Tris -diketonates

Tris(bipyridyl) complexes structure, 1, 63 Tris(diketonate) complexes structure, 1,65 Trisdithiolencs metal complexes synthesis, 2, 597... 

The complex [Fe"(bpca)2][Fe"(hfac)2]2, where Hbpca = bis(2-pyridylcarbonyl)amine, (230), consists of a pair of high-spin tris-/ -diketonate units bridged by a low-spin Ng entity." [Fe" (hfac)2] can bridge through the pyridyltriazine tptz, (231), to molybdenum(O), in Mo(CO)4( tptz), and rhenium(I) in ReCl(CO)3( tptz). ... 

Metal alkoxides constitute a useful class of starting materials for the synthesis of the metal / -diketonates. The ethoxides of Nbv, Tav and Uv react with diketones. Here, only partial substitution of the ethoxy groups occurs and materials of the type M(diketonate)3(OEt)2 are formed.194,195 Similar reactions with lanthanide alkoxides, however, provide pure, unsolvated lanthanide tris(diketonates). The virtue of such syntheses lies in their ability to yield anhydrous diketonate complexes. Removal of water from the hydrates without decomposition is sometimes difficult.196,197... 

Rearrangements of six-coordinate tris(diketonate) metal complexes have been the subject of numerous intense and careful investigations and the great body of literature has been incisively reviewed.77,283 A principal conclusion is that in no case has a unique rearrangement been unambiguously established and indeed, one may not exist. The difficulty arises from the consideration that the various five-coordinate transition states (or intermediates) which result from bond rupture processes can have quite similar energies. Thus, combinations of mechanisms can obtain which lead to extremely complicated DNMR spectra or isomerization kinetics. 

Figure 5-7. The direct nitration of a co-ordinated 2,4-diketonate ligand. The 2,4-diketonate complexes are not usually stable to nitric acid and the nitration is effected by milder reagents, such as a mixture of copper(n) nitrate and acetic anhydride (which generates N204). When tris(diketonate) complexes, such as [Co(acac)3] are nitrated, mixtures of mono-, bis- and tris- substituted products are obtained.

The same group most recently reported the use of neutral lanthanide(III) tris-diketonates of type 88 for the determination of chloride [63]. The response in luminescence of the Eu(III) complex for chloride in acetonitrile solution was large enough to be seen by the naked eye. Incorporation of the complexes in... 

Comparative absorption spectrophotometry has been used in the studies of lanthanide /J-diketonatc complexes in solids as well as in solutions. The neutral hexacoordinated lanthanide tris diketonate on dissolution in a polar nonaqueous solvent, increased its coordination to eight by accepting two solvent molecules [204]. The addition of water or other oxygenated solvent to Nd(diket)3 in solution resulted in significant changes in the shape and intensity of the band due to 4l9/2 —> 4Gis/2, transition. These changes have been attributed to an increase in coordination number of Nd(III) from 6 to 8 by the coordination of two solvent molecules [238-241]. 

The binuclear lanthanide-silver reagent is formed by combining silver diketonate such as Ag(fod) with a lanthanide tris diketonate like Yb(fod)3 to give Ag+[Yb(fod)3]-. 

And there is a recent example of a sexadentate tris(/ -diketone) ligand (124). Perhaps not surprisingly the trianion of this ligand gives a very robust Mn111 neutral molecule, which can be reduced to Mn and this latter species also is kinetically stable to ligand exchange.318... 

Chiral lanthanide tris(/ -diketonates) have been used with many classes of organic compounds that have oxygen- and nitrogen-containing functional groups, as well as metal... 

Geometrical isomerism is potentially possible among many of the lanthanide chelates. The 1,3-diketone chelates, the species derived from the aminepolycarboxylic acids, the tropolonates, and many other complex derivatives are asymmetric and, thus, potentially capable of exhibiting optical isomerism. That the only resolutions reported have been limited to some tris (diketone) compounds (35) may refiect more the tendency of these ionically-bonded species to racemize rapidly in polar environments than in the absence of asymmetry. The existence of more than a single modification of each of several tetrakis(di-keto)europium(III) compounds may refiect asymmetry also (1). 

The most stable oxo-complexes are chelate compounds. Gallium and indium form tris- -diketone complexes, soluble in alcohol and benzene, and structurally similar to those of aluminium (Fig. 155). Gallium and thallium form trioxalato compounds like the oxalato-aluminates MJ[Ga ( 304)3]HgO. All the metals form tris-complexes with oxine (Fig. 156). 

In the case of the much more labile tris-diketonate complexes of aluminum and gallium, the techniques of study are more complex since it is impossible to isolate even partially resolved samples. The most probable mechanisms for these labile complexes appear to be certain twist processes along with bond rupture to give spy transition states. 

As a consequence of the success of rationally designed tris-bidentate ligands for the straightforward synthesis of [M4L4] tetrahedra (see Sect. 2.4.1), the three-fold symmetric, tris-bidentate pyrazolone-based ligand H3L 30 was prepared. Tris-diketone ligand 30 is generated from 3-methyl-1-phenyl-2-... 

There has been some work on interactions between LSRs and transition metal complexes, both NMR shifts and relaxation rates being studied. Presumably the mode of interaction is by means of bridges formed by the donor atoms of one complex which bond in a labile manner to the metal ion of the second complex. Interactions examined include those between [Eu(fod-[Pg.2943]

X-ray crystal structures, 397 tetrakis(perfluoroalkanesulfonates), 418 tetraphenylporphyrin, 440 thioacetylacetonato, 439 thiocyanates, 380 thioethers, 418 thiolates, 418 thiosemicarbazones, 434 thiourea, 421 tin-containing ligands, 370 trialkyIsilyloxides, 389,391 triazenes, 378 triethylamine, 371 trihydroxyglutaric acid, 412 tris(diketonates), 399 tropolonates, 402 urea, 382 water, 384... 

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