作者:Montserrat Diéguez、Aurora Ruiz、Carmen Claver、Franco Doro、Maria G Sanna、Serafino Gladiali
DOI:10.1016/j.ica.2004.03.039
日期:2004.7
Mononuclear cationic Ir(I)-cyclooetadiene complexes containing three different C-2-symmetrical binaphthalene-templated sulfide ligands, featuring alkyl groups of increasing steric demand onto the donor centres, have been prepared and characterized. Variable temperature NMR spectra provide evidence that, regardless of the bulk of the alkyl substituent on the sulfur, the chelate coordination of the ligands proceeds in all cases with complete stereo selectivity at the newly generated S-stereocentres affording just one stereoisomer. This species features a seven-membered chelate ring in a frozen conformation where the diequatorial S-alkyl substituents are disposed in anti-relationship and the stereogenic S-donors display the same configuration. The oxidative addition of hydrogen to these complexes proceeds smoothly affording in every case one single cis-dihydride complex whose structure in one case has been cleared by correlated NMR spectra. The cationic complexes derived from these ligands are catalysts of modest value for the hydrogenation of alpha,beta-unsaturated acid derivatives where they produce nearly racemic products in moderate yields. (C) 2004 Elsevier B.V. All rights reserved.