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Combinations of Acidic and Basic Monodentate Binaphtholic Phosphites as Supramolecular Bidentate Ligands for Enantioselective Rh‐Catalyzed Hydrogenations
Author(s) -
Pignataro Luca,
Lynikaite Benita,
Cvengroš Ján,
Marchini Mattia,
Piarulli Umberto,
Gennari Cesare
Publication year - 2009
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200900158
Subject(s) - chemistry , denticity , rhodium , enantioselective synthesis , ligand (biochemistry) , medicinal chemistry , amine gas treating , intramolecular force , carboxylic acid , asymmetric hydrogenation , stereochemistry , nuclear magnetic resonance spectroscopy , supramolecular chemistry , catalysis , organic chemistry , molecule , crystal structure , biochemistry , receptor
A small library of chiral BINOL‐derived monodentate phosphites containing either a carboxylic acid (‐COOH, A1 – A3 ) or a tertiary amine (‐NMe 2 , B1 – B4 ) was synthesized. The ligand combinations were screened in the enantioselective rhodium‐catalyzed hydrogenation of methyl 2‐acetamidoacrylate. The heterocombinations of the amine‐derived phosphite ( R )‐ B2 and of a carboxylic‐phosphite [( R )‐ A1 , ( R )‐ A2 , ( R )‐ A3 ] displayed a slightly higher level of enantioselectivity compared to the corresponding homocombinations [up to 90 % ee using ( R )‐ A1 /( R )‐ B2 ]. The nature and extent of the interaction between the acidic and basic ligands in the rhodium complexes were studied by IR and 31 P‐NMR spectroscopy. The formation of an intramolecular salt in the Rh‐heterocomplex, between the carboxylic acid and the tertiary amine, was suggested by the IR spectra. The selective formation of the Rh‐heterocomplex was quantitatively assessed by 31 P‐NMR spectroscopy, using a modified acidic ligand ( R )‐ A1‐Me . In this way, a moderate (ca. 70:30) heterocomplex/homocomplexes ratio was determined.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)