Ytterbium derivatives

The adduct derived from (a-benzyloxyacetaldehyde (97 % ee) is an important intermediate en route to compactin and mevinolin [76]. In contrast, modest enantioselectivity was attained when the cycloadditions were catalyzed by a chiral BINOL-ytterbium-derived catalyst [77]. Pyridines were used as additives, and the best enantioselection (93% ee) was attained only in the case of p-methoxybenzaldehyde using 2,6-lutidine. 

Anhydrous LnTp3 precipitates from aqueous solutions by interaction of LnCl3 with KTp (1 3) [180]. The molecular structure of the ytterbium derivative... 

Ln[CH(SiMe3)2]3CI Li(thf)4 19). The ytterbium derivative of the latter complex was crystallographically shown to have a pseudotetrahedral arrangement of ligands around the metal with Yb—C bond lengths of 2.37-2.39 A. 

The isolated compounds (table 16) show identical infrared spectra with a characteristic band at 1195 cm for a methyl group attached to a rare earth metal. The single crystal X-ray analysis of the yttrium (table 18, fig. 25) and of the ytterbium derivative (table 18) show both compounds to be isostructural with an approximately tetrahedral metal environment and a R(ju-CH3)2R unit like the trimethyl aluminum dimer. The and NMR spectra of the diamagnetic yttrium complex were invariant between — 40°C and +40°C with a triplet for the bridging methyl protons due to the coupling with the two equivalent yttrium atoms (tables 17, 19). 

Tricyclopentadienyl ytterbium and tricyclopentadienyl neodymium react with various terminal alkynes by liberating cyclopentadiene although CjHg is a stronger protic acid. While the formation of dimeric dicyclopentadienyl ytterbium derivatives... 

Three other pentamethylcyclopentadienyl ytterbium derivatives containing transition metals in the same molecule have been prepared by Tilley and Andersen (1981a, 1982). (C5Me5)2Yb (Et20) splits the cobalt-cobalt bond in Co2(CO)g with forma-... 

The first organolanthanoide sulfur compounds have been obtained from (C5Me5)2LnCl with sodium dithiocarbamate. In the ytterbium derivative the dithiocarbamate group functions as a bidentate ligand (Figure 25) (163) ... 

The interaction with the other reagents leads as a rule to the oxidation of metal to Ln(III) with retention of Cp2Ln moiety. The main attention in the investigation of these compounds was paid to the samarium and ytterbium derivatives. 

The divalent state of the metal in complexes is confirmed by the diamagnetism of ytterbium derivative and the EPR spectrum of Eu compound, which is characteristic of Eu(II) complexes. The presence or absence of coordinately linked NH3 does not essentially influence the spectrum. It testifies to the ionic character of complex. Both compounds are pyrophoric on air and quickly hydrolysed in water. They interact with Lewis bases to form the coordination complexes. It results in a change of the compound colour. Heating in vacuum (200°C/10 mm Hg) gives back unsolvated compound. Complexes of ytterbium with the substituted ligand t-BuCgH7 has been synthesized by the same method [21]. 

The spectra of ytterbium derivatives (v(CO) 1958, 1966, 1976, 1986, 1995, 2008 cm ) differ from those of the other REM complexes. The reasons for such difference are unclear. It has been noted, however, that the oxidation degree of ytterbium in the carbonyl complexes is close to 2+, whereas that for Pr, Nd, Gd and Ho atoms is 3+. 

Wayda et al. (1984) reported the preparation of novel divalent Cp Eu and Yb, NH3 adducts, by reacting the metal in liquid ammonia with CsMesH in vacuum line. The ytterbium derivative has been characterized crystallographically. 

The solubility in THF of some divalent samarium and ytterbium derivatives. 

---