Synthesis and characterisation of neutral and cationic alkyl aluminium complexes bearing N,O-Schiff base chelates with pendant donor arms

The Schiff base ligands [3,5-Bu(2)(t)-2-(OH)C(6)H(2)CH=NL] [L = CH(2)CH(2)NMe(2) (1a), 2-(PhO)C(6)H(4) (1b), 2-CH(2)C(5)H(3)N (1c), 8-C(9)H(6)N (quinoline) (1d) and 2-(PPh(2))C(6)H(4) (1e)] are accessed in good yields (>85%) via standard imine condensation reactions. Reaction of 1a-e with Me(3)Al at room temperature affords the corresponding complexes [(3,5-Bu(2)(t)-2-(O)C(6)H(2)CH=NL)AlMe(2)] (2a-e); in the case of L = 8-quinoline, the same reaction conducted in refluxing toluene affords binuclear {[3,5-Bu(2)(t)-2-(O)C(6)H(2)CHMeN-8-C(9)H(6)N]AlMe}(2) (3) by methyl migration from metal to ligand. Further reaction of the dimethyl compounds with B(C(6)F(5))(3) in CD(2)Cl(2) or C(6)D(6) affords the cationic systems [(3,5-Bu(2)(t)-2-(O)C(6)H(2)CH=NL)AlMe](+) (4a-e). The crystal structures of 2a, 2c, 2e and 3 have been determined. In 2a and 2c the respective ligands bind to the metal centre via all three heteroatoms, the aluminium having a trigonal bipyramidal geometry, whereas in 2e coordination is via nitrogen and oxygen only, and the aluminium is tetrahedral. Complex 3 has a dimeric structure with the ligand adopting both tridentate and binucleating roles; the aluminium centres are trigonal bipyramidal.