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C 1 ‐Symmetric Diphosphite Ligands Derived from Carbohydrates: Influence of Structural Modifications on the Rhodium‐Catalyzed Asymmetric Hydroformylation of Styrene
Author(s) -
Gual Aitor,
Godard Cyril,
Claver Carmen,
Castillón Sergio
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.200801093
Subject(s) - chemistry , hydroformylation , rhodium , moiety , catalysis , styrene , isopropyl , stereochemistry , medicinal chemistry , nuclear magnetic resonance spectroscopy , alkyl , carbonylation , carbon monoxide , organic chemistry , polymer , copolymer
New 3,5‐diphosphite‐substituted xylofuranoside ( 1b , 25a , b , and 26a , b ) and glucofuranoside ( 3a , 7a , 8a , b ) ligands with C 1 symmetry have been prepared and used in the Rh‐catalyzed asymmetric hydroformylation of styrene. The main structural features of these ligands are a) the presence of a 6‐ O ‐isopropyl group in ligands with a gluco configuration, b) the absence of 1,2‐ O ‐isopropylidene, a common group in many ligands with a furanoside skeleton, c) the presence of an alkyl chain bound to the 2‐OH, and d) modification of the diol in the phosphite moiety. Modification of the carbohydrate backbone and diphosphite bridge affects the activity and selectivity of the reaction. Catalytic systems with ligands 1b and 8b were not active at 40 °C, although the formation of the expected hydride species [RhH(CO) 2 ( 1b )] was demonstrated by NMR spectroscopy. The highest enantioselectivity (83 %) was obtained with the catalytic system Rh/ 8a . The complex [RhH(CO) 2 ( 8a )] was characterized by NMR spectroscopy using high‐pressure techniques and was shown to exist in solution as two isomers in equilibrium; the two isomers adopt an equatorial–equatorial (eq–eq) configuration. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)