71886-65-2Relevant articles and documents
Chiral iridium spiro aminophosphine complexes: Asymmetric hydrogenation of simple ketones, structure, and plausible mechanism
Xie, Jian-Bo,Xie, Jian-Hua,Liu, Xiao-Yan,Zhang, Qian-Qian,Zhou, Qi-Lin
supporting information; experimental part, p. 899 - 908 (2011/10/02)
The iridium complexes of chiral spiro aminophophine ligands, especially the ligand with 3,5-di-tert-butylphenyl groups on the P atom (1 c) were demonstrated to be highly efficient catalysts for the asymmetric hydrogenation of alkyl aryl ketones. In the presence of KOtBu as a base and under mild reaction conditions, a series of chiral alcohols were synthesized in up to 97%ee with high turnover number (TON up to 10 000) and high turnover frequency (TOF up to 3.7× 104 h-1). Investigation on the structures of the iridium complexes of ligands (R)-1 a and 1 c by X-ray analyses disclosed that the 3,5-di-tert-butyl groups on the P-phenyl rings of the ligand are the key factor for achieving high activity and enantioselectivity of the catalyst. Study of the catalysts generated from the Ir-(R)-1 c complex and H2 by means of ESI-MS and NMR spectroscopy indicated that the early formed iridium dihydride complex with one (R)-1 c ligand was the active species, which was slowly transformed into an inactive iridium dihydride complex with two (R)-1 c ligands. A plausible mechanism for the reaction was also suggested to explain the observations of the hydrogenation reactions. The chiral iridium complexes of spiro aminophosphine ligands were demonstrated to be highly efficient catalysts for the hydrogenation of aromatic ketones, providing chiral alcohols in high enantioselectivities (up to 97%ee) with high turnover number (TON up to 10 000) and turnover frequency (TOF up to 3.7× 104 h-1).
Racemization of secondary alcohols catalyzed by cyclopentadienyl-ruthenium complexes: Evidence for an alkoxide pathway by fast β-hydride elimination-readdition
Martin-Matute, Belen,Aberg, Jenny B.,Edin, Michaela,Baeckvall, Jan-E.
, p. 6063 - 6072 (2008/02/13)
The racemization of sec-alcohols catalyzed by pentaphenylcyclopentadienyl- ruthenium complex 3 a has been investigated. The mechanism involves ruthenium-alkoxide intermediates: reaction of tert-butoxide ruthenium complex 4 with a series of sec-alcohols with different electronic properties gave ruthenium complexes bearing a secondary alkoxide as a ligand. The characterization of these alkoxide complexes by NMR spectroscopy together with a study of the reaction using in situ IR spectroscopy is consistent with a mechanism in which the alkoxide substitution step and the β-hydride elimination step occur without CO dissociation. The alkoxide substitution reaction is proposed to begin with hydrogen bonding of the incoming alcohol to the active ruthenium-alkoxide intermediate. Subsequent alkoxide exchange can occur via two pathways: i) an associative pathway involving a η3-CpRu intermediate; or ii) a dissociative pathway within the solvent cage. Racemization at room temperature of a 1:1 mixture of (S)-1-phenylethanol and (5)-1-phenyl-[D4]-ethanol gave only rac-1-phenylethanol, and rac-1-phenyl-[D4]-ethanol, providing strong support for a mechanism in which the substrate stays coordinated to the metal center throughout the racemization, and does not leave the coordination sphere. Furthermore, racemization of a sec-alcohol bearing a ketone moiety within the same molecule does not result in any reduction of the original ketone, which rules out a mechanism where the intermediate ketone is trapped within the solvent cage. These results are consistent with a mechanism where η3-Ph5C5-ruthenium intermediates are involved. Competitive racemization on nondeuterated and α-deuterated α-phenylethanols was used to determine the kinetic isotope effect k H/kD for the ruthenium-catalyzed racemization. The kinetic isotope effect kH/kD for p-X-C6H 4CH(OH)CH3 was 1.08, 1.27 and 1.45 for X = OMe, H, and CF3, respectively.
On the steric course of transmetallations on enantiomerically defined α-carbamoyloxy organolithiums
Tomooka, Katsuhiko,Shimizu, Hideo,Nakai, Takeshi
, p. 364 - 366 (2007/10/03)
The steric courses of the transmetallations of the title organolithiums to the Sn(IV)-, Mg(II)-, Ce(III)-, Zn(II)-, and Cu(I)-species are described.
