870641-27-3Relevant articles and documents
Dynamic Kinetic Resolution of Alcohols by Enantioselective Silylation Enabled by Two Orthogonal Transition-Metal Catalysts
Oestreich, Martin,Seliger, Jan
supporting information, p. 247 - 251 (2020/10/29)
A nonenzymatic dynamic kinetic resolution of acyclic and cyclic benzylic alcohols is reported. The approach merges rapid transition-metal-catalyzed alcohol racemization and enantioselective Cu-H-catalyzed dehydrogenative Si-O coupling of alcohols and hydrosilanes. The catalytic processes are orthogonal, and the racemization catalyst does not promote any background reactions such as the racemization of the silyl ether and its unselective formation. Often-used ruthenium half-sandwich complexes are not suitable but a bifunctional ruthenium pincer complex perfectly fulfills this purpose. By this, enantioselective silylation of racemic alcohol mixtures is achieved in high yields and with good levels of enantioselection.
Synthesis of pincer ruthenium RuCl(CNN)(PP) catalysts from [RuCl(μ-Cl)(η6-p-cymene)]2
Zhang, Shuanming,Baratta, Walter
, p. 3339 - 3342 (2013/07/19)
The cationic [RuCl(η6-p-cymene)(HCNNa)]Cl (1a) (HCNNa = 1-(6-arylpyridin-2-yl)methanamine) and the neutral RuCl 2(η6-p-cymene)(HCNNb) (1b) (HCNN b = 2-aminomethylbenzo[h]quinoline) complexes have been obtained by reaction of the precursor [RuCl(μ-Cl)(η6-p-cymene)] 2 with the corresponding nitrogen ligand (HCNNa and HCNNb) in THF. Complex 1a reacts cleanly with monodentate (P = PPh3) and bidentate phosphines (PP = dppb, dppf) in ethanol in the presence of NEt3, affording the pincer catalysts RuCl(CNN a)(PPh3)2 (2) and RuCl(CNNa)(PP) (PP = dppb 3, dppf 4). Similarly, the benzo[h]quinoline pincer derivative RuCl(CNNb)(dppb) (5) is obtained from 1b and dppb. Complex 3 has also been prepared in a one-pot reaction from [RuCl(μ-Cl)(η6-p- cymene)]2, HCNNa, and dppb in ethanol. Similarly, the chiral complex RuCl(CNNa)((R,S)-Josiphos) was isolated as a single stereoisomer by treatment of [RuCl(μ-Cl)(η6-p-cymene)] 2 with HCNNa and (R,S)-Josiphos in 1-butanol. Reaction of 1a and 1b with dppb affords cymene diphosphine species by displacement of the HCCN ligand.
Terdentate RuX(CNN)(PP) (X = Cl, H, OR) complexes: Synthesis, properties, and catalytic activity in fast transfer hydrogenation
Baratta, Walter,Bosco, Marco,Chelucci, Giorgio,Del Zotto, Alessandro,Siega, Katia,Toniutti, Micaela,Zangrando, Ennio,Rigo, Pierluigi
, p. 4611 - 4620 (2008/10/09)
Terdentate ruthenium(II) complexes of general formula RuX(CNN)(dppb) (X = chloride, hydride, alkoxide; dppb = Ph2P(CH2) 4PPh2), where CNN is a deprotonated 2-aminomethyl-6- arylpyridine ligand, have been prepared. The orthometalated derivative RuCl(b)(dppb) (1) has been obtained by reaction of RuCl2(PPh 3)(dppb) with N,N-dimethyl-2-aminomethyl-6-(4-methylphenyl)pyridine (Hb) in 2-propanol and in the presence of triethylamine by elimination of PPh3 and HCl. Similarly, RuCl(a)(dppb) (2) and the chiral analogue RuCl(c)(dppb) (3), containing primary amine ligands, have been isolated starting from 2-aminomethyl-6-(4-methylphenyl)pyridine (Ha) and (R)-2,2-dimethyl-1-(6- phenylpyridin-2-yl)-propylamine (Hc), respectively. The synthesis of the functionalized pyridines Ha-Hc is here described, whereas the crystal structure of 3 has been determined through an X-ray diffraction experiment. Treatment of 1-3 with sodium or potassium isopropoxide gives the corresponding hydrides RuH(b)(dppb) (4), RuH(a)(dppb) (5), and RuH(c)(dppb) (6) from the ruthenium isopropoxide complexes, via a β-H elimination process. Studies in solution show that the isopropoxides bearing a NH donor group are in equilibrium with the corresponding hydrides (5 and 6). Reaction of 5 with benzophenone leads to the alkoxide Ru(OCHPh2)(a)(dppb) (7), which has been proven to interact with benzhydrol in C6D6, leading to the adduct 7·(HOCHPh2), the alkoxide ligand, and the alcohol being in rapid exchange. Complexes 2 and 3 display a remarkable high catalytic activity for the transfer hydrogenation of ketones to alcohol in 2-propanol using a very small amount of catalyst. With the chiral complex 3 (0.005 mol %) methyl-aryl ketones can be quickly reduced (TOF ranging from 5.4 × 105 to 1.4 × 106 h-1) with an enatiomeric excess up to 88%.
