Acetylacetone transition metal complexes

The curing reaction can be carried out thermally or with the addition of a catalyst. The thermal cure is strongly influenced by impurities associated with the synthesis. The greater the degree of monomer purity, the more slowly the thermal cure proceeds. If the monomer is sufficiently purified, the cure rate can be predictably controlled by the addition of catalysts. As with the aromatic cyanate esters, the fluoromethylene cyanate esters can be cured by the addition of active hydrogen compounds and transition metal complexes. Addition of 1.5 wt% of the fluorinated diol precursor serves as a suitable catalyst.9 The acetylacetonate transition metal salts, which work well for the aromatic cyanate esters,1 are also good catalysts. 

The structure of bis(salicylaldoxime)beryllium has been proposed as being trans octahedral by comparison of the space group and unit cell volume with those of related transition metal complexes it is presumably a dihydrate if it is indeed octahedral in geometry.297 Stability constants have been reported for a range of beryllium /3-ketoamines derived from both salicylaldehyde and acetylacetone precursors. They show strong complexes which are stable to hydrolysis under the conditions used.298,299... 

Acetylacetone usually forms transition metal complexes by coordination through bidentate oxygens. Since platinum forms unusually strong bonds to carbon, acetylacetonato complexes of platinum(II) are frequently C-bonded. When Pt(acac)2 is treated with 1 mole of pyridine, a bidentate oxygen-bonded acetylacetonate ligand is converted to a y-carbon-bonded ligand. 

To reduce the nuclei s Tx relaxation time, relaxation agents are used. Relaxation agents are usually transition metal complexes, primarily ferric ethylenediaminetetraacetate or chromium acetylacetonate. Transfer of en-... 

This method was successfully applied using acetates [64,65], acetylacetonates [66,67], alkoxides [16,68,69] and [Pd2(dba)j] [70]. In fact, the first NHC transition metal complex reported by WanzUck and Schonherr in 1968 [3] used mercury(II) acetate and 1,3-diphenylimidazolium perchlorate as the starting materials. 

Acetylacetone (acac) and related ) -diketones continue to be extensively used as ligands for transition metal complexes. This section deals with tris(acac) complexes followed by a discussion of the spectra of adducts of bis(acac) complexes. Cramer and Chudyk (75) have studied [Ni(acac)3]2C104. INDO calculations show that the major spin delocalization is into the highest filled ligand orbital which possesses cr-symmetry plus a minor contribution from delocalization into the lowest empty 7i-orbital. This is in contrast to the spin delocalization in Ni(acac)3 and Ni(acac)py2 where the major de-localization is into the highest filled ligand orbital of Ti-symmetry. 

The superior catalytic activity of Ni catalysts over other transition metal complexes was proven by a comparison of a series of metal acetylacetonates as catalysts for the polymerization of ethyl isocyanide in chloroform (Scheme 14) [15]. Fe(acac)3, Mn(acac)2, Zn(acac)2, and Cd(acac)2 showed either no, or an extremely low, catalytic activity, whereas Cr(acac)3 and Co(acac)3 afforded almost 10% yield of poly (isocyanide). Co(acac)2, Pd (acac)2, and Cu(acac)2 exhibited moderate activity, resulting in the formation of the polymer in 29-61% yields. Ni(acac)2 showed almost the same catalytic activity as Co2(CO)8, whose remarkable catalytic activity had already been established by Yamamoto et al. [5]. 

A variant on this theme is to attach a transition-metal complex of a smart polymer, the solubility of which can be dramatically influenced by a change in a physical parameter, e.g., temperature [23] (cf. Sections 4.6 and 4.7). Catalyst recovery can be achieved by simply lowering or raising the temperature. For example, block copolymers of ethylene oxide and propene oxide show an inverse dependence of solubility on temperature in water [24]. Karakhanov et al. [25] prepared water-soluble polymeric ligands comprising bipyridyl (bipy) or acetylacetonate (acac) moieties covalently attached to poly(ethylene glycol)s (PEGs) or ethylene oxide/propene oxide block copolymers 9 and 10. 

