Tetramethylaluminate complexes

Q tetramethylaluminate complex (dormant, inactive species III, Al-mediated chain transfer)... 

Scheme 16 Formation of lanthanidocene tetramethylaluminate complexes via [carb-oxylate] [alkyl] interchange [142]...

Scheme 20 Synthesis of heteroleptic tetramethylaluminate complexes via [carboxylate] [alkyl] exchange (top) or [alkyl] - [carboxylate] exchange (bottom, tetramethylaluminate route ) [147,148]...

Scheme 31 Formation of mono(TMA) adducts and mono(tetramethylaluminate) complexes [188]...

Scheme 53 Generation of heteroleptic tetramethylaluminate complexes via [aluminate] [amide] interchange [223]...

Scheme 58 Synthesis of homoleptic lanthanide tris(tetramethylaluminate) complexes Ln[(/x-Me)2AlMe2]3 (Ln = Y, La, Ce, Pr, Nd, Sm, Gd, Lu)...

The above-mentioned donor-induced cleavage reactions reveal that tetra-alkylaluminate complexes can behave as metal alkyls in disguise . This bonding feature is in accordance with various alkane elimination reactions observed for homoleptic and heteroleptic tetramethylaluminate complexes. 

Preformation of homoleptic lanthanide tris(tetramethylaluminate) complexes Ln(AlMe4)3 (Ln = Y, La, Ce, Pr, Nd, Sm, Gd) and Et2AlCl generated extremely active and highly cis-1,4-slcrcosclective binary diene polymerization initiators (Fischbach et al., 2006, personal communication) [150]. Optimal performance in isoprene polymerization was observed for most of the lanthanide metal centers for (Cl) (Ln) ratios of 2 1 (Table 16). Only the samarium... 

Chart 8 Heteroleptic tetramethylaluminate complexes examined via VT-NMR spectroscopy... 

The high mobility of the methyl ligands of Ln/Al organometallics in solution was also evidenced for heterobridged trimethylaluminum adduct complexes (Scheme 75). As for the homobridged tetramethylaluminate complexes, this fluxional process may be suppressed at lower temperature and/or in the presence of sterically demanding ligand environments and smaller rare-earth metal centers. 

Yttrocene tetramethylaluminate complex 38a was found to be less reactive towards ethylene and a-olefins than the corresponding scandocene, 38b. This reactivity trend is consistent with the observed reactivity for 39/H2(g). Compounds 38a-c and 39/H2( ) were tested for the polymerization of propylene and 1-pentene. 1-pentene polymerizations were carried out in neat monomer, either at 0 °C or at room temperature ( 22 °C). Propylene polymerizations were carried out either in neat monomer or with a 50/50 (v/v) mixture with toluene, all at -5 °C. In general, scandocenes 38b and 38c provided higher polymer Mn values and were more active for polymerization than yttrocenes 38a and 39/H2(g). 

Rare-earth tetramethylaluminate complexes have been identified as key intermediates in Ziegler-Natta-type olefin polymerizatiOTi and may be readily prepared by reaction of rare-earth precursors with organoaluminum reagents [112]. The first homoleptic Ln(AlR4)3 species (Ln = Y, Nd R = Me) were reported by Evans et al. in 1995 [114], The synthesis of these heterobimetallic... 

Scheme 21 Synthesis of half-sandwich rare-earth bis(tetramethylaluminate) complexes from homoleptic tris(tetramethylaluminate) rare-earth precursors...

Various half-sandwich rare-earth bis(tetramethylaluminate) complexes have been readily synthesized by methane elimination reactions between Ln(AlMe4)3 derivatives and appropriate HCp ligands (Scheme 21, A) [119-121]. Reaction of homoleptic tetramethylaluminate derivatives with phospholide salts also allowed access to the corresponding half-sandwich bis(tetramethylaluminate) complexes through a salt-metathesis route (Scheme 21, B) [122]. 

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