Actinide hydride complexes

Several general review articles [19-41] dealing mostly with the synthesis of new actinide complexes confirm the broad and rapidly expanding scope of this field. Those reviews dealt with the structure, stability, and reactivates of complexes with cyclopentadienyl, dienyls (pentadienyl, cyclohexadienyl, indenyl, phospholyl), cyclooctatetraenyl, arene ligands, hydrocarbyls, and hydrides ligands. 

Thorocene, uranocene and plutonocene can also be synthesized by the reaction of cyclooctatetraene with the finely divided metals obtained by heating the metal hydrides.i7 in this reaction, a sealed Pyrex tube containing the actinide-cyclooctatetraene mixture was heated in a tube furnace at 150-160 C. The reaction product was isolated by sublimation. This preparative method provides demonstration of the thermodynamic stability of the bis([8]annulene)actinide complexes. 

The second review is due to Pepper and Bursten (1991). This review focussed on the electronic structure of actinide-containing molecules. Note that the present chapter complements this in that our chapter is mostly on lanthanide-containing species. Consequently, the reader is referred to the excellent review by Pepper and Bursten (1991) for a comprehensive summary of the electronic structure of actinide-containing species. The review by Pepper and Bursten (1991) contains the details of calculations on actinide hydrides, actinide halides, actinide oxides, cyclopentadienyl-actinide complexes, aetinocenes, metal-metal bonding in actinide systems and miscellaneous other actinide systems. This review also consists of descriptions of theoretical techniques employed to study the actinide-containing molecules. The reader is directed to this review for further details on such calculations on actinide-containing molecules. 

The hydride complexes of actinides usually contain a coligand, such as, for example, OR, dmpe, or Cp, and can be monomeric or oligomeric. Thus, the borohydrides An(BH4)4 produced according to (5.68) are polymeric (An = Th, U) or monomeric (An = Np, Pu), whereas the An(BH3Me)4 are all monomeric. Their volatility increases from Th to Pu, whereas their stability goes in the opposite direction [282] ... 

Some examples of hydride and borohydride complexes of actinides are presented in Table 5.14. 

Actinides react directly with Hj to form hydrides of different stoichiometries. Thorium forms a tetragonal dihydride, related to the fluorite structure, and a higher hydride, Th Hjj, which has a complex bcc structure. The trihydrides of U and Pa have the bcc 3-W structure, and U also forms a low-T trihydride with a different bcc structure. Hydrides similar to the third group of the lanthanides (see 1.12.4.1), i.e., an fee dihydride and a hexagonal trihydride, are formed by Np through Bk. 

The lanthanides and actinides are also active in electrophilic attack on arenes. Bis(pentamethylcyclopentadienyl)lutetium methyl or hydride complexes react readily with benzene to give phenyl complexes and methane or dihydrogen . Similar reactions are observed for Sc and Th In a remarkable reaction benzene can be dimetallated by Lu, yielding II ... 

Actinide Hydrides. Thorium and other actinides form complex systems with non-stoichiomelric and stoichiometric phases. Uranium hydride is of some importance chemically as it is often more suitable for the preparation of uranium compounds than is the massive metal. Uranium reacts rapidly and exothermically with hydrogen at 250-300° to give a pyrophoric black powder. The reaction is reversible ... 

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