Transition metals ligand activation

Coordinated transition metal redox-active macrocycles, 39 108-124 ammonium cation, 39 128-133 crown ether and bis crown ether ligands containing bipyridyl transition metal recognition sites, 39 111 crown ether dithiocarbamate and dithiolene complexes, 39 123-124 metalloporphyrin crown ether compounds, 39 108-109... 

The first report of transition-metal peroxides active in the BV oxidation of cyclic ketones was due to Mares and coworkers in 1978 . These authors found that Mo-peroxo complexes, containing picolinato 101 and especially dipicolinato ligands 105, are able to mediate the transformation of some cyclopentanones and cyclohexanones to the corresponding lactones by concentrated H2O2 (equation 70) with yields in the range... 

Atom transfer radical polymerization (ATRP) [52-55]. Active species are produced by a reversible redox reaction, catalyzed by a transition metal/ligand complex (Mtn-Y/Lx). This catalyst is oxidized via the halogen atom transfer from the dormant species (Pn-X) to form an active species (Pn ) and the complex at a higher oxidation state (X-Mtn+1-Y/Lx). 

Cationic transition-metal complexes activate small molecules and serve as homogeneous catalysts, especially for selective hydrogenation of unsaturated organics. Section 1.10.4.2 deals with coordinativeiy unsaturated complexes in which the ligands remain coordinated after the oxidative addition of Hj. In 1.10.4.4 the complexes may or may not be coordinativeiy unsaturated complexes that are not must lose ligand(s) before oxidative addition of Hj. Coordinativeiy unsaturated complexes are described that exchange ligands either before or after the oxidative addition of Hj. 

A new family of hybrid organic-inorganic catalysts with dispersed active sites inside ordered mesoporous materials has been prepared by anchorage of transition-metal ligands of Schiff base-type and chiral amino alcohols like (li ,2S)-ephedrine on micelle-templated silicas [180]. Metalation of the grafted ligands with manganese was followed by UV-VIS spectroscopy. 

TRANSITION METAL REDOX ACTIVE LIGAND SYSTEMS FOR RECOGNISING CATIONIC AND ANIONIC GUEST SPECIES. 

A convenient way to append a transition metal to any organic molecule is making use of a cyclam ring. This 14-membered tetramine macrocycle incorporates 3d metal ions, to give complex species that are very stable both in a thermodynamic and a kinetic sense. Moreover, the firmly encircled cation keeps or enhances the interesting features typically presented by transition metals redox activity through fast and reversible one-electron transfer processes, affinity towards ligands (which will go to occupy the two axial positions left available by the co-planarly coordinated tetra-aza macrocycle). Thus, on reaction of 9-bromomethylanthracene with an excess of cyclam, the two-component system 4 was obtained (cyAn). 

Concerted metalation deprotonation (CMD)/ambiphilic metal ligand activation (AMLA) lA.CMD through 6-membered transition states... 

For the combinatorial selection of RNA (or DNA)-transition-metal catalysts, further elements have to be developed and integrated into the scheme (Figure 18.3). In addition to a tethered substrate, a site-specifically attached transition metal ligand needs to be present in each molecule of the hbrary. After loading with the metal, it should allow formation of the catalytically active species, preferably with the reactant tethered to the same RNA molecule. The other reactant carries a purification tag, allowing the selective isolation of only those species in which a reaction had taken place. A further nontrivial requirement is that the attachment of the metal-hgand complex to DNA or RNA does not interfere with the enzymatic copying steps (transcription, reverse transcription (RT), polymerase chain reaction (PCR)). 

This process is also referred to as ambiphilic metal-ligand activation (AMLA-6), where the 6 refers to a six-membered transition state. AMLA-6 and CMD, in essence, describe the same mechanism, see D. L. Davies, S. M. A. Donald and S. A. Macgregor,/. Am. Chem. Soc., 2005,127,13754-13755. 

Metallocene (Section 14 14) A transition metal complex that bears a cyclopentadienyl ligand Metalloenzyme (Section 27 20) An enzyme in which a metal ion at the active site contributes in a chemically significant way to the catalytic activity... 

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