Metallocenes lanthanide

Scheme 6.11 Enantioselective hydrogenation Group III and lanthanide metallocene catalysts.

Table 12.7 Ethylene polymerization based on supported group 3 and lanthanide metallocene complexes-examples from relevant patents.

Molander has developed effective protocols for the cyclization/hydrosilylation of 1,6-enynes catalyzed by lanthanide metallocene complexes/ For example, reaction of cyclohexyl-substituted 1,6-enyne 15a with phenylsilane catalyzed by Cp 2YMe(THF) in cyclohexane at room temperature for 2h gave silylated alkylidene cyclopentane 16a as a 6.5 1 mixture of trans. cis isomers (Table 5, entry 1). The diastereoselectivity of the reaction depended strongly on the nature of the allylic substituent. For example, yttrium-catalyzed cyclization/ hydrosilylation of the ethyl-substituted enyne 15b gave silylated cyclopentane 16b in 88% yield as a single diastereomer (Table 5, entry 2). 

Cyclization/Hydrosilylation of Dienes 11.11.4.1 Lanthanide Metallocene Catalysts... 

Bercaw has investigated the application of the 6 2-symmetric, enantiomerically pure lanthanide metallocene derivative (i ,A)-BnBpYH 34 as a catalyst for the asymmetric cyclization/hydrosilylation of 1,5- and 1,6-dienes. Although 34 displayed high activity for the reaction of a number of dienes, asymmetric induction was low. In the best case, reaction of 3,3-dimethyl-1,5-hexadiene with phenylsilane catalyzed by 34 gave silylated cyclopentene 35 in 95% yield with 50% ee (Equation (25)). 

Edelmann FT (1996) Rare Earth Complexes with Heteroallylic Ligands. 179 113-148 Edelmann FT (1996) Lanthanide Metallocenes in Homogeneous Catalysis. 179 247-276 Ekhart CW, see de Raadt A (1997) 187 157-186... 

Edelmann FT (1996) Rare Earth Complexes with Heteroallylic Ligands. 179 113 -148 Edelmann FT (1996) Lanthanide Metallocenes in Homogeneous Catalysis. 179 247-276 Effenhauser CS (1998) Integrated Chip-Based Microcolumn Separation Systems. 194 51 - 82 Ehrfeld W, Hessel V, Lehr H (1998) Microreactors for Chemical Synthesis and Biotechnology -Current Developments and Future Applications. 194 233 - 252 Ekhart CW, see de Raadt A (1997) 187 157-186... 

The ytterbium(III) product 14o was isolated as large colorless crystals in 33% yield. A comparable pentamethylcyclopentadienyl derivative, (C5Me5)2Yb(S2CNEt2) was described by Andersen et al. in 1982 [52]. The bent [PhC(NSiMe3)2]2Yb unit in 14o structurally resembles the bent lanthanide metallocenes containing (C5Me5)2Ln moieties (Fig. 5). 

In addition to achiral precatalysts the chiral lanthanide metallocenes (R)-[Me2SiCp" ( — )-menthylCp ]SmCH(SiMe3)2 and (S)-[Me2SiCp" ( - )-men-thyl Cp ]SmCH(SiMe3)2 have been employed [71]. The hydrocarbyl derivatives have been shown to mediate the enantioselective hydrosilylation of 2-phenyl-l-butene by PhSiH3 with exclusive 1,2-addition and with N, 50h 1. In this case enantioselection proceeds with 68% ee ((R) product) and 65% ee ((S) product) for the (R)-Sm and (S)-Sm catalysts (70% enantiopure), respectively. 

Lanthanide metallocene compounds are also active catalysts for the dimerization of terminal alkynes, giving predominantly the linear head-to-head enyne dimer with a double bond of E configuration [17]. In recent years, however, novel organo-lanthanide [13] and organoactinide [18, 19] systems have shown their ability to produce, with high selectivity, Z and geminal enyne products, respectively. 

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