Chelation 1-diketones

Pt(btp)(acac), in MeTHF at 77 K. The 0A0-chelated /1-diketone ligand is omitted from the structures shown. Reprinted with permission from [109]. (2002) American Chemical Society... 

Complexes of the type Cp2Yb L and CpYb L2, where L = 1,3-diketone have been characterized and these complexes have chelated diketone [93]. 

Hhfac = hexafluoroacetylacetone Hdbm = dibenzoylmethane.) A full report has appeared on a series of these compounds [Ln(terpy)(N03)2(acac)(H20) ] (Ln = La, Pr, =1 Ln = Nd-Lu, n = Q) They exhibit three different solid-state structures. [La(terpy)(N03)2(acac)(H20)] is 10-coordinate, with two bidentate nitrates and a chelating diketonate and a coordinated water [Pr(terpy)(N03)2(acac)(H20)] is nine-coordinate, with one monodentate and one bidentate nitrate and a chelating diketonate and a coordinated water and the remainder are [Ln(terpy)(N03)2-(acac)]. (Nd-Lu) with two bidentate nitrates and a chelating diketonate. 

AIPO4 were obtained from AICI3.6H2O and H3PO4 (85 wt%) by precipitation with aqueous ammonia [1]. Two chelating diketone organic agents were used ... 

C-Alkylation. This chelated -diketone reacts with primary alkyl halides in DMF to give mainly C-monoalkylation products. C-Dialkylation products are obtained in addition from alkylation with benzylic or allylic halides. O-Alkylation has not been observed. 

FIGURE 113 Synthesis and crystal structure of [Lu4(/i3-OH)4(FcacacPh)8], featuring eight ferrocenyl groups anchored onto a cubane-like [Lu4(/i3-OH)4] via bridging/chelating diketonate ligands (redrawn after Baskar and Roesky, 2006). 

In the tetranuclear complexes [Mn4(/u,3-OMe)4(MeOH)4L4] (L = 2,6-tetramethyl-heptane-3,5-dionate l,3-diphenyl-propane-l,3-dionate) the Mn4(/u,3-OMe)4 core has a cubane-like configuration (Fig. 4.6) with each metal having one chelating diketonate and a coordinated methanol to give an octahedral configuration. ... 

The catalysis by chelated diketonates of vanadium(iv) and by [MoOa(acac)a] of the reactions of t-butyl hydroperoxide with cyclohexene or cyclo-octene have been investigated, the products being only t-butyl alcohol and the corresponding epoxycycloalkanes. The reactions are highly selective and in the case of the vanadium-catalysed systems the rate law is of the form... 

A number of organic compounds, eg, acetylacetone [123-54-6] and cupferron [135-20-6] form compounds with aqueous actinide ions (IV state for reagents mentioned) that can be extracted from aqueous solution by organic solvents (12). The chelate complexes are especially noteworthy and, among these, the ones formed with diketones, such as 3-(2-thiophenoyl)-l,l,l-trifluoroacetone [326-91-0] (C4H2SCOCH2COCF2), are of importance in separation procedures for plutonium. 

Because the stmcture of 1,3-diketones comprise a methylene group between two activating carbonyls, equiUbrium is shifted toward the enol form. The equihbrium distribution varies with stmcture and solvent (303,306) (Table 13). The enol forms are cycHc and acidic and form covalent, colored, soHd chelates with metals ... 

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. 

P-Diketone Chelates. P-Diketones, reacting as enols, readily form chelates with titanium alkoxides, Hberating in the process one mole of an alcohol. TYZOR AA [17927-72-9] (6) is the product mixture from TYZOR TPT and two moles of acetylacetone (acac) reacting in the enol form. The isopropyl alcohol is left in the product (87). The dotted bonds of stmcture (6) indicate electron... 

P-Ketoester Chelates. p-Ketoesters react in a fashion similar to the p-diketones. TYZOR DC [27858-32-8] is the hght-yeUow Hquid from TYZOR TPT and two moles of ethyl acetoacetate (eaa) after removal of the isopropyl alcohol. TYZOR BEAT, the bis-ethylacetoacetate [20753-28-0] derived from the tetra- -butyl titanate, and TYZOR IBAY [83877-91-2] the isobutoxy analogue, perform similarly to TYZOR DC. Both, however, have better cold-storage stabiHty. 

The tetracyclines are strong chelating agents. Both the A-ring and 11,12 P-diketone systems are active sites for chelation (16). This abiUty to chelate to metals, such as calcium, results in tooth discoloration when tetracycline is administered to children (17). 

Deprotonation of enols of P-diketones, not considered unusual at moderate pH because of their acidity, is faciUtated at lower pH by chelate formation. Chelation can lead to the dissociation of a proton from as weak an acid as an aUphatic amino alcohol in aqueous alkaU. Coordination of the O atom of triethanolamine to Fe(III) is an example of this effect and results in the sequestration of iron in 1 to 18% sodium hydroxide solution (Fig. 7). Even more striking is the loss of a proton from the amino group of a gold chelate of ethylenediamine in aqueous solution (17). 

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... 

The carbanions derived from acylthiophenes have been condensed with aldehydes,and, through the Claisen condensation with esters, thienylsubstituted -diketones have been obtained. 2-Thenoyl trifluoroacetone, first prepared by Reid and Calvin through the Claisen condensation of 2-acetylthiophene with ethyl trifluoracetate, has become an extremely useful chelating agent for the extraction of numerous elements from strongly acidic solutions, The tautomeric form which dominates in aqueous solution is the ketone hy-drate. Other thiophenes have also proved useful for analytical purposes. ... 

The photochemistry of transition metal 1,3-diketone chelate complexes has been known for some time [30,31], and their photophysical and photochemical properties and photocatalytic activity in different chemical reactions were reviewed in 1990 by Marciniak and Buono—Core [32]. Further discussion on the photochemistry of meta] chelate will not take place here since this subject is out of the scope of this chapter. 

A number of metal chelates containing transition metals in their higher oxidation states are known to decompose by one electron transfer process to generate free radical species, which may initiate graft copolymerization reactions. Different transition metals, such as Zn, Fe, V, Co, Cr, Al, etc., have been used in the preparation of metal acetyl acetonates and other diketonates. Several studies demonstrated earlier that metal acetyl acetonates can be used as initiators for vinyl polymeriza-... 

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. 

Bond character of (3-diketone metal chelates. B. Bock, K. Flatau, H. Junge, M. Kuhr and H. Muses, Angew. Chem., Int. Ed. Engl., 1971,10, 225-235 (114). 

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... 

Figure 9.1 Chelating agents capable of forming cements, (a) 2-methoxyphenol type. Guaiacol Rj = = H. Eugenol Rj =-CH2-CH=CH2, Rj = H. (b) y -diketone type.

Active zinc oxide is capable of forming chelate cements with a number of liquid organic chelates. These include the ) -diketones, ketoacids and ketoesters as well as the 2-methoxy phenols (Nielsen, 1963). 

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