Lanthanide compounds electron-transfer reactions

Redox reactions with synthetic potential have been developed by use of dialkyl phosphonate, early transition metals, and lanthanides. The Lewis acidic nature of metallic compounds is another key factor in their reactivities in addition to the redox properties. Controlling the metal-based redox systems leads to greater selectivities in their electron transfer reactions. Likewise, fine-tuning the ligands coordinated to metals results in more efficient redox systems. These approaches yield a variety of fruitful redox reactions for organic synthesis as observed in the ligand coupling and haloperoxidase-inspired reactions. 

Topics which have formed the subjects of reviews this year include photosubstitution reactions of transition-metal complexes, redox photochemistry of mononuclear and polynuclear" complexes in solution, excited-state electron transfer processes, transition-metal complexes as mediators in photochemical and chemiluminescence reactions, lanthanide ion luminescence in coordination chemistry, inorganic photosensitive materials," and photocatalytic systems using light-sensitive co-ordination compounds. Reviews have also appeared on the photoreduction of water.Finally, various aspects of inorganic photochemistry have been reviewed in a single issue of the Journal of Chemical Education. 

The reactivity of the early lanthanide oxide cations CeO+ (Heinemann et al., 1996) and NdO " (Comehl et al., 1997a) was also examined with several alkanes and aUcenes, but no reactions were observed by FTICR-MS. On the contrary, Ce02 was quite reactive with linear and branched alkanes by C—H bond activation and with simple alkenes and aromatic compounds by both oxygen-atom transfer and C—H bond activation (Heinemann et al., 1996) the high reactivity was ascribed to the radical nature of the CeOi ion, which has one unpaired electron based on theoretical calculations. CeOa" " was also observed to mediate the catalytic oxidation of ethene in the presence of NO2, as illustrated in Fig. 9. 

The role of bond ionicity in three-electron reactions is manifested in the reactions of lanthanide cations (Ln ) with R-F compounds which result in F abstraction and formation of LnF, as shown in equation (12). Here the promoted state which in covalent situations involves a triplet excitation of the molecule (Scheme 2) changes to a charge transfer state as 17 in Scheme 3. Thus, the finding of the Berlin group of an extended correlation between the efficiency of C-F bond activation by lanthanide cations and the second ionization potential of the metal cation is in line with an avoided crossing of ground and charge transfer states. ... 

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