Lanthanide and actinide

Gagliardi and Roos conducted a series of studies on actinide compounds. They follow a combined approach with DKH/AMFI Hamiltonians combined with CASSCF/CASPT2 for the energy calculation and an a posteriori added spin-orbit perturbation expanded in the space of nonrelativistic CSFs. This strategy aims to establish a balance of sufficiently accurate wave function and Hamiltonian approximations. Since the CASSCF wave function provides chemically reasonable but not highly accurate results (as witnessed, for instance, in the preceding section), it is combined with a quasi-relativistic Hamiltonian, namely the sc alar-relativistic DKH one-electron Hamiltonian. Additional effects — dynamic correlation and spin-orbit coupling — are then considered via perturbation theory. 

The calculation of spectroscopic parameters of the uranium dimer, U2, received considerable attention [1135]. The bonding situation of the U2-molecule implies a large number of nearly-degenerate electronic states, which require the multi-configurational approach for the calculation of the electronic wave function. This approach was also successfully applied to [1136], to the actinide dimers Th2, Ac2 and Pa2 [1137], and to the dinuclear clusters PhU-UPh [1138], U2CI6 and U2(OCHO)6 [1139]. 

1195 j Gajda, B. Gyurcsik, T. Jakusch, K. Burger, B. Henry, and J.J. Delpuech, Inorg. Chim. Acta, 1998, 276, 130. 

Giovenzana, R. Pagliarin, M. Sisti, and E. Terreno, Magn. Reson. Chem., 1998, 36, S200. 

Photoelectron spectroscopic studies have been carried out a CpgTh- and Cp,U- containing complexes, and related tris-cyclopentadienyl metal alkoxides. The synthesis, structure and oxidative addition reactions of Cp3U-nitrile complexes, the structure of CpsUfSCN) and the 

LiAlH(OCMe3). Some catalytic selective hydrogenation results (1,5- or 1,3 cyclooctadiene to cyclooctene) are also presented. A tetraphenylzirconacyclopentadiene derivative has been used as a synthon towards tetraphenylthiophene monoxide. Bis[(dialkylamino)-(phenylethynylboryl)l methanes on treatment with zirconocenes give metallacycles.  

The complex 21 was prepared from 22, X = Cl, Br on reaction with HCl/Brj followed by reaction with MeLi and hydrolysis. The zirconocene RCH2CH(-9BBN)ZrClCp2, prepared from Schwartz s reagent has been used in the synthesis of a-bromoboranes. The cycloaddition of cumulene and heterocumulene with vinylidenetitanocene proceeds with unexpected differences four and five membered metallacycles are formed. Nine complexes have been prepared from the reaction of acyl- and thioacylhydrazones with Cp2ZrCl2.  

The catalyst precursor Cp2ZrCl2/nBuU has been used in the condoisation of secondary 

An unsymmetrically substituted zirconocene was prepared by reaction of trimethylsilylcyclopentadienyl lithium and 1,3-bis(trimethylsilyl cyclopentadienyl lithium) with ZrCl4.2THF. The first well characterised compounds which contain a methylsiloxane coordinated to zirconium have been prepared by reaction of deprotonated hexamethyldisoloxane with Cp2ZrCl2. Insertion of RNCS, R = Ph, 2-m hthyl, cyclohexyl, butyl, into the Zr-H bond in Cp2Zr(H)Cl leads to the isolation of CpiZrClISC(H)NR].  

In consecutive ptq ers, Maries group have carried out mechanistic work on asymmetric olefin hydroamination using chiral organolantfumides, and the configurational inimeonversions and full structural characterisatitMi of the catalyst precursor conq)Iexes.  

2 Titanium, Zirconium, Hafnium - The catalytic asymmetric hydrogenation of imines has been reported using a chiral titanocene catalyst. An enantiopure titanocene catalyst has been used in the catalytic asymmetric hydrogaution of disubstituted enamines. Kinetic resolution of a racemic disubstituted pyrroline has been effected by asymmetric reduction with a chiral titanocene catalyst. Poly(methylhydrosiloxane) has been used as a stoichiometric 

A patent has been processed which documents the preparation of titanocenes for antitumour activity - these are titanocene bisaryloxy derivatives. The preparation of [CpTi(iiS-C3H4C(Et)3l,2-CtH40-)Cl] from CpTiCl2 and the lithium salt Li[3-(o- 

Cr(CO)5, W(CO)s, CpRe(C0)2, Mnj(CO)9, etc have been synthesised from the reactions of titanacycles.  

