Diketones anions

The monoketone bis(2,2, /V,/V -bipyridyl)ketone forms a [CoinL2]+ complex on reaction with [Co(NH3)4(C03)]+ in water.981 As reported for a quite different Co11 complex, the ketone is hydrated to form the gem diol which binds as a monodeprotonated O-donor along with the two pyridine groups in a tridentate chelate, with very little distortion from octahedral observed in the complex. This appears to represent a facile route for this type of inherently poor donor to achieve coordination. Chelated /3-diketonate anions are long-studied examples of O-donor chelates, and continue to be examined. A simple example is the m-[Co(acac)2(NH 3)2]1 (acac = 2,4-pentane-dionate), structurally characterized and utilized to produce molecular mechanics force field parameters for /3-diketones bound to Co111.982... 

Another class of molecules related to the metalla-/3-diketonates are the metalla-B-diphosphinites, LnM(R2PO)2 (7-10). These anionic complexes can be protonated to give neutral enolic tautomers or coordinated to main group elements or metal ions to give polynuclear complexes. The metalla-/3-diketonate anions form the same types of complexes. 

Metalla-/3-diketones are readily prepared by protonation of metalla-/3-diketonate anions. The first reported metalla-j8-diketone was the rhenaacetylacetone molecule [ds-(OC)4Re(MeCO)2]H (10) (1,24). Diagnostic indications of the formation of this type of complex are (1) the appearance of a cw-L2M(CO)4 pattern in the carbonyl C—O stretching... 

A large number of complexes have been prepared in which metalla-/3-diketonate anions coordinate to either metal ions or B(X)(Y) moieties. The chemistry of such metal complexes has been reviewed previously (7). To summarize briefly, tris-chelate complexes (3) of Al(III) or Ga(III)... 

Metalla-j3-diketones or metalla-/3-diketonate anions react with trigonal boron compounds, BX2Y, in which X = Y = halogen or X = Cl and Y = Ph, to afford neutral (metalla-/3-diketonato)B(X) (Y) complexes. Complexes of this type are known with mangana-, rhena-, and ferra-/3-diketonato ligands. The earlier chemistry of these complexes has also been previously reviewed (J). 

The general interligand C—C coupling reaction shown in Eq. (8) for (metalla-/3-diketonato)BF2 compounds also occurs directly with metalla-/3-diketonate anions, thereby precluding the need to prepare the neutral difluoroboron complexes (53). As a one-pot synthesis, metal carbonyl acetyl compounds can be converted to neutral 77-allyl complexes [Eq. (12)]. 

The LSR itself consists of a lanthanide ion, commonly europium (Eu3 + ), praseodymium (Pr3+) or ytterbium (Yb3+), and three /1-diketone anions with alkyl or perfluoroalkyl groups Rl and R2 as ligands. Perdeuterated LSRs, which do not give H signals, are commercially available. Incorporation of chiral /J-diketone ligands, mostly derived from substituted camphors, allows chiral recognition. 

The methine proton in the keto form and the hydroxyl proton in the enol form of jS-diketones are acidic and their removal generates 1,3-diketonate anions (2), which are the source of an extremely broad class of coordination compounds referred to generically as diketonates or acetylacetonates. The synthesis, structure and properties of these compounds form the focus of this chapter. Di-ketonate anions are powerful chelating species and form complexes with virtually every transition and main group element. The scope of this chemistry is very large and it has been assessed earlier in several excellent reviews.9-14... 

The (3-diketonate chelate complexes are very stable and exhibit properties which are rather typical of aromatic systems. Many of their reactions such as halogenation, alkylation and acylation can be compared with those of the P-diketonate anions associated with alkali metal cations. However, complexes of transition and other metals add to the stability of the system, so that quite vigorous reaction conditions can be employed. In most of the work carried out on P-diketonate chelates, the modified ligand has not been removed from the metal ion, but this can usually be effected if desired. 

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). 

Metalla /3-diketonate anions may be obtained by reactions of the type... 

Figure 3 Examples of some of the coordination modes known for S-diketonate anions...

Although formally an a-diketone, tropolone gives rise to a monoanion (equation 16) with coordination chemistry similar to that of the /3-diketonate anions. The tropolonate ion forms a five-membered chelate ring, which has a smaller Bite Angle (see Bite Angle) than /3-diketonate anions. This feature, in combination with its rigid planar nature, makes the tropolonate ion suitable for the formation of complexes... 

Synthetic routes for the preparation of lanthanide monoporphyrinate complexes with non-diketonate anionic axial ligands have been developed in recent years. Wong and coworkers developed a convenient synthetic route for the preparation of cationic lanthanide(III) monoporphyrinate complexes [Ln(porphyrin)(H20)3]Cl via the protonolysis of lanthanide(III) amide... 

Silicon-containing S-diketonate anions (14) provides an attractive, novel approach to modification of the thermal stability and volatility of Cu(II) MOCVD precursors based on / -diketonato ligands. Multinuclear NMR studies suggest that the sUa-/ -diketons exist as the enolic tautomer with a C=C—Si structure. 

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