Yttrium isopropoxide

Yttrium isopropoxide and yttrium 3-oxapentoxide initiators were the first lanthanide alkoxides described in the literature for the ROP of e-CL [93]. The discovery of lanthanide-based initiator systems allowed the block copolymerization of e-CL with compounds such as ethylene [94], tetrahydrofuran [95], L-LA [96], trimethylene carbonate [97], and methyl methacrylate [98]. This type of initiator has also been used to prepare poly((3-butyrolactone)s [99,100]. 

Ceramic powders of exceptional purity with very fine particle sizes (ca. 10 nm) have been prepared by precipitation of hydrolyzed oxides from high purity alkoxides . Yttria-stabilized zirconia is prepared by mixing high purity zirconium and yttrium isopropoxides in n-hexane, with water added dropwise to precipitate the oxides quantitatively. The homogeneity of the oxides results in stabilized cubic Zr02 at very low temperatures. Cyclic organoaluminum amides are used to prepare nonoxides such as sulfides and AIN- . 

Cyanohydrin silyl ethers Yttrium isopropoxide-more likely, the ((-PrO),3Y50 species—complexes with l,3-bis(2-methylferrocenyl)propane-l,3-dione (1) to afford a highly efficient catalyst for the asymmetric silylcyanation of electron-rich aromatic aldehydes with MCjSiCN. 

Yttrium Isopropoxide Y(0 C3H7)3 Yellowish-brown liquid... 

Thus, although the yttrium isopropoxide certainly has its merits, the limited availability of different yttrium alkoxides also limits the array of macromolecular structures that can be prepared. An approach to more flexible systems has been developed, in which the active initiator is generated in situ The concept is based on sterically very crowded tri(2,6 i-t-butylphenoxy) lanthanides that can not initiate lactone polymerization, but do exchange with sterically less crowded alcohols to generate alkoxides that turn into active initiators for e.g. lactide, E-caprolactone or 5-valerolactone polymerization. In this way, any alcohol can effectively be used to functionalize a polyester chain as shown in Fig 2 (vide supra). In a similar way the in situ formation of such a catalyst/initiator system from the commercially available [tris(hexamethyldisilyl)amide]Yttrium with isopropanol can be performed . 

Hydroxide suspensions of mullite with partially stabilized zirconia were prepared from metal alkoxide starting materials. Zirconium isoamyloxide and yttrium isopropoxide were mixed in the proper proportions for the partially stabilized zirconia. Aluminum isopropoxide and silicon ethoxide were added in the proper proportions for mullite. These solutions were refluxed for 4 to 8 h and then hydrolyzed to a pH of 0.5 using HNO3. The solutions were then neutralized to a pH of 8 using NH4OH. The resulting suspensions then contained the proper amount of each component as a hydroxide to form the mullite partially-stabilized zirconia matrix materials. With MgO as a stabilizer, procedures were identical to the above, except that MgO ethoxide was used instead of yttrium isopropoxide. Batch sizes were 25 to 100 g of final material. 

Samarium, neodynium, and yttrium isopropoxide have been used in combination with benzyl alcohol, which is a transfer agent, for the -CL polymerization. The catalytic activity is higher compared with aluminum and zirconiiun coim-terparts. The apparent propagation rate constant first increases with the alco-hol/metal molar ratio up to an optimum value, and then decreases according to an egg-shaped curve (20,57). Once again, the use of a catal5d ic amount of lanthanide alkoxides is a valuable strategy to decrease the polyester contamination by metallic residues. 

It was discovered that a 1 1 complex of (R,R)-BMPD [l,3-bis(2-methylferrocenyl) propane-1,3-dione] and yttrium isopropoxide, prepared in situ, was a remarkable catalyst for asymmetric silylcyanation (Scheme 12.83) [181, 182]. In the presence of 0.2 mol% of the catalyst, the reaction of benzaldehyde with TMSCN proceeded smoothly to give the desired adduct in 95% yield with 87% ee. The turnover number of this catalyst was 500. The remarkably high catalytic activity of the BMPD-yttrium isopropoxide complex showed a possibility of a practical application of this chiral Lewis acid catalyst. 

The polymerization of PDL, initiated by yttrium isopropoxide, has been carried both in bulk and in solution over the temperature range of 60-100 °C [39]. All isopropoxide groups of the initiator participated in the initiation, and the polymerization proceeded by acyl-oxygen cleavage of the monomer. The molecular mass of the polymer could be controlled effectively by varying the initial monomer-to-initiator molar ratio. An induction period which was observed for the bulk polymerization at 60 °C was attributed to structural rearrangement processes of the initiator to form the actual active sites. The molecular weight distribution (PDl) was approximately 1.6. 

Controlled ring-opening polymerization of m-penladecalactone with yttrium isopropoxide as an initiator. Macromolecular Chemistry and Physics,... 

Despite the typical behavior of five-membered cycUc carbonates to result in polyether carbonates upon polymerization at higher temperatures (T> 150°C), five-membered cyclic carbonates derived from methyl-4,6-0-benzylidene-glucopy-ranoside (39) [79] and 1,2-O-isopropylidene-D-xylofuranose (40) [80] were polymerized at temperatures below 70 °C, without any eUmination of carbon dioxide, to produce polycarbonates. The polymerization of 39 was carried out with 1,8 diaz-abicyclo [5.4.0]undec-7-ene (DBU) or potassium tert-butoxide, while that of 40 was performed with potassium tert-butoxide or yttrium isopropoxide as initiator. After removal of the protection groups, the carbohydrate polymers with carbonate main-chain linkages were obtained. 

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