Acetylacetonate ion

Although acetylacetonate ion forms very stable complexes with many metal ions, acetate ion does not. Explain the difference in complexing behavior. 

Fig. 4.10 Extraction of Cu(II) from 1 M NaC104 into benzene as a function of pH (large figure) and of free acetylacetonate ion concentration (insert) at seven different total concentrations of acetylacetone ([HA]aq 0.05-0.0009 M). (From Ref. 18.)... 

Figure 5. Representation of possible structures for adsorbed carboxylate and acetylacetonate ions on aluminum oxide...

MCI reactions of alkynyliodonium salts with enolates derived from active methylene compounds containing two acidic CH bonds follow a divergent course that leads to furans, presumably via carbenic insertion into enolic OH bonds (equation 122)28. In the reaction of acetylacetonate ion with the l-decynyl(phenyl)iodonium ion, CH insertion is competitive with OH insertion (equation 123)28. 

Explain why complexes that contain acetate ions as ligands are much less stable than those of the same metal ion when acetylacetonate ions are the ligands. 

If NH3 is present, the acetylacetonate ion, acac, coordinates readily owing to the increased concentration of the anion and the stability of the complexes. The reaction with CrCI3 is illustrative of this process ... 

These /3-ketoenolate ions form very stable chelate complexes with most metal ions. The commonest ligand is the acetylacetonate ion (acac) , in which R = R" = CH3 and R = H. A general abbreviation for /3-ketoenolate ions in general is dike. 

Galhnm tris-jS-diketonate complexes are formed by the addition of acetylacetonate ions to aqneons solntions of Ga + (e.g. eqnation 22). However, at jS-diketonate to gaUinm ratios less than three, basic hydroxo complexes are also formed. 

Spectrophotometric studies of the interactions in solutions containing Ga and acetylacetonate ions show that at acetylacetone Ga ratios less than 3, hydrolysis equilibra leading to the formation of hydroxo-complexes are superimposed on the complex-formation equilibria of Ga . ... 

In the monomeric compound, (CH3)3Pt(dipy)(02C5H7), six rather than seven coordination is achieved by the formation of only one bond to the acetylacetonate ion (Fig. 26-H-2b) as in the Pt11 complexes noted earlier. The great strength of the Pt—C bond is shown by the fact that in the preparation of this compound from [(CH3)3Pt(02C5H7)]2 by the action of bipyridine, it is the Pt—O rather than Pt—C bonds that are broken. 

Two independent n.m.r. studies of the effect of alkali-metal cations (Na ) on the conformational equilibrium of the acetylacetonate ion have been effected. Experiments have demonstrated that the two configurations... 

The acetylacetone ion forms very stable complexes with many metallic ions. It acts as a bidentate ligand, coordinating to the metal at two adjacent positions. Suppose that one of the CH3 groups of the ligand is replaced by a CF3 group, as shown here. 

The formation of complexes Ni(L )2 with L 18C6 or R NBr was also proved by spectrophotometry under analysis of UV spectra of absorption of Ni(L )2 and R NBr (18C6) mixtures solutions. At that coordinate with metal ion with preservation of ligand L in internal coordination sphere of complex [90, 92]. Under formation of complexes of Ni(L )2 with U in spite of axial coordination by the fifth coordination place of nickel (II) ion the outer sphere coordination of (H-bonding) with acetylacetonate-ion is also possible. 

In the case of catalysis by the Fe(III)(acac)3 + DMF system the complexes Fe(II) (acac)y(OAc) (DMF), formed in the process, are not stable, though DMF like CTAB forms H-bonds with acetylacetonate ion [67]. The rapid decrease in was observed. S pppj at the catalysis by the Fe(III)(acac)3 + DMF system was not higher in fact than at... 

In the product of (6.466) and similar metal salts which can be made, the metal atoms are beheved to be coordinated by both carbonyl and phosphoryl oxygen (6.469). Analogous salts with only phosphoryl coordination but with similar physical properties can be obtained from bis(diethoxyphosphonyl) methane by reacting it with potassium in THF (6.468). Various canonical forms probably contribute to these bidentate hgands, and both types of salt are analogous to acetylacetonate ions (6.469c). 

Nucleophiles other than OH also give stereospecific additions at alkenes. The acetylacetonate ion adds to co-ordinated cis- or trans-C J z in [Pd(CsH5)-(PPh3)(CHD=-CHD)]+ to give [Pd(C5H5)(PPh3) CHDCHDCH(COMe)2 ] by fra 5-addition, and the overall c/j-diamination of alkenes has been achieved by rraAZ5-aminopalladation of alkenes followed by oxidative amination in which the amine displaces the oxidized palladium by an 5 n2 displacement so that there is inversion at the Pd-bound carbon atom. Other carbon-centred nucleophiles (aryl, alkyl, or methoxycarbonyl) had previously been shown to add cis to alkenes, presumably by prior co-ordination at the metal. 

The stereochemistry of the centrosymmetric dimer [Mn (acac)j-(CH2 CHCH2NH2)]j (Figure 1) is essentially the same as that of the [Co(acac)2(HaO)]2 (ref. 3) and [Co(acac)2(cyclohexylamine]2 (ref. 4) complexes (acac = acetylacetonate ion). The molecule consists of two octhedra sharing two bridging oxygen atoms. The acetylacetonate chelate rings are... 

Multidentate Leaving Groups.—The stepwise perchloric acid-catalysed dissociations of AA from [Co(AA)a(XX)]"+ ions (AA=biguanidine, XX=phenylbiguanidineor acetylacetonate ion) have been studied kinetically. Loss of the first biguanidine molecule is characterized for the acac complex by AH = 15.0 kcal mol, A5 = — 21 cal mol", and for the phenylbiguanidine complex by Afl = 15.4 kcal moL, AS = —20 cal K" mol. Loss of the second biguanidine occurs at elevated tem-... 

In many situations, crown ethers compete effectively with anions for the associated cations in solution. An example of this is found in the case of acetylacetonate ion [10]. In the absence of crown ether, the sodium ion appears to be positioned as one might anticipate for the Z,Z-conformation of the unperturbed (chelated) ion-pair. When 18-crown-6 is present, there is competition between the crown and oxygen anions for solvation of the cation and the Z,Z-conformation is destabilized relative to the E ,Z-conformation to the extent the cation is dissociated (see Eq. 15.1). 

---