1,3,5-Triketones metal complexes

Another area where metal /3-diketonates have made a significant impact is in the oxidation of aLkanes , alkenes and alcohols A number of different metal complexes have been used in these reactions, including Pd(acac)2 (29) , Co(acac)3 (30) , Fe(acac)3 (31), a bimetallic Pd(II) complex containing a 1,3,5-triketone ligand, MCI (acac)(PPh3) (32) where M = Ni, Co, Cu, Mn(acac)3 (33) , Mo02(acac)2 (34) , VO (acac)2 (35) and VO(hfac)2 (36) . In the latter study, the oxidation of a-acetylenic... 

Preparation and Characterization of Heteronuclear Chelates. Once it was established that the two sites in SchiflF-base derivatives of 1,3,5-triketones may specifically coordinate diflFerent metal ions, it became feasible to prepare pure mixed metal complexes in which the position of the two metal ions is known. As a matter of preparative convenience in the early stages of this work, we chose to use Ni[H2(BAA)2en] as a ligand to bind a diflFerent metal ion which has a preference for the available oxygen donor site (Reaction 2). The major rationale for using the... 

Of the 33 papers presented at the symposium 32 are included in this volume. They are of two general types. One type discusses inorganic compounds exhibiting a specific property, most frequently electrical or photochemical. The second type reviews recent developments in the synthetic chemistry of a class of inorganic compounds— most often transition metal or lanthanide complexes— which are of potential interest to persons looking for new systems with unusual properties. Classes of compounds covered by this second type include metal alkyls, metal alk-oxides, metal alkylamides, metal chelates, and metal clusters as well as metal complexes with polyboranes, polyphosphines, macrocyclic derivatives, di- and triketones, and polypyrazolylborates as ligands. 

The latest developments in this class of metal complexes were concerned with the structural modification of the triketone ligands to the [3, 6-type. Two series of dicopper complexes were obtained with six and eight peripheral chains respectively ((68) R = H or OC H2 +i)." Not surprising, they all showed a Coin phase, the complexes with eight chains having lower transition... 

Mononuclear V02+ and heterodinuclear V02+ complexes (with Cu2+, Ni2+, Mn2+, Zn2+, Pd2+ as the second metal ion) have been reviewed.894 In this section, we shall mainly discuss more recent work. Many complexes were with Schiff bases from the reaction of /3-triketones or /3-ketophenols with ethylenediamine. One important aim has been to compare the magnetic, spectral and chemical properties for the metal ion Ma in [Ma(diken)] and Mb in [Mb(diketonato)2], with the corresponding properties in the binuclear complexes formed (see equation 66). 

Triketones and similar polyketones exhibit keto-enol tautomerism and have been found to coordinate to one or more metal atoms (24). Such complexes can bring metal atoms in close proximity, resulting in interesting magnetic properties (see Magnetism of Transition Metal Ions). 

The presence of S-carbonyl groups with at least one proton on the carbon between them allows a keto/enol tautomerism to occur and, under appropriate conditions, the eno-lic proton can be removed. The S-5-tricarbonyl compounds are the higher analogues of the / -diketonates and can take triketone, monoenol and dienol forms in their tautomeric equilibrium (equation 86) accordingly, they can behave as bidentate or tridentate ligands to form metal chelate complexes. ... 

The 1,3,5-triketones are potentially dinegative, tridentate ligands and the well-developed JT-system of the dianion gives to the ligands a preference for a planar configuration, thus precluding tridentate coordination to one metal ion. For example, copper(ll) and heptane-2,4,6-trione give mononuclear (132) and dinuclear complexes (133) ". ... 

As pointed out some time ago, the electrochemistry of the dicopper complex of the series M2(l,3,5-triketonate)2 (140) posed some problems of interpretation. It was at first thought that the copper(II) complexes should display a single two-electron reduction [Cu(II)—Cu(II) Cu(I)—Cu(I)], with features of chemical reversibility in the short reaction times of cyclic voltammetry . Later, it was stated that they undergo a single two-electron reduction only in the presence of alkali metal ions. In the absence of such cations, the Cu2(l,3,5-triketonate)2 derivatives undergo the stepwise sequence Cu(II)—Cu(II) Cu(II)—Cu(I) Cu(I)—Cu(I), the second one-electron reduction being irreversible and located at rather negative potential values " . ... 

Interested by the effect of other structural modifications on the thermal behavior, and the possibility to combine several metal centers within the same compound, Swager and co-workers pursued this research, and reported series of homo-dinuclear, hetero-dinuclear 1,3,5-triketonate (79), and 1,3,5,7-tetraketonate Schiff-base complexes (80). " Providing a minimum of at least six lateral chains and short diamine spacers ((79) M, M = Cu, Ni, Mn, Pd, Co X = C2H4, CsHg), complexes (79) displayed Colh mesophases, being as such the first heterodinuclear metallomesogens (Table 48). The mesophase existed over broader temperature ranges than those of the related... 

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