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Tetrathiaheterohelicene Phosphanes as Helical‐Shaped Chiral Ligands for Catalysis
Author(s) -
Monteforte Marco,
Cauteruccio Silvia,
Maiorana Stefano,
Benincori Tiziana,
Forni Alessandra,
Raimondi Laura,
Graiff Claudia,
Tiripicchio Antonio,
Stephenson G. Richard,
Licandro Emanuela
Publication year - 2011
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.201100726
Subject(s) - chemistry , rhodium , ligand (biochemistry) , catalysis , medicinal chemistry , adduct , itaconic acid , chelation , ethanol , stereochemistry , organic chemistry , copolymer , polymer , biochemistry , receptor
Tetrathia[7]helicene‐based phosphanes thiaheliphos ( 2a ), n Pr‐thiaheliphos ( 2b ) and di‐ n Pr‐thiaheliphos ( 2c ) have been prepared from the 2,13‐dilithio derivatives of thiahelicenes 1a – c by reaction with an excess of Ph 2 PCl. Protection of the air‐sensitive products as BH 3 adducts, from which the phosphanes 2a – c are easily regenerated on heating with ethanol, is described. New rhodium(I) complexes 8 and 9 were obtained by reaction of 2c with [Rh(COD) 2 ] + [BF 4 ] – and [BARF] – ,respectively, which were converted by oxidation into thechelating phosphane–phosphane oxide Rh I complexes 10 and 11 . The monophosphane 5 was similarly prepared, and reaction of the dilithio species with ClP(O)(OEt) 2 gave the diphosphonate 17 , which was characterized by X‐ray crystallography. Comparison of data from DFT calculations (B3LYP/SVP) on 2c , 8 and 10 and X‐ray data for 17 reveals a strong tension within the thiaheliphos ligands that is partially relaxed by increasing the Rh–P distances and the bite angle of the chelating ligand. Compound ( P ) ‐ (+) ‐1c , obtained by chromatographic resolution, was transformed into optically pure ( P ) ‐ (+) ‐2c , which was used in the asymmetric hydrogenation of itaconic acid ester and methyl 2‐acetamidoacrylate (product ee s up to 40 %).