Scandium complexes allyl

Very recently, Hou and coworkers have reported that rare earth half-metallocene complexes (Figure 14.16, 85-88) activated with [Ph3C] [B(C6F5)4] afford highly active systems for syndio-specific styrene polymerization, producing sPS with high syndiotacticities rrrr > 99%) and rather narrow polydispersities (Mw/Mn = 1.29-1.55). The activity of scandium complex 85 is comparable with that for the most active titanium catalysts (1.36 x 10 g sPS/(mol Sc-h)). The neutral allyl lanthanide complexes 89-92 (Figure 14.16) in the absence of a cocatalyst are also active for the syndiospecific polymerization of styrene (rrrr > 99%), but with lower activities that are in the order... 

Chiral scandium-bis(oxazolinyl)pyridine (Sc-pybox) complexes catalyze various catal5dic asymmettic addition reactions with carbonyl compounds. The first report of this complex was addition and annulation reactions of allenylsi-lanes with etiiyl glyoxylate using the scandium complex. The application of these complexes was expanded to various catalytic asymmetric transformations such as aldol reactions, allylation, and ene reactions. ... 

Jorgensen et al. reported that C2-symmetric bis(oxazoline)-copper(II) complex 25 also acts as chiral Lewis acid catalyst for a reaction of allylic stannane with ethyl glyoxylate [37]. Meanwhile, p-Tol-BINAP-CuCl complex 26 was shown to be a promising chiral catalyst for a catalytic enantioselective allylation of ketones with allyltrimethoxysilane under the influence of the TBAT catalyst [38]. Evans and coworkers have developed (S,S)-Ph-pybox-Sc(OTf)3 complex 27 as a new chiral Lewis acid catalyst and shown that this scandium catalyst promotes enantioselective addition reactions of allenyltrimethylsilanes to ethyl glyoxylate [39]. But, when the silicon substituents become bulkier, nonracemic dihydrofurans are predominantly obtained as products of [3+2] cycloaddition. 

The first allyl derivative of a rare earth was the complex dicyclopentadienyl allyl scandium, prepared by Coutts and Wailes (1970) from dicyclopentadienyl scandium chloride and allyl magnesium chloride in benzene-tetrahydrofuran. The orange compound shows an NMR spectrum with a singlet for the cyclopentadienyl protons at 5.90 ppm, and a quintet at 7.29 and a doublet at 3.05 ppm for the fluxional allyl group. The fluxional allyl group is also implicated by the IR band at 1475 cm for a delocalized C—C stretching vibration. 

Scandium group elements as well as the lanthanides form allyl complexes in which the central atom has H- 3 oxidation state, while the actinides give compounds possessing + 4 oxidation states (Table 7.14). These complexes are formed by reactions of metal halides with allyl compounds of magnesium, lithium, tin, etc. " " ... 

---