title: CO assistance in ligand exchange of a ruthenium racemization catalyst: identification of an acyl intermediate.
abstract: An acyl intermediate in the activation of eta(5)-(Ph(5)Cp)Ru(CO)(2)Cl by t-BuOK was identified by means of in situ FT-IR measurements and NMR spectroscopy. This strongly supports the conclusion that the ligand exchange takes place via CO assistance, i.e., that the activation occurs via nucleophilic attack by tert-butoxide on one of the CO ligands. The tert-butoxycarbonyl intermediate shows stretching vibrations at 1933 and 1596 cm(-1), corresponding to the CO and COOt-Bu groups, respectively. In the (13)C NMR spectrum, the CO group appears at 209.5 ppm and the COOt-Bu group at 208.7 ppm. The NMR assignments were confirmed by density functional theory calculations. The subsequent alcohol-alkoxide exchange is also thought to take place via CO assistance. However, no intermediate in that step could be detected.
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
authors.forename: Jenny B
authors.initials: JB
authors.lastname: Aberg
authors.forename: Jonas
authors.initials: J
authors.lastname: Nyhlén
authors.forename: Belén
authors.initials: B
authors.lastname: Martín-Matute
authors.forename: Timofei
authors.initials: T
authors.lastname: Privalov
authors.forename: Jan-E
authors.initials: JE
authors.lastname: Bäckvall