Actinide complexes arene

Although several phenyl derivatives of the lanthanides and actinides have been characterized, only one re-arene complex of the / transition metals is known to date. This is the uranium(III) benzene complex, U(AlCl4)s CeHe 153), prepared by the combination of uranium tetrachloride, aluminum trichloride and aluminum powder in refluxing benzene, the Fischer-Hafner method [154). The molecular geometry of the complex is shown in Fig. 18. 

Related complexes are obtained with Pd, where one face of a benzene ring is shared by two Pd atoms . Mono-f/ -benzene ligands on a pentacobalt cluster also form from the aluminum halide-aluminum metal conditions . The preparation of -arene complexes of the lanthanides and actinides has been more diflScult, presumably because of the proclivity of these metals to form ionic bonds. Reactions between hexamethylbenzene and metal halides in the presence of AlClj-Al or AlCl-Zn reagents in the isolation of a mononuclear Sm complex, in addition to di- and trinuclear U complexes. ... 

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. 

The rapid development of cyclopentadienyl chemistry of the early transition metals, lanthanides and actinides is a noteable feature of the 1986 literature. In arene chemistry, further reports of uranium arene complexes and the report of the first lanthanide arene complex confirm that these complexes are isolated examples of an emerging class. 

In the second project, gathering nine teams from six EC countries, more than 150 new extractants were prepared and studied, and the target was reached for the decategorization of waste. Dialkoxy calix[4]arene-crown-6 for cesium, octaamide calix[8] arenes, and CMPO-like calixarenes for actinides display much higher complexing and extracting abilities than other classical extractants, crown ethers, or dicarbollides proposed and sometimes used for this purpose. 

Distribution ratios and transport were carried out on real HAW arising from dissolution of a mixed oxide of uranium and plutonium (MOX) fuel (burnup 34,650 MW d/tU), where uranium and plutonium have been previously extracted by TBP.86 The experiments were performed in the CARMEN hot cell of CEA Fontenay aux Roses with two dialkoxy-calix[4]arene-crown-6 derivatives (diisopropoxy and dini-trophenyl-octyloxy). High cesium distribution ratios were obtained (higher than 50) by contacting the HAW solution with diisopropoxy calix[4]arene-crown-6 (0.1 M in NPHE). Moreover, the high selectivity observed with the simulated waste was confirmed for most of the elements and radionuclides (actinides or fission products Eu, Sb, Ce, Mo, Zr, and Nd). The residual concentration or activity of elements, other than cesium, was less than 1% in the stripping solution, except for iron (2%) and ruthenium (8%) the extraction of these two cations, probably under a complexed... 

Carbonyl complexes with actinides, 4, 192 (7 5-acyclic)Re(CO)3 complexes, 5, 919 allylation, 10, 663 with allylic tins, 9, 354 into 7 3-allyl palladium complexes, 8, 364 arene chromium carbonyls... 

As an example of actinide dimeric complexes, the series of compounds [M(0-2,6-z-Pr2C6H3)3]2 970 (M = La, Nd, Sm, Er, U), sterically demanded by z-propyl substituents, were isolated [308,310a] they are held both in the solid state and in solution by 7i-arene interactions ... 

Actinide n-Complexes with Allyl, Cyclopolyene, Arene, and Related Ligands... 

The unsubstituted para-t-butyl calixarenes themselves complex metals via their aryloxide groups. Since aryloxide complexes are frequently oligomeric, the simple calixarenes do not give monomeric complexes. Aryloxides are hard ligands, therefore they readily form complexes with oxo-philic hard metal ions such as alkali metals, early transition metals, lanthanides, and actinides. Complexation is often inferred because the calixarene acts as a carrier for the metal ion from an aqueous to an organic phase. With the /wa-/-butylcalix[ ]arenes in alkaline solution, a value of n = 6 gives the best carrier for lithium(I), sodium(I), and potassium(I), with a value of n 8 giving the best carrier for rubidium(I) and caesium(I).15,16 Titanium(IV) complexes have been characterized,17-19 as well as those of niobium(V) and tantalum(V).20-22 These complexes are classified as... 

