Metalation heterometallic species

Interesting examples of simple substituted heterometallic species are [(thf)M p-N(SiMe3)2 2M (th 2] (M/M = Li/Na, Li/K and Na/K) which were obtained from solutions of 1 1 mixtures of the metal salts.The unsolvated ( LiXtSiMe J , K- lSiXleO, ), has a polymeric, one-dimensional chain structure formed by alternating lithium and potassium centres bridged through the hexamethyldisilazides (Li—N= 1.935(1) A and K—N = 2.86(1) A) with linear coordination at K and almost linear coordination (N-Li= 176.4(3)°) atLi. ... 

In addition to the heterometallic species involving group 1 and group 2 metals there is also an example featuring two alkahne earth elements in the heterobimetallic compound which has a puckered (MgNCaN) ring... 

The reaction of metal halides with an alkoxide or aryloxide (most commonly an alkali metal alkoxide), can resnlt in metathetic exchange to give the required complex (equation 6). Such reactions can also result in the formation of heterometallic species (such as NaZr2(OR)4) this can be a problem when homometallic aUcoxides are desired, but it is an important route to heterometallic alkoxides and aryloxides. The nature of the product can be influenced by the alkali metal, the alkoxide ligand, and the relative amounts of the reactantsd ... 

Finally, elemental analysis results may pose difficulties in arriving at the correct composition of tin(II) heterometallic compounds due to changes in metal-ligand ratio. However, with the help of X-ray structural analysis, the CHN results may prove fruitful to prove the stoichiometry of the heterometallic species. 

A key issue in the activity of these catalysts concerns the specific role of the Cu and Cr active sites which are expected to be located on the surface of the catalyst particles. Since both Cu(II) and Cr(III) are paramagnetic, EPR spectroscopy can be used to identify the nature of the heterometallic species within the catalyst matrix after different thermal and chemical treatments. However, a detailed picture of the local environment of tlie transition metal center camiot be obtained by conventional continuous wave EPR spectroscopy alone. These can, nevertlieless, be obtained by pulsed EPR methods, namely the electron spin echo envelope modulation (ESEEM) tecluiique. 

Reaction of a reduced Philipps catalyst with Fischer-type molybdenum or tungsten carbene or carbyne complexes led to very active bimetallic, heterogeneous olefin metathesis catalysts. Surface metal ions might be involved in bonding interactions with the organometallic complex, possibly leading to heterometallic species on inorganic oxides. ... 

Determination of the stoichiometry of the reaction is best achieved if it is conducted in a solvent in which one of the reactants is poorly soluble. Since the heterometallic species is more soluble than the parent alkoxide, the progressive dissolution of the most insoluble species allows control of the stoichiometry between the two different metals. Metal NMR ( Li and Nb) may also be used as tool to follow the reaction, as shown for LiNb(OR)6 [91], The following reactions, which all proceed at room temperature, are examples of this approach ... 

Although metal b-diketonates can be solubilized in the presence of a metal alkoxide and thus form heterometallic species, at least as intermediates, most reactions are more in favor of the formation of redistribution products [Af(OR)n-x(P-dik) c] as the final result [92]. 

Whereas extensive information on the metal-binding abilities of mammalian MTs has been compiled, current knowledge of those of non-mammalian species is more limited and rather dispersed. In order to fill this gap, existing data have been summarized in Table 1. A feature commonly found in several MTs is that they contain heterometallic mixtures of two (Zn,Cd Cu,Cd Zn,Cu) or three (Zn,Cd,Cu) metal ions. Still more striking is the great diversity of stoichiometries reported for certain homometallic metal-MT species, as shown in S. cerevisiae, where the copper-to-MT mole ratios range from 4 to 10, and in N. crassa, with a cadmium-to-MT mole ratio of 2 or 3. With this information on the metal-binding properties of MTs, it seems reasonable to conclude that the systematization of these data is hard indeed to achieve. 

In addition to the previously mentioned heterometallic species formed by alkali metal, alkaline earth, or yttrium and lanthanide ions with titanium, zirconium, or hafnium, a number of other heterometallic complexes of the latter elements with transition and nontransition metals have been reported. 

To conclude on aluminum hydroxides, it is noteworthy that deprotonation by an organometallic base of the Al-OH moiety has been developed to access the corresponding heterobimetallic Al-O-M-bonded analogues (M = a main group, a transition or a lanthanide metal center) [170]. Such discrete heterometallic species... 

There are, of course, metal-containing dendrimers that belong to more than one of the above-mentioned categories. Examples are the heptametallic dendrimer made of a central Fe(Cp)(C6Me6)+ core and coated with 6 ferrocene moieties [ 12], and the heterometallic dendrimers made of an organic core, containing up to 6 Pt(IV)-based organometallic species in the branches, and coated with up to 12 ferrocene units [13]. 

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