Lanthanide atoms, reactions

A new class of organolanthanide complex has been reported from the metal-atom reaction of lanthanide atoms and butadiene (BD) or 2,-... 

Some of the earliest experimental studies of neutral transition metal atom reactions in the gas phase focused on reactions with oxidants (OX = O2, NO, N2O, SO2, etc.), using beam-gas,52,53 crossed molecular beam,54,55 and flow-tube techniques.56 A few reactions with halides were also studied. Some of these studies were able to obtain product rovibrational state distributions that could be fairly well simulated using various statistical theories,52,54,55 while others focused on the spectroscopy of the MO products.53 Subsequently, rate constants and activation energies for reactions of nearly all the transition metals and all the lanthanides with various oxidant molecules... 

Lanthanides in combination with transition metals have been shown to have a positive effect in promoting heterogeneous catalytic reactions. The bimetallic Yb—Pd catalyst obtained from the precursor (pMF)i0Yb2 Pd(CN)4]3 K on a titania surface offers improved performance over a palladium-only catalyst for the reduction of NO by CH4 in the presence of 02.99 100 The structure, shown in Figure 6, consists of two inverted parallel zigzag chains that are connected through the lanthanide atoms by trans-bridging [Pd(CN)4]2- anions.101... 

Fig. 4.15 The system La(III) acetylacetone (HA) - IM NaC104/benzene at 25°C as a function of lanthanide atomic number Z. (a) The distribution ratio Hl (stars, right axis) at [A ] = 10 and [HA] rg = 0.1 M, and extraction constants (crosses, left axis) for the reaction Ln + 4HA(org) LnA3HA(org) + 3FE. (b) The formation constants, K , for formation of LnA " lanthanide acetylacetonate complexes (a break at 64Gd is indicated) circles n = 1 crosses n = 2 triangles w = 3 squares w = 4. (c) The self-adduct formation constants, for the reaction of LnA3(org) + HA(org) LnA3HA(org) for org = benzene. (A second adduct, LnA3(HA)2, also seems to form for the lightest Ln ions.) (d) The distribution constant Ajc for hydrated lanthanum triacetylacetonates, LnAs (H20)2 3, between benzene and IM NaC104. (From Ref. 28.)...

The reaction of the same lanthanide starting material with the steri-cally more hindered benzenethiol afforded an anionic tetranuclear complex Li[R4 (/i4-Cl)Nd4(/t-SPh)g] wherein a /t4-Cl group rather than a /t4-SPh as in the example above was found to form a square pyramid with four basal lanthanide atoms (Eigure 67). Good catalytic activity of this cluster in the ROP of 8-caprolactone has been demonstrated (Li et al., 2005). 

A series of heterometallic 3d-4f cluster compounds have recently been reported, where structurally well-defined polyhedral motifs composed of solely lanthanide atoms are identified (Kong et al., 2007, 2008a,b). Under hydrothermal conditions, reaction mixtures containing R(N03)3, Ni (N03)2, and iminodiacetate (IDA) produced a variety of pol)muclear... 

The reduction in the propagation rate constant under the effect of aromatic hydrocarbon is due to hydrocarbon and diene monomer competing for coordination at the active centre. The effect of slowing down the polymerisation reaction is due to the fact that aromatic hydrocarbon forms an arene complex with the lanthanide atom. The higher the 7t-electron-donating ability of the aromatic hydrocarbon, the lower the rate constant for polydiene chain propagation. Thus, the rate of polymerisation of dienes decreases in the series benzene > toluene > xylene [11, 14, 26, 28]. 

A more general synthetic procedure for the synthesis of Ln2(CQHg)3 is by the reaction of neutral cyclooctatetraene with the lanthanide atom vapor at -198 C.S3... 

Frechet and coworkers [221] have recently described a similar self-assembly of benzyl ether dendrons, possessing carboxylic acid substituents at their focal points by metal-ligand coordination around a core of trivalent lanthanide metals (e.g., Er, Eu, or Tb). These self-assembled dendrimers were isolated by using ligand exchange reactions to produce structures derived from metal-ligand ionic interactions as shown in Fig. 11. As a consequence, these self-assembled dendrons served as a dendritic shell, which shielded the lanthanide atoms from one... 

An examination of the preparation of all the molecular divalent samarium and ytterbium compounds leads to the schematic classification given below, where A, X, Y, Z are atoms or groups of atoms, M is a metal or the cation of a metal, H is hydrogen and Ln stands for Yb or Sm. The preparation of organic divalent compounds is detailed in the text and in tables 1-3 of section 2.3. The following classification takes into account the fact that divalent lanthanide compounds can be derived either from the corresponding metal, from the corresponding trivalent lanthanide precursor or from another divalent lanthanide compound. Reaction types marked with an asterisk are described more fully below. 

A combination of the promoting effects of Lewis acids and water is a logical next step. However, to say the least, water has not been a very popular medium for Lewis-acid catalysed Diels-Alder reactions, which is not surprising since water molecules interact strongly with Lewis-acidic and the Lewis-basic atoms of the reacting system. In 1994, when the research described in this thesis was initiated, only one example of Lewis-acid catalysis of a Diels-Alder reaction in water was published Lubineau and co-workers employed lanthanide triflates as a catalyst for the Diels-Alder reaction of glyoxylate to a relatively unreactive diene . No comparison was made between the process in water and in organic solvents. 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

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