Asymmetric hydrogenation of prochiral olefins catalysed by furanoside thioether-phosphinite Rh(I) and Ir(I) complexes.
Thioether-phosphinite ligands (P-SR, R = Ph, Pr(I) and Me) bearing substituents with different steric demands on the sulfur centre were tested in the rhodium- and iridium-catalysed asymmetric hydrogenation of prochiral olefins. High enantiomeric excesses (up to 96%) and good activities (TOF up to 860 mol product x (mol catalyst precursor x h)(-1)) were obtained for alpha-acylaminoacrylates derivatives. Our results show that enantiomeric excesses depended strongly on the steric properties of the substituent in the thioether moiety, the metal source and the substrate structure. A bulky group in the thioether moiety along with the metal Rh had a positive effect on enantioselectivity. Reaction of these chiral ligands with [M(cod)2]BF4(M = Ir, Rh; cod = 1,5-cyclooctadiene) yielded complexes [M(cod)(P-SR)]BF4, which were present in only one diastereomeric form having the sulfur substituent in a pseudoaxial disposition. The addition of H2 to iridium complexes gave the cis-dihydridoiridium(iii) complexes [IrH2(cod)(P-SR)]BF4. For complexes [IrH2(cod)(P-SPh)]BF4 and [IrH2(cod)(P-SMe)] only one isomer was present in solution. However, for the complex [IrH2(cod)(P-Si-Pr)]BF4, which contained the more hindered substituent on sulfur, two isomers were detected. In all cases there was a pseudoaxial disposition of the sulfur substituents.
Guimet
Eugeni
E
Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, C/ Marcel.lí Domingo s/n, 43007 Tarragona, Spain.
Diéguez
Montserrat
M
Ruiz
Aurora
A
Claver
Carmen
C
D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D006865:Hydrogenation; D007495:Iridium / Q000737:chemistry*; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010721:Phosphinic Acids / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry*; D013237:Stereoisomerism; D013440:Sulfides / Q000737:chemistry*
D000475:Alkenes; D009942:Organometallic Compounds; D010721:Phosphinic Acids; D013440:Sulfides; D007495:Iridium; D012238:Rhodium