acetylacetone has been investigated [418, 419] and is found to be enhanced by the decreasing basicity of the rare earth ions. The gas chromatographic separation of rare earth complexes with 2,2,6,6-tetramethyl-3,5-heptanedione has already been mentioned. The acetylacetonate complexes of the rare earths are reported to exist as either anhydrous [420, 421], mono- [422], di- [422] or trihy-drates [422, 423], Stites et al. [424] have studied the pH of the precipitation of several rare earth acetylacetonates and reported the melting points of the complexes. The europium acetylacetonate precipitated at pH 6.5, and melted at 144—45° C. The existence of monomers and dimers for these complexes in nonaqueous solvents has been proposed [421, 425-427],... 

Solvent extraction technique has been used in the synthesis of tris chelates of l,l,l,5,5,6,6,7,7,7-decafluoro-2,4-heptanedione. An aqueous solution of lanthanide chloride is equilibrated with an ether solution of ammonium diketonate, with the condition of an excess of lanthanide in the aqueous phase to prevent the formation of the tetrakis complex [46]. 

Photo substitution reactions of Pr, Eu and Ho complexes with the ligand L = 2,2,6,6-tetramethyl-3,5-heptanedione (thd) of the formula Ln(thd)3 have been studied by irradiation into the f-f bands [110]. The corresponding thermal reactions are slow. The ligand thd is replaced by solvent thus... 

Complexes (VO)L2 with L = acac, 3,5-heptanedionate, dpm, bzac, dibzm and acac NMe2 show a shift to the blue of the absorption band" as the axial interaction increases. Also, IR spectroscopy points to changes in strength of the V=0 bond. For example, in noncoordinating solvents (e.g. methylene chloride or chloroform) the absorption spectra are the same as for the pentacoordinated VO(acac)2 complex (i.e. = 676 nm and... 

A number of volatile rare earth chelates containing the ligands, l,l,l,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedi-one, [H(fod)], and 2,2,6,6-tetramethyl-3,5-heptanedione, [H(thd)] have been synthesized and investigated. The fod complexes are more volatile than other known compounds of the lanthanide elements. The fod complex of Sc(III) and the lanthanide thd compounds are anhydrous. The fod chelates of Y(III) and the lanthanides are isolated as hydrates but can easily be dehydrated in vacuo over P Oio. Gas chromatographic and thermo gravimetric data reveal that the volatilities of the complexes increase as the ionic radii of the metal ions become smaller. 

Since the oxygen atoms as well as the alpha carbon on the /3-keto-enolate ring can function as bases to coordinate with metal ions (5, or to hydrogen bonding solvents (14)f it should be recognized that /3-keto-enolate complexes may have a stereochemistry quite different from that expected—based on the stoichiometry of the complex. However, by a suitable choice of a /3-ketoenol ligand, such as 2,2,6,6-tetramethyl-3,5-heptanedione (dipivaloylmethane), H-DPM, intermolecular effects can be reduced or eliminated with the result that the metal complex formed has the stereochemistry expected for the monomeric acetylacetonate complex of that metal ion. For example, nickel(II) acetylacetonate is trimeric as a solid and in solution (11), but the dipivaloylmethane complex is a monomeric, undoubtedly planar species, in solution, as well as in the solid state (37), This stereochemistry occurs with the monomeric acetylacetonate in dilute solution or in the vapor phase, as indicated by absorption spectra and electron diffraction (SO). 

---