Recent advances in the chemistry of organometallic compounds of the actinide elements
A brief history of the preparation of organometallic compounds (the tricyclopentadienyls) of the Sf-electronic series, the actinides. is presented. The special micro-techniques employed for the heavier actinides. available for investigation in only microgramme quantities. are described. The compounds of the heavier actinides are characterized by largely ionic bonding. The more recent preparation of cyclooctatetraenyl compounds of the actinides is also described. The uranium(IV) compound is relatively stable. covalent, with a sandwich it-electron structure involving Sf-electrons since this structure is analogous to ferrocene. the name uranocene has been proposed. These organometallic compounds are relatively volatile and thus sublime at relatively low temperatures. The prospect for preparing organometallic compounds of the heaviest actinides and the transactinides. presently available only on a one-atom-at-atime basis. is also examined on the basis of inorganic chemistry experiments that have already been performed with such small quantities of these and similar elements. Organometallic chemistry has its origin in the discovery of diethyizinc by Frankland in 1849 and even still earlier work on platinum chemistry performed by the Danish chemist Zeise in 1827. The interest of most transition metal chemists, however, dates from the preparation of ferrocene in 1951. Other d-transition metal 'sandwich' compounds and also compounds of an ionic nature between cyclopentadiene and the 41-transition metals, the lanthanides, were then prepared. In order to study possible metal to carbon bonding in the 51-electronic series, the actinides, Reynolds and Wilkinson1 extended organometallic chemistry to element 92 in 1956 by preparing uranium tricyclopentadienyl chloride, U(Cp)3C1 (where Cp C5H5). The reaction of uranium tetrachioride with sodium cyclopentadienide, NaCp, in tetrahydrofuran (THF), yielded sublimable dark-red crystals of composition U(C5H5)3C1. Unlike the ionic cyclopentadienides of the lanthanide rare earth series, the actinide compound did not react in THF with FeCI2 to form ferrocene. Other chemical and physical properties showed that covalent bonding rather than ionic bonding is important. For example, the absorption spectra of the lanthanide cyclopentadienides in THF show very sharp