Although the elements of the lanthanide and actinide series have long been known to exhibit a quite extensive organometallic chemistry, it is only within the last decade that typical sandwich species have been prepared and studied. These systems however, although resembling the familiar metallocene and bis-arene compounds of the d-block elements, are not strictly their analogues since in both f-orbital series the known sandwich complexes are derived only from the cyclooctatetraenyl dianion. 

The remainder of this section will focus on true SBMs, which have been the subject of vigorous research. Despite the electron deficiency of early transition metal, lanthanide, and actinide complexes, several groups reported that some of these d f" complexes do react with the H-H bond from dihydrogen and C-H bonds from alkanes, alkenes, arenes, and alkynes in a type of exchange reaction shown in equation 11.32. So many examples of SBM involving early, middle, and late transition metal complexes have appeared in the chemical literature over the past 20 years that chemists now consider this reaction to be another fundamental type of organometallic transformation along with oxidative addition, reductive elimination, and others that we have already discussed. 

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 ... 

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. 

The calix[4]arene molecule was modified at both the upper (para) and lower (phenolic) rims by the introduction of phosphate and phosphonate groups, mainly by the group of Kalchenko (Fig. 4B). Such derivatives complex and allow the extraction of lanthanide and actinide tri- and tetravalent cations. Detoxification of radioactive waters may be possible in this way, as the chemieal and physical robustness of the calix[n]arenes makes them particularly suitable for this task. 

The parent oxacalix[3] arenas show little ability to bind alkali metals,however, a range of quaternary ammonium cations are attracted to the symmetric cavity. Deprotonation of the phenol moieties allows them to bind to transition metals (scandium, titanium, vanadium, rhodium, molybdenum, gold, etc.), lanthanides (lutetium. yttrium, and lanthanum), and actinides (uranium as uranyl). Oxacalix[3]arenes derivatized on the lower rim can complex gallium, mercury, and alkali metals, including sodium, in a manner reminiscent of natural transmembrane cation filters. One major use was to purify crude samples of fullerenes. The pseudo-Cs symmetry of the macrocyclic cavity is complementary to threefold symmetry elements of Cgo. which binds preferentially in... 

Hanowfield. J.M. Ogden. M.I. White, A.H. Actinide complexes of the calixarenes. Part 1. Syntheses and crystal structure of bis(homo-oxa)-/ -r rr-butylcalix[4]arene and its uranyl ion complex. J. Chem. Soc.. Dalton Trans. 1991. 

Owing to the unique host-guest properties of calixarene macrocycles, calixarene-functionalized silica particles were used as cation-selective receptor colloids [81], and separator of lanthanides and actinides [82]. Calixarenes were also used for the syntheses of Ru, Pt and Pd NPs [83-85]. Furthermore, photoluminescence and charge-transfer complexes of calixarenes and calix[4]arene-based glycoclusters were grafted onto the surface of Ti02 NPs [64, 86]. 

Theoretical studies [59] indicate that the lowest unoccupied molecular orbital (LUMO) of such molecules is localized primarily on the acyl carbon atom, similarly to the situation in Fischer complexes. An example of such a compound is shown in Fig. 23.9, where the shortness of the Th-O distance (2.37(2) A) relative to Th-Cg (2.44(2) A) is unprecedented for a dihapto-acyl. A second example of an actinide dihapto-acyl is shown in Fig. 23.10. It should be noted that the orientation of the C-O vector is in the opposite direction from that in Fig. 23.9. The relative magnitudes of the Th-O and Th-C distances appear to reflect both the orientation of the C-O vector and conjugation with the arene n system. The intricate chemistry exhibited by actinide dihapto-acyls is summarized in Fig. 23.11. Important reactions include C-C coupling to form monomeric (10) or dimeric enediolates [57,58,60,61], isomerization to yield enolates (//) [60,62], catalytic hydrogenation to yield alkoxides (/2) [63], CO tetramerization to form dionediolates (13) [62, 64], coupling with ketenes 14), coupling with CO and phosphines 15) [62, 64], and addition to isocyanides to yield ketenimines [62, 64] 16). 

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