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Importance of Ligand Exchanges in Pd(II)-Bronsted Acid Cooperative Catalytic Approach to Spirocyclic Rings

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Title Importance of Ligand Exchanges in Pd(II)-Bronsted Acid Cooperative Catalytic Approach to Spirocyclic Rings
 
Creator JINDAL, G
SUNOJ, RB
 
Subject C-H ACTIVATION
BETA-KETO-ESTERS
BOND ACTIVATION
PALLADIUM COMPLEXES
SEMIPINACOL REARRANGEMENT
NONCOVALENT INTERACTIONS
MECHANISTIC INSIGHTS
ASYMMETRIC CATALYSIS
DENSITY FUNCTIONALS
ALLYLIC ALKYLATION
 
Description Increasing number of reports in the most recent literature convey the use of palladium and Bronsted acids as cooperative catalytic partners. However, the mechanistic understanding of several such cooperative catalytic reactions and the origin of cooperativity continue to remain limited. In transition metal catalysis, it is typically assumed that the native ligands, such as the acetates in palladium acetate, are retained throughout the catalytic cycle. Herein, we convey the significance of invoking ligand exchanges in transition metal catalysis by using the mechanism of a representative cooperative dual-catalytic reaction. Density functional theory (M06 and B3LYP) computations have been employed to decipher the mechanism of Pd(II)-Bonsted acid catalyzed migratory ring expansion reaction of an indenyl cyclobutanol to a spirocyclic indene bearing a quaternary carbon. The molecular role of water, benzoquinone and phosphoric acid has been probed by computing the energetics using several combinations of all these as ligands on palladium. Of the two key mechanistic possibilities examined, a Wacker-type pathway (involving a semipinacol ring expansion of cyclobutanol followed by a reductive elimination) is found to be energetically more preferred over an allylic pathway wherein the ring expansion in a Pd-p-allyl intermediate occurs subsequent to the initial allylic CH activation. The Gibbs free energies of the transition states with the native palladium acetate are much higher than a Pd-bis-phosphate species generated through ligand exchanges.
 
Publisher AMER CHEMICAL SOC
 
Date 2014-12-29T05:43:21Z
2014-12-29T05:43:21Z
2014
 
Type Article
 
Identifier JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 136(45)15998-16008
0002-7863
http://dx.doi.org/10.1021/ja5076629
http://dspace.library.iitb.ac.in/jspui/handle/100/17223
 
Language English