Lanthanide reduction chemistry

Newton, T. W and F. B. Baker Aqueous Oxidation-Reduction Reactions of Uranium, Neptunium, Plutonium, and Americium. In if. F. Gould (Ed.), Lanthanide/Actinide Chemistry, Advances in Chemistry Series, Vol. 71, p. 268. Washington American Chemical Society 1967. 

The fact that the complex of trivalent Sm acts as a one-electron reductant, the reduction purportedly taking place due to the Cp ligand, suggests that this chemistry can be extended to other trivalent lanthanide ions if the analogous Cp 3Ln precursors can be prepared. This approach would be very useful for extending the one-electron reduction chemistry to Ln(III) ions that do not have readily accessible divalent states. 

However, there is still a lot to do. The chemistry of lanthanide carbonyl and olefin complexes, and the complexes containing a lanthanide to transition metal bond and/or a lanthanide to lanthanide bond is still underdeveloped. To fully utilize these new aspects of reductive chemistry clever approaches will be needed. The development of highly active activatorless olefin polymerization catalysts and chiral versions of these families of complexes, and the catalysts for Cl chemistry are still the challenges. So, organolanthanide chemistry will continue to be an attractive field for organometallic chemists and there are many opportunities for the future. 

This article has reviewed the synthesis and reactivity towards small molecules of a range of U(lll) cyclooctatetraene and pentalene complexes. It is evident that in many cases the uranium centre is capable of tt back-bonding through the 5/ orbitals additionally, a C - C agostic interaction between a bound substrate and a U(IV) centre has been observed. Clearly uranium is capable of bonding with a degree of covalency , and this is perhaps why the reduction chemistry of U(III) is so rich and diverse, and not simply an iteration of low-valent lanthanide chemistry. 

Interest in the aqueous medium spread quickly and many, sometimes surprising, discoveries were made [3]. Today pericyclic [4], condensation [5], oxidation [6] and reduction [7] reactions are routinely carried out in aqueous medium. The recent discovery of water-tolerant Lewis acids such as lanthanide triflates, Bi(OTf)j, Sc(OTf)j and Y(OTf)j has revolutionized organometallic chemistry [5a, 7]. 

The synthetic potential of transition metal atoms in organometallic chemistry was first demonstrated by the formation of dibenzenechrom-ium (127). Apart from chromium, Ti, V, Nb, Mo, W, Mn, and Fe atoms each form well-defined complexes with arenes on condensation at low temperatures. Interaction has also been observed between arenes and the vapors of Co, Ni, and some lanthanides. Most important, the synthesis of metal-arene complexes from metal vapors has been successful with a wide range of substituted benzenes, providing routes to many compounds inaccessible by conventional reductive preparations of metal-arene compounds. 

Morss, L.R. 1994. Comparative thermochemical and oxidation-reduction properties of lanthanides and actinides. In Handbook on the Physics and Chemistry of Rare Earths, eds. K.A. Gschneider, J.L. Eyring, G.R. Choppin, G.H. Lander, pp. 239-257. Elsevier Science B.V., Amsterdam. 

Lanthanide contraction has important consequences for the chemistry of the third-row transition metals. The reduction in radius caused by the poor shielding ability of the 4f electrons means that the third-row transition metals are approximately the same size as their second-row congeners, and consequently exhibit similar chemical behavior. For instance, it has been shown that the covalent radius of gold (125 pm) is less than that of silver (133 pm). 

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