Lanthanide organometallics from metals

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. 

Since their isolation in 1991,1 N-heterocyclic carbenes (NHCs) have become ubiquitous in organometallic chemistry. In more recent years investigations into the coordination of NHCs to other elements have expanded, and there are examples of their coordination to elements across the whole periodic table. This report gives an overview of NHC complexes of non-transition metal elements, ranging from the s-block elements, through the p-block and on to the lanthanides. 

Lanthanide alkoxide complexes can be prepared using a number of methods. The key difference lies in the nature of lanthanide starting materials. These include elemental metals, halides, alkoxides, amides, carboxylates, hydrides, and organometallic species [1, 11], The organic ligands come from aliphatic alcohols, phenols, or their metal salts. 

Zhongning Chen received his Ph.D. in Chemistry from Nanjing University in 1994. He worked as an Alexander von Humboldt Research Fellow at Feiburg University (Germany) in 1998 and as a JSPS Fellow at Hokkaido University (Japan) in 1999-2001. He has been a chemistry professor at the Fujian Institute of Research on the Structure of Matter since 2001. His research interest is focused on luminescent transition metal and lanthanide complexes, organometallic wires, and molecular switches. 

Although zirconium is only one out of over 50 potentially usable metals in this class (including the lanthanides and actinides), virtually all synthetic applications of hydrometallation with transition metals involve zirconium Why is this so The primary reason derives from the near requirement of a d -metal center for hydrometallation of a general alkene or alkyne. For later transition metals, hydrometallation to give a stable organometallic product can usually be achieved only for special cases—conjugated dienes, alkenes with electronegative substituents, etc. This is due to the relative stability of the ti -complex, as discussed previously. 

Anhydrous lanthanide trihalides, particularly the trichlorides, are important reactants for the formation of a variety of lanthanide complexes, including organometallics. Routes for the syntheses of anhydrous lanthanide trihalides generally involve high temperature procedures or dehydration of the hydrated halides.The former are inconvenient and complex for small scale laboratory syntheses, while dehydration methods may also be complex and have limitations, for example, use of thionyl chloride. - Moreover, the products from these routes may require purification by vacuum sublimation at elevated temperatures. Redox transmetalation between lanthanide metals and mercury(II) halides was initially carried out at high temperatures. However, this reaction can be carried out in tetrahydrofuran (THF, solvent) to give complexes of lanthanide trihalides with the solvent. These products are equally as suitable as reactants for synthetic purposes as the uncomplexed... 

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