Associative metal exchange

The same considerations apply to rate laws developed to describe the kinetics of Al3 complexation by humic substances. This fact can be illustrated by the associative metal-exchange reaction 11,... 

Metal-chelate affinity chromatography is a powerful purification technique whereby proteins or other molecules can be separated based upon their ability to form coordination complexes with immobilized metal ions (Porath et al., 1975 Lonnerdal and Keen, 1982 Porath and Belew, 1983 Porath and Olin, 1983 Sulkowski, 1985 Kagedal, 1989). The metal ions are stabilized on a matrix through the use of chelating compounds which usually have multivalent points of interaction with the metal atoms. To form useful affinity supports, these metal ion complexes must have some free or weakly associated and exchangeable coordination sites. These exchangeable sites then can form complexes with coordination sites on proteins or other molecules. Substances that are able to interact with the immobilized metals will bind and be retained on... 

The intensive research activities recently focused on late transition metal complexes as polymerization catalysts are justified by decisive improvements in the development of new polymer materials and indicate even more their high potential for future applications. However, up to now they often only dimerize or oligomerize a-olefms due to competing hydride elimination and associative olefin exchange reactions [19]. A new concept of new diimine ligands and complexes bearing 2,6-diphenyl-modified aniline moieties (Fig. 2.5) is stiU focused on sterically demanding substituents in the 2,6-positions, but it aims further towards the facile modification of the steric and electronic properties of the active species. 

As shown in Table XXXVI, transition metal-exchanged faujasites have catalytic activity for the conversion of halobenzenes to anilines in the presence of NH3 (155a). The use of CuX was associated with higher... 

Organometallic compounds with a 17-electron configuration are often labile toward associative ligand exchange. Radical chain mechanisms are well established for phosphine substitution on metal carbonyl hydrides (Scheme 23), the 17-electron chain carrier being in most cases non hydridic. This mechanism, however, was also shown to operate for OsH2(CO)4 via the 17-electron hydride complex OsH(CO)4 [137]. Thus, phosphine addition to the radical prevails over the dimerization, which indeed occurs in the absence of phosphine [33] (section 6.5.7), and over other possible decomposition pathways. The second step of the chain propagation process in Scheme 23, for this osmium system, is another example of atom transfer to a hydride radical (section 6.5.6). 

In many metalloproteins, two or more metal ions are closely associated. The strength of the exchange interactions between the associated metal ions is the most important factor in determining the EPR properties of these systems. The exchange interactions arise from overlap of the magnetic orbitals (the orbitals containing the unpaired electrons These... 

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