Cerium complexes

Two other dimeric complexes which are related in structure to [Yb-(C5H4(CH3))2C1]2 are [Ce(C8H8)Cl 2THF]2 and [Sc(C5H5)2Cl]a. The cerium complex was discussed earlier. The structure of the scandium complex 118) is the same as that in Fig. 11. For the planar unit with symmetrical bridges, changing... 

A homobimetallic cerium(IV)-calix[8]arene complex was used together with hydrogen peroxide in the regioselective hydroxylation of simple phenols (Eq. 38), Just 0.5 mol of the cerium complex was sufficient to convert 1 mol phenolic substrate [260],... 

The cerium complex can be obtained undegraded in neutral solution130. ... 

Tetrakis-cyclopentadienyl cerium (CeCp4) has been reported to be formed by the reaction of bis(pyridinium) hexachlorocerate with sodium cyclopentadienide [17]. Similarly indenyl and fluorenyl derivatives were prepared. Later work showed the same reactants in tetrahydrofurane to yield, Ce(Cp3), tricyclopentadienyl cerium complex instead of Ce(Cp4) [18]. 

The structure of the cerium complex [162] consists of a centrosymmetric tetranuclear unit with a doubly metallated Cp group with r 5, rf, ij C5(CH2)2Me3 shared between three Ce atoms. 

The cerium complexes given above [201] are monomeric, and Ce(III) is five-coordinated and the unsaturation of these complexes favours interactions with the available C-H and Si-C bonds. 

In the cerium complex an unusual 12-membered ring has been observed. The ring is formed by Ce-0=C-W units with the O-C-W angle nearly linear (178°) while the Ce-O-C angle is 154°. This structure has been found to be unstable [258]. 

Figure 33 Cerium complexes of a tripodal triamidoamiue hgand...

Lithium(l) NHC adducts are extremely rare, but some examples have been isolated as stable crystalline solids when a ftmctional group is involved for their stabilization, the amino group, for instance. Since these showed to be effective in transmetallation processes, they represent an interesting alternative to the expensive silver complexes. As an example, Arnold reported the synthesis of covalently tethered lanthanide carbene complexes (214) using adduct (213) as source ofNHC (equation 39). Using (213) and the same methodology, unusual cerium complexes (215) and (216) were isolated and characterized (equation 40). ... 

Figure 4.26 Schematic representation of the synthesis of the double-decker bis(porphyrinato) cerium complexes from LiiPor and Ce(acac)3.

The first Ce(IV) complex stabilized by an alkoxo functionalized Ai-heterocyclic carbene anion has recently been reported. The complex is made by oxidation of the corresponding trivalent cerium complex using benzoquinone (Figure 8.36). The cerium cation is coordinated by two bidentate ligands and two monodentate ligands, in which the NHC groups are unbound [123],... 

A number of crystal structures of derivatives containing the [Eu(dik)4] are available but, at variance with the cerium complexes, the electrochemical investigation of a number... 

Thiiranes can be prepared directly from alkenes using specialized reagents. Thiourea with a tin catalyst gives the thiirane, for example. " Interestingly, internal alkynes were converted to 1,2-dichorothiiranes by reaction with S2CI2 (sulfur monochloride).It is noted that epoxides are converted to thiiranes with ammonium thiocyanate and a cerium complex. " A trans-thiiration reaction occurs with a molybdenum catalyst, in which an alkene reacts with styrene thiirane to give the new thiirane. 

ON2S3, Nitrogen sulfur oxide, 25 52 ONjSijCjHi, Urea, N,N -dimethyl-A/,N -bis(trimethylsylyl)-, 24 120 OPCijHis, Phosphine, triphenyl-, oxide cerium complexes, 23 178 OPC His, Benzaldehyde, 2-(diphenylphos-phino)-, 21 176... 

As in the work by Johnson, a distinct difference was noted in the magnesium- and lithium-derived cerium species. The Uthium/cerium complex has been used by Fuchs and coworkers to synthesize allylsilane derivatives (20) from acyl chlorides (18 Scheme S). This work is summarized in Table 5. 

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