Yttrium alkyls

First structural evidence for the formation of heterobimetallic Ln/Al complexes in carboxylate-based catalytic systems was obtained from the reaction of homoleptic rare-earth metal trifluoroacetates with equimolar amounts of z -Bu2A1H and EtsAl, respectively [132], Alkylated yttrium, neodymium, and... 

Bis(pentamethylcyclopentadienyl) alkyls, yttrium Bis(pentamethylcyclopentadienyl) amides, yttrium Bis(pentamethylcyclopentadienyl) alkyls, yttirum, Bls(pentamethylcyclopentadienyl) yttrium hydride... 

The acetylacetonates are stable in air and readily soluble in organic solvents. From this standpoint, they have the advantage over the alkyls and other alkoxides, which, with the exception of the iron alkoxides, are not as easily soluble. They can be readily synthesized in the laboratory. Many are used extensively as catalysts and are readily available. They are also used in CVD in the deposition of metals such as iridium, scandium and rhenium and of compounds, such as the yttrium-barium-copper oxide complexes, used as superconductors. 1 1 PI Commercially available acetyl-acetonates are shown in Table 4.2. 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

Marks et al. reported the co-polymerization of ethylene and 1-hexene by using ansa-type complexes of lanthanide metals [127]. Recently, bulky alkyl substituted ansa-type metallocene complexes of yttrium have been reported to exhibit high activity for the polymerization of 1-hexane. [114, 119, 128]... 

Table 10 shows the results of polymerization of oc-olefins catalyzed with trivalent complexes. When a bulkiler tBuMe2Si group instead of the Me3Si group was introduced into the yttrium complex, the racemic complex was formed exclusively [74c]. However, this alkyl complex did not react with olefins, and hence it was converted to a hydride complex by reaction with H2. The complex obtained was reactive to various olefins and produced polymers at... 

Limited research studies [6] show that the minerals from the yttrium groups can be recovered using alkyl hydroxamate collectors which form complex reactions with REO. 

Neutral lanthanide complexes are convenient models for the cationic zirconocene systems and avoid complications due to the presence of counteranions and the limited solubility of ionic compounds. Dynamic NMR studies on yttrium complexes 44-46 has allowed the determination of the alkene binding enthalpy, the activation enthalpy of alkene dissociation, and the relative rates of dissociation and alkyl site exchange (site epimerisation) (Scheme 8.20). Compared to the Zr... 

Yttrium bis(alkyl) and bis(amido) complexes of the type [LY(CH2SiMe3)2] bearing N,0-multidentate ligands (L), such as p-diimines, displayed high activity for the ROP of L-lactide at room temperature (100% conversion in most experiments in THF within 2-60 min). In this case, an influence of the ligand framework and the geometry of the alkyl(amido) species (single site or double site) on the catalytic activity have been reported [106]. 

Yttrium-catalyzed enyne cyclization/hydrosilylation was proposed to occur via cr-bond metathesis of the Y-G bond of pre-catalyst Cp 2YMe(THF) with the Si-H bond of the silane to form the yttrium hydride complex Ig (Scheme 8). Hydrometallation of the C=G bond of the enyne coupled with complexation of the pendant G=G bond could form the alkenylyttrium alkyl complex Ilg. Subsequent / -migratory insertion of the alkene moiety into the Y-C bond of Ilg could form cyclopentylmethyl complex Illg. Silylation of the resulting Y-C bond via cr-bond metathesis could release the silylated cycloalkane and regenerate the active yttrium hydride catalyst. Predominant formation of the /ra //j--cyclopentane presumably results from preferential orientation of the allylic substituent in a pseudo-equatorial position in a chairlike transition state for intramolecular carbometallation (Ilg —IHg). 

Yttrium-catalyzed cascade cyclization/hydrosilylation of 3-(3-butynyl)-l,5-hexadienes was stereospecific, and syn-19 (R =Gy, R = OGPh3) underwent cascade cyclization/hydrosilylation to form 80b (R = Gy, R = OGPh3) in 97% yield as a single diastereomer (Scheme 20). The regio- and stereoselective conversion of syn-19 to 80b was proposed to occur through an initial 5- x -intramolecular carbometallation via a chairlike transition state that resembles alkenyl olefin eomplex syn- m. followed by S-exo intramolecular carbometallation via a boatlike transition state that resembles alkyl olefin complex boat-llm. The second intramolecular carbometallation presumably occurs via a boatlike transition state to avoid the unfavorable 1,3-interaction present in the corresponding chairlike transition state (Scheme 20). 

An interesting selectivity in the transfer of alkyl groups (n-Alk>Me) is observed in these addition reactions. The regioselectivity of the reaction of crotylmagnesium chloride (213) with benzaldehyde strongly depends on the presence of various rare-earth metal chlorides. The a- to y ratio of products can be switched to the opposite by using only another metal salt. Yttrium trichloride gives exclusively y-product, while neodymium trichloride leads to 89% of the a-attack (with 92% of ( )-isomer) (equation 142) °. 

Bambirra, S., van Leusen, D., Meetsma, A., Hessen, B., and Teuben, J.H. Neutral and cationic yttrium alkyl complexes with linked 1,4,7-triazacyclononane-amide monoanionic ancillary ligands synthesis and catalytic ethene polymerisation, Chem. Comm. (2001), 637-638. 

The hydrides 44b have been found to polymerize ethylene and react with a variety of protic reagents such as terminal alkynes and nitriles. Catalytic effects in the hydroboration of olefins have also been observed [27]. A well-defined /i-ethynyl complex of yttrium is formed by protolysis of the alkyl derivative 38b with acetylene (Eq. 18). Figure 14 shows the dimeric structure of 45b with bridging ethynyl ligands [27, 65]. 

The polymerisation proceeds quite slowly, presumably owing to the inactivity of the formally d° 16-electron yttrium species of the dimeric catalyst. A formally d° 14-electron monomeric hydride or alkyl derivative is probably required for olefin polymerisation [187],... 

In the course of these studies key features such as olefin coordination [19,20], olefin insertion (propagation) [16,21,22], /(-hydrogen elimination [16,21,22], and /3-alkyl elimination [23] could be spectroscopically and structurally proven. In particular, yttrium aluminates have been proposed to model isoelectronic cationic homo- and heterobridged Zr/Al heterobimetallic complexes as dormant species and potential polymer chain transfer candidates [24]. Such zirconium aluminate complexes seem to be elusive [25], while the first structurally characterized titanium alumi-... 

Alkylated rare-earth metal complexes with rare-earth metal centers surrounded exclusively by oxygen donor ligands were reported from facile ligand redistribution processes in 2,6-dimethylphenolate/trialkylaluminum mixtures. As shown in Scheme 29 for the yttrium derivatives Y(0ArMe,II)2[(//-OArMe>H)2AlR2](THF)2 (R= Me, Et), heterobimetallic 1 1-species were ac-... 

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