New neutral and cationic dialkylaluminium complexes bearing imino-amide or imino-phenoxide ligands: synthesis, characterization and reactivity with olefins

The synthesis and the characterization of some new aluminium complexes carrying bidentate monoanionic iminoamide or imino-phenoxide ligands are described. Reaction of 1-(o,o′-diisopropylphenylamino)-6- (o,o′-diisopropylphenyl-imino)cyclohexene with A1Me3 proceeded by methane elimination to produce the yellow compound dimethylaluminium N-(o,o′-diisopropylphenyl)-6-[N- (o,o′-diisopropylphenyl)-imido]-1-cyclohexen-1-amide (1). In contrast, reaction of the same ligand with AlEt3 under the same experimental conditions involved the 1,4-addition of AlEt3 to the α, β-unsaturated imine, and led to the highly crystalline diethylaluminium N-(o, o′-diisopropylphenyl)-2- [(o, o′-diisopropylphenyl)amino]-3-ethyl-1-cyclohexen-1-amide (2). The structures of compounds 1 and 2 were determined by single-crystal X-ray diffraction. Thermolysis of 2 gave rise to ethane elimination, and led to the oily bis(amido) monoethyl derivative. Treatment of the salicylaldimine ligands 3-tBu-2-(OH)C6H3CH=N-R with AlMe3 yielded the dimethylaluminium compounds {3-tBu-2-(O)C6H3CH=N-R}AlMe2 [R = C6H3 (3); 2,6-iPr2C6H3 (4); and C6F5 (5)]. Compounds 1, 3, and 5 underwent methyl abstraction reactions with B(C6F5)3; trapping of the cationic species was accomplished in the presence of THF in dichloromethane solution. Preliminary polymerization tests were carried out for the synthesized A1 complexes. Toluene solutions of 3, 4, and 5, when activated with 1 equiv. of B(C6F5)3, polymerised ethylene (1 atm) to solid polyethylene with low activity.