Diketone complex Subject

The first ionic hexacoordinate complexes, silicon-tris-acetylacetonate cations (176), were reported as early as 1903 by Dilthey196a and Rosenheim and coworkers196b. Subsequently many other /i-diketonate complexes were studied197-199, and the subject was extensively reviewed7,200 and will not be discussed further here. 

Complexes of acac and Related Ligands.—Mechanisms of isomerization of -diketone complexes have been the subject of a review. Two studies of isomerization and racemization rates of diketone complexes establish orders of relative reactivity for complexes of various cations. For complexes M(tfac)a, rates of isomerization are in the following order ... 

Isomerization and racemization of jS-diketone complexes of aluminium and of gallium are still the subject of kinetic investigations recently reported results are collected in Table 16. As for these reactions of transition-metal... 

Rare-earth jS-diketonate complexes with hemicyanine or related chromophotes have been studied for their potential as nonlinear optical materials (NLO materials). Such nonlinear optical materials could have applications in the domains of opto-electronics and photonics (Verbiest et al., 1997). Nonlinearity of the optical properties means that when a molecule is placed in an intense light beam, there is no linear relationship between the induced electric dipole moment and the applied electric field. When a molecule is subjected to an intense light field, the induced dipole moment is given by eq. (12). 

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. 

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. 

The keto-enol equilibrium of the 1,3-diketones has been the subject of intensive studies using various physical techniques and theoretical calculations [78-80], Recently, X-ray crystal analysis of acetylacetone (83) was carried out at 110 K, and it was found that it exists as an equilibrium mixture of the two enol forms 83b and 83c [81]. Room-temperature studies show an acetylacetone molecule with the enolic H-atom centrally positioned, which can be attributed to the dynamically averaged structure 83d. Application of a crystal engineering technique showed that a 1 1 inclusion complex of83 can be formed with l,l/-binaphthyl-2,2/-dicarboxylic acid in which the enol form is stabilized by a notably short intramolecular hydrogen bond [82],... 

Several quite stable complexes can be formed with Cf(iii) (see Table 11.9). Complexes of diketones and aminopolycarboxylic acids are considerably more stable than those of tartrate, lactate, oxalate, etc. In some cases, adduct chelates can be formed with Cf (iii), as with californium thenoyltrifluoroacetone chelate and methyl isobutyl ketone (Cf(TTA)3 + MIBK- Cf(TTA) MIBK or Cf(TTA)3 -2MIBK) [23]. With the monodentate ligand tributyl phosphate, the extractable californium adduct from nitric acid solution has been assigned as the 1 3 species Cf(N03)3 3TBP [227]. Quaternary ammonium bases and alkylpyro-catechols (i.e. 4-(a,a -dioctylethyl)pyrocatechol) can form complexes in alkaline solutions [228]. One recent extraction study has examined the influence of the extractant s structure on the extraction behavior of californium [229]. A large number of materials have been investigated for forming extractable complexes of californium and the reader is referred to reviews on the subject [27, 32, 33]. 

Total synthesis of baconipyrone C, summarized in Scheme 12.5 [10], is the first and only application of Ru-catalyzed enantioselective olefin metathesis to natural product synthesis. Treatment of oxabicycle 11 with styrene and 2mol% chiral Ru complex [Ru]-XV [11] leads to the formation of pyran 12 in 62% yield and with an enantiomeric ratio of 94 6. Ru-carbene [Ru]-XV is generated in situ by subjecting the corresponding Ag-based N-heterocyclic carbene (NHC) to an achiral Ru-PCys complex and Nal. It is also worthy of note that the diketone fragment of baconipyrone C was synthesized through a tandem double-allylic alkylation process promoted by a chiral NHC-Cu complex that is structurally related to carbene [Ru]-XV. 

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