Dipivaloylmethanate complex

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). 

Melby et al., 1964). Even though the tetrakis-dipivaloylmethane complex does not exist, the tris-chelate is still capable of adding one or two additional ligands, such as pyridine, picoline, or o-phenanthroline, to form seven- and eight-coordinate species (Selbin et al., 1971). 

Complexes of acetylacetone (acacH), benzoylacetone (bzacH) and dipivaloylmethane (dpmH) have been reported. The acetylacetonate [Cr(acac)2] has been prepared from chromium(II) acetate and acetylacetone.142,143 It can also be obtained by the addition of aqueous sodium acetylacetonate to an aqueous solution of chromium(II) chloride, but in any preparation the yellow solid must be filtered off and dried as rapidly as possible, otherwise the chromium(III) compound is obtained. Its magnetic moment is 4.99 BM at room temperature consistent with a high-spin d4 configuration. 142The powerful reducing ability of [Cr(acac)2] has been used to prepare iron(II) and chromium(II) complexes80 of porphyrins and related ligands. 

Diketonato complexes of the dibenzostib(V)ole ring system have also been reported. These are formed when 5,5,5-trichlorodibenzostib(V)ole are reacted with acetylacetone or dipivaloylmethane. The two stereoisomers (71) and (72) are formed and are in equilibrium with each other (equation 15) (78JOM(160)435). 

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... 

With dipivaloylmethane, the zinc(II), cobalt(II) (12), and iron(II) complexes (19) are all isomorphous. A three-dimensional x-ray structural determination (12) of the Co(DPM)2 shows a tetrahedral configuration. The copper(II) complex of this ligand and the nickel(II) derivative are planar. The 3-phenyl-2,4-pentanedione derivative of copper(II) also is planar (7). 

Eu(dpm)3 is a metal chelate (chele, Greek, claw). The /3-diketone dipivaloylmethane (2,2,6,6-tetramethylheptane-3,5-dione) is a ligand—in this case a bidentate ligand—attached to the europium at two places. Since Eu is hexacoordinate, three dipivaloylmethane molecules cluster about this metal atom. However, when a molecule with a basic group like an amine or an alcohol is in solution with Eu(dpm)j the europium will expand its coordination sphere to complex with this additional molecule. Such a complex is weak and so its nmr spectrum is an average of the complexed and uncomplexed molecule. 

Tetrakis(dipivaloylmethanato)niobium(iv), [Nb (Bu CO)2CH 4] has been prepared by treating NbCl4 with dipivaloylmethane in MeCN containing EtjN. X-Ray crystallographic studies have shown that this compound is the first example of an M(bidentate)4 complex whose stereochemistry is based on an idealized D4 square antiprism (38). In the absence of oxygen and moisture, [Nb (Bu CO)2CH 4] affords stable, very weakly conducting solutions in CH2CI2 which contain the monomer. ... 

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