Alkyl rare-earth metal complexes

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-... 

Zhang, L.X., Suzuki, T., Luo, Y. et al. (2007) Cationic alkyl rare-earth metal complexes bearing an ancillary bis(phosphinophenyl)amido ligand a catalytic system for living cis-1,4-polymerization and copolymerization of isoprene and butadiene. Angewandte Chemie International Edition, 46, 1909. 

Scheme 90 Synthesis of heteroscorpionate tri- and di-alkyl rare-earth metal complexes.

Although heterobimetallic complexes with alkylated rare-earth metal centers were proposed to promote 1,3-diene polymerization via an allyl insertion mechanism, details of the polymerization mechanism and of the structure of the catalytically active center(s) are rare [58,83,118-125]. Moreover, until now, the interaction of the cationizing chloride-donating reagent with alkylated rare-earth metal centers is not well-understood. Lanthanide carboxylate complexes, which are used in the industrial-scale polymerization of butadiene and isoprene, are generally derived from octanoic, versatic, and... 

Heterogeneous diene polymerization catalysts based on modified and unmodified silica-supported lanthanide complexes are known as efficient gas-phase polymerization catalysts for a variety of support materials and activation procedures (see Sect. 9). Metal siloxide complexes M(()SiR3 )x are routinely employed as molecular model systems of such silica-immobilized/ grafted metal centers [196-199]. Structurally authenticated alkylated rare-earth metal siloxide derivatives are scarce, which is surprising given that structural data on a considerable number of alkylated lanthanide alkoxide and aryloxide complexes with a variety of substitution patterns is meanwhile available. 

The ability of organo-rare-earth metal complexes to undergo alkene or alkyne insertion provides the possibility to perform polyene cyclizations, producing metal-alkyl species which can then undergo o-bond metathesis with an appropriate reagent to produce a cyclic compound. Thus, termination via protonolysis (6) results in cycloalkane derivatives however, termination via silylation is more desirable as a functionalized cyclic framework is formed (Fig. 9). 

Pioneering work of Watson described the scrambling of CH4 into soluble rare-earth metal complexes Cp 2LnCH3 (Ln = Lu, Y) (59) [212], The lutetocene system was also shown to activate C-H bonds of arenes and alkyl silanes [6,213],... 

By using type II-B aniline-phosphinimines (Scheme 20), various bisalkyl rare-earth metal complexes were synthesized. All complexes 52-58 were obtained by the reaction of the corresponding aniline-phosphinimines HL12-HL15 with [Ln(CH2SiMe3)3(THF)2] (Ln = Sc, Y, Lu) in toluene via alkyl elimination (Scheme 21) [54]. 

Keywords Living polymerization, Living copolymerization, Rare earth metal complexes, Alkyl methacrylate, Alkyl acrylates, Lactones, Ethylene, 1-Olefins, Conjugated dienes, Acetylene... 

Alkyl acrylates were for the first time polymerized in a living fashion with the aid of the unique catalytic action of rare earth metal complexes [4]. Since these monomers have an acidic a-H, termination and chain transfer reactions occur so frequently that their polymerizations generally do not proceed in a living manner. By taking advantages of the living polymerization ability of both MMA and alkyl acrylate, ABA or ABC type tri-block copolymerization was performed to obtain thermoplastic elastomers. 

Living polymerization of lactones has been successfully performed by the catalysis of rare earth metal complexes producing Mw/Mn values of 1.07-1.08 [5]. Polymerizations of acrylonitrile and alkyl isocyanates have been successfully realized using La[CH(SiMe3)2]2(C5Me5) as initiator, and those of various oxiranes have been made using Ln(acac)3/AlR3/H20 system [6]. 

Ihara, E. Morimoto, M. Yasuda, H. Living polymerizations and copolymerizations of alkyl acrylates by the unique catalysis of rare earth metal complexes. Macromolecules 1995, 28, 7886-7892. 

A review article entitled "Bulky amido ligands in rare-earth chemistry Syntheses, structures, and catalysis" has been published by Roesky. Benzamidinate ligands are briefly mentioned in this contexD The use of bulky benzamidinate ligands in organolanthanide chemistry was also briefly mentioned in a review article by Okuda et al. devoted to "Cationic alkyl complexes of the rare-earth metals S mthesis, structure, and reactivity." Particularly mentioned in this article are reactions of neutral bis(alkyl) lanthanide benzamidinates with [NMe2HPh][BPh4] which result in the formation of thermally robust ion pairs (Scheme 55). ... 

Immobilization of Rare-Earth Metal Hydride, Alkyl, and Cyclopentadienyl Complexes... 

Like rare-earth metal hydride and alkyl complexes [141, 206, 207], silylamide derivahves catalyze the hydrosilylation of alkenes and dienes with phenylsilane [208-210]. Accordingly, materials [Ln N(SiMe3)2 3] AS-380.7oo (12a-d, Table 12.3) featuring monopodal bis(silylamide) surface complexes have been exploited as catalysts for the reaction of 1-hexene and styrene with PhSiH3 (Scheme 12.20) [118]. 

The regio- and stereoselective dimerization of terminal alkynes into disubstituted enynes is efficiently catalyzed by rare-earth metal alkyl and hydride complexes, as reported independently by Bercaw et al. and Teuben et al. in 1987 [211,212]. Takaki and coworkers have shown that complexes Ln[N(SiMe3)2]3 when combined with an amine additive (typically, ArNH2 compounds) afford an active species for the... 

A series of mono(amidinate) rare earth metal bis(alkyl) complexes (104-110) with different amidinate ligands are shown in Fig. 16. The activity of the mono(amidinate) rare earth bis(alkyl) complexes [CyC(Ai-2,6- Pr2C6H3)2]Ln(CH2SiMe3)2(THF) (Ln = Y 104, Lu 105), [CyC(A-2,6-Me2C6H3)2jLn(CH2SiMe3)2(THF)2 (Ln = Y... 

On the basis of these initial results, various rare earth metal triflates, including Sc(OTf)3, Hf(OTf)4 and Yb(OTf)3 were applied as catalysts [27-29]. Recently Beller and coworkers developed efficient Friedel-Crafts alkylations with catalytic amounts of Rh, W, Pd, Pt and Ir complexes [30] or FeCl3 [31-34] as Lewis acid catalysts. However, in the latter cases high catalyst loadings had to be applied. To overcome these major drawbacks, we decided to develop a Bi(III)-catalyzed Friedel-Crafts alkylation of arenes with benzyl alcohols. Although bismuth-catalyzed Friedel-Crafts acylations were well known at this time, Friedel-Crafts alkylations using benzyl alcohols had not been reported. 

Fig. 21 Stoichiometric reaction of C02 with rare-earth metal alkyl complexes to produce carboxylate dimeric catalysts...

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... 

X-ray structure analysis revealed a 7-coordinate rare-earth metal center with two asymmetrically / -coordinating tetramethylaluminate ligands, an asymmetrically / -coordinating siloxide ligand and one methyl group of a trimethylaluminum donor molecule (Fig. 28). Such heteroleptic complexes can be regarded as molecular models of covalently bonded alkylated silica surface species. Moreover, isoprene was polymerized in the presence of 1-3 equivalents of diethylaluminum chloride, with highest activities observed for (Cl) (Ln) ratios of 2 1 (Table 12) (Fischbach et al., 2006, personal communication) [150]. 

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