Polymerisation vs. Grafting in the Preparation of Polymer-Supported Aluminium Catalysts for the Diels-Alder Reaction: The Role of the Polymeric Backbone

摘要

Several polymers containing Al Lewis acids anchored to chiral prolinol moieties have been prepared and studied as catalysts for the Diels-Alder reaction of cyclopentadiene and methacrolein. The chiral fragment has been introduced by grafting and by polymerisation procedures using different crosslinking agents and ratios. All supported catalysts prepared show a good activity, but the polymeric network seems to play a very important role in the determining the selectivity observed. Best results, in terms of enantioselectivity, are obtained when the chiral fragment is introduced through polymerisation of the appropriate chiral monomer, but only when a high crosslinking degree (90% DVB) is used. It is shown that the presence of coordinating atoms in the polymeric backbone is clearly detrimental for the selectivity observed.