In:
European Journal of Inorganic Chemistry, Wiley, Vol. 2003, No. 5 ( 2003-03), p. 830-838
Abstract:
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)
Type of Medium:
Online Resource
ISSN:
1434-1948
,
1099-0682
DOI:
10.1002/ejic.v2003:5
DOI:
10.1002/ejic.200390113
Language:
English
Publisher:
Wiley
Publication Date:
2003
detail.hit.zdb_id:
1475009-0
