Ytterbium complexes alkyls

Pendant-arm amido-cyclopentadienyl ligands have also been shown to be useful in the stabilization of highly reactive mono(cyclopentadienyl)lanthanide alkyl and hydrido complexes. When the tris(trimethylsilylmethyl) complexes of lutetium and ytterbium, Ln(CFI2SiMe3)3(TFIF)2, were treated in pentane solution with 1 equiv. of (CsMe4H)SiMe2NHCMe2R (R = Me, Et) at 0°C, the new complexes (rfir)1-... 

Similar ortfo-metallation products have been obtained from reactions of (775 7]1-CsMe4SiMe2NBut) Y(CH2SiMe3)(THF) with anisole and 3- and 4-methylanisole.290 Both the lutetium and ytterbium alkyl complexes were subjected to hydrogenolysis with dihydrogen or with phenylsilane in pentane at room temperature to give the... 

In contrast to this result, the enones with an alkyl moiety in the a-keto position were best converted to the corresponding epoxides when replacing lanthanum by ytterbium in the corresponding catalytically active complex of the above mentioned type. Using TBHP (1.5 equiv) as oxidant in the presence of 5 mol% of Yb-51 gave enantioselectivities up to 94%. However, the use of either Yb-50 catalyst or a La-CMHP system afforded the product of type 53 with less satisfactory results. It seems likely that the difference in ionic radius between lanthanum and ytterbium, as well as the difference in Lewis acidities, accounts for the observed center metal effects. 

Watson s investigations of mixed alkyl/pentamethylcyclopentadienyl complexes of ytterbium and lutetium have shown that the polymerization occurs due to the successive insertion of olefine into the Ln-C bond. The process includes the p-hydride or p-alkyl decomposition of Ln-R intermediates. The splitting-off of the coordinative bonded ligand from REM precedes the above mentioned reactions (see Scheme XIII.l). 

---