Titanium, tris(acetylacetone)-structure, 65 Titanium(III) complexes magnetic behavior, 271 spectra, 250 Titanium tetrachloride photoreactivity, 406 Titrimetry, 552 T oluene-3,4-dithiol in gravimetry, 534 metal complexes liquid-liquid extraction, 547 Topochemical reactions, 463 Topotactic reactions, 463 Trans effect, 16, 26,315 six-coordinate compounds, 49 Trans influence square planar complexes, 38 Transition metal complexes d... 

C-H bond in active methylene compounds is acidic and can also oxidatively add to low-valent transition metal complexes giving transition metal enolates. Eor example, acetylacetone oxidatively adds to low-valent Mo complexes giving hydrido(acetylacetonato)metal complexes [197]. 

The interpretation of the experimental a constants for the fluoroalkyl and nitroxide radicals is complicated because the stereochemistry at the radical center is not well defined. This complication does not exist for radicals derived from aromatic compounds. Consequently, several research groups have investigated aromatic radicals to characterize the factors governing spin delocalization to /3-fluorine atoms. One aspect of this work concerns the epr spectra of nitrobenzene anion radicals. Another concerns the contact chemical shifts of paramagnetic transition metal complexes. The latter approach was initiated by Eaton, Josey, and Sheppard who examined stable bis(phenylaminotroponiminato)-nickel(II) complexes (55a). More recently, we have examined the contact chemical shifts in the nmr spectra of nickel acetylacetonate complexes of aniline derivatives (556). 

This is the most commonly utilized method for synthesis of transition metal complexes with M —C a bonds. The following substrates are utilized halides, acetylacetonates, acetates, /-electron element alcoholates, as well as organometallic compounds of lithium, magnesium, aluminum, sodium, zinc, mercury, elements of group 14, etc. Ethers and hydrocarbons are used as solvents. In general, the synthesis should be carried out at lower temperatures and under inert atmosphere. 

As homogeneous catalysts, alkali metals. Li —amide,and transition metal complexes such as Ni[P(OC2Hs)3]4, Ni acetylacetonate, PdBr2(Ph2PCH2PPh2),... 

To the best of our knowledge, 1, 2, and 4 represent the first examples of cationic transition metal complexes bearing an open coordination site that possess substantial solubilities in alkane and perfluoroalkane solvents. These species are probably tightly ion paired in these media but still appear to be ionic, since the molecular complexes 3 and 5 exhibit considerably higher solubilities. The results of this study provide a rational basis for increasing the solubility of transition metal complexes in nonpolar media through the use of polysilylated cyclopentadienes and substituted acetylacetonates. The fact that the worst case scenario (i.e., cationic complex solubility in cyclohexane and perfluoromethylcyclohexane) is easily achieved implies that simple ligand modification should allow the use of less reactive nonpolar solvents in cases where solvent coordination or reactivity is a problem. 

The flavin is an efficient electron-transfer mediator, but rather unstable. Several transition metal complexes, for instance vanadyl acetylacetonate, can also activate hydrogen peroxide and are capable of replacing the flavin in the dihydroxylation reaction [18]. 

Transition-metal mixed oxides active in combustion catalysis have been prepared by two main procedures i) classical coprecipitation / calcination procedures starting from metal nitrates and/ or alkoxides ii) preparation based on the supercritical drying of gels prepared from organic complexes (alkoxides, acetylacetonates or acetates), producing aerogels . Details on the second preparation can be found in Ref. 13. 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

As shown by Breslow et al. during the mid-1960s, most transition-metal alkox-ide or acetylacetonate complexes catalyze the hydrogenation of alkenes in the presence of an activator (Table 6.19) [5]. Other precursors have been used such as [CpCr(CO)3]2, but it is more difficult to understand how the active species are formed [133]. 

A broad range of metal centers have been used for the complexation of functional ligands, including beryllium [37], zinc, transition metals such as iridium [38], and the lanthanide metals introduced by Kido [39], especially europium and terbium. Common ligands are phenanthroline (phen), bathophenanthrolin (bath), 2-phenylpyridine (ppy), acetylacetonate (acac), dibenzoylmethanate (dbm), and 11 thenoyltrifluoroacetonate (TTFA). A frequently used complex is the volatile Eu(TTFA)3(phen), 66 [40]. 

---