Macrocyclic cyclooctene-supported AlCl-salen catalysts for conjugated addition reactions: effect of linker and support structure on catalysis.
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.
Madhavan
Nandita
N
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Takatani
Tait
T
Sherrill
C David
CD
Weck
Marcus
M
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
D003432:Cross-Linking Reagents; D034242:Cyclooctanes; D005029:Ethylenediamines; D047028:Macrocyclic Compounds; C011452:disalicylaldehyde ethylenediamine; D000535:Aluminum