Anion coordination

In studying two-component polymerization catalysts, beginning with Feldman and Perry (161), a radioactive label was introduced into the growing polymer chain by quenching the polymerization with tritiated alcohols. The use of these quenching agents is based on the concept of the anionic coordination mechanism of olefin polymerization occurring... 

The first and third examples illustrate a nuance of the naming rules. Iron and silver in anionic complexes are named by their Latin roots,/err- and argent-, from which their symbols (Fe and Ag) are derived. Metals taking their Latin names in anionic coordination complexes are listed in Table 20-4. 

Subsequently, an in situ Pd(OAc)j-imidazolium salt mixture, developed by Nolan and Grasa, has demonstrated its efficiency for the coupling of aryl bromides and even chlorides with aryl and vinylstannanes. This improved reactivity is due to the TBAF additive, whereby F anions coordinate to Sn forming hypervalent fluorostannate anions that are more reactive towards transmetallation to Pd [121] (Scheme 6.37). 

VI. Anion Coordination by Protonated Tris(pyrazolyl)hydroborato Derivatives... 

For other structurally-characterized anion coordination complexes, see ... 

Fig. 11 Fragment of the crystal structures of tetracyanobenzene/bromide complex showing different modes of anion coordination to the acceptor moieties (coordinates from [24])...

L-L)]OTf (L-L = bipy, phen).1889 The compound (Et4N)4KAuAs4Te8 contains two As2Te44-anions coordinating to a Au3+ cation forming a square-planar AuTe4 unit (327).1890... 

Polystyrene Styrene Free radical Cationic Anionic Coordination... 

A large number of complexes have been prepared in which metalla-/3-diketonate anions coordinate to either metal ions or B(X)(Y) moieties. The chemistry of such metal complexes has been reviewed previously (7). To summarize briefly, tris-chelate complexes (3) of Al(III) or Ga(III)... 

Gale, P. A. Anion coordination and anion-directed assembly highlights from 1997 and 1998. Coord. Chem. Rev. 2000, 199, 181-233. 

The substitution by two Nd for three AE ions in the solid solutions should provoke one cation vacancy formation for attaining electroneutrality. The created vacancies render the nearby oxide anions coordinatively unsaturated and more basic what was supported by C02-TPD data. The more pronounced shift of Tmilx in the SG samples confirmed the better incorporation of Nd. 

According to detailed XRD analyses, the two catalyst preparation procedures under study formed solid solutions. The application of sol-gel method led to improved selectivity to olefins in the reaction of propane ODH, compared to the simple procedure of evaporation and decomposition. However, the propane conversion on the sol-gel catalysts was lower at the same experimental conditions, while the catalysts surface area was higher. Moreover, the sol-gel samples presented higher basicity as shown by C02 TPD. It could be explained by a better incorporation of Nd into the AEO lattice, creating cationic vacancies for attaining electroneutrality and thus rendering the nearby oxide anions coordinatively unsaturated and more basic. 

The reaction of the tetranuclear mercuracarborand 166 with 2 or 3 equiv. of KNO3/I8-C-6 in acetone affords two different nitrate complexes namely [166-(N03)2(H20)]2 and [166-(N03)2]2 (Figures 15 and 16). In both cases, the nitrate anions are ligated to the mercury centers by Hg-O interactions ranging from 2.60 to 3.08 A. In [166-(N03)2]2, the two anions coordinate with all four mercury atoms in a face-on trihapto fashion from either side of the plane.216... 

The study of anion coordination has implications for a number of areas in chemistry and biochemistry. These include analytical applications concerned with anion sensing or separation as well as model studies for anion-specific biochemical systems. With respect to the latter, it is of interest that the majority of enzymic systems so far characterized bind substrates which are anionic. 

The above reactions are rather slow because the insertion reactivity is directly related to the rate of dissociation of the THF ligand, which is also present as the solvent. The most reactive cationic complexes are therefore base-free, i. e. they do not contain coordinating solvents or ligands. Logically, anion coordination is a problem in such systems. Ion pairing reduces the reactivity of the cationic zirconocenes, but in the presence of B(C6F5)4, RB(C6F5)3 (R = H, Me), or BARF", this interaction is only weak. 

Fig. 2 Chemical structures of fluorescent ligands (anion coordination sites are indicated in blue) and tentative reaction schemes on interaction of 6 with chloride and fluoride in dichloromethane according to the color patterns observed in [41]. The wavelengths of absorption given in brackets have been calculated for the geometry optimized species 6, 6-C1 and 6 in the gas phase by semiempirical AMI calculations (Ampac V6.55, Semichem)...

The anion coordination properties of receptors such as compound [93] (Fig. 51) are currently under investigation. This molecule contains both a redox-active ruthenium bipyridyl moiety and also a cobaltocenium unit. This type of host has already been shown by 1H nmr and fluorescence emission spectroscopy to exhibit remarkable selectivity for the chloride anion in preference to dihydrogenphosphate (Beer and Szemes, 1995). 

Vibrational spectra, especially infrared spectra, have been obtained for a wide variety of lanthanide complexes. The main conclusions that emerge from infrared spectral studies concern the site of coordination of the ligand, the nature of anion coordination and the relative strength of metal-ligand interactions. 

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