An unprecedented coordination mode for hemilabile pendant-arm 1,4,7-triazacyclononanes and the synthesis of cationic organoaluminium complexes

Reaction of AlMe3 or [AlMe3. py] with the pendant arm OH-funtionalised 1,4, 7-triazacyclononane proligands, HL1 or HL2, affords the four- and five-coor dinate derivatives [Al(L-1)Me-2] 1 or [Al-2(L-2)(2)Me-4] 2 in which the pen dant alkoxide O-donor and only one macrocycle N-donor is bound to Al; methy l anion abstraction from 1 yields cationic, pentacoordinate [Al(L-1)Me](+) in which L-1 has a tetradentate coordination mode [L-1 = 1-(2-hydroxy-3,5-d i-tert-butylbenzyl)-4,7-diisopropyl-1,4,7-triazcyclononane; L-2 = 1-(2-hy- droxy-2-methylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane].