Trimethylaluminum adduct complexes

Activation of such homoleptic trimethylaluminum adduct complexes with 1 -3 equivalents of the chloride source Et2AlCl produced binary catalyst mixtures revealing the expected activity and cis- 1,4-stereospecificity in isoprene polymerization (Table 9) [142]. High-yield polymeric materials with relatively narrow molecular weight distributions were obtained. No activity was observed for a n(Cl) n(Ln) ratio of 3 1. 

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. 

Organoaluminum reagents have been used in the copper-catalyzed conjugate addition to enones with some success. Iwata and co-workers (182) demonstrated that dimethoxyphenyl oxazoline (247) provides modest selectivities in the copper-catalyzed conjugate addition of trimethylaluminum to 3,4,4-trimethylcyclohexadi-enone to provide the adduct in 68% ee, Eq. 145. The use of TBSOTf is crucial to attain high conversion and selectivity in this process. Woodward and co-workers (183) subsequently reported that a Cu(I) complex of thiocarbamate 248 provides modest facial discrimination in the addition of trimethylaluminum to a linear enone to afford 245b in 51% ee, Eq. 146. The authors note that this catalyst system decomposes under the reaction conditions at ambient temperature. 

C5Me5)Ln[(/i.-OCH2f-Bu)(/i.-Me)AlMe2]2 (Ln = Y, Lu) [142] were obtained from the reactions of cyclopentadienyl-substituted derivatives. According to Scheme 27, the addition of stoichiometric amounts of trimethylaluminum (n(Ln) n(Al) = 1 2) to the dimeric half-lanthanidocene bis(alkoxide) complexes quantitatively gave bis(TMA) adducts. 

Other Lewis acids that complex with thietane are titanium tetrachloride or bromide,boron trifluoride,trimethylaluminum, and tin tetrachloride. The enthalpies of formation of the aluminum complex (— 16.04 kcal/mole) and the tin complex (— 14.2 kcal/mole) and the wavelength of the charge transfer band of the tin complex (270 nm) have been determined. The titanium tetrahalides form both a 1 1 and a 1 2 adduct (titanium halide thietane). °° Treatment of 3-methyl-thietane with aluminum chloride or tin tetrachloride yields a rubbery white soUd." "... 

Shih and coworkers prepared adducts of several organoaluminum compounds with an NHC featuring a pendant JV-t-butylethylamine branch. The resulting complexes were found to undergo insertion reactions with benzaldehyde, with the carbonyl carbon inserting between the C—A1 bond [29]. These trimethylaluminum complexes have also been used in conjunction with [Ni(cod)2] to facilitate the meta- and j ara-alkenylation of pyridine (with 4-octyne) [135]. These complexes were compared to the corresponding triphenylborane adduct and found to be generally more reactive and more prone to react with imsaturated substrates [136]. 

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