title: Macrocyclic cyclooctene-supported AlCl-salen catalysts for conjugated addition reactions: effect of linker and support structure on catalysis.
abstract: AlCl-salen (salen=N,N'-bis(salicylidene)ethylenediamine dianion) catalysts supported onto macrocyclic oligomeric cyclooctene through linkers of varying length and flexibility have been developed to demonstrate the importance of support architecture on catalyst activity. The role played by the support and the linkers in dictating catalyst activity was found to vary for reactions with contrasting mechanisms, such as the bimetallic cyanide and the monometallic indole addition reactions. While the flexible support significantly enhanced the cyanide addition reaction, most likely by improving salen-salen interactions in the transition state, it lowered the reaction rate for the monometallic indole reaction. For both reactions, significant increase in catalytic activity was observed for catalysts with the longest linkers. The effect of the flexible macrocyclic support on catalysis was further exemplified by the enhanced activity of the supported catalyst in comparison with its unsupported analogue for the conjugate addition of tetrazoles, which is known to be catalyzed by dimeric mu-oxo-salen catalysts. Our studies with the cyclooctene supported AlCl-salen catalysts provides significant insights for rationally designing highly efficient AlCl-salen catalysts for a diverse set of reactions.
authors.affiliation: School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.
authors.forename: Nandita
authors.initials: N
authors.lastname: Madhavan
authors.forename: Tait
authors.initials: T
authors.lastname: Takatani
authors.forename: C David
authors.initials: CD
authors.lastname: Sherrill
authors.forename: Marcus
authors.initials: M
authors.lastname: Weck
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D002384:Catalysis; D003432:Cross-Linking Reagents / Q000737:chemistry; D034242:Cyclooctanes / Q000138:chemical synthesis* / Q000737:chemistry; D005029:Ethylenediamines / Q000138:chemical synthesis* / Q000737:chemistry; D047028:Macrocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013379:Substrate Specificity
chemical_list: D003432:Cross-Linking Reagents; D034242:Cyclooctanes; D005029:Ethylenediamines; D047028:Macrocyclic Compounds; C011452:disalicylaldehyde ethylenediamine; D000535:Aluminum