The two dimensional potential energy surface for the chair to chair rearrangement of [Cp2Ti(/x-C2S4)4] has been described to be via a boat shaped transition state. Extended Huckel calculations have been carried out on a range of complexes e.g. Cp2TiSiHPh, [(CpiTijC/i-HSi(HPh)( t-H)] which are important polymerisation intermediates.  

Inclusion of 1,3-nonbonded interactions1285-2871 was achieved in the same way as was used firstly for the modeling of cobalt(III) complexes11481 and more recently for a wide range of transition metal compounds14,5 451. That is, standard models with M-L harmonic bond stretching terms were used, but the L-M-L harmonic terms were deleted and L...L nonbonded interactions were used in their place. In the first of 

Recently, a similar approach has been used to study eight- to twelve-coordinate aqua and nitrato complexes of the complete series of the lanthanides12871. Again, good agreement between observed and calculated geometries was obtained. In all three of these studies, modified versions of MM2 were used and electrostatic interactions were not explicitly included. 

The same method was used to study a similar series of polyaminepolycarboxylato complexes of europium(III)12891. This study included a series of dimeric complexes and the Eu.., Eu distances were compared with those determined from luminescence spectra. A number of different conformations and the energy differences between them were also investigated. 

Exploration of the potential applications of molecular mechanics to compounds of s-, p- and f-block elements is only just beginning. The difficulties arising from the electrostatic bonding in the s- and f-block elements have been tackled in a number of different ways, in most cases with reasonable success. In general, p-block elements are modeled relatively readily however, the problems of sterically active lone pairs have yet to be tackled. 

29 Comba, P., Maeder, M. Zipper, L. Helv. Chim. Acta (1989) 72, 1029. 

The metal complexes that we have discussed so far are all that of d elements, i.e., transition metals. As we will see later, most homogeneous catalytic processes are indeed based on such metal complexes. However, at the research level, homogeneous catalytic applications of lanthanide and actinide complexes have been extensively explored. 

Structures 2.64 and 2.65 are two examples. Structure 2.64 is of relevance for activation of alkanes (see Section 2.3.4). It has also been used as a catalyst for propylene polymerization. Structure 2.65 is a catalyst for hydroamination reaction (see Section 5.7). Both these complexes have bulky Cp as the spectator ligand. By making the metal less accessible, the Cp ligand imparts additional stability to these complexes without compromising their catalytic activity. 

Two important points to note are that, unlike transition metal-based homogeneous catalysts where the metal ions can have a wide range of oxidation states, the lanthanides are almost always in the 3+ oxidation state. Complexes 2.64 and 2.65 are no exceptions. Second, valence electron count for the metal has no significance for complexes of the/elements. 

This is because, unlike transition metal complexes where the metal-ligand interaction usually has a significant degree of covalent contribution, the lanthanide-ligand bonds are essentially ionic in character. The electrons in the 4/shell have little spatial extension and remain buried within the lanthanide ion. 

There is a similarity between high oxidation state early transition metal complexes and those of lanthanides. In both cases the substrates are activated by direct interaction with small, highly electropositive 

Relativistic effects are significant for the heavier metals. The method of choice is nearly always relativistically derived effective core potentials. Explicit spin-orbit terms can be included in ah initio calculations, but are seldom used because of the amount of computational effort necessary. Relativistic calculations are discussed in greater detail in Chapter 33. 

Lanthanide and actinide compounds are difficult to model due to the very large number of electrons. However, they are somewhat easier to model than transition metals because the unpaired / electrons are closer to the nucleus than the outermost d shell. Thus, all possible spin combinations do not always have a significant effect on chemical bonding. 

Relativistic effects should always be included in these calculations. Particularly common is the use of core potentials. If core potentials are not included, then another form of relativistic calculation must be used. Relativistic effects are discussed in more detail in Chapter 33. 

Molecular mechanics force fields are sometimes parameterized to describe lanthanides and actinides. This has been effective in describing the shape of the molecule, but does not go very far toward giving systematic energies. A few semiempirical methods have been parameterized for these elements, but they have not seen widespread use. 

Ah initio calculations with core potentials are usually the method of choice. The researcher must make a difficult choice between minimizing the CPU time requirements and obtaining more accurate results when deciding which core potential to use. Correlation is particularly difficult to include because of the large number of electrons even in just the valence region of these elements. 

