Diketonate Ligands

The acylstannanes 874 and 875 are prepared by the reaction of acyl chlorides with (MciSnl - The symmetrical 1,2-diketones 877 can be prepared by the reaction of an excess of benzoyl chloride with (EtjSn) . Half of the benzoyl chloride is converted into the benzoyltin reagent 876, which is then coupled with the remaining benzoyl chloride under a CO atmosphere to afford the a-diketone 877[748], Triethyl phosphite is used as a ligand. 

When a bidentate phosphine is used as a ligand for the reaction of J-keto esters or /i-diketones, no dimerization takes place. Only a 2-butenyl group is introduced to give 68[49,62], Substituted dienes such as isoprene, 1,3-cyclohexa-diene, and ocimene react with carbon nucleophiles to give a mixture of possible regio- and stereoisomers of 1 1 adducts when dppp is used as a ligand[63,64]. 

Tris(2,4-pentanedionato)iron(III) [14024-18-1], Fe(C H202)3 or Fe(acac)3, forms mby red rhombic crystals that melt at 184°C. This high spin complex is obtained by reaction of iron(III) hydroxide and excess ligand. It is only slightly soluble in water, but is soluble in alcohol, acetone, chloroform, or benzene. The stmcture has a near-octahedral arrangement of the six oxygen atoms. Related complexes can be formed with other P-diketones by either direct synthesis or exchange of the diketone into Fe(acac)3. The complex is used as a catalyst in oxidation and polymerization reactions. 

Titanium chelates are formed from tetraalkyl titanates or haUdes and bi- or polydentate ligands. One of the functional groups is usually alcohoHc or enoHc hydroxyl, which interchanges with an alkoxy group, RO, on titanium to Hberate ROH. If the second function is hydroxyl or carboxyl, it may react similarly. Diols and polyols, a-hydroxycarboxyflc acids and oxaUc acid are all examples of this type. P-Keto esters, P-diketones, and alkanolamines are also excellent chelating ligands for titanium. 

For elimination of intramolecular energy losses, we have synthesized ligands with high hydrophobisity - perfluoro-P-diketones R -CO-CH -CO-R, (R = CgF j or CgF R = phenyl or a-thienyl), that without second ligand eliminate completely water molecules from the inner coordination sphere. These ligands we have used in analysis at determination of Sm, Eu, Nd, Yb microamounts in high-purity lanthanide and yttrium oxides. 

In addition to the oxide carboxylates, beryllium forms numerous chelating and bridged complexes with ligands such as the oxalate ion C204 , alkoxides, /9-diketonates and 1,3-diketonates. These almost invariably feature 4-coordinate Be... 

Copper(II) also forms stable complexes with O-donor ligands. In addition to the hexaaquo ion, the square planar /3-diketonates such as [Cu(acac)2l (which can be precipitated from aqueous solution and recrystallized from non-aqueous solvents) are well known, and tartrate complexes are used in Fehling s test (p. 1181). 

Several carboxylates, both simple salts and complex anions, have been prepared often as a means of precipitating the An ion from solution or, as in the case of simple oxalates, in order to prepare the dioxides by thermal decomposition. In K4[Th(C204)4].4Fl20 the anion is known to have a 10-coordinate, bicapped square antipris-matic structure (Fig. 31.8b). -diketonates are precipitated from aqueous solutions of An and the ligand by addition of alkali, and nearly all are sublimable under vacuum. [An(acac)4], (An = Th, U, Np, Pu) are apparently dimorphic but both structures are based on an 8-coordinate, distorted square antiprism. 

Metal-centered emission is found in several rare-earth complexes, for example europium diketone chelates [29]. These compounds emit relatively narrow spectra associated with the d-f transitions of the metal ion. Relatively few comprehensive studies of this class have been carried out to date, but the available evidence [30] seems to indicate that the photoluminescent efficiencies are somewhat lower than the ligand-centered emitters. 

Complexes of O-donors are relatively rare, explicable by the soft nature of the divalent ions. A telling indication is that sulphoxide ligands will only bind through O if steric effects make S-bonding impractical. The most important complexes are diketonates and carboxylates (for the aqua ions see section 3.5). 

The / -diketonates demonstrate that, like platinum(II), platinum(IV) can bond to both carbon and oxygen atoms in the diketonate ligand. 

Chromium, (ri6-benzene)tricarbonyl-stereochemistry nomenclature, 1,131 Chromium complexes, 3,699-948 acetylacetone complex formation, 2,386 exchange reactions, 2,380 amidines, 2,276 bridging ligands, 2,198 chelating ligands, 2,203 anionic oxo halides, 3,944 applications, 6,1014 azo dyes, 6,41 biological effects, 3,947 carbamic acid, 2,450 paddlewheel structure, 2, 451 carboxylic acids, 2,438 trinuclear, 2, 441 carcinogenicity, 3, 947 corroles, 2, 874 crystal structures, 3, 702 cyanides, 3, 703 1,4-diaza-1,3-butadiene, 2,209 1,3-diketones... 

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