Cationic metal complexes

DNA is electrochemicaUy inactive under ordinary conditions. Many cationic metal complexes are known as DNA-binding ligands [13 6]. Typical examples of such 

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FIGURE 14.1 Percentages of TLC/HPTLC publications on metal cations, metal complexes, and anions that appeared during the period 1980 to 2004. 

The intercalated catalysts can often be regarded as biomimetic oxidation catalysts. The intercalation of cationic metal complexes in the interlamellar space of clays often leads to increased catalytic activity and selectivity, due to the limited orientations by which the molecules are forced to accommodate themselves between sheets. The clays have electrostatic fields in their interlayer therefore, the intercalated metal complexes are more positively charged. Such complexes may show different behavior. For example, cationic Rh complexes catalyze the regioselective hydrogenation of carbonyl groups, whereas neutral complexes are not active.149 Cis-Alkenes are hydrogenated preferentially on bipyridyl-Pd(II) acetate intercalated in montmorillonite.150 The same catalyst was also used for the reduction of nitrobenzene.151... 

Molecular Conductors Based on Cationic Metal Complexes. 40... 

Compared with the conducting anion radical salts of metal complexes, the number of molecular conductors based on cationic metal complexes is still limited. Donor type complexes M(dddt)2 (M = Ni, Pd, Pt Fig. 1) are the most studied system. The M(dddt)2 molecule is a metal complex analogue of the organic donor BEDTTTF. Formally, the central C=C bond of BEDT-TTF is substituted by a metal ion. The HOMO and LUMO of the M(dddt)2 molecule are very similar in orbital character to those of the M(dmit)2 molecule. In addition, the HOMO of the M(dddt)2 molecule is also very similar to that of BEDT-TTF. More than ten cation radical salts of M(dddt)2 with a cation (monovalent) anion ratio of 2 1 or 3 2 are reported [7]. A few of them exhibit metallic behavior down to low temperatures. The HOMO-LUMO band inversion can also occur in the donor system depending on the degree of dimerization. In contrast to the acceptor system, however, the HOMO-LUMO band inversion in the donor system leads a LUMO band with the one-dimensional character to the conduction band. 

Scheme 2.38. Reactions between copper-zinc reagents and cationic metal complexes.

Figu re 7.1 Relative stability of the most stable isomers in the hydroboration of vinylarenes with cationic metal complexes modified with QUINAP. 

There are numerous studies of metal complexation by whole cells indicating that complexation depends on the bacterium, the metal, and pH. It has been found that at low pH, cationic metal complexation is reduced however, binding of anionic metals such as chromate (Cr042 ) and selenate (Se042 ) is increased. Bacteria seem to show selective affinities for different metals. This was demonstrated by a study of the complexation of four metals by four different bacterial genera that... 

A mixture of enantiomers of cationic metal complexes was applied to a cation-exchange column and eluted by one enantiomer of tartrate anion. The tartrate has... 

Bis-cationic metal-complex dyes are suitable for dyeing leather. Cationic monoazo dyes in which a trialkylammonium group is linked via a carboxamide group to the diazo component [116] and disazo dyes are known. The latter are prepared from dialkylamino compounds by quatemization with alkylene dibromides. They are suitable for dyeing paper [117],... 

Acid-base equilibria in aqueous solutions are a source of enormous possibilities in terms of altered (increased or decreased) reactivity for practical purposes or as a tool in the mechanistic toolbox. The same is true for coordination and ion-pairing equilibria involving typically cationic metal complexes and anions, although oppositely charged reactants can also be involved. 

Several cationic metal carbonyls have been prepared by carbonylation of cationic metal complexes. The metal remains in the same oxidation state in this process, but can either change or retain its coordination number. 

A major question is whether heterolytic cleavage of the H3C-H bond occurs as depicted in Scheme 10 (maintaining the Ptn state) or whether oxidative addition to a PtIV methyl hydride complex takes place. In such systems transfer of protons would be expected to be very facile because of the extremely high mobility of H +, and even a short-lived, very weak a complex could be a key intermediate. The C-H bond is likely to be polarized towards Cs H5+ on such highly electrophilic cationic metal complexes, where H+ can very rapidly split off and transfer to either a cis ligand or the anion as soon as the... 

All crystals in this class are either insulators or semiconductors, and with a single exception (discussed in Sect. 3.3), they are ionic charge-transfer salts. The cations are generally either planar aromatics, such as TMPD+ and TTT+ (Sect. 3.2) or onium counter ions, such as Et4N+ and MePh3P+ (Sect. 3.3), although some cationic metal complexes are also known. For a majority of the systems, the anionic components are bis-1,2-dithiolene metal complexes, which have been studied and reviewed extensively81-84. ... 

Figure 30 Hydrogen-bonded sheet in crystal structure of [Zn(SC(NH2 )NHiVH2 )2 (OH2)2][l, 4-02CC6H4C02] 2H20 [73a], Cationic metal complexes [Zn(SC(NH2)NHAH2)2 (OH2)2]2+ (open circles) serve as hydrogen bond donors to anionic terephthalate bridges (shaded). Layers are linked via N-H O and O-H O hydrogen bonds to solvent water molecules (not shown).

H2TPPS and [Ru(phen)3]2+. Interaction is indicated by variation in the absorption spectra (Fig. 22) and, especially, by the appearance of an induced circular dichro-ism (Fig. 23) band in the absorption region of the achiral porphyrin. The relationship between chirality of the cationic metal complex and that transferred to the anionic porphyrins is straightforward because interactions of H2TPPS with the A- and A-[Ru(phen)3]2+ lead to mirror-image ICD signals (Fig. 23) [51]. 

In this case, the duplex formation is commonly detected in connection with the use of appropriate electroactive hybridization indicators such as cationic metal complexes (Co(phen)33+, Co(bpy)33+, [Cu(phen)2]2+, Ru(bpy)32+ among others [18-22,32]), or organic compounds (anthracyclines, phenoth-iazine, etc. [15,24,25,28,29]). These compounds interact in different ways with ss- or dsDNA but preferentially with dsDNA undergoing reversible... 

We then focus on the Pichler-Schulz CO insertion mechanism (39). This reaction has been much less investigated than the carbide mechanism. We recognize that in homogeneous catalysis, alkene hydroformyla-tion has been investigated extensively it appears that hydroformylation is much more difficult on metallic surfaces than in the presence of mononuclear cationic metal complexes (40). 

Several new cationic metal complexes have been isolated with the 1-Et-CBnFn anion, including Ag(p3-r J-CHPh,)+, Cu(CO)4+, (ti6-C6H6)Rh(CO)2+, and Rh(CO)4+. The first three of these have been structurally characterized and are shown in Figure 4. 

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