Irradiation of t.h.f. solutions of CpjUR (R — Me or Bu ) gives CpaU t.h.f., although elevated temperatures e.g. 60 °C) are required for efficient reaction. Homolytic cleavage of the U—R bond is presumed to be the first step. Photo-induced cleavage of the Yb—Me bond allows the conversion of [(MeCp)2YbMe]2 into (MeCp)2Yb.  

Klahne, C. Giannotti, H. Marquet-Ellis, G. Folcher, and R. D. Fischer, J. Organomet. Chem., 1980, 201, 399. 

Cyclopentadienyl uranium complexes react with TiW-0,q anions to 

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As regards the transition elements, the first row in particular show some common characteristics which define a substantial part of their chemistry the elements of the lanthanide and actinide series show an even closer resemblance to each other. 

Table 3. Electronic Configurations for Gaseous Atoms of Lanthanide and Actinide Elements...

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

Both arsonic and arsinic acids give precipitates with many metal ions, a property which has found considerable use in analytical chemistry. Of particular importance are certain a2o dyes (qv) containing both arsonic and sulfonic acid groups which give specific color reactions with a wide variety of transition, lanthanide, and actinide metal ions. One of the best known of these dyes is... 

There is no single best form of the periodic table since the choice depends on the purpose for which the table is used. Some forms emphasize chemical relations and valence, whereas others stress the electronic configuration of the elements or the dependence of the periods on the shells and subshells of the atomic structure. The most convenient form for our purpose is the so-called long form with separate panels for the lanthanide and actinide elements (see inside front cover). There has been a lively debate during the past decade as to the best numbering system to be used for the individual... 

The reaction is general and has been applied to many transition metals as well as lanthanides and actinides. Variants use metal carbonyls and other complexes to supply the capping unit, e.g. 

The three series of elements arising from the filling of the 3d, 4d and 5d shells, and situated in the periodic table following the alkaline earth metals, are commonly described as transition elements , though this term is sometimes also extended to include the lanthanide and actinide (or inner transition) elements. They exhibit a number of characteristic properties which together distinguish them from other groups of elements ... 

G, Meyer and L. R, Morss (eds,). Synthesis of Lanthanide and Actinide Compounds, Kluwer Acad, Publ, Dordrecht, 1991, 367 pp. 

T. Moeller, The lanthanides. Chap. 44, pp. 1-101, in Comprehensive Inorganic Chemistry, Vol. 4, Pergamon Press, Oxford, 1973 Lanthanides and actinides, Vol. 7, MTP International Review of Science, Inorganic Chemistry (Series Two) (K. W. Bagnall, ed.), Butterworths, London, 1975, 329 pp. 

Thenoyltrifluoroacetone(TTA), C4H3S,CO,CH2,COCF3. This is a crystalline solid, m.p. 43 °C it is, of course, a /1-diketone, and the trifluoromethyl group increases the acidity of the enol form so that extractions at low pH values are feasible. The reactivity of TTA is similar to that of acetylacetone it is generally used as a 0.1-0.5 M solution in benzene or toluene. The difference in extraction behaviour of hafnium and zirconium, and also among lanthanides and actinides, is especially noteworthy. 

Unsubstituted bisphthalocyanines 2 are formed in the presence of several elements which exist in a stable oxidation state of + III or +IV such as titanium, zirconium, hafnium, indium and most of the lanthanide and actinide elements. 

Covalent transition metal lanthanide and actinide tetrahydroborate complexes. T. J. Marks and... 

The quantum chemistry of unusual oxidation states of the lanthanides and actinides. V. I. Spitsyn and G. V. Ionova, Russ. Chem. Rev. (Engl. Transl.), 1984, 53, 725 (138). 

The chemical similarity between lanthanide and actinide metals suggests that C2H I2 might also react with actinide metals. Preliminary experiments found no reaction between thorium or uranium metals and a THF solution of Plutonium and neptunium... 

Thus the rather easily obtained atomic sizes are the best indicator of what the f-electrons are doing. It has been noted that for all metallic compounds in the literature where an f-band is believed not to occur, that the lanthanide and actinide lattice parameters appear to be identical within experimental error (12). This actually raises the question as to why the lanthanide and actinide contractions (no f-bands) for the pure elements are different. Analogies to the compounds and to the identical sizes of the 4d- and 5d- electron metals would suggest otherwise. The useful point here is that since the 4f- and 5f-compounds have the same lattice parameters when f-bands are not present, it simplifies following the systematics and clearly demonstrates that actinides are worthy of that name. 

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