Bridged electron transfer remote attack

A related example of inner-sphere reaction is shown in reaction (5), where an additional mechanistic subtlety appears.10 As shown by the products, inner-sphere electron transfer also occurs but now by remote attack in which the sites of bridging ligand binding to the reductant and oxidant are at different atoms on the bridging ligand. 

Two separate but somewhat interwoven themes have emerged from the study of inner-sphere reactions. The first is the use of product and rate studies to establish the existence of inner-sphere pathways and then the exploitation of appropriate systems to demonstrate such special features as remote attack . In the second theme the goal has been to assemble the reactants through a chemical bridge and then to study intramolecular electron transfer directly following oxidation or reduction of the resulting dimer (note equation 7). It is convenient to turn first to chemically prepared, intramolecular systems since many of the theoretical ideas and experimental results for outer-sphere reactions can be carried over directly as an initial basis for understanding the experimental observations. 

Both monomeric (213), chelated (214) and bridged dimeric (215) and (216) complexes are known. The latter were first prepared by Werner689 and in the last decade have received some attention in relation to remote attack and outer-sphere electron transfer (see below). The monomeric complexes... 

These results confirm (c/. ref. 145) that terephthalate ion is not an effective electron-transfer bridge. Remote attack does occur in the reactions of (23 R=C=CCOjjH) with Cr + (ref. 146) and V + (ref. 147), and of (23 K = trans-CH=CHCOaH) with The rate laws are equation (70) for the acetylene-... 

The preparation of europium metasilicate hydrate from solutions of europium bromide and sodium metasilicate has been described.The kinetics and mechanism of the reduction of thiocyanato- and isothiocyanato-penta-amminecobalt(iii) ions by europium(ii) in acid solution have been discussed in terms of europium(ii) attack on the ambidentate bridging ligand at the end remote from the cobalt centre. The differences in the activation enthalpies for the reduction of the complexes were attributed to (a) differences in enthalpy of formation of the precursor complex Eu - X - Co (NH3)5, and (b) ease of stretching of the Co—S or Co—N bond in the precursor complex. The low-temperature Mossbauer spectrum of EUH2 suggested the covalent transfer of electron density. to the metal 6s orbital to be more marked in EuH2 than EuO. ... 

---