Lutetium adduct

By controlling the stoichiometry of the reaction between lanthanide trichlorides and sodium cyclopentadienide it is possible to replace the chloride ions stepwise. Equihbria are rapidly established, so the addition of Ln(C5H5)3 to one or two equivalents of LnCls will produce M(C5H5)2C1 and M(C5H5)Cl2, respectively. The dichlorides are known only for the lanthanides from samarium to lutetium and are obtained from THF solutions as tris-THF adducts. 

The organometallic chemistry of scandium is generally similar to that of the later lanthanides. It thus forms a cyclopentadienyl ScCps that has mixed mono- and pentahapto-coordination like LuCps. An anionic methyl [Li(tmed)]3[M(CH3)6] is formed by scandium, as by the lanthanides. However, there are often subtle differences that should be borne in mind. The pentamethylcyclopentadienyl compound [ScCp 2Me] is a monomer but the lutetium compound is an asymmetric dimer [Cp 2Lu(/u.-Me)LuCp 2Me]. Similarly, whilst triphenylscandium is obtained as a bis(thf) adduct, [ScPh3(thf)2], which has a TBPY structure with axial thf molecules, the later lanthanides form octahedral [LnPh3(thf)3]. Triphenylscandium and the phenyls of the later lanthanides are made by different routes. 

The use of Ln(OTf)3 in the activation of aldehydes other than formaldehyde was also investigated [18]. The model reaction of 1-trimethylsiloxycyclohexene (2) with benzaldehyde under the influence of a catalytic amount of Yb(OTf)3 (10 mol%) was examined. The reaction proceeded smoothly in H20-THF (1 4), but the yields were low when water or THF was used alone. Among several Ln(OTf)3 screened, neodymium triflate (Nd(OTf)3), gadolinium triflate (Gd(OTf)3), Yb(OTf)3, and lutetium triflate (Lu(OTf)3) were quite effective, while the yield of the desired aldol adduct was lower in the presence of lanthanum triflate (La(OTf)3), praseodymium triflate (Pr(OTf)3) or thulium triflate (Tm(OTf)3) (Table 2). 

The effect of other Ln(OTf)3 was also examined. As shown in table 31, the choice of lanthanide element strongly influenced the yields and selectivities. A slight difference between the two catalyst systems (catalysts A and B) on the effect of the lanthanide elements was also observed. In catalyst A, lutetium triflate (Lu(OTf)3) was also effective in generating the endo Diels-Alder adduct in 93% ee. The yields and selectivities diminished rapidly in accordance with the enlargement of the ionic radii. In catalyst B, on the other hand, the best results were obtained when thulium triflate (Tm(OTf)3) or erbium triflate (Er(OTf)3) was employed. Deviations to either larger or smaller ionic... 

The methane exchange reaction, T.3 and T.12, also should occur more easily for scandium-methyl than for lutetium-methyl. As seen from Table IV, Adduct I, Cl2LuCH3(CH4), is calculated to be only kinetically stable and lies 4.6 kcal/mol higher than reactants. The transition state separating reactants and the CH4 complex was not located. However, Adduct I for Sc, Cp2ScCH3(CH4), is thermodynamically stable by 6.0 kcal/mol relative to the reactants. The barrier for methane exchange is calculated to be 25.9 and 10.8 kcal/mol relative to the reactants, respectively, for the Lu and Sc compounds. In the transition state the distances of the two reacting CH bonds... 

In this section we reviewed the latest theoretical studies on the metathesis reaction. In general, it has been shown that the metathesis reaction at first yields adduct complex then activation of the H-R bond takes place with a four-center transition state, which leads to the second adduct. It occurs more easily for scandium complexes than for lutetium analogues. The a-metathesis reactivity between R-H and M-R bonds decreases in the order of R C2H... 

Bis(pentamethylcyclopentadienyl)scandium-methyl, -phenyl and -benzyl are prepared from bis(pent amethylcyclopentadienyl)scandiumchloride and LiCHs, LiCeHs or KCH2C6H5 respectively, in ether-hexane solution. In THF solution, the methyl derivative is in equilibrium with the THF adduct. The solvent-free compound is monomeric in solution. An agostic Diethyl group is discussed. The X-ray structure of the reaction product with pyridine proves the C-H-activation discussed above for the corresponding lutetium derivative (Figure 10) (58). 

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