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An Atropo‐Stereogenic Diphosphane Ligand with a Proximal Cationic Charge: Specific Catalytic Properties of a Palladium Complex Thereof
Author(s) -
Debono Nathalie,
Canac Yves,
Duhayon Carine,
Chauvin Remi
Publication year - 2008
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.200800157
Subject(s) - chemistry , cationic polymerization , palladium , ligand (biochemistry) , stereocenter , carbene , stereochemistry , medicinal chemistry , electrophile , oxidative addition , catalysis , photochemistry , enantioselective synthesis , polymer chemistry , organic chemistry , biochemistry , receptor
A class of cationic diphosphane ligands combining phosphane and amidiniophosphane moieties is illustrated on the N ‐methyl, N ‐naphthylbenzimidazolium framework. The palladium(II) complex thereof is described and compared to the corresponding complex of the analogous neutral diphosphane. Contrary to first‐level expectations, the N 2 C–P and N 2 CP–Pd bonds in the cationic diphosphane complex are not longer than those occurring in its neutral counterpart. In the cationic ligand, the proximal positive charge is indeed conjugated to one phosphanyl group, and the coordination scheme is tentatively interpreted by resonance of the phosphane→metal dative bond ( + N 2 C–P : →[Pd]) with a carbene→phosphenium dative bond (N 2 C : →[ + P : →Pd]). Despite this peculiar structural feature, the electronic σ donation (vs. π acceptation) towards the palladium centre remains lowered in the cationic ligand. This specific property can be a priori valuable in a catalytic process where oxidative addition is not the limiting step. It is indeed shown that although the neutral complex is more active in Suzuki coupling reactions, the cationic complex is more active in Sonogashira‐type coupling reactions involving predissociated halide substrates, namely an acyl chloride. These likely atropo‐chiral ligands deserve to be resolved for application in asymmetric catalysis.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)