Ligand control of the catalytic activities of Al3+-immobilized solid Lewis acids

Treatment of anthracenebisresorcinol 1 (a tetraol) with Al(CH3)(2)Cl or Al((OPr)-Pr-i)(3) affords an amorphous solid formulated as 1(4)- 2[AlCl](2+) or 1(4-). 2[(AlOPr)-Pr-i](2+) (1(4-) is the deprotonated tetraanionic species of host 1). These solids (AlCl and (AlOPr)-Pr-i hosts) as recoverable and reusable Lewis acids catalyze the Diels-alder reaction of acrolein with 1,3-cyclohexadiene, where the former (AlCl) at 3 mol% exhibits a much higher catalytic activity with a halflife of the reaction of tau = 1 min than the latter ((AlOPr)-Pr-i) with tau = 80 min. The efficient solid-state catalysis by the AlCl host with a turnover rate of 30/min is based on the combination of space vacancy (microporosity) and coordination vacancy (coordinative unsaturation) as revealed by Al-27 MAS NMR spectroscopy. (C) 2000 Elsevier Science B.V. All rights reserved.