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para ‐Functionalized NCN‐Pincer Palladium( II ) Complexes: Synthesis, Catalysis and DFT Calculations
Author(s) -
Dijkstra Harm P.,
Slagt Martijn Q.,
McDonald Aidan,
Kruithof Cornelis A.,
Kreiter Robert,
Mills Allison M.,
Lutz Martin,
Spek Anthony L.,
Klopper Wim,
Klink Gerard P. M. van,
Koten Gerard van
Publication year - 2003
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200390113
Subject(s) - chemistry , pincer movement , catalysis , palladium , substituent , medicinal chemistry , cationic polymerization , homogeneous catalysis , lewis acids and bases , mulliken population analysis , ketone , density functional theory , polymer chemistry , stereochemistry , organic chemistry , computational chemistry
Several para ‐substituted NCN‐pincer palladium( II ) complexes ( 1a − g and 6a − g ) {NCN = [C 6 H 3 (CH 2 NMe 2 ) 2 ‐2,6] − , para = 4‐position} have been prepared and the electronic influences of the para substituents were studied in catalysis as well as by DFT calculations (B3LYP/LANL2DZ). From DFT calculations, it was found that the para substituent exerts only a minor effect on the partial charge, investigated by means of the Mulliken population analysis, at the palladium( II ) center. Also, when the para ‐functionalized, cationic NCN−Pd II complexes 6a − g were applied as Lewis acid catalysts in the double Michael reaction between methyl vinyl ketone and ethyl α‐cyanoacetate, only small differences in the activities of the various catalysts were observed. These results, when translated to immobilized multipincer catalysts, imply that various para functionalities can be used for immobilization of the pincer−metal complexes without affecting the catalytic activity of the individual sites. The application of a number of shape‐persistent nanosize (NCN−Pd II ) n complexes ( 7 , n = 3; 8 , n = 3; 9 , n = 8; 10 , n = 12) as homogeneous catalysts in the same Michael reaction, confirmed this expectation. For complexes 7 , 8 and 9 , the catalytic activity per Pd II center was found to be the same as for the monopincer analogs. Only dodecakis(NCN−Pd II ) complex 10 showed an almost threefold enhancement in catalytic activity per Pd II center, which is ascribed to the high catalyst concentration at the periphery of this material. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)