Amides of the Actinide Metals

Early (1987-1995) reviews of organoAn chemistry, including bibliographies on amides, are in Refs. 2-6. the greatest and most up-to-date information is to be found in the survey by Burns et al. which includes material in the 2002 literature. 

The bulk of the researches on the amidoAn compounds have been on U and, to a lesser extent, Th. The only examples in the open literature of transuranic amides are on the homoleptic Np and Pu bis(trimethylsilyl)amides, prepared from the appropriate [Anl3(thf)4] and 3Na N(SiMe3)2 in thf this was also the preferred procedure for [U N(SiMe3)2 3]. Pu N(SiMe3)2 3 was cited as a catalyst precursor its molecular structure has been reported recently. 

Metal Amide Chemistry Michael Lappert, Andrey Protchenko, Philip Power and Alexandra Seeber 

The literature is most prolific on neutral An amides, but neutral U and amides are also well documented. There are only few publications on amides,one being on three alkali metal amidouranate(VI)s. ° There is a paper on a compound (18) which couid be classified as of U° and two on mixed valence U /U amides (see Section 5.4 for these types). There are a number of articles on monocationic amidol/ tetraphenylborates, three on dicationic analogues, three on a cationic U salt and four on alkali metal amidoactinate(IV)s and three on corresponding U salts. For crystalline uranium amides containing only monodentate ct-bonded ligands, metal coordination numbers of 3-7 are 

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Insertion of carbon monoxide, which is so common for metal-alkyl bonds, is very rare for metal amides but has been documented for amides of the actinides (equations 81 and 82),225... 

The extensive chemistry of amido complexes, and, more particularly, of alkylamido complexes, reveals that the planar form is almost invariably found, along with bridging amides (221). Much attention has been paid to the synthesis of metal amido complexes of early transition metals, lanthanides and actinides. The amido group, particularly where it is bulky, confers unusual low coordination numbers on the metals and can also produce materials with considerable kinetic stability toward attack by nucleophiles (42, 67). However, the relevance of this extensive and fascinating chemistry to nitrogen fixation is somewhat problematic. 

Alkoxide and aryloxide ligands are excellent ligands for the actinides. As a result, these ligands have been studied extensively in the coordination chemistry and reactivity of tri-, tetra-, penta-, and hexavalent actinides. The alkoxides and aryloxides can be synthesized by a variety of routes the two most popular routes include direct reaction of actinide halides with alkali metal salts of the alkoxide or aryloxide of interest and protonolysis of actinide amides by alcohols. 

The silyl amide type ligands have been used extensively in rare earth chemistry, as well as in actinide and transition metal chemistry, to stabilize electronically unsaturated metal centers due to the available lone pair on the nitrogen donor atom. Because of the relatively larger steric encumbrance, the rare earth complexes with silyl amide type ligands often exhibit low coordination numbers. As a consequence, the large and electropositive rare earth metal centers are accessible to external reagents, which make them more active in many reactions. 

Although insertion of CO into a metal-Me bond is well known in transition metal chemistry, among metal amides it appears to have been unambiguously observed only for alkali and actinide metal derivatives. In the NaN(SiMe3)2/CO system the expected product Na[CON(SiMe3)2], if formed, decomposes ... 

The monochlorotris-silylamides, [(Me3Si)3N]3MCI, of the two most readily accessible actinide elements, thorium and uranium, have been prepared by reaction of three molar equivalents of sodium bis(trimethylsilyl)amide and the metal chloride in tetrahydrofuran. The thorium derivative is a colorless, diamagnetic, pentane soluble compound which is rtionomeric in the gas phase (by mass spectrometry) (19, 20). The tan uranium analogue is paramagnetic (yB = 2.8 B.M.) (20). 

The hydroamination of olefins has been shown to occur by the sequence of oxidative addition, migratory insertion, and reductive elimination in only one case. Because amines are nucleophilic, pathways are available for the additions of amines to olefins and alkynes that are unavailable for the additions of HCN, silanes, and boranes. For example, hydroaminations catalyzed by late transition metals are thought to occur in many cases by nucleophilic attack on coordinated alkenes and alkynes or by nucleophilic attack on ir-allyl, iT-benzyl, or TT-arene complexes. Hydroaminations catalyzed by lanthanide and actinide complexes occur by insertion of an olefin into a metal-amide bond. Finally, hydroamination catalyzed by dP group 4 metals have been shown to occur through imido complexes. In this case, a [2+2] cycloaddition forms the C-N bond, and protonolysis of the resulting metallacycle releases the organic product